Project Drawdown Transportation Highlights

Transport produces 7 gigatons of carbon dioxide-equivalent greenhouse gas emissions annually, or 23 percent of energy-related emissions, which is around 14 percent of all emissions. In individual countries, transport can account for much higher shares, even 35 percent of all emissions. Growth rates in emissions for some subsectors like air transport and international shipping are very high, so the Transport Sector requires special focus to keep emissions from ballooning out of control, as some projections indicate. Transport, however, is a service derived from economic growth. We find that wealthier people travel more, locally and internationally, and demand more goods and services. So, as a country develops economically, movement of people and goods increases.

In terms of greenhouse gas emissions reduction, transport is constrained in some subsectors where few economically viable alternative fuels exist. Some transport, therefore, can only currently be made more efficient at using existing fossil fuels; others, however, do have alternative fuels, such as electricity for cars instead of gasoline. Other modes of transport can be avoided completely using information and communication technologies. Project Drawdown has examined 13 of these transport solutions, some of which are included in the Buildings and Cities section of Drawdown for communications reasons. However, we include them here since they form key parts of making the global transport sector less carbon-intensive.


Included in the Project Drawdown list are 13 of the most impactful solutions for reducing emissions in the transport sector. The list excludes some solutions that are impactful, but future work of Project Drawdown will include as many other solutions as possible.

AIRPLANES – increased use of technologies to reduce aircraft fuel burn

BIKE INFRASTRUCTURE – increased installation of bike paths to encourage more bike usage (placed with Buildings and Cities in Drawdown)

CARS – increased use of hybrid cars

ELECTRIC BIKES – increased use of electric bikes instead of cars for urban travel

ELECTRIC VEHICLES – increased use of battery and plug-in hybrid vehicles

HIGH-SPEED RAIL – track construction for increased use of high-speed rail for intercity travel

MASS TRANSIT – increased usage of mass transit or public transport to get around cities

RIDESHARING – increased ride-sharing when commuting in North America

SHIPS – the use of technologies to make maritime shipping less fuel-intensive

TELEPRESENCE – replacing flying for business meetings with telepresence technologies

TRAINS – increased electrification of freight railways

TRUCKS – increased use of fuel reduction technologies and approaches for trucking

WALKABLE CITIES – increased walking instead of driving for urban travel (placed with Buildings and Cities in Drawdown)

Methodology and Integration

Modeling Methodology

Each solution in the Transport Sector was modeled individually, and then integration was performed to ensure consistency across the sector and with the other sectors. Information gathered and data collected are used to develop solution-specific models that evaluate the potential financial and emission-reduction impacts of each solution when adopted globally from 2020 to 2050. Models compare a Reference Scenario that assumes current adoption remains at a constant percent of the current total land area, with high adoption scenarios assuming a reasonably vigorous global adoption path. In doing so, the results reflect the full impact of the solution, i.e. the total 30-year impact of adoption when scaled beyond the solution’s current status.


Total Addressable Market

The groupings shown in Figure 1 indicate the proximity of the constituent solutions to each other, and how the total addressable markets for the Transport Sector are shared. Each market was defined at the cluster level using several sources, including the International Energy Agency (IEA), the International Council for Clean Transportation (ICCT), the Institute for Transportation and Development Policy (ITDP), and the University of California at Davis (UCD). All urban passenger transport solutions, for instance, share the urban transport market; thus, the adoption of each is related to the adoption of others. Note that ship-borne freight is less substitutable by land modes; hence, we consider the land modes independent of maritime freight, and we do not consider air freight. We do, however, consider the use of electric vehicles and hybrids in the urban and non-urban realms by ensuring market and adoption consistency. Integration is discussed in greater detail below.

The Transport Sector solutions clusters are described below:

  1. Urban Passenger Transport – the movement of people within built-up areas, which are often not fully within the administrative limits of a city. In reality, many cities’ metropolitan areas extend well outside of the city, and the movement of people within this entire area is considered urban transport by many in transport policy and research. All solutions in this cluster use passenger-kilometers as their units.
  2. Non-Urban Passenger Transport – the movement of people either completely outside of urban areas (that is, rural transport), or between urban areas. Three facts motivate the interpretation of travel in this cluster as chiefly between urban areas: i) more than half of the world’s population already lives in urban areas, with around 50 percent of all travel happening within cities; ii) urban populations are growing faster than non-urban population; and iii) long-distance travel (travel of over 50 kilometers, which is around 40 percent of all travel [Hayashi et al, 2015]) is made more often by wealthier people who live in cities.  We therefore use the terms “non-urban” and “intercity” for this cluster interchangeably. All solutions in this cluster use passenger-kilometers as their units.
  3. Freight Transport – the movement of goods anywhere by any means. The shipssolution uses billion ton-nautical miles as its units for consistency with the industry, but the other two solutions use million ton-kilometers.

Adoption Scenarios

Three general Project Drawdown scenario were developed for the Transport Sector:

  • Plausible Scenario: this scenario represents incremental but optimistic and realistic adoption of the solution to 2050.
  • Drawdown Scenario:  this is a scenario optimized to reach drawdown by 2050.
  • Optimum Scenario:  this represents what the modeling team saw as the maximum potential for a solution’s adoption or impact.


Several Drawdown Transport Sector solutions have published adoption projections, variables, and supporting technologies that affect other solutions. We have attempted to account for the most impactful of these relationships by: i) ensuring that all solutions in the same market use the same market data (and that adoptions in passenger-kilometers are bounded by the data); ii) ensuring that all variables used in several solutions have the same values; and iii) ensuring that the increased demand for grid electricity can be provided by the energy sector.

To ensure bounding of projected adoptions by total market projections, we prioritized the modes of transport by their energy use, space efficiency, and potential impact on energy use within each cluster. The adoption of high-priority solutions was not reduced, but that of other solutions was reduced, particularly in the Drawdown and OptimumScenarios. The prioritized order of solutions is:

Urban Passenger

  1. Walkable Cities
  2. Bike Infrastructure
  3. Electric Bikes
  4. Mass Transit
  5. Ridesharing
  6. Electric Vehicles
  7. Cars
Non-urban Passenger

  1. Telepresence
  2. High-Speed Rail
  3. Airplanes
  4. (Electric Vehicles)
  5. (Cars)

  1. Ships
  2. Trains
  3. Trucks

This prioritization does not imply that we see higher-ranked solutions as being adopted globally before others, but that adoption of those solutions should be promoted to the maximum extent prior to lower ones in order to maximize the impact of the sector. It also implies that the emissions impact of lower solutions could be greater if they were of a higher priority (and those of higher solutions could have lower impact if deprioritized). We do acknowledge that mode choice analysis, for estimating actual demand for a solution is a complex activity that is not possible at the global level, especially not to 2050. Our simplified approach therefore attempts to illustrate how, with the adoption of each solution in a particular scenario, the greatest emissions and other benefits could be attained.

The adoption of electric vehicles (EVs) and efficient cars (hybrids) was adjusted to prevent exceeding the total addressable market. We have classified them as urban modes of transport, but have also ensured consistency with the non-urban passenger market. This was dependent on the split in car usage between urban and non-urban travel. We assumed that hybrid cars have a 50:50 split in usage in the urban and non-urban realms, and that the split remains constant throughout the analysis period (except in the Optimum Scenario, where the urban share declines 5 percent per year to 0 percent after 2030). For EVs, we assume that “range anxiety”[1] limits non-urban travel to 0 percent until 2020, when battery capacity technology develops enough to encourage EV users to drive outside of cities. After 2020, the non-urban share of EV travel rises by 5 percent per year until it levels off at 45 percent of all EV travel (except for the Optimum Scenario, where it levels off at 75 percent of all EV travel.) Note that the Optimum Scenario involves increased use of more environmentally-sound modes like biking and walking in urban areas, and the use of less space-efficient modes (EVs and hybrids) mainly outside of cities.

[1] Range anxiety is the fear of not having sufficient battery power or charging stations to complete a long trip by electric vehicle. This would be akin to the early days of gasoline-powered car use, when gas stations were much more rare and long-distance trips were harder.


Results from the entire Transport Sector have been presented in the book Drawdownwithout bike infrastructure or walkable cities, which were analyzed as part of the Transport Sector but were placed in the Buildings and Cities section for communications reasons. We therefore present results both with those two solutions (“All 13 Transport+ Solutions”) and without (“The 11 Transport-only Solutions”).

Mitigation Impact

All 13 Transport+ solutions show a potential of 51 gigatons of carbon dioxide-equivalent greenhouse gas reductions over 2020-2050 in the Plausible Scenario, or an average of 1.6 gigatons per year (the 11 Transport-only Solutions show 45.8 gigatons). This is below most of the other sectors analyzed by Project Drawdown. Figure 2 compares the results for each sector, showing the 11 Transport-only Solutions as “Transport”.

Total Atmospheric CO2-eq avoided (Gt)Plausible ScenarioDrawdown ScenarioOptimum ScenarioBuildings and CitiesEnergyFoodLand UseMaterialsTransportWomen and Girls0100200300400500600

© 2017 Project Drawdown


The more ambitious Drawdown Scenario shows a potential for 109 gigatons of emissions reductions over the specified period, or 3.5 gigatons on average per year, for the 13 Transport+ solutions (94 gigatons for the 11 Transport-only solutions). Finally, the Optimum Scenario results in 183 gigatons of reduction over the entire period, or 5.9 gigatons per year, for the 13 Transport+ solutions. The equivalent values for the 11 Transport-only solutions were 160 gigatons for the entire period and 5.2 gigatons per year.

Electric vehicles 21.17%10.8 GT CO2-EQhover for details

© 2017 Project Drawdown

Airplanes 5.05 5.27 6.47
Bike infrastructure 2.31 6.49 11.36
Cars 4.00 11.05 15.70
Electric bikes 0.96 3.45 7.11
Electric vehicles 10.80 25.26 52.38
High-speed rail 1.52 3.37 4.80
Mass transit 6.57 16.78 26.29
Ridesharing 0.32 0.36 3.23
Ships 7.87 9.03 9.52
Telepresence 1.99 7.19 17.18
Trains 0.52 0.85 4.00
Trucks 6.18 11.37 13.37
Walkable cities 2.92 8.77 11.10
TOTAL: 51.01 109.24 182.51

© 2017 Project Drawdown

Project Drawdown’s 13 Transport+ solutions show reductions compared to the Reference Scenario of:

  • 0.97, 2.0, and 3.5 gigatons of carbon dioxide in 2030 for the PlausibleDrawdown, and Optimum Scenarios, respectively.
  •  3.7, 7.7, and 12.4 gigatons of carbon dioxide in 2050 for the PlausibleDrawdown, and Optimum Scenarios, respectively.

Financial Results

The key financial results of the Plausible Scenario show US$26 trillion in operating savings over the study period for the entire sector, but at a marginal investment cost of US$15.7 trillion.[1] The detailed financial results for each solution are shown in Table 2.




Airplanes 662.42 3,187.80
Bike infrastructure -2,026.97 400.47
Cars -598.69 1,761.72
Electric bikes 106.75 226.07
Electric vehicles 14,148.03 9,726.40
High-speed rail 1,038.42 368.13
Mass transit N/A 2,379.73
Ridesharing N/A 185.56
Ships 915.93 424.38
Telepresence 127.72 1,310.59
Trains 808.64 313.86
Trucks 543.54 2,781.63
Walkable cities N/A 3,278
TOTAL: 15,725.79 26,344.58

© 2017 Project Drawdown

[1] All monetary values are presented in US2014$.

Sector-Level Benchmarks

To compare Project Drawdown’s results to those of other major organizations, the team embarked on a benchmarking exercise using mainly data from the International Transport Forum (ITF) and the International Energy Agency (IEA) (both parts of the Organisation for Economic Cooperation and Development, OECD).

Overall, Project Drawdown’s Drawdown Scenario is in line with the ITF’s 2017 models, though some points of difference are noted:

  • The reference scenario for the ITF shows lower total emissions than the references used by Project Drawdown; and,
  • The ITF shows greater reliance on global maritime, truck freight, and aviation solutions to reduce emissions than do Project Drawdown’s models, which emphasize urban transport.

The Project Drawdown analysis for the Transport Sector also shows results similar to the IEA’s results for a shift from the 6°C to the 2°C Scenario. There are a few points to note, however:

  • Project Drawdown and the IEA show similarly aggressive and close to maximum impact in the light road/urban transport segments, with the IEA result being close to Project Drawdown’s most aggressive scenarios;
  • Project Drawdown is, however, more aggressive in the maritime and trucking segments than the IEA, with the IEA’s results falling closer to Project Drawdown’s least aggressive scenarios;
  • Finally, Project Drawdown’s most aggressive aviation result is below that of the IEA, indicating that the IEA sees much more emphasis on the aviation sector in reducing emissions than Project Drawdown does.

Conclusions and Limitations


The overall need to reduce the emissions impact of transport is clear, and the potential for reducing its emissions is shown in the scenarios developed by Project Drawdown. These scenarios were developed by a research team of 14 transportation and mobility researchers throughout the world, and draws on hundreds of scientifically supported sources. The scenarios show significant reductions in transportation emissions over 2020-2050, which are found to be aligned with publications by other international bodies such as the IEA and the ITF.


The global nature of this work comes with strong restrictions on modeling to 2050. The data available at the global level was generally relevant for a few dominant economies like the European Union, the USA, and China. This could have skewed our results, except in a few cases where the sector is global in nature (such as airplanes and ships) or is heavily concentrated in those economies (such as high-speed rail). Additionally, we did not create a global mode-choice model to estimate the uptake of each solution over time, again due to very limited data availability. Our integration effort was extensive, but still some connections between different solutions could not be realistically represented. Finally, not all currently developing solutions were included in the set of Project Drawdown Transport solutions, and some that other bodies have included in their models, such as biofuels, could lead to projections of an increased impact of the transport sector relevant to Project Drawdown. Still, the work of Project Drawdown shows that high adoption of solutions for reducing transport emissions is critical for getting the world towards drawdown.



Electric vehicles:

Since the first electric vehicle (EV) prototype was built in 1828, the central challenge has been making good on a lightweight, durable battery with adequate range. In its absence, internal combustion engines have dominated the automotive landscape since the 1920s, and the atmosphere has paid the price.

Luckily, there are now more than 1 million EVs on the road, and the difference in impact is remarkable. Compared to gasoline-powered vehicles, emissions drop by 50 percent if an EV’s power comes off the conventional grid. If powered by solar energy, carbon dioxide emissions fall by 95 percent. The “fuel” for electric cars is cheaper too. EVs will disrupt auto and oil business models because they are simpler to make, have fewer moving parts, and require little maintenance and no fossil fuels.

What is the catch? With EVs, it is “range anxiety”—how far the car can go on a single charge. Typical today is a range of 80 to 90 miles, long enough for most daily travel. Carmakers are closing in on ranges of 200 miles, while keeping batteries affordable.

The rate of innovation in EVs guarantees they are the cars of the future. The question is how soon the future will arrive.

Most light duty vehicles in use today rely on liquid fuel for energy storage and propulsion in an internal combustion engine. Electric vehicles (EVs) use a more energy-efficient electric motor, and have high-capacity batteries on board that can be charged from the electric grid. [1] The EV market is still in its infancy, with early adopters driving the high growth seen over the past five years. Even though EVs are still only a small fraction of vehicle sales and stock, they are expected to grow dramatically over the coming decades, replacing a large share of conventional vehicles and causing a dent in the carbon dioxide emissions from road transportation. For purposes of this work, both battery EVs and plug-in hybrid EVs are included, assuming a 60 percent share of the entire EV market is battery EVs. All relevant variables are weighted according to this share.


Total Addressable Market [2]

The total addressable market for electric vehicles represents the total number of urban and non-urban passenger-kilometers projected by sources such as the International Energy Agency (IEA) and the International Council on Clean Transport (ICCT) to 2050. Current adoption [3] of EVs is taken as 0.07 percent of the passenger-kilometers driven by all light duty vehicles, derived based on IEA data. The total passenger-kilometers of light duty vehicles was averaged from data provided by the IEA, ICCT, and the Institute for Transportation and Development Policy (ITDP) and University of California–Davis (UCD).

Adoption Scenarios [4]

Impacts of increased adoption of electric vehicles from 2020-2050 were generated based on three growth scenarios, which were assessed in comparison to a Reference Scenario where the solution’s market share was fixed at the current levels.

  • Plausible Scenario: Adoption is aligned with the IEA projection for EV stock. [5] 100 percent of EV passenger-kilometers are assumed to be urban only until 2021, after which the nonurban share increases by 5 percent annually until 2029. From 2030 on, the share of urban to long-distance EV passenger-kilometers remains at 55-45 percent. [6]
  • Drawdown Scenario: IEA (2016) projections and historical EV sales are combined to project the total stock of EV cars out to 2050. This scenario includes an annual rise in average EV car occupancy, resulting in a 50 percent increase by 2050. [7]
  • Optimum Scenario: In this optimal “sharing” scenario, electric car use increases in line with the Drawdown Scenario; however, the total passenger-kilometer demand shrinks because of the doubling of average car occupancy. Only usage of battery EVs is included, no plug-in hybrids. [8] Variable costs drop as electricity in battery EVs is cheaper than gasoline in plug-in hybrid EVs. 100 percent of EV passenger-kilometers are urban only until 2021, when they start to decrease by 5 percent annually until reaching 25 percent in 2035.

Emissions Model

Emissions estimates used the same electricity and fuel usage data as the operating costs, with emissions factors calculated based on the guidelines from the Intergovernmental Panel on Climate Change (IPCC). EV production generated up to 5 percent higher indirect emissions than ICE vehicles.

Financial Model

First costs for purchasing an EV or ICE vehicle were estimated using US Energy Information Agency (EIA) data (weighted by vehicle market segment) and global vehicle price data. [9] A learning rate of 2.1 percent was applied to the EV first cost only, based on projected EIA prices. Purchase costs for the EV were averaged to be US$20,000 higher than the ICE vehicle in the base year. [10]

Operating costs and emissions included grid electricity for the EV (dependent on the ratio of battery to plug-in hybrid EVs in each scenario), and fuel (for the plug-in hybrid). Electricity and fuel use were based on EIA data. The weighted global average fuel prices were derived from recent IEA estimates, and electricity prices were calculated using data from 51 countries over 10 years. Additionally, operating costs included the maintenance costs for vehicles and fixed operating costs. [11]

Integration [12]

As noted earlier, some inputs were harmonized across solutions for consistency. [13]The additional demand on the electricity grid resulting from the growth of EV usage was accounted for in the integrated total market for electricity. To avoid double-counting emissions benefits, the results presented for EVs do not reflect the increasingly cleaner grid; instead, the additional emissions benefits are accounted for directly in the supply-side energy solutions.


EV adoption in the Plausible Scenario leads to 885 million EVs on the roads in 2050, compared to only 305,000 EVs sold in 2014. This rapid growth in the EV fleet results in the reduction of 10.8 gigatons of carbon dioxide-equivalent greenhouse gas emissions between 2020 and 2050, and US$9.7 trillion in net operating savings. [14] The purchase cost is high, however, at $14 trillion. The Drawdown Scenario projects that 1.3 billion EVs would join the global fleet by 2050, resulting in 25 gigatons of emissions avoided. The Optimum Scenario would have 1.2 billion battery EVs on the road, lower than the Drawdown Scenario since car occupancy is higher. [15] These EVs would avoid 52 billion tons of emissions from 2020-2050.


EV adoption is beneficial for the climate, and our financial analysis shows that it will also save operating costs for households, although at a higher purchase cost in the PlausibleScenario. For other scenarios, the operating savings are higher due to increased occupancy of EVs. It is important to note that higher adoption can lead to higher reductions in battery (and EV) costs, due to more battery investment. Consumer education is a key component of EV adoption, in order to relieve concerns about the upfront price premium and the reduced range of EVs compared to ICE cars. As battery technology matures, the price of manufacturing high-capacity batteries will decrease, so both the purchase price and range of EVs will become more attractive to consumers. There are some potential problems from increased battery production that would have to be managed, for instance sourcing of key metals such as cobalt, copper, and nickel, whose supply chains can have negative environmental and social impacts around the world. These issues should be managed alongside the growth of the EV market.

[1] The grid in general is much less polluting than conventional vehicles, and is growing cleaner annually around the world.

[2] For more on the Total Addressable Market for the Transport Sector, click the Sector Summary: Transport link below.

[3] Current adoption is defined as the amount of functional demand supplied by the solution in the base year of study. This study uses 2014 as the base year due to the availability of global adoption data for all Project Drawdown solutions evaluated.

[4] For more on Project Drawdown’s three growth scenarios, click the Scenarios link below. For information on Transport Sector-specific scenarios, click the Sector Summary: Transport link.

[5] Based on the 2°C Scenario from the IEA’s Energy Technology Perspectives Report (2016).

[6] This assumption addresses the perceived “range anxiety” problem of EVs – drivers are often hesitant to use them when they drive long distance (such as between cities), due to the perceived risk of being able to arrive at the destination or a charging station before the battery drains to empty. Battery technology is advancing rapidly, however, so the passenger-kilometers are confined to urban environments as described to account for a declining range anxiety over time.

[7] Knock-on impacts of this are that other variables, such as the electricity used and the fuel saved per passenger-kilometer, change.

[8] This has knock-on effects: electricity use and the fuel usage reduction from conventional cars increases.

[9] From, where thousands of data points exist on the differences in price of common vehicle models across countries.

[10] That is US$47,000 versus US$27,000.

[11] Insurance was the only fixed operating cost accounted for, but this was assumed the same for all vehicle types.

[12] For more on Project Drawdown’s Transport Sector integration model, click the Sector Summary: Transport link below.

[13] Common variables across solutions include: vehicle prices, fuel prices, operating costs, etc.; total addressable market, and market data.

[14] All monetary values are presented in US2014$.

[15] High occupancy should help reduce the number of cars purchased, and hence result in first cost reductions.

Full models and technical reports coming in late 2017.

From Paul Hawken et al. Drawdown, 2016.  See website – the team has updated their anticipated capability of EVs and other technologies.

Lerner saw that implementing any system based on rail would be too expensive and slow. (He is famous for saying, “If you want creativity, cut one zero from the budget. If you want sustainability, cut two zeros!”) Lerner devised an alternative that focused on something wholly unfashionable—buses—but he gave them the advantages of rail. The main advantage was dedicated lanes along main thoroughfares—separate corridors allowing buses to avoid entanglement with automobiles—at installation costs fifty times less than that of rail. Then, in the early 1990s, Curitiba’s bus stops were redesigned to be more like metro stations, facilitating passenger flow. Instead of paying onboard, riders pay at the station; instead of a single point of entry, there are multiple. These signature tubelike stations now pepper the city’s terrain (and anchor its brand), and 2 million passengers move through them every day. (By comparison, London’s Tube has 3 million riders on the average day.) Curitiba pioneered what is known as bus rapid transit (BRT), a model replicated across Latin America (e.g., Bogotá’s famously successful TransMilenio) and in more than two hundred cities worldwide. BRT is one of the modes of mass transit currently vying with cars for passengers and their miles. Whatever its form, public transportation uses scale to its emissions advantage. When someone opts to ride a streetcar or bus rather than driving a car or hailing a cab, greenhouse gases are averted. To use technical parlance, it is all about modal shift. The transport sector is responsible for 23 percent of global emissions. Urban transport is the single greatest source and growing—largely because the use of cars is on the rise. Of course, most transit was mass transit until World War II, when the automobile became affordable to the masses in high-income countries. Freedom from fixed routes and schedules had—and continues to have—strong allure, while urban and suburban spaces designed around cars made them increasingly essential. Cars and sprawl became coconspirators,

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Mass transit also has a crucial social advantage: It makes cities more equitable by serving those who cannot drive—the young and the old, those with physical limitations, and those unable to afford car ownership. They are far from its sole users, but they might otherwise be excluded from accessing mobility. Mass transit is one manifestation of the public square, in which people of many stripes encounter and share space with one another. As Adam Gopnik put it in The New Yorker, “A train is a small society, headed somewhere more or less on time, more or less together, more or less sharing the same window, with a common view and a singular destination”—a unique civic experience, as well as a means of conveyance. Despite its advantages, mass transit has faced—and continues to reckon with—a variety of challenges. The appeal of cars is strong and culturally entrenched in many places (less so among younger generations), and shifting habits is difficult, especially if behavior change requires more effort, more time, or more money. Public transportation is most successful where it is not just viable but efficient and attractive. One key piece is making the use of multiple modes more seamless, such as a single card to pay for metro, bus, bike share, and rideshare, or a single smartphone app to plan trips that use more than one. Beyond appealing to passengers, mass transit relies on overall urban design. A city’s density is the pivotal factor, necessary for ensuring people live and work close enough to transit to use it (what is known as the first-mile/last-mile problem) and for achieving the high-occupancy rates that make transit profitable and efficient.

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Achieving that density may pre-sent some cities with the need for fundamental reorganization and “redensification,” and those still growing with an opportunity to plan ahead. Compact urban spaces can readily become connected urban spaces, at lower cost. Even in ideal conditions, investing in transit infrastructure can be a challenge fiscally or politically, but those investments pay dividends. The benefits of mass transit accrue to all city dwellers, not just those who use it. (And its absence places burdens none can escape.) Without putting money where buses, subways, and streetcars are, or could be, modal shift may go towards private cars and their attendant congestion and pollution, rather than lower-emissions transit options.

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According to the International Union of Railways, there are more than 18,500 miles of high-speed rails worldwide. That number will increase by 50 percent when current construction is completed; many more thousands of miles are planned and under consideration. China has by far the most high-speed rail lines—more than 35 percent of the total—with Japan and Western Europe not far behind. China, Japan, and South Korea have introduced a variation of high-speed rail, the maglev train, which deploys magnets that lift the train off its supporting structure, propelling it at astonishingly smooth and quiet speeds—to the order of 270 miles per hour in the run between Shanghai and its distant airport. High-speed rail (HSR) is powered almost exclusively by electricity, not diesel. Compared to driving or flying, it is the fastest way to travel between two points between one hundred and seven hundred miles apart and reduces carbon emissions up to 90 percent. HSR’s market advantage is on trips of seven hours or less.

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new trains have comfortable cabins, wonderful visibility, and full connectivity. The long-term success of HSR is well established on medium-distance (four-hour) high-density corridors. In certain popular markets in Western Europe and Asia, fast trains have captured more than half of the overall travel business on those routes. HSR virtually owns the London–Paris, Paris–Lyon, and Madrid–Barcelona routes. In 2013, high-speed trains recorded 220 billion passenger miles globally, about 12 percent of the total rail market.

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The trains themselves are expensive, as are any new stations. The heavy-duty roadbeds range from $3.7 million to $52.8 million per mile; and then there are bridges, tunnels, and viaducts. In the Northeast Corridor, Amtrak estimates that creating a high-speed rail system rated at 220 miles per hour would cost $160 billion. A lower, 160-mph system would save only a little. Given the numbers, government subsidies and excise taxes are necessary, but opponents of high-speed rail cite subsidies as proof that it is not economical. However, any assessment should include the costs if a high-speed rail line is not built, as all of our transportation systems enjoy significant government subsidies, hidden or otherwise. The public, not private enterprise, pays for new highways, new lanes for old highways, bigger airports, traffic jams, wasted time, and ever more greenhouse gases. The public costs that any HSR project would avoid need to be subtracted from the capital cost of the system.

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High-speed rail requires high passenger miles to break even. Only certain places in the world have sufficient population density to support HSR. The carbon footprint of an up-and-running HSR is lower than that of planes and cars, but only when it replaces significant air and vehicle miles. Another factor to take into account: There are significant greenhouse gas emissions associated with HSR construction, in particular large amounts of cement required to build railroad tracks strong enough to support trains travelling at high speeds (also true of runways and roads). One of the advantages that HSR has over air, automobile, and conventional rail is that its energy source is more likely to get cleaner as time passes.

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This advantage must be tempered by the fact that automobile travel is becoming less carbon intensive as electric vehicles become more prevalent. Air travel is less likely to make big gains in efficiency, however, maintaining HSR’s per-passenger emissions benefit as long as ridership meets or exceeds expectations. Moreover, HSR can be an important component of smart growth and help revitalize city centers. Hub-and-spoke designs for HSR, with city-center stations sharing space with mass transit and properly planned mixed-use zones nearby, can contribute to wider climate, health, and social benefits. As part of a sustainable transportation system, HSR can compound its emissions benefits. There are other economic and environmental benefits that argue for expanded HSR travel. For example, as travelers… Some highlights have been hidden or truncated due to export limits.

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IMPACT: If HSR construction and ridership continue at their projected pace, this solution can deliver 1.5 gigatons of carbon dioxide emissions reductions by 2050. A global network of 64,000 miles of track, with an average trip length of 186 miles, could support 6 to 7 billion riders annually. Regionally, most impact will come from Asia, especially China. If HSR is concentrated between cities with heavy, short-haul flight routes, impact can be greater. Implementation comes at a steep cost of $1… Some highlights have been hidden or truncated due to export limits.

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Ships are the most carbon-effective way we have to move materials from one geography to another, where an efficient rail system does not exist or cannot be used due to geography. A plane emits forty-seven times more carbon dioxide to transport the same quantity of goods the same distance. Even though shipping is an industry essential to the world’s economy, it is largely invisible. Shipping oil, iron ore, rice, and running shoes across oceans produces 3 percent of global greenhouse gas emissions, and those emissions grow as world trade continues to increase. Forecasts predict they could be 50 percent to 250 percent higher in 2050, depending on economic and energy variables.

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Because of huge shipping volumes, increasing shipping efficiency can have a sizable impact. It begins with design of the ships. The most efficient vessels are larger and longer than others. They trim out unnecessary parts of their structure and use lightweight materials. Some new vessels have ducktails at the rear—flat extensions that project from the ship’s aft to lower resistance—and compressed air pumped through the bottom of the hull to create a layer of bubbles that “lubricate” passage through the water. These two innovations alone can reduce fuel use by 7 to 22 percent depending on the type of boat. Efficient ships may also have additional machinery on board, such as solar panels to provide electricity and automation systems that take the guesswork out of optimizing a ship’s performance. Some design and technology approaches are applicable only to new ship builds; others are viable for retrofitting—particularly important because vessels currently in use will remain so for decades. Two important efforts aim to improve ship design and the technology onboard. In 2011, the International Maritime Organization (the United Nations agency tasked with making shipping safer and cleaner) established the Energy Efficiency Design Index (EEDI) for new builds. Like fuel-economy standards for cars, EEDI requires that new ships meet a minimum level of energy efficiency and raises that bar over time. The Sustainable Shipping Initiative is a partnership between fifteen of the leading shipping companies, the World Wildlife Fund, and Forum for the Future, working together to create a completely sustainable shipping industry by 2040. In 2011, a joint effort by RightShip and the Carbon War Room produced an A-to-G Greenhouse Gas Emissions Rating system for commercial vessels new and old, benchmarking each ship against its peers based on carbon dioxide pollution. The rating scheme, like other specialized indices, creates transparency and addresses a key challenge for upping ship efficiency: split incentives. Because companies that send cargo pay the bulk of fuel costs, shipowners have little reason to upgrade their vessels, especially if performance is opaque.

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Maintenance and operations are also vital for marine fuel efficiency. Techniques can be as simple as removing debris from propellers or smoothing the surface of a hull with a sharkskin-like coating. Marine organisms easily plant themselves on the hulls of ships, where they add weight, create drag, and lower fuel efficiency. This biofouling can increase fuel consumption by 40 percent. The rough, toothlike scales of sharks prevent algae and barnacles from attaching to their skin. Harnessing these attributes of sharkskin, University of Florida professor Anthony Brennan developed a biomimetic coating to keep hulls clean for smoother sailing. It is one of many technologies and practices that can make cargo ships more hydrodynamic and energy efficient. Reducing a ship’s operating speed—what the business calls “slow steaming”—lowers fuel consumption more than any other practice, up to 30 percent. An upside of the 2009 global recession is that slow steaming has become standard across much of the industry. Route and weather planning are also critical. When the small gains from design, technology, maintenance, and operations are collectively applied, industry-leading ships can be twice as efficient as laggards. In sum, available efficiency approaches can reduce shipping emissions by 20 to 40 percent by 2020 and 30 to 55 percent by 2030. In addition to improving climatic health, making oceanic freighting more efficient is important for air quality and human health. Ships are powered by low-grade bunker fuel, the dregs of the oil refining industry, which contains thirty-five hundred times more sulfur than the diesel used in cars and trucks. The port cities where ships congregate suffer most from the nitrous and sulfur oxides and particulate matter they spew into the air. Researchers… Some highlights have been hidden or truncated due to export limits.

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Considering that $19.5 trillion in goods are shipped annually, it may fall to the companies whose goods are being transported to pressure maritime shipping into being a responsible industry. RightShip and Carbon War Room initiatives may be the means to reduce global carbon emissions in a workable amount of time. Cutting shipping’s greenhouse gases remains a voluntary act; this alone is not driving change quickly enough. As with fish, buildings, food, and timber, it may be time for a clean shipping certification. Economics work in favor of improvement. Fuel costs are the main expense of ship operation, which means carriers, the companies that… Some highlights have been hidden or truncated due to export limits.

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IMPACT: With an efficiency gain of 50 percent across the international shipping industry, 7.9 gigatons of carbon dioxide emissions can be avoided by 2050. That could save… Some highlights have been hidden or truncated due to export limits.

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TRANSPORT ELECTRIC VEHICLES RANKING AND… Some highlights have been hidden or truncated due to export limits.

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Electric cars have been romanced for nearly two hundred years, since the first prototype was built in 1828. In 1891, Henry Ford worked for Thomas Edison at the Edison Illuminating Company in Detroit. Edison and Ford became fast friends for life, and it was Edison who supported and encouraged his friend—early in Ford’s career—to build a gasoline-powered automobile. Ironically, Edison was hard at work making better, less expensive batteries, some specifically designed for electric vehicles. At one point, he turned the tables on Ford, writing, “Electricity is the thing. There are no whirring and grinding gears with their numerous levers to confuse. There is not that almost terrifying uncertain throb and whirr of the powerful combustion engine. There is no water-circulating system to get out of order—no dangerous and evil-smelling gasoline and no noise.” The young Ford was not convinced and went on to create the Model A and the Model T. Sales of the $360 car surpassed $250,000 in 1914, but in that year, Edison’s prodding seemed to take effect. Ford, satisfied that Edison soon would deliver on an inexpensive, lightweight battery, announced that he would manufacture an electric automobile in collaboration with Edison—the Edison-Ford. Months and then years went by and the Edison-Ford never came to pass, because Edison could not make good on that lightweight, durable battery.

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Early nineteenth-century inventors in Britain, the Netherlands, Hungary, and the United States all created various types of small-scale electrical vehicles (EVs), but the first practical vehicles weren’t created until the last half of the century. In 1891, William Morrison, a chemist from Iowa, made a six-passenger vehicle capable of reaching speeds up to fourteen miles per hour. By the end of the century, vehicles were available in the United States with gasoline, electric, and steam power trains. Electric vehicles outsold both gasoline- and steam-powered cars for a variety of reasons: They did not require hand cranking to start, it was unnecessary to change gears, and they had a longer range than steam-powered cars. Like electric vehicles today, they were quieter and did not pollute. By the 1920s, Americans were traveling farther because of an improved road network, so the shorter range of EVs compared to gasoline vehicles started to become a limitation. Meanwhile, gasoline vehicles gained in appeal: Henry Ford commenced mass production, making them cheaper than EVs.

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Charles Kettering invented the electric starter, eliminating the need for hand cranking, and crude oil was discovered in Texas, making gasoline affordable for the average consumer. Internal combustion… Some highlights have been hidden or truncated due to export limits.

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Fortuitously, there are currently more than 1 million electric vehicles on the road, and the difference in impact… Some highlights have been hidden or truncated due to export limits.

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Two-thirds of the world’s oil consumption is used to fuel cars and trucks. Transport emissions are second only to electricity generation as a source of carbon dioxide, accounting for a 23 percent share of all emissions. As developing nations industrialize, the number of motor vehicles is projected to surpass 2 billion by 2035. Electric vehicles are powered by the grid or distributed renewables, and this includes hydrogen-powered vehicles employing fuel cells to generate onboard electricity. They are about 60 percent efficient compared to gasoline-powered vehicles, which are about 15 percent efficient. The “fuel” for electric cars is cheaper too. The Nissan LEAF, an all-electric vehicle, will travel 3.3 miles on 1 kilowatt-hour of electricity. If the car is charged in the middle of the night at 7 cents per kilowatt-hour, that is… Some highlights have been hidden or truncated due to export limits.

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Carbon dioxide emission per gallon of gasoline is 25 pounds, whereas the emissions for 10 kilowatt-hours of electricity are 12.2 pounds on average—a 50 percent reduction in carbon dioxide if power comes off the grid. If the electricity is… Some highlights have been hidden or truncated due to export limits.

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Increasingly, the electric car is the preferred option. Sales volume has multiplied tenfold in less than a decade. From 2014 to 2015, sales jumped from 315,000 to 565,000 vehicles, thanks mainly to Chinese enthusiasts. Two-thirds of EV sales worldwide are in the three… Some highlights have been hidden or truncated due to export limits.

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The United States and China now mandate that at least 30 percent of government car purchases be nonpolluting. India wants to be all-electric by 2030—and it has the incentives to make it happen. Electric vehicles will disrupt auto and oil business models—the two biggest economic sectors in the United States—because EVs are simpler… Some highlights have been hidden or truncated due to export limits.

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Change is coming more quickly in the heavy-duty market, building on a long tradition of electric trains, subways, and industrial equipment (forklifts and the like). Commercial operators are more able and willing to make the extra capital investment because costs can be amortized. Fleet operators, with depots easily retrofitted for charging purposes, are natural candidates for converting to all-electric trucks, vans, and cars. Thousands of electric buses and delivery trucks, including portions of the UPS and FedEx fleets, ply the streets of North American, Asian, and European cities. China has eighty thousand electric buses; London’s iconic double-deckers will soon join the grid. What is the catch? With electric cars, it is “range anxiety.” In order to keep the first EVs affordable, the batteries on those models were engineered to go less than 100 miles per charge. Typical today is a range of 80 to 90 miles. A hybrid… Some highlights have been hidden or truncated due to export limits.

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The ultimate solution to the range issue is the network of charging stations. The global stock more than doubled between 2012 and 2014 to more than a hundred thousand charging points, and their numbers will increase dramatically with demand. The stations themselves are not that expensive, at $3,000 to $7,500 per port. They can utilize solar installation to charge the car off-peak, when electricity is cheapest, or “fuel” up when the grid has an abundance of solar or wind power. Malls and chains are installing ports at their outlets. Apps will pinpoint the closest charging stations, whether public or private. The charging network will expand, innovate, and improve, alleviating range anxiety while providing the electricity storage that the twenty-first-century power grid needs. Projections for the electric-car market vary. Will there be 100 million on the road within several decades? A hundred and fifty million? Bloomberg takes the 2015 figure of 60 percent sales increase, projects it for the next twenty-five years, and arrives at 400 million cumulative sales by 2040, including 35 percent of all new sales. What also remains to be seen is how the natural synergy between electric cars and self-driving cars will play out, as both become software platforms on four… Some highlights have been hidden or truncated due to export limits.

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IMPACTS: In 2014, 305,000 EVs were sold. If EV ownership rises to 16 percent of total passenger miles by 2050, 10.8 gigatons of carbon dioxide from fuel combustion could be avoided. Our analysis accounts for emissions from electricity generation and higher emissions of producing EVs compared to internal-combustion cars. We include slightly declining EV prices, expected due to declining battery costs.

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In 2015, the Oxford English Dictionary added the verb ride-share to its official inventory. A new word for an old practice, ridesharing is the simple act of filling empty seats by pairing drivers and riders who share common origins, destinations, or stops en route. (It excludes taxi-like services in vehicles driven by the average Joe, which often receive the same moniker.) The first example of carpooling for the common good emerged during World War II with the advent of car-sharing clubs. “When you ride alone, you ride with Hitler!” Americans were told. To carpool was to conserve resources for the war effort, and employers were responsible for helping riders and drivers connect, typically via a workplace bulletin board. When the 1970s oil crisis hit, concurrent with growing public concern about air pollution, another round of employer-sponsored and government-funded initiatives proliferated. To conserve fuel, high-occupancy vehicle (HOV) lanes incentivized people to ride together, and ad hoc, informal carpools known as “slugging” took hold among commuters in Washington, D.C., and beyond. In the 1970s, the heyday of ridesharing, one in five people carpooled to work. By the time the U.S. Census Bureau asked about carpooling again in 2008, the trend of sharing rides to work had slacked off considerably. Just 10 percent of Americans commuted jointly, despite efforts to encourage ridesharing as a way to address traffic congestion and air quality during the 1990s and early 2000s. But thanks to global economic woes, the ubiquity of smartphones and social networks, and declining interest in car ownership among urban millennials, ridesharing is again riding high. This resurgence is timely, given the climate crisis. When trips are pooled, people split costs, ease traffic, lighten the load on infrastructure, and may reduce commuting stress, while curtailing emissions per person.

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For every one hundred cars being driven to work in the United States today, only six carry another commuter. Imagine the impact of shifting that number just slightly—of drivers becoming passengers a mere one day each week. Ridesharing can also make other forms of transit more viable by addressing the “first and last mile” challenge, closing the gap that often exists between point A, mass transit, and point B. While it is not a novel idea, a new wave of technologies is accelerating ridesharing today. Smartphones allow people to share real-time information about where they are and where they are going, and the algorithms that match them with others and map the best routes are improving daily. Comfort with social networks buoys trust, so individuals are more likely to hop in with someone they have not met or open the door to strangers. By reaching the critical mass needed to ensure reliability, flexibility, and convenience, popular ridesharing platforms make it possible to find rides when and where required—a persistent limitation for ridesharing in the past. Indeed, matching kindred spirits, whether for a one-off pool trip or on a long-term basis, is the focus of numerous peer-to-peer business models. BlaBlaCar enables its 25 million members in twenty countries to share long-distance trips. UberPool and Lyft Line both group passengers along chains of pickups and drop-offs, using algorithms that link people heading the same way or to neighboring destinations. In China alone, Uber is running 20 million pooled trips each month. With a tech-based take on slugging, Google’s Waze has matched commuters for carpooling in Israel since 2015, and is now piloting the concept in San Francisco.

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With a dense base of users, these companies can try interesting things, betting that if drivers can make money or save time, they will share their seats, and if riders can ride cost… Some highlights have been hidden or truncated due to export limits.

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when passengers and drivers do link up, community, connection, and engagement are catalyzed along the way. Beyond getting around, ridesharing is an invitation to imagine. For many, cars have seemed indispensable to day-to-day life. But some are beginning to conceptualize mobility as a service to access. When cars are used more collaboratively, as something shared rather than something each person must own, you can catch a glimpse of the future—one with fewer cars overall.

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So what can be done to fill a car’s empty seats anytime it is on the road? Macro changes in areas such as oil pricing and city design will certainly play a role in ridesharing’s future, but its key to success is to become ever more dynamic, flexible, and cost-effective. That means technology will have a significant impact on ridesharing’s future, just as it does on its present, not least because it can help achieve a critical mass of users. The best algorithms in the world will not work without multitudes, and though business interests may run counter, sharing data across platforms could enable the most effective matching yet. In addition to entrepreneurs and coders, employers and governments also have roles to play, just as they did in ridesharing’s halcyon days gone by. Policies to promote and encourage ridesharing range from pretax programs for ridesharing expenses to reduced tolls and parking fees for carpools. Ultimately, if hopping into a car with someone can be as easy and sensible as taking your own, perhaps more so, ridesharing can become self-reinforcing—and emissions-reducing as well. •

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IMPACT: Our projection for ridesharing focuses solely on people commuting to work in the United States and Canada, where rates of car ownership and driving alone are high. We assume that carpooling rises from 10 percent of car commuters in 2015 to 15 percent by 2050, and from an average of 2.3 to 2.5 people per carpool. Ridesharing has no implementation costs and can reduce emissions by 0.3 gigatons of carbon dioxide. TRANSPORT ELECTRIC BIKES RANKING AND RESULTS BY 2050 #69 .96 GIGATONS $106.8 BILLION $226.1 BILLION REDUCED CO2 NET COST NET SAVINGS Electric bikes are all the rage in China. The trend dates to the mid-1990s, when China’s booming cities put strict antipollution rules in place in an attempt to redeem some of the world’s dirtiest urban air. Tens of millions of people now commute by e-bike, and Chinese e-bike owners outnumber car owners by a factor of two. According to one expert, this is “the single largest adoption of alternative fuel vehicles in history.” It is little surprise, then, that China accounts for some 95 percent of global e-bike sales, but these pedal-motor hybrids are on the rise in many parts of the world, as urban dwellers seek convenient, healthy, and affordable ways to move around their congested cities, curbing carbon emissions in the process. Half of all urban trips are less than 6 miles, an easy distance for e-bikes. But few people live in the perfectly flat, perfectly temperate locales that make moving around by bicycle a breeze. Some are older or less able. Others face lengthy commutes or time constraints, or need to reach a destination without perspiring… Some highlights have been hidden or truncated due to export limits.

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On e-bikes, pedals still turn a crank that moves a chain that rotates a wheel. But these quintessential bike parts do not ride alone. They are accompanied by a small battery-powered motor that can add speed—typically capped at twenty miles per hour—or assist legs when they tire.

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That battery, of course, gets its charge from the nearest outlet, which taps into whatever electricity is on hand, from coal based to solar powered. That means e-bikes inevitably have higher emissions than a regular bicycle or simply walking, but they still outperform cars, including electric ones, and most forms of mass transit. (Jam-packed trains or buses can, at times, do better than e-bikes on energy efficiency per passenger mile traveled.) When it comes to carbon, the mode of mobility from which a rider switches makes all the difference.

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Electric bicycles are expensive, easily five times the price of a classic bike and often more. The battery is a major driver of cost, though that can range widely depending on the type used.

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the man who first filed a patent for an electric bicycle in 1895. He was an Ohio-based inventor named Ogden Bolton, and though it was developed more than 125 years ago, his design was strikingly modern.

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Electric bicycles are already the most common and fastest-selling alternative-fuel vehicles on the planet. Given that e-bikes are the most environmentally sound means of motorized transport in the world today, that popularity bodes well for their continued growth. • IMPACT: In 2014, e-bike riders traveled around 249 billion miles, largely in China. Based on market research, we project travel can increase to 1.2 trillion miles per year by 2050. Shifting from cars will drive that growth, which promises to be greatest across Asia and in higher-income countries. This solution could reduce 1 gigaton of carbon dioxide emissions and save e-bike owners $226 billion by 2050.

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Gasoline- or diesel-powered engines excel at sustaining high speeds (highway driving) but have a harder time overcoming inertia to get moving. Electric motors are uniquely efficient at low speeds and going from stop to start. They also can keep a car’s air-conditioning and accessories running while idling at a traffic light, sans engine; capture the kinetic energy typically released as heat during braking and convert it back into electricity; and boost the engine’s performance, allowing it to be smaller and more efficient. Where the engine is weak, the motor is strong, and vice versa. The pairing that gives a hybrid car its name means the internal combustion engine need only do part of the work; thus, gasoline need only provide part of the energy required. Battery-stored electricity augments it, enabling a vehicle to travel more miles for each gallon—or kilometers for each liter—and produce fewer emissions along the way. According to the International Energy Agency, hybrid cars realize fuel economy improvements of 25 to 30 percent over engine-only vehicles. (Used primarily in a city, that number moves higher.) Already on the rise, electric cars are the future. But hybrids are a key car now, largely because they are unhampered by the issues their full-electric kin face, from limited driving ranges to additional infrastructure needs.

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Hybridization is the most effective technology we have for driving up vehicle fuel efficiency until society transitions to a fleet that is not powered by fossil fuels.

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In 1900, Ferdinand Porsche built on the design of his electric vehicle, combining battery-powered wheel-hub motors and two petrol engines. Dubbed the Lohner-Porsche Semper Vivus—“always alive”—it was “able to cover longer distances purely on battery power until the combustion engine had to be engaged to recharge the batteries.” The same basic technology can be found today in the Chevrolet Volt and newly minted Hyundai Ioniq. Porsche debuted his hybrid prototype at the Paris Motor Show in 1901, before refining it as the Lohner-Porsche Mixte and selling five of them by the year’s end. The technical complexity of the Mixte kept its price and maintenance costs high, and batteries of that era were expensive and heavy. Ultimately, Porsche’s hybrid could not compete with conventional petrol cars.                  Chevrolet Volt Concept is a highly advanced, plug-in electric hybrid. However, the 1.0-liter, three-cylinder turbocharged motor never powers the wheels directly. Instead, the Volt uses the combustion engine, which… Some highlights have been hidden or truncated due to export limits.

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As of 2014, 83 percent of the global car market had fuel economy regulations. These obligatory benchmarks have compelled car manufacturers to wrestle with energy inefficiency. Between engine heat loss, wind and rolling resistance, braking, idling, and other drags on performance, only 21 percent of a petrol car’s energy consumption propels it forward on average. Of the resulting force, 95 percent powers the car, not the driver. In essence, 99 percent of the energy used in a car is waste: It moves three… Some highlights have been hidden or truncated due to export limits.

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The International Energy Agency estimates that hybridization adds $3,000 in price premium, but owners see overall savings through reduced fuel costs over a car’s lifetime. Nonetheless, higher up-front cost can be prohibitive. There also is some concern that hybrids may hasten an increase in vehicle miles traveled, thus overall fuel consumption. Studies have shown, however, that this so-called “rebound effect” is typically small, just a few percentage points where personal transportation is concerned. More than 1 billion motor vehicles exist worldwide. By 2035, there will be more than 2 billion. Despite growth in carpooling, car sharing, telecommuting, and transit, cars are not going away. People continue to be drawn to the freedom, flexibility, convenience, and comfort they offer. Can we grow the number of cars, especially in emerging economies such as China and India, while drawing down emissions? Hybrids have been called the vanguard of a revolution, catalyzing fuel efficiency and challenging the auto industry to innovate. But that is true only if they pave the way for full-electric vehicles. While 97 percent of the world’s cars still contain just internal combustion engines, that number is shifting. It could shift with greater speed, heading toward all-electric motors and no engines at all. • IMPACT: Under some business-as-usual projections, 23 million hybrid vehicles will be in operation in 2050, less than 1 percent of the car market. We estimate growth in 2050 to reach 6 percent of the market, or 315 million hybrid vehicles. Those additional 315 million cars can reduce carbon dioxide emissions by 4 gigatons by 2050, saving owners $568 billion in fuel and operating costs over three decades.

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NASA has long been the leading experimenter in future aircraft design. They believe new designs could save airlines $250 billion in coming decades. Along with reducing fuel and pollution by 70 percent, these prototypes make 50 percent less noise than conventional passenger planes. The aircraft shown here is one of several N + 3 designs—aircraft that can be used three generations into the future. Dubbed the Double Bubble, this MIT model places three engines at the rear of a double-wide fuselage, enabling the wings to be smaller and lighter. Rear engine placement allows for smaller engines and reduced weight. Each optimization on large aircraft has cascading benefits to other components, resulting in groundbreaking efficiency.

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More than 3 billion plane tickets were sold in 2013, and air travel is growing faster than any other transport mode.

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(About half of air freight volume travels in the “belly” of passenger planes; the other half, in designated cargo planes.) Some twenty thousand airplanes are in service around the world, producing at minimum 2.5 percent of annual emissions. With upwards of fifty thousand planes expected to take to the skies by 2040—and take to them more often—fuel efficiency will have to rise dramatically if emissions are to be reduced. Efficiency trends are headed in the right direction, chiefly because fuel represents 30 to 40 percent of airlines’ operating costs and aircraft purchase decisions are often driven by efficiency. From 2000 to 2013, the fuel efficiency of domestic flights in the United States increased by more than 40 percent. Over the same period, fuel efficiency of international flights, which use heavier jets, improved by 17 percent. Those gains were largely thanks to fleet upgrades, while airlines also sought to maximize the capacity of each plane on each journey. Propulsion technologies, aerodynamic aircraft shapes, lightweight materials, and improved operational practices can push efficiency advances further. As with all modes of transport, engines are a key area of opportunity. Jet engines work by sucking in air, which gets compressed, combined with fuel, and combusted. The energy from combustion both turns the engine’s turbines and creates thrust. Industrial-strength turbofans at the front of the engine direct some air into the engine’s core to feed that process. They also divert air around the engine core, improving thrust and efficiency and reducing noise. Engines with high rates of air bypass improve fuel efficiency by roughly 15 percent. For the engine maker Pratt & Whitney, adding a gear to its turbofan engine design cut fuel use by an additional 16 percent. That gear allows the engine fan to operate independently of the engine’s turbine, so it… Some highlights have been hidden or truncated due to export limits.

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When it comes to aircraft design, changes range from minor to wholesale. What Boeing calls “winglets” and Airbus calls “sharklets”—upturned birdlike tips that improve a wing’s aerodynamics—trim fuel use by up to 5 percent on both new models and retrofitted older vessels. With one fin curving up and a second curving down, split scimitar winglets (named after the curved scimitar sword) can add an additional 2 percent to that total. Winglets are currently a fundamental of efficient design. The U.S. National Aeronautics and Space Administration (NASA) is working with research universities and corporate engineering teams on a host of more sweeping advances: placement of engines, fuselage width, length, width, and placement of wings, and even comprehensive redesign of the airplane body. Boeing and NASA, for example, are collaborating on an aircraft that resembles a manta ray and seamlessly blends wings into the aircraft body. Today, a 6 percent scale model is flying in NASA’s subsonic wind tunnel, but the real thing could be ready for use in a decade. The two organizations are also working on a longer, thinner, and lighter wing design with a brace or truss for added support. By moving engines to the rear of a vessel, finer wings become viable. Estimates suggest more dramatic redesigns such as these would result in efficiency gains of 50 to 60 percent. They herald the planes of the not-too-distant future. Existing aircraft can achieve significant fuel savings with simple operational shifts, treating taxi, takeoff, and landing as uniquely fuel-consuming legs. Research out of the Massachusetts Institute of Technology identifies taxiing on a single engine, rather than both, as the most effective measure for reducing fuel use on the ground, where aircraft spend 10 to 30 percent of their transit time. Fuel burn from gate to runway or vice versa can drop 40 percent and save a single large airline $10 million to $12 million a year. Towing planes with their engines off is another tactic for efficient taxiing, though it is more time consuming. The landing methods of continuous and late descent are gaining traction. They save fuel by reducing the time planes fly at low altitudes, where efficiency is lowest.… Some highlights have been hidden or truncated due to export limits.

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Because airplanes will continue to be dependent on liquid fuels for the foreseeable future, investment in jet biofuels, such as those made from algae, is on the rise. The Carbon War Room (CWR) calls sustainable aviation fuels “the most challenging emissions reduction opportunity,” as well as “the greatest potential for achieving carbon-neutral growth in aviation.” Jet biofuel options exist today, but cost is high, supply is limited, and infrastructure is poor. CWR pinpoints airports as being pivotal to aggregate demand at scale and orchestrate supply, and the organization is working to bring a viable business model to life. For now, though, the impact biofuels could have on aviation emissions remains uncertain. Despite the clear economic advantages of fuel efficiency for airlines, regulation also has a role to play. When the International Council on Clean Transportation (ICCT) investigated the relationship between fuel efficiency and airline profitability, it found that the relationship was not corollary, much less causal. In fact, the most profitable American airline in 2010 was its least fuel efficient. As the ICCT put it: “Fuel prices alone may not be a sufficient driver [for] efficiency. . . . Fixed equipment costs, maintenance costs, labor agreements, and network structure can all sometimes exert countervailing pressures.” Requiring airlines to report… Some highlights have been hidden or truncated due to export limits.

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For many years, the contribution of airplanes (and ships) to climate change escaped international regulation. That changed in October 2016, when 191 nations agreed to curb aviation emissions through the Carbon Offset and Reduction Scheme for International Aviation (CORSIA). Instead of defining a cap or charge for emissions, the accord enlists airlines in a scheme—initially voluntary—to offset aviation’s emissions with projects that sequester carbon. (Emissions in 2020 will be the benchmark above which most emissions must be offset.) It is meant to give airlines a greater stake in reducing emissions from their industry: By improving their fuel efficiency, airlines can avoid the cost of offsets, projected to be about 2 percent of aviation’s annual revenue. For the industry to make sufficient headway, other levers for change will be needed. • IMPACT: This analysis focuses on adoption of the latest and most fuel-efficient aircraft; retrofitting existing aircraft with winglets, newer engines, and lighter… Some highlights have been hidden or truncated due to export limits.

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“The greenest gallon of gas, diesel, heating oil, or ton of coal is the one you don’t burn.” So said Ray Anderson, the late founder and CEO of Interface and corporate sustainability luminary. Swap the word greenest with cheapest and the same holds true. The cheapest gallon or ton is the one you do not burn—and do not have to buy. It is this combination of saving money and preempting pollution that lies at the heart of energy-efficiency measures. For the global freight trucking industry, this integration of financial and environmental benefits is particularly pertinent in the era of climate change. Evolving from its horse-and-wagon and rail predecessors, trucking pitter-pattered along until World War I, when trucks became key to operations of the military. A combination of improved truck technology and better roads made them more viable for transport. Diesel trucks were first introduced in the 1930s, hit their stride in the 1950s, and now dominate the movement of freight. Trucks convey nearly 70 percent of all domestic freight tonnage in the United States—more than 8 billion tons annually. Even when goods move by rail or on water, they typically start and end their journeys on trucks. Transporting all that freight, in the United States and around the world, requires diesel fuel in mass quantities. In the United States alone, trucks guzzle 50 billion gallons of diesel each year, and the role they play in greenhouse gas emissions is as oversize as they are. Making up just over 4 percent of vehicles in the United States and 9 percent of total mileage, they consume more than 25 percent of the fuel.

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Worldwide, road freight is responsible for about 6 percent of all emissions. Carbon emitted by transport has ballooned in recent decades, with emissions from trucking substantially outpacing that of personal transportation. Because freight activity appears to be increasing as incomes rise, and road freight emissions are projected to continue climbing, dramatic efficiency improvements are imperative. There are two main tracks for reducing the ratio of fuel used per freight ton-mile: building it into the design of new trucks and driving it up in rigs already on the road. In 2011, the Obama administration issued the first fuel-efficiency standards for new heavy-duty trucks manufactured between 2014 and 2018. A second round aims to continue innovation and adoption of fuel-efficient technologies. These call for better engines and aerodynamics, lighter weights, less rolling resistance for tires, hybridization, and automatic engine shutdown. Top-notch automatic transmissions can overcome poor driving habits when operating manually. Based on 2010 U.S. prices, investing in these modernizations for a new truck can cost around $30,000, but save almost that much in fuel costs per year. Payback periods are short—as little as one to two years.

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Tractor-trailers remain on the road for many years, an average of nineteen in the United States, often more in lower-income countries. In light of trucks’ long life, addressing the efficiency of existing fleets is essential. That is especially true in parts of the world where trucks are significantly older—and significantly less efficient. An array of measures can trim energy waste and increase fuel performance: making improvements to a truck’s aerodynamics, installing anti-idling devices, making upgrades that reduce rolling resistance, altering transmissions, and integrating automatic cruise-control devices. The effect of each measure in and of itself may be relatively small, but when they are advanced together, they can make a substantial difference. Improving existing truck efficiency is relatively low cost but delivers a big financial return on investment. According to the Carbon War Room, for a typical heavy-duty truck in the United States, reducing fuel use by 5 percent results in a yearly savings of over $4,000. Compounded cost savings matter in an industry in which the fuel tank and bottom line are tightly tied. Still, capital to make that up-front investment can be a challenge—especially for small players, who often struggle to obtain financing. Split incentives… Some highlights have been hidden or truncated due to export limits.

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Along with making new and existing trucks more efficient, optimizing the best routes from point A to point B, avoiding legs with empty trailers, and training and rewarding drivers for fuel frugality can decrease total miles traveled and accelerate miles per gallon. In the long-term, transitioning the industry to trucks that use low-emissions fuels or electric engines will be imperative. Making bigger trucks that can carry heavier loads could also move the needle. Along the way, society will benefit from reductions in air pollution—sulfur dioxide, nitrous oxide, and particulate matter, which plague many urban areas and impact public health. From voluntary truck retrofits to national policies that set fuel-efficiency standards, ongoing efforts to make road freight more efficient will be good for the industry and the climate. • IMPACT: If adoption of fuel-saving technologies grows… Some highlights have been hidden or truncated due to export limits.

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By integrating a set of high-performance visual, audio, and network technologies and services, people who are geographically separated can interact in a way that captures many of the best aspects of an in-person experience. Imagine Skype or FaceTime on steroids. When it is possible to exist and function remotely, the need to travel becomes less necessary; herein lies telepresence’s potential impact on climate. In a world of global business footprints and international collaboration, if people can work together without being in the same place, they can dodge a host of travel-related carbon emissions. According to CDP (formerly the Carbon Disclosure Project), by activating ten thousand telepresence units, businesses in the United States and the United Kingdom could cut 6 million tons of carbon dioxide emissions by 2020—the “equivalent to the annual greenhouse gas emissions from over one million passenger vehicles” —and save almost $19 billion in the process.

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Using a mobile telepresence robot, a surgeon can advise on a rare procedure in real time, without traveling from Austin to Amman. Gathering in telepresence conference rooms in Sydney and Singapore, executives can debate a possible acquisition without taking a single flight. Companies that have embraced telepresence with gusto are finding not all trips can be trimmed, but many can be. Beyond staving off carbon emissions, telepresence affords many other benefits: cost savings from avoided travel, of course, as well as less grueling schedules for employees, more productive remote meetings, the ability to make decisions more quickly, and enhanced interpersonal connection across geographies. To achieve the fullness of these benefits, a significant initial investment is required, higher than that of standard videoconferencing. But while initial cost and ongoing expenses are higher for telepresence systems, they tend to be used much more heavily, making the cost per use commensurate. Payback happens quickly—in as little as one to two years. Telepresence also depends on strong network infrastructure, skilled technical support, and dedicated space if specific meeting rooms are used. Once telepresence technology is installed, companies can encourage employees to use it by educating them, establishing policies around avoiding travel, and tracking and rewarding its use. Costs are going down, while simplicity, reliability, and efficacy are on the rise, but the adoption of technology and accompanying behavioral change—using it and using it well—still takes time.

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The U.S. passenger service Amtrak reduced energy consumption by 8 percent with regenerative braking. Distributing the power of locomotives throughout a train also improves fuel use. Better locomotives, more strategically placed, are enhanced by better cars—lighter, more aerodynamic, able to hold more cargo, and equipped with low-torque bearings. Eliminating gaps between cars reduces drag, while longer, heavier trains often prove more efficient. The rails themselves can be better lubricated to reduce friction. Even with hyperefficient design, how a train is driven remains critical. Software can control train speed, spacing, and timing, as well as provide efficiency information and “coaching” to locomotive engineers, improving performance. The number of electric trains is increasing, but to what extent that reduces emissions depends on the efficiency of the grid supplying the power. According to the International Energy Agency, “rail electrification can lead to an efficiency gain of around 15 percent on a life-cycle basis.” As electricity production shifts to renewables, rail has the potential to provide nearly emissions-free transport. In the meantime, improving the fuel efficiency of trains, whether diesel powered or electric, reduces cost and makes them more competitive, especially for moving freight. As the Rocky Mountain Institute notes, “[Trains], one of the [world’s] oldest transportation platforms . . . can move four times more ton-miles per gallon than trucks, typically at a lower cost.” Cost advantages may encourage companies to move freight by train rather than by truck, thereby reducing emissions from the mass movement of goods.

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Forging recycled aluminum products, for example, uses 95 percent less energy than creating them from virgin materials. Of course, even the most efficient recycling, such as aluminum, is not without emissions of its own. Collection, transport, and processing are, for the

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Pay-as-you-throw programs, such as the one used in San Francisco, bill households for rubbish sent to landfill but carry away recycling and compost for free. (San Francisco also includes clothing, a rapidly growing but often-overlooked waste stream, in its recycling mix.) Mechanisms that require consumers to pay a redeemable deposit at purchase can be applied broadly, from bottles to electrical goods, and also raise recovery rates. One common approach has produced mixed results.

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Extended producer responsibility (EPR) is an increasingly popular policy approach that makes companies responsible not just for creating goods but for managing them post-use. Otherwise, the public bears the brunt of disposal. EPR can be purely financial, charging producers for the cost of recovery and recycling; it can be physical as well, getting them directly involved in that process. Since 2006, the Dutch have used EPR for packaging. Where they exist, producer “take-back” laws help address e-waste. Companies such as carpet tile manufacturer Interface voluntarily seek to retrieve their product, so discarded tiles can provide feedstock for new ones. The outdoor clothing company Patagonia collects “worn wear” for repair or, if too far gone, for recycling. But voluntarily taking such responsibility is unusual. Formalizing it encourages companies to think now about what will happen then and make their products longer lasting, easier to fix, and as recyclable as possible. In other words, while recycling happens at end of life, it is best considered from the beginning.

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Enhancing the exchange of recyclable and reusable goods is essential. As a step in this direction, the U.S. Materials Marketplace was launched in 2015 as a matchmaker for secondary materials. The initiative actively identifies opportunities and links the relevant parties, brokering transactions between companies if need be. In parallel, the science and processes of recycling have to evolve. Writing in the journal Nature, Swiss architect Walter Stahel urges, “To close the recovery loop we will need new technologies to de-polymerize, de-alloy, de-laminate, de-vulcanize, and de-coat materials.” Innovative conversion technologies can increase recycling rates significantly. Of course, recycling is just one piece of the integrated strategy needed: swapping virgin materials with recycled ones, making more efficient use of materials, and extending product life through good design and solid construction. Trash cannot always become treasure, but a growing body of evidence suggests significant environmental and economic gains can be realized when that transformation is managed and circularity is embedded into industry. • IMPACT: As mentioned above, household and industrial recycling were modeled together. The total additional implementation cost of both is estimated at $734 billion, with a net operational savings of $142 billion over thirty years. On average, 50 percent of recyclable materials come from industrial and commercial sectors. At a 65 percent recycling rate, the commercial and industrial sectors can avoid 2.8 gigatons of carbon dioxide by 2050.

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Roman concrete was used in creating the magnificent Pantheon temple in Rome. Completed in 128 AD, it is famed for its five-thousand-ton, 142-foot dome made of unreinforced concrete—still the world’s largest almost two thousand years later. If it had been built with today’s concrete, the Pantheon would have crumbled before the fall of Rome, three hundred years after its dedication. Roman concrete contained an aggregate of sand and rock just like its modern kin, but it was bound together with lime, salt water, and ash called pozzolana, from a particular volcano. Blending volcanic dust into the mixture of opus caementicium even enabled underwater construction. The art and science of concrete largely fell away with the Roman Empire itself, until it was revived and evolved in the nineteenth century. Today, concrete dominates the world’s construction materials and can be found in almost all infrastructure. Its basic recipe is simple: sand, crushed rock, water, and cement, all combined and hardened. Cement—a gray powder of lime, silica, aluminum, and iron—acts as the binder, coating and gluing the sand and rock together and enabling the remarkable stonelike material that results after curing. Cement is also employed in mortar and in building products such as pavers and roof tiles. Its use continues to grow—significantly faster than population—making cement one of the most used substances in the world by mass, second only to water.

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Manufacturing a single ton of cement requires the equivalent energy of burning four hundred pounds of coal. Add those emissions up and for every ton of cement produced, nearly one ton of carbon dioxide puffs skyward. In total, the industry produces roughly 4.6 billion tons of cement each year, more than half of it in China, and generates 5 to 6 percent of society’s annual anthropogenic carbon emissions in the process. More efficient cement kilns and alternative kiln fuels, such as perennial biomass, can help address the emissions from energy consumption. To reduce emissions from the decarbonization process, the crucial strategy is to change the composition of cement. Conventional clinker can be partially substituted for alternative materials that include volcanic ash, certain clays, finely ground limestone, and industrial waste products, namely: blast furnace slag, a by-product of making iron that was used in constructing the Empire State Building and Paris Metro, and fly ash, a powdery residue from coal-burning power plants that found its way into the Hoover Dam. Because these materials do not require kiln processing, they leapfrog the most carbon-emitting, energy-intensive step in the cement production process. Already, more than 90 percent of blast furnace slag is used as clinker substitute. One-third of fly ash is, and that portion could grow. Fly ash and Portland clinker can be mixed together at various ratios depending on the cement’s final use and type of fly ash used, with fly ash regularly comprising 45 percent of the blend.

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According to the United Nations Environment Programme, the average global rate of clinker substitution could realistically reach 40 percent (accounting for all alternative materials) and avoid up to 440 million tons of carbon dioxide emissions annually. Depending on their particular composition, alternatives to Portland cement offer benefits beyond the atmosphere: They can be more workable, less water intensive, denser, more resistant to corrosion and fire, and longer lasting. Though they can be slower to set and not as strong early on, their ultimate strength can actually be higher. Governments and corporations have begun to concretize the possibilities of clinker substitutes. With regional standards, the European Union reuses most of its available fly ash. Prior to those policy changes, utilization rates varied widely and were as little as 10 percent in some places. New York City has embraced ground bottle glass as an emerging substitute that can be sourced regionally and saves landfill space—an innovation that may be poised for growth. From municipal to international levels, standards and product scales are key for shifting practices within the construction industry and advancing the use of alternative cements in sidewalks and skyscrapers, roads and runways. • IMPACT: Because fly ash is a by-product of burning coal, each ton created is accompanied by 15 tons of carbon dioxide emissions. Using fly ash in cement can offset only 5 percent of those emissions. Even so, if 9 percent of cement produced between 2020 and 2050 is a blended mix of conventional Portland cement and 45 percent fly ash, 6.7 gigatons of carbon dioxide emissions could be avoided by 2050. The production savings of $274 billion are largely a result of longer cement life span.

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Refrigerants continue to cause planetary trouble, however. Huge volumes of CFCs and HCFCs remain in circulation, retaining their potential for ozone damage. Their replacement chemicals, primarily hydrofluorocarbons (HFCs), have no deleterious effect on the ozone layer, but their capacity to warm the atmosphere is one thousand to nine thousand times greater than that of carbon dioxide, depending on their exact chemical composition. In October 2016, officials from more than 170 countries gathered in Kigali, Rwanda, to negotiate a deal to address the problem of HFCs. Despite challenging global politics, they reached a remarkable agreement. Through an amendment to the Montreal Protocol, the world will begin phasing HFCs out of use, starting with high-income countries in 2019 and then expanding to low-income countries—some in 2024, others in 2028. HFC substitutes are already on the market, including natural refrigerants such as propane and ammonium. Unlike the Paris climate agreement, the Kigali deal is mandatory, with specific targets and timetables for action, trade sanctions to punish failure to comply, and commitments by rich countries to help finance the cost of transition. It was a monumental achievement on the path to drawdown, called by then secretary of state John Kerry “the biggest thing we can do [on climate] in one giant swoop.” Scientists estimate the accord will reduce global warming by nearly one degree Fahrenheit.

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Still, the process of phasing out HFCs will unfold over many years, and they will persist in kitchens and condensing units in the meantime. With adoption of air-conditioning soaring, especially in rapidly developing economies, the bank of HFCs will grow substantially before all countries halt their use. According to the Lawrence Berkeley National Laboratory, 700 million air-conditioning units will have come online worldwide by 2030. All of this means parallel action is requisite: addressing the refrigerants coming out of use, as well as transitioning those going in. Refrigerants currently cause emissions throughout their life cycles—in production, filling, service, and when they leak—but their damage is greatest at the point of disposal. Ninety percent of refrigerant emissions happen at end of life. If the chemicals (or appliances that use them) are not disposed of effectively, they escape into the atmosphere and cause global warming. On the other hand, refrigerant recovery has immense mitigation potential. After being carefully removed and stored, refrigerants can be purified for reuse or transformed into other chemicals that do not cause warming. The latter process, formally called destruction, is the one way to reduce emissions definitively. It is costly and technical, but it needs to become standard practice.

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In less than a century, air-conditioning in the United States went from being a luxury good to a widespread commodity. Today, 86 percent of U.S. homes have systems that provide cool air. They became common, if not universal, in urban Chinese households in just fifteen years. And why would they not? In seasons of heat and humidity, air-conditioning increases comfort and productivity and can save lives during heat waves. And yet, a great irony of global warming is that the means of keeping cool make warming worse. As temperatures rise, so does reliance on air conditioners. The use of refrigerators, in kitchens of all sizes and throughout “cold chains” of food production and supply, is seeing similar expansion. As technologies for cooling proliferate,… Some highlights have been hidden or truncated due to export limits.

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Downtown Singapore, showing the ubiquity of air-conditioning units on Asian streets. IMPACT: Our analysis includes emissions reductions that will be achieved through the 2016 Kigali accord, as well as additional practices to manage refrigerants already in circulation. We model adoption of practices to (1) avoid leaks from refrigerants and (2) destroy refrigerants at end of life. Over thirty years, 87 percent of refrigerants that may be released can be contained, avoiding emissions equivalent to 89.7 gigatons of carbon dioxide. Although some revenue can be generated from resale of recovered refrigerant gases, the costs to establish and…