Pearce says that he and his team were generous to coal-fired power plants in how they calculated the efficiency of carbon capture and storage when scaled up. They also did not consider new ways that solar farms are being used to make them even more efficient, like using higher efficiency black silicon solar cells, putting mirrors in between rows of panels so light falling between them can also be absorbed, or planting crops between rows (agrivoltaics) to achieve greater land use.
Pearce says future research should focus on improving the efficiency of solar panels and solar farms, not on carbon capture of fossil fuel-powered plants in an attempt to become zero-emission energy-not when this data shows it isn’t realistic in order to protect our changing climate.
James Gunnar Groesbeck, Joshua M. Pearce. Coal with Carbon Capture and Sequestration is not as Land Use Efficient as Solar Photovoltaic Technology for Climate Neutral Electricity Production. Scientific Reports, 2018; 8 (1) DOI: 10.1038/s41598-018-31505-3
Michigan Technological University. “Cover the U.S. In 89 percent trees, or go solar.” ScienceDaily. ScienceDaily, 7 September 2018. <www.sciencedaily.com/releases/2018/09/180907091523.htm>.
A new study by scientists at the University of Bristol has shown that ancient global warming was associated with intense rainfall events that had a profound impact on the land and coastal seas.
The Palaeocene-Eocene Thermal Maximum (PETM), which occurred about 56 Million years ago, is of great interest to climate scientists because it represents a relatively rapid global warming event, with some similarities to the human-induced warming of today.
Although there have been many investigations of how much the Earth warmed at the PETM, there have been relatively few studies of how that changed the hydrological cycle.
This newly published work shows that rainfall increased in some places and decreased in others, according to expectations, but that much of the world experienced more intense and episodic (or ‘flashy’) rainfall events.
Lead author Dr Matt Carmichael from the University’s Schools of Chemistry and Geographical Sciences, said: “With the same climate models used to study future climate change, we studied how a doubling of carbon dioxide concentrations would affect rainfall patterns on a world with Eocene geography.
“This increased the overall global precipitation — warmer air holds more water. But it also changed the pattern and frequency of extreme events.
“The tropics became wetter and the incidence of extreme events increased, by as much as 70 percent in some tropical regions.
“In other places, total annual precipitation and the number of extreme events became decoupled; in other words, they became drier, with less frequent but more extreme events. All of this illustrates the complexity of how global warming will affect our local, regional and global rainfall patterns.”
Co-author Professor Rich Pancost from Bristol’s School of Earth Sciences, explained how these findings agree with a range of geological and chemical features of the Palaeocene-Eocene global warming.
He said: “This warming event is associated with major changes in how soil and sediment were eroded and moved around the landscape.
“In many places, river systems that had been transporting silt or sand became associated with fist-sized rocks or even boulders; and more sediment was transported to and buried in coastal margins. In some locations, the rate of sediment accumulation increased by a factor of ten. But at the same time, there is also evidence that these systems became more arid.
“Our climate simulations reconcile this for many locations, showing an increase in aridity with fewer but more intense rainfall events. Those events were likely responsible for increased energy in these systems, moving around more material and larger objects. Ultimately it flushed more sediment to the ocean, causing eutrophication, blooms of algae and in some cases hypoxia.”
Co-author Professor Dan Lunt from the School of Geographical Sciences added: “There are many similar events in Earth history, where warming appears to have been associated with changes in rainfall and sedimentary systems.
“Although we have not investigated them here, it is very likely that our results are translatable — because the physics that underpins them remains the same. Thus, the collective body of research confirms that global warming in the past and the future will be associated with more ‘flashy’ rainfall, with implications for flooding and water management.”
Professor Pancost said: “Past climate has lessons for our future. Not only do the models show evidence for more intense rainfall events — with all of the implications that entails — but they are consistent with all of our other data.
“In fact, they explain inconsistencies in our other data and confirm some long-established hypotheses. In doing so, they foreshadow our potential future with complex and dramatic changes in rainfall, more flooding and more soil erosion.”
Matthew J. Carmichael, Richard D. Pancost, Daniel J. Lunt. Changes in the occurrence of extreme precipitation events at the Paleocene–Eocene thermal maximum. Earth and Planetary Science Letters, 2018; 501: 24 DOI: 10.1016/j.epsl.2018.08.005
Millennia ago, ancient farmers cleared land to plant wheat and maize, potatoes and squash. They flooded fields to grow rice. They began to raise livestock. And unknowingly, they may have been fundamentally altering the climate of Earth.
A study published in the journal Scientific Reports provides new evidence that ancient farming practices led to a rise in the atmospheric emission of the heat-trapping gases carbon dioxide and methane — a rise that has continued since, unlike the trend at any other time in Earth’s geologic history.
It also shows that without this human influence, by the start of the Industrial Revolution, the planet would have likely been headed for another ice age.
“Had it not been for early agriculture, Earth’s climate would be significantly cooler today,” says lead author, Stephen Vavrus, a senior scientist in the University of Wisconsin-Madison Center for Climatic Research in the Nelson Institute for Environmental Studies. “The ancient roots of farming produced enough carbon dioxide and methane to influence the environment.”
The findings are based on a sophisticated climate model that compared our current geologic time period, called the Holocene, to a similar period 800,000 years ago. They show the earlier period, called MIS19, was already 2.3 degrees Fahrenheit (1.3 C) cooler globally than the equivalent time in the Holocene, around the year 1850. This effect would have been more pronounced in the Arctic, where the model shows temperatures were 9-to-11 degrees Fahrenheit colder.
Using climate reconstructions based on ice core data, the model also showed that while MIS19 and the Holocene began with similar carbon dioxide and methane concentrations, MIS19 saw an overall steady drop in both greenhouse gases while the Holocene reversed direction 5,000 years ago, hitting peak concentrations of both gases by 1850. The researchers deliberately cut the model off at the start of the Industrial Revolution, when sources of greenhouse gas emissions became much more numerous.
For most of Earth’s 4.5-billion-year history, its climate has largely been determined by a natural phenomenon known as Milankovitch cycles, periodic changes in the shape of Earth’s orbit around the sun — which fluctuates from more circular to more elliptical — and the way Earth wobbles and tilts on its axis.
Astronomers can calculate these cycles with precision and they can also be observed in the geological and paleoecological records. The cycles influence where sunlight is distributed on the planet, leading to cold glacial periods or ice ages as well as warmer interglacial periods. The last glacial period ended roughly 12,000 years ago and Earth has since been in the Holocene, an interglacial period. The Holocene and MIS19 share similar Milankovitch cycle characteristics.
All other interglacial periods scientists have studied, including MIS19, begin with higher levels of carbon dioxide and methane, which gradually decline over thousands of years, leading to cooler conditions on Earth. Ultimately, conditions cool to a point where glaciation begins.
Fifteen years ago, study co-author William Ruddiman, emeritus paleoclimatologist at the University of Virginia, was studying methane and carbon dioxide trapped in Antarctic ice going back tens of thousands of years when he observed something unusual.
“I noticed that methane concentrations started decreasing about 10,000 years ago and then reversed direction 5,000 years ago and I also noted that carbon dioxide also started decreasing around 10,000 years ago and then reversed direction about 7,000 years ago,” says Ruddiman. “It alerted me that there was something strange about this interglaciation … the only explanation I could come up with is early agriculture, which put greenhouse gases into the atmosphere and that was the start of it all.”
Ruddiman named this the Early Anthropogenic Hypothesis and a number of studies have recently emerged suggesting its plausibility. They document widespread deforestation in Europe beginning around 6,000 years ago, the emergence of large farming settlements in China 7,000 years ago, plus the spread of rice paddies — robust sources of methane — throughout northeast Asia by 5,000 years ago.
Ruddiman and others have also been working to test the hypothesis. He has collaborated with Vavrus, an expert in climate modeling, for many years and their newest study used the Community Climate System Model 4 to simulate what would have happened in the Holocene if not for human agriculture. It offers higher resolution than climate models the team has used previously and provides new insights into the physical processes underlying glaciation.
For instance, in a simulation of MIS19, glaciation began with strong cooling in the Arctic and subsequent expansion of sea ice and year-round snow cover. The model showed this beginning in an area known as the Canadian archipelago, which includes Baffin Island, where summer temperatures dropped by more than 5 degrees Fahrenheit.
“This is consistent with geologic evidence,” says Vavrus.
Today, the Arctic is warming. But before we laud ancient farmers for staving off a global chill, Vavrus and Ruddiman caution that this fundamental alteration to our global climate cycle is uncharted territory.
“People say (our work) sends the wrong message, but science takes you where it takes you,” says Vavrus. “Things are so far out of whack now, the last 2,000 years have been so outside the natural bounds, we are so far beyond what is natural.”
The reality is, we don’t know what happens next. And glaciers have long served as Earth’s predominant source of freshwater.
“There is pretty good agreement in the community of climate scientists that we have stopped the next glaciation for the long, foreseeable future, because even if we stopped putting carbon dioxide into the atmosphere, what we have now would linger,” says Ruddiman. “The phenomenal fact is, we have maybe stopped the major cycle of Earth’s climate and we are stuck in a warmer and warmer and warmer interglacial.”
Stephen J. Vavrus, Feng He, John E. Kutzbach, William F. Ruddiman, Polychronis C. Tzedakis. Glacial Inception in Marine Isotope Stage 19: An Orbital Analog for a Natural Holocene Climate. Scientific Reports, 2018; 8 (1) DOI: 10.1038/s41598-018-28419-5
