Sea level rise and city flooding update

The safety band of Antarctic ice shelves, Johannes Jakob FürstGaël Durand, et al.  Many communities have 20 years or less to prepare before rising seas begin to regularly impact homes, neighborhoods, and families. Other communities are already facing this disruptive reality.

Scientists estimate that 275 million people worldwide live in areas that will eventually be flooded at 3C of global warming.  Osaka is facing $1tn in flooding.  In Miami-Dade county alone, almost $15bn of coastal property is at risk of flooding in just the next 15 years.  Although sea levels will not rise instantaneously, the calculated increases will be “locked in” at a temperature rise of 3C, meaning they will be irreversible even if warming eventually slows down.  The IPCC reported that Alexandria’s beaches would be submerged even with a 0.5-metre sea-level rise, while 8 million people would be displaced by flooding in Alexandria and the Nile Delta if no protective measures are taken. A 3C world threatens far greater damage than that.

Yet for many residents, there is little public information to connect the increasingly chaotic weather and floods with climate change. “The vast majority of Alexandrians don’t have access to knowledge, and that’s what worries me. I don’t expect the government to raise awareness of this problem until it’s already happening,” said 22-year-old student Kareem Mohammed.

“Everyone thinks we should act on this problem 50 or 80 years from now,” agreed his friend, Hazem Hassan, a student in marine biology at the nearby Alexandria University.

Half of Modern Global Warming Caused by 90 Companies, New Study Concludes, by Bobby Magill Union of Concerned Scientists study, reported in Climate Liability News

Researchers have for the first time tied a group of the world’s largest fossil fuel companies, including ExxonMobil, and their products to specific increases in greenhouse gases, global warming and sea level rise. A study published Thursday in the journal Climatic Change concludes that since 1880, 90 of the largest carbon producers are responsible for up to 50 percent of global temperature rise, 57 percent of the increase in carbon dioxide in the atmosphere and between 26 and 32 percent of global sea level rise.

The research could open the door for those who have suffered losses due to climate change to sue major oil companies for damages. The study also links each individual company to its percentage impact on climate change.

This study could inform approaches of juries and judges who are looking to monetize damages,” said study lead author Brenda Ekwurzel, a climate scientist at the Union of Concerned Scientists.

Three suits have already been filed against a group of fossil fuel companies by three California communities attempting to hold them accountable for damages caused by climate change. The new research helps assign percentages of blame to those companies.

“This is a very important study that further confirms key elements of the lawsuits against many of these fossil fuel companies,” said Vic Sher, partner in Sher Edling, the law firm representing the three California communities. “The science is clear that these companies have caused a substantial portion of the sea level rise that is damaging San Mateo County, Marin County, the City of Imperial Beach, and communities like them around the country.”

The research—conducted by a team of scientists from UCS, the Climate Accountability Institute and Oxford University—estimates each major oil company’s greenhouse gas emissions dating back to 1880 and calculates how much those emissions contributed to climate change.

The paper breaks those results into two separate categories: individual energy companies’ overall contributions to climate change between 1880 and 2010 and their contributions to climate change between 1980 and 2010 — a period during which the firms’ own science showed their products cause global warming.

In the century prior to 1980, companies may not have been aware of the harm their products cause, Ekwurzel said. After 1980, the firms had sufficient scientific data showing carbon dioxide from burning the fossil fuel they produce was harmful.  Investigations by journalists as well as scholarly research concluded that ExxonMobil knew decades ago that their products are harmful to the climate and that instead of taking action to mitigate the harm, the company misled the public and cast doubt on climate science. Exxon did not respond to requests for comment.

“Once it became clear no later than the 1960s that continuing CO2 emissions would progressively undermine the climate, the major carbon producers could see that they were marketing harmful products,” said Henry Shue, a professor emeritus of politics and international relations at Oxford University, wrote in a commentary published alongside the study.  He said responsible fossil fuel companies should have either developed methods to capture and store carbon emissions associated with their products or substituted them with non-carbon-based forms of energy.  “If ExxonMobil and similar companies had acted on their own scientists’ research about the risk of their product, climate change would be far more manageable and less costly today,” Ekwurzel said.

The study finds that state-owned Saudi Aramco of Saudi Arabia and Gazprom of Russia contributed more to global warming than any other company since 1980. But Exxon, BP, Chevron, Shell, and Peabody Energy are the world’s largest investor-owned companies that contributed to global warming and sea level rise in that time.  Exxon contributed more climate pollution than any investor-owned company. It and its predecessor companies alone are responsible for nearly 1.5 percent of the historical rise in global atmospheric carbon dioxide concentrations between 1980 and 2010 and Exxon and its predecessors are responsible for more than 2.75 percent since 1880, the study said. The company’s emissions have contributed more than 1 percent to the rise in global average surface temperature since 1980, and about 0.5 percent to sea level rise during that period.

Overall, Saudi Aramco has contributed more to the rise of atmospheric carbon dioxide since 1880 than any other company — more than 3 percent. Chevron is the leading contributor to both the historical rise in surface temperatures and sea levels since 1880 — just more than 2.75 percent on both counts.

The research builds upon 2013 research by Climate Accountability Institute founder Richard Heede, which quantified the total historical carbon dioxide and methane emissions of the top 90 fossil fuel companies and other carbon producers.  Kevin Trenberth, a climatologist at the National Center for Atmospheric Research in Boulder, Colo., said the study makes a “reasonable guess” about each fossil fuel company’s responsibility for global warming.  But he said the study is flawed because the researchers did not test the climate model they used on independent data. The model may also be overly simplistic, leading to errors, he said.  “For example, it uses global mean surface temperature but has no hydrological cycle, no land-versus-ocean, no Arctic amplification and no validation,” Trenberth said. “It does not provide any information about how good any of the relationships are that the model is based on and how stable they are over time.”

Legal experts say the study opens the door to legal liability for oil companies and possibly tobacco-style lawsuits, which found that tobacco companies misled the public to cast doubt on the dangers of cigarettes.

“Litigants will still face a number of hurdles to win a tobacco-style climate lawsuit, but this study helps considerably to quantify shares of causal responsibility,” said Douglas Kysar, a Yale Law School professor whose research focuses on product liability and climate change law.  “The need to assign liability has increased significantly in recent years as we have learned more about the fossil fuel industry’s decision to ignore its own internal evidence regarding the catastrophic threats posed by climate change and to intentionally mislead the public and policymakers regarding those threats,” he said.

Mary Wood, a natural resources law professor at the University of Oregon Law School, said the study is a major leap forward in laying the scientific groundwork for a liability suit against fossil fuel companies for damages from climate change and sea level rise.  “It takes on the task of translating emissions into actual damage to these vital planetary systems,” she said.

But Michael Burger, executive director of the Sabin Center for Climate Change Law at Columbia University, warned that the study itself does not determine any company’s legal liability.

“The study offers another piece of scientific evidence that supports attributing some specific portions of climate change impacts to a set of some 90 fossil fuel production companies,” Burger said. “The body of literature on attribution science is large and growing. The new UCS study makes a contribution to that body of literature, but it is not determinative in and of itself of any company’s or companies’ liability.”


A new study quantifies the impacts of emissions traced to major fossil fuel producers on our changing climate.

recent study published by Brenda Ekwurzel and others takes this sea level rise attribution one step further by showing that about 30% of global sea level rise since the Industrial Revolution was caused by the burning of products from 90 major fossil fuel companies.  Tracing Who’s Responsible for Temperature Increase and Sea Level Rise (2017)

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The impacts of global warming are here and they are costly. Sea level rise floods towns and erodes shorelines. Frequent and intense heatwaves threaten our workers’ health and damage our infrastructure. Extreme weather ruins our crops and corrodes businesses, factories and homes. In New York City alone, officials estimate that it will cost $19.5 billion dollars to prepare the city for sea level rise. And globally, climate adaptation costs are staggering.  Will top fossil fuel producers help shoulder the costs? They should.

As early as 1977, investor-owned fossil fuel companies knew their business was risky—that the use of their products released dangerous amounts of carbon dioxide and methane emissions that could destabilize our climate.  These companies could have taken steps to reduce the risks. Instead, they chose to misinform the public and their investors, block action to limit carbon emissions and carried on with business as usual.

But, we now have the science to determine how much the emissions related to fossil products have contributed to global temperature rise and sea level rise.    A peer-reviewed study, authored by Brenda Ekwurzel, James Boneham, Mike Dalton, Rick Heede, Roberto Mera, Myles Allen and Peter Frumhoff and published in Climatic Change, analyzed and quantified the climate change impacts of carbon dioxide and methane emissions traced to each company for two time-periods: 1880 to 2010 and 1980 to 2010.


Antarctic Contribution to Sea Level Rise

In the past couple of years major developments in the ability to model the response of the Antarctic ice sheets to warming have begun to hone our understanding of Antarctica’s potential contribution to sea level rise this century.

The CSSR is unequivocal that Antarctica (and Greenland) are losing ice, and there is a growing body of evidence suggesting that the pace of that loss is accelerating. The rate of ice loss is about 100 gigatons per year–an amount that this Washington Post article can help us to wrap our heads around.

The Thwaites Glacier, part of the West Antarctic Ice Sheet, appears to be in “an irreversible state of decline,” according to a 2014 study by Eric Rignot and others.

Models suggest that ice loss from Antarctica could contribute more than three feet to global sea level rise this century on top of rise from other sources. This growing body of knowledge is reflected in what the CSSR calls an “extreme” scenario in which sea level rises by an average of 8.5 feet by 2100. The previous NCA report’s highest sea level rise scenario projected about 6.6 ft by 2100.

There’s a concerted effort in the CSSR to incorporate the latest science about Antarctic ice loss into sea level rise projections. But there’s still enough uncertainty that Antarctica’s potential contribution couldn’t be fully accounted for when assigning probabilities to potential sea level rise futures.

Communities will be affected by more frequent, more severe flooding before they are permanently underwater

Since 2014, there’s been an increased focus on what happens between now and the point at which coastal regions are permanently underwater due to sea level rise. This in-between time will be characterized by an increase in the number and extent of high tide flooding events, and a number ofstudies in the past three years have painted a picture of what that looks like quantitatively and qualitatively.


King tide flooding in Charleston, SC, on October 7, 2017. The local National Weather Service office has issued 38 Coastal Flood Advisories for the region already this year.

The CSSR puts this issue of tidal flooding up front in key message #4: “As sea levels have risen, the number of tidal floods each year that cause minor impacts…have increased 5- to 10-fold since the 1960s…Tidal flooding will continue increasing in depth, frequency, and extent this century.”

While the tidal flooding findings described here won’t be news to regular readers of this blog or to residents of flood-prone places like Charleston and Annapolis, their elevation to key finding status will hopefully highlight the insidious threat of frequent flooding that hundreds of communities in the U.S. could face in the coming decades. The East Antarctic ice sheet is 10 times larger than the West Antarctic ice sheet and estimates are that it would raise sea level nearly 200 feet if it completely melted. Hence the concern among scientists and the need to study the potential impacts of a melting West Antarctic ice sheet on its neighboring ice sheet.

Arthern, R. J., and C. R. Williams (2017), The sensitivity of West Antarctica to the submarine melting feedback, Geophys. Res. Lett., 44, 2352–2359, doi:10.1002/2017GL072514. Even without additional forcing from changes in climate, ice shelf collapse, or ice cliff collapse, the model predicts slow, sustained retreat of West Antarctica, driven by the marine ice sheet instability and current levels of ocean-driven melting. When observed rates of melting are included in new subglacial ocean cavities, the simulated sea level contribution increases, and for sufficiently intense melting it accelerates over time. 25 Oct 2017

Climate Central has ranked the U.S. cities most vulnerable to major coastal floods using three different metrics:

  1. The total population within the FEMA 100-year floodplain
    2. The total population within the FEMA 100-year floodplain as augmented by sea level rise projections for the year 2050
    3. The total high social vulnerability population within the same areas as group #2

Each analysis examined coastal cities with overall populations greater than 20,000. For the first one, we tabulated “at risk” population by overlaying 2010 Census block population counts against FEMA’s 100-year coastal floodplains (Crowell et al 2013) using methods adapted from Strauss et al (2012). FEMA 100-year coastal floodplains factor in storm surge, tides, and waves, and include all areas determined to have an at least one percent annual chance of flooding. Based on locations meeting these criteria and population density, New York City ranked first, with over 245,000 people at risk, followed by Miami and then Pembroke Pines, also in South Florida.

In our second analysis, we re-ranked cities based on which have the largest populations in the expanded areas that could be threatened in the year 2050 — due to sea level rise driven by climate change, plus nonclimatic factors such as local land subsidence. We determined these areas by using median local sea level rise projections for midcentury (Kopp et al 2014) under an unrestricted emissions scenario (“Representative Concentration Pathway 8.5”) to additively elevate the FEMA 100-year floodplain, and accordingly extend it as topography allows, following methods detailed in States at Risk: America’s Preparedness Report Card Technical Methodology. After this adjustment, New York City still had the greatest number of people on threatened land, followed by Hialeah, Florida and Miami. 36 cities in Florida placed in the top 50.

The top five cities with the greatest increase in population on land at risk when adding on sea level projections were New York City, with a difference exceeding 181,000, plus Hialeah, Boston, Fort Lauderdale, and The Hammocks, Florida.

The yellow, orange and red show areas at or below Sandy’s peak flood elevation at The Battery.

Finally, we also ranked coastal cities by their “high social vulnerability” population within the areas delineated by our second analysis. High social vulnerability was determined using the Social Vulnerability Index developed by the Hazards and Vulnerability Research Institute, which incorporates 29 different socioeconomic variables to evaluate the ability of communities to prepare and respond to environmental hazards such as floods. New York City, Philadelphia, Houston, Baltimore, and Miami were ranked as the top five cities with the largest high social vulnerability populations within the future FEMA 100-year floodplain — and thus face a difficult double jeopardy over time.

Sea level rise is a key indicator and consequence of climate change.

To learn more about coastal cities at risk visit Climate Central’s States at Risk and Risk Finder.

Analysis by Scott Kulp, PhD and Benjamin Strauss, PhD. Dyonishia Nieves, Shari Bell, and Dan Rizza contributed to this report



Steady increase in nuisance flooding

more than 90 coastal communities in the United States are battling chronic flooding, meaning the kind of flooding that’s so unmanageable it prompts people to move away.  That number is expected to roughly double to more than 170 communities in less than 20 years.

By the end of the century, chronic flooding will be occurring from Maine to Texas and along parts of the West Coast. It will affect as many as 670 coastal communities, including Cambridge, Massachusetts; Oakland, California; Miami and St. Petersburg, Florida; and four of the five boroughs of New York City. The magnitude of the coming calamity is so great, the ripple effects will reach far into the interior.

The Union of Concerned Scientists, in a new report published today in the peer-reviewed journal Elementa, mapped the rate of sea-level rise for the first time for hundreds of coastal communities—in an online feature that allows viewers to zoom in from a bird’s eye view all the way down to street level. The report also creates a timeline when sea-level rise is projected to inundate various percentages of coastal communities—and then delves into the politically and economically sensitive arena of what to do about it.

Options are limited. All are costly, whether adapting to a watery future with seawalls and other barriers, or retreating and finding a new place to call home.

says Erika Spanger-Siegfried, the report’s co-lead author. “We recognized we were going to have to offer something useful to communities in the way of solutions. We wanted people to see this coming, to give them a sense of the time they have before this becomes untenable, and outline things they can do to respond.”

The new coastal project, Spanger-Siegfried says, began with several practical questions:

How many times a year would residents tolerate chronic flooding that overwhelmed their neighborhood? If saltwater flooding regularly soaked homeowners’ first floor or damaged their cars, how often would it have to occur before residents began to look for a new place to live? How long would it be before they could no longer afford to insure or sell their home?

“We are not mapping the so-called ‘bathtub approach,’ which is just measuring sea-level rise over time. In other words, where will high tide be every day with a foot of sea-level rise?” says Spanger-Siegfried. “That’s not how people plan and live their lives. They will make decisions based on what is chronically inundated decades before things are permanently inundated.”

Chronic, disruptive flooding was defined as 10 percent or more of a community’s usable land flooding 26 times a year, or every other week. Most of the 90 communities that experience such flooding already are in Louisiana and Maryland, where land subsidence has intensified the effects of sea-level rise. Life has already been altered in those places, where flood advisories are normal and residents have learned to avoid low-lying streets. (Watch an island disappear from the Gulf.)

For perspective, the report’s authors note that Miami Beach, considered Ground Zero for sea-level rise, has not reached the 10 percent threshold, even as it experiences high-tide flooding and has invested more than $400 million to rebuild the city’s storm sewers. Likewise, flooding in Annapolis, Maryland, home to the U.S. Naval Academy, is not expected to reach the 10 percent threshold, although key parts of the city, including the academy campus and downtown, now flood 40 times a year.

But over time, disruptive flooding will spread, engulfing the Jersey shore, the mainland side of North Carolina’s Pamlico Sound, and throughout South Carolina’s Low Country.


The study examined three scenarios: a “low” scenario that assumes carbon emissions decline dramatically and global warming is limited to 2 degree Celsius; an “intermediate” scenario, which projects carbon emissions peaking at mid-century, resulting in four feet of sea-level rise globally; and “high” scenario, which occurs toward 2100, with polar ice melting fast enough to produce about 6.5 feet of sea-level rise. Scientists consider the “high” scenario to be increasingly plausible, the study notes, as the melting of ice sheets accelerates.

“This is a much nearer-term and more widespread problem,” Spanger-Siegfried says. “We are going to have to appreciate that we are at the front end of a climate change adaptation century. Our coasts face a certain amount of transformation with sea-level rise and a huge share of our population lives, and GDP is generated, on the coasts. And as tens of communities turn into hundreds of communities, we are going to have to marshal federal resources to enable this change to unfold in a manageable way.”

On the West Coast, which lacks the East Coast’s long, shallow offshore shelf, rising seas will be less serious, but cities in the San Francisco Bay area will flood by 2060, the reports says.

There is time enough to prevent some of the flooding, the report’s authors contend, if the world’s nations can successfully cut greenhouse gas emissions as outlined in the Paris climate accords. But for hundreds of other communities, including the small towns that dot Maryland’s Eastern Shore, as well as Savannah, Georgia, New Orleans and Miami, it may already be too late. Chronic flooding can be avoided only by adaptation measures—seawalls, levees, and other barriers—or by moving away.

It’s the inclusion of that last option, and others, such as halting development along coastal areas at risk to flooding, that sets this study apart from others. Community groups in Miami, Norfolk, Virginia, and other vulnerable places along the coast are already planning, but are cautious about sounding the note of “retreat” too loudly, lest they crash the local economy decades prematurely.

Spanger-Siegfried says she understands the dilemma. But her team decided to include a discussion of options in the study after a climate change expert who works with communities advised them to. “If you want to do anything useful for coastal communities,” she said,”Tell them how much time they have to act.”

“With this report,” the team writes, “we tried to do just that.”

Laura Parker is a staff writer who specializes in covering climate change and marine environments.

The steady rise in sea level is unlikely to cause flooding directly as coastline developments are designed to withstand the larger ebb and flow of the tides. But the rising level gives a higher starting point for the storm surges and big waves that can overwhelm coastal defences.

The research, published in the Scientific Reports journal, is the first to analyse these factors, particularly waves, on a global scale. It found that the most at-risk areas were in the low latitudes, where tidal ranges are smaller meaning sea level rise is proportionally more significant.

Sea level rise: Miami and Atlantic City fight to stay above water

In those locations, just 2.5cm of sea level rise leads to extreme water levels being seen twice as often, while a 5-10cm increase means coastal floods are twice as likely across all the tropics. A rise of 20cm leaves almost every coast with twice the risk.

Recent research has suggested the great ice caps are more vulnerable than expected in a warming world and that oceans levels could rise more rapidly to reach 200-300cm by the end of the century.  Previous research estimated the damages from coastal flooding could soar to $1tn a year by 2050.

The rise of 5-10cm, likely to occur within a couple of decades, would mean major cities including San Francisco in the US, Mumbai in India, Ho Chi Minh in Vietnam and Abidjan in Ivory Coast facing a doubled risk of coastal floods. “The maps of increased flooding potential suggest a dire future,” write the scientists.

“This study shows how even small changes in mean sea level can significantly increase the frequencies with which critical thresholds are exceeded,” said Thomas Wahl, professor of coastal risks at the University of Central Florida



LA Times May 2017

Rising sea levels could mean twice as much flood risk in Los Angeles and other coastal cities

Rising sea levels could mean increased flood risks for Los Angeles. (May 19, 2017)

Amina Khan

The effects of rising oceans on coastal flooding may be even worse than we thought. Scientists have found that a mere 10 to 20 centimeters of sea-level rise — which is expected by 2050 — will more than double the frequency of serious flooding events in many parts of the globe, including along the California coastline.

The findings, described in Scientific Reports, highlight the environmental and economic impacts of sea-level rise on coastal areas, and the need to properly predict and prepare for these effects.

As global warming marches onward and land-ice reserves continue to melt into the seas — thanks in large part to human-produced greenhouse gases — oceans are continuing their upward creep.

Researchers have long made global-scale estimates of sea-level rise and analyzed what effects the ocean’s ascent will have on coastal erosion, on the environment and on human communities. Those estimates have taken into account storm surge and tidal fluctuations, among other variables. But they haven’t included a crucial factor: waves.

“Most of these tide gauges are within harbors or in protected areas, so they don’t record any water level associated with waves,” said Sean Vitousek, a coastal scientist at the University of Illinois at Chicago.

Waves might seem like small potatoes compared with high tides, but they can have a big impact, Vitousek said.

“Waves often generate a pretty significant portion of the actual flood levels,” he explained. “For instance, if you think about just tides and storm surge, then in some areas, waves can add an additional 50-to-100% of that existing water level.”

That’s particularly true in California. Much of the flooding here is dominated by wave-driven events — which is why El Niño years with extremely large waves can have such profound effects on coastal erosion. A recent paper by one of Vitousek’s co-authors showed that the 2015-16 El Niño season caused unprecedented levels of erosion across much of the West Coast.

Even on islands in the Pacific and other equatorial regions where waves are smaller and the tides bring only a few centimeters of change, waves can have an outsize impact — in part because humans may build closer to the water line in those areas and be unprepared for the changes that come with sea-level rise.

For this paper, Vitousek and his colleagues combined wave, tidal and storm surge models with their data on sea-level projections. The results showed that 10 to 20 centimeters of sea-level rise happening no later than 2050 could have major impacts in many parts of the globe, including around India, the Indian Ocean and the tropical Atlantic along the west coast of Africa.

“Often these areas are fairly low-lying, have a lot of development, and those areas would also be fairly impacted by future sea-level rise,” he said. “As you go to higher latitudes, you’ll still get these effects, but not quite as much, because the waves are larger, the tide is larger and so sea-level rise doesn’t represent the same percent or relative contribution to those areas.”

The effects will be most pronounced in the tropics, the researchers found. Areas such as the Marshall Islands in the central Pacific are particularly vulnerable.

“You’ll still see impacts at higher latitudes — the California coast, the Pacific Northwest — but you probably won’t see the same dramatic effects that you would in the tropics,” Vitousek said. “It’s really going to happen everywhere, [but] it’ll happen faster in the tropics.”

The southern portion of Southern California may experience the brunt of sea-level rise in the region, he said. That includes beaches from around Point Loma all the way up to Laguna Beach, including La Jolla, Del Mar and Oceanside.

“These areas have very limited stretches of sandy beach providing a buffer from storms, so they will certainly be the ones that experience the largest impact,” he said.

Beaches in the Los Angeles area, such as in Santa Monica and Redondo Beach, and Dockweiler Beach by LAX, are much wider, with extremely large buffers of sand between land and water (thanks in part to decades of “nourishment” as humans dredged sand and brought it to shore).

But many areas in Malibu and Santa Barbara will feel the hit. Thanks to waves, higher sea levels in California come not just with flooding, but with erosion and cliff retreat.

The scientists are sharing this information with state and local agencies to try to figure out where the most vulnerable areas may be — and what should be done to prepare them. For the moment, Vitousek said, one of the easiest solutions may be more beach nourishment, even though it’s a temporary solution at best.

The scientists hope to calculate how much economic damage could be incurred by the effects of sea-level rise. In the meantime, they’re continuing to study its impact on the California coastline in ever more granular detail — and that in-depth understanding may help scientists continue to improve their models for the world.

“I think it calls to attention the future consequences of sea level rise,” said William Sweet, an oceanographer with the National Oceanic and Atmospheric Administration in Silver Spring, Md., who was not involved in the work.

Sweet recently led a NOAA report showing that sea-level rise will progress faster in some places and slower in others — variations that would be key in understanding coastal flooding effects in different areas. The Scientific Reports paper did not take this into account.

“In reality it’s not going to be a uniform rise,” he said. “The change in land elevation itself, changes in circulation, change in gravity in the future as the ice caps change are all going to cause a very non-uniform rise in sea levels.”

Future, increasingly detailed assessments of the impacts of sea-level rise, he added, will need to take that variability into account.



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5 p.m.: This story has been updated to include comments from William Sweet, an oceanographer with the National Oceanic and Atmospheric Administration.

MacAyeal notes that when the ice sheets that once covered Canada, Sweden and Norway started melting some 20,000 years ago sea levels rose some 450 feet, sometimes as fast as 10 feet per century. That’s the speed of change he believes we are going to have to deal with.

“Even if we do a good job (of combatting climate change), I think the entire world will have to be dealing with rising ocean levels on the order of 5-10 feet per century,” he said.

Seth Darling, a local scientist and author of the book “How to Change Minds About Our Changing Climate,” points out that while it is the developed world that is most responsible for human-induced climate change, the developing world will pay the highest price.

“The sad truth about climate change is that it is the developed world which is really primarily responsible for putting us in the situation that we are in today and we are, however, going to feel less of the impacts than the developing world who are really not responsible for the problem,” he said.

“Southeast Asia for example is going to be absolutely hammered by the impacts of climate change and they carry very little blame for the amount of carbon that currently exists in the atmosphere. But the ramifications will hit everybody. There are no winners from climate change.”

But Darling is at pains to point out that the situation is not hopeless.

“We have today technologies on the shelf ready to go – technologies that can make a huge difference,” said Darling. “The choices are clear and we have at our hands the technologies to get us most of the way there already.”

happening now all around the Amundsen Sea. The Pine Island Ice Shelf, about 1,300 feet thick over most of its area, is a dramatic case: It thinned by an average of 150 feet from 1994 to 2012. But even more worrisome is the neighboring Thwaites Glacier, which could destabilize most of the West Antarctic Ice Sheet if it collapsed.

“These are the fastest retreating glaciers on the face of the Earth,” says Eric Rignot, a glaciologist at the NASA Jet Propulsion Laboratory in Pasadena, California. Rignot has studied the region for more than two decades, using radar from aircraft and satellites, and he believes the collapse of the West Antarctic Ice Sheet is only a matter of time. The question is whether it will take 500 years or fewer than a hundred—and whether humanity will have time to prepare.

Ian Howat, of the Byrd Polar and Climate Research Center in Columbus, Ohio, is another glaciologist who’s watching Pine Island closely. Last November he reported two ominous new rifts spreading across the ice shelf that threaten to prune it to its shortest length in recorded history. As Howat looked back through monthly satellite photos, he realized that the rifts had been triggered by a singular event that had happened, unnoticed, three years before. The strip of torn-up ice anchoring the ice shelf to its northern bank had suddenly fallen apart, suggesting it had been undermined by melting from below. It blew out “just in a matter of days,” Howat says, “like a zipper, unzipping the side of the glacier.”It’s unclear when the entire ice shelf might disintegrate. The “warm” water flowing underneath it from offshore is only 4 to 6 degrees Fahrenheit above freezing. But roughly 3,000 cubic miles of it arrives every year, which means the ice shelf is receiving an amount of heat that exceeds the output of a hundred nuclear power plants, operating 24/7.

In fact, research by Rignot and others over the past few years indicates that the collapse of several major glaciers flowing into the Amundsen Sea is now unstoppable. Between 2002 and 2009 alone, the ice shelf in front of the Smith Glacier thinned by 1,500 feet in some places, the one in front of the Pope Glacier by up to 800 feet. The grounding lines of the Amundsen glaciers have retreated so far—tens of miles in some cases—that they now rest on seafloor that slopes down toward the center of the ice sheet. Each increment of retreat exposes a greater ice surface to warm ocean water. It’s a runaway process—and scientists are urgently trying to figure out how fast it will run.

The ice shelves, Fricker says, “are the canary in the coal mine.” Because they’re already floating, they don’t raise sea level themselves when they melt—but they signal that a rise is imminent, as the glaciers behind them accelerate. Fricker and her team have found that from 1994 to 2012, the amount of ice disappearing from all Antarctic ice shelves, not just the ones in the Amundsen Sea, increased 12-fold, from six cubic miles to 74 cubic miles per year. “I think it’s time for us scientists to stop being so cautious” about communicating the risks, she says.

The retreat and hemorrhage of these glaciers “will accelerate over time,” agrees Rignot. “Maybe you don’t care much about that for the next 30 to 40 years, but from 2050 to 2100 things could get really bad, and at that point listening to scientists is irrelevant.” Yet after things get really bad, they could still get worse.

Most of the heat trapped by our fossil fuel emissions since the industrial revolution began in the 19th century has gone into the ocean. Most of the heat now hitting the Antarctic ice shelves, however, comes from another effect of climate change: Intensified circumpolar winds and currents have driven warmer water from offshore onto the continental shelf and under the floating ice. Much more ocean warming is yet to come, even if we begin to cut emissions. A lot more heat is on the way to Antarctica.

Scientists are especially concerned about the Thwaites Glacier, which by itself could raise global sea level four feet; last fall the British and American science foundations announced a coordinated $20 million to $25 million field campaign that will deploy ships, planes, satellites, and underwater robots to assess the glacier’s status starting in 2018. For now, the best estimates suggest that Antarctica will sweat off enough ice to raise global sea levels by 1.5 to 3.5 feet by 2100, depending on how quickly humans continue to pump out greenhouse gases. Throw in Greenland and other rapidly melting glaciers around the world, and sea level could plausibly rise three to seven feet by 2100.

To consider the worst case, then, scientists must turn their eyes toward East Antarctica, home to more than three-fourths of all the ice on Earth.

Until recently the East Antarctic Ice Sheet was considered secure; unlike West Antarctica, it sits on high ground. But mapping with ice-penetrating radar has revealed a low-lying region cut by glacially carved channels that drop as far as 8,500 feet below sea level—perfect for guiding warm ocean water deep into the heart of the ice sheet. The Totten Glacier is the largest coastal outlet in this region. If it collapsed, global sea level could rise 13 feet—“roughly as much as all of West Antarctica,” Rignot points out. “One glacier alone.”

In January 2015, the Australian icebreaker Aurora Australis became the first ship to reach the front of Totten. Like the Palmer at Pine Island in 1994, it found deep, warm water flowing under the ice shelf, at a rate of 4.5 cubic miles a day. The glacier is already losing a couple of cubic miles of ice per year—small potatoes, in Antarctic terms. But Donald Blankenship, a University of Texas glaciologist who oversees the aerial survey, fears it could blow up.

In 2016 his team reported evidence from the bedrock that Totten repeatedly has retreated 100 to 200 miles inland from its current position—meaning it might help explain why sea level was so much higher three million years ago. Blankenship’s surveys have also identified two seafloor grooves deep enough to let warm water under Totten’s ice shelf. Last January the team was refining those seafloor maps.

Totten will lose its ice more slowly than West Antarctica. The worst case coming out of Antarctica still seems to be centuries away. But it would mean abandoning many of the world’s largest cities, including New York, Los Angeles, Copenhagen, Shanghai, and dozens of others—and it’s looking less crazy all the time. “The fuse is lit,” says Blankenship. “We’re just running around mapping where all the bombs are.”

How likely is a 1-3 meter sea level rise in the next 50 or 100 years?

The panel concluded that it could not “provide a best estimate or an upper bound for sea level rise” over the next century due to their lack of knowledge about Earth’s ice. We know that there is 5-6 meters worth of sea level in the Greenland ice sheet, and 6-7 meters in the West Antarctic Ice Sheet. (The much larger East Antarctic Ice Sheet is probably not vulnerable to widespread melting until beyond the next century). However, when the last ice age ended around 12,000 years ago, rapid melting of continental ice sheets caused a sea level rise of 11 mm a year- or a meter in 100 years,