No laughing matter: Nitrous oxide rose at end of last ice age

Researchers measured increases in atmospheric nitrous oxide concentrations about 16,000 to 10,000 years ago using ice from Taylor Glacier in Antarctica. -  Adrian Schilt
Researchers measured increases in atmospheric nitrous oxide concentrations about 16,000 to 10,000 years ago using ice from Taylor Glacier in Antarctica. – Adrian Schilt

Nitrous oxide (N2O) is an important greenhouse gas that doesn’t receive as much notoriety as carbon dioxide or methane, but a new study confirms that atmospheric levels of N2O rose significantly as the Earth came out of the last ice age and addresses the cause.

An international team of scientists analyzed air extracted from bubbles enclosed in ancient polar ice from Taylor Glacier in Antarctica, allowing for the reconstruction of the past atmospheric composition. The analysis documented a 30 percent increase in atmospheric nitrous oxide concentrations from 16,000 years ago to 10,000 years ago. This rise in N2O was caused by changes in environmental conditions in the ocean and on land, scientists say, and contributed to the warming at the end of the ice age and the melting of large ice sheets that then existed.

The findings add an important new element to studies of how Earth may respond to a warming climate in the future. Results of the study, which was funded by the U.S. National Science Foundation and the Swiss National Science Foundation, are being published this week in the journal Nature.

“We found that marine and terrestrial sources contributed about equally to the overall increase of nitrous oxide concentrations and generally evolved in parallel at the end of the last ice age,” said lead author Adrian Schilt, who did much of the work as a post-doctoral researcher at Oregon State University. Schilt then continued to work on the study at the Oeschger Centre for Climate Change Research at the University of Bern in Switzerland.

“The end of the last ice age represents a partial analog to modern warming and allows us to study the response of natural nitrous oxide emissions to changing environmental conditions,” Schilt added. “This will allow us to better understand what might happen in the future.”

Nitrous oxide is perhaps best known as laughing gas, but it is also produced by microbes on land and in the ocean in processes that occur naturally, but can be enhanced by human activity. Marine nitrous oxide production is linked closely to low oxygen conditions in the upper ocean and global warming is predicted to intensify the low-oxygen zones in many of the world’s ocean basins. N2O also destroys ozone in the stratosphere.

“Warming makes terrestrial microbes produce more nitrous oxide,” noted co-author Edward Brook, an Oregon State paleoclimatologist whose research team included Schilt. “Greenhouse gases go up and down over time, and we’d like to know more about why that happens and how it affects climate.”

Nitrous oxide is among the most difficult greenhouse gases to study in attempting to reconstruct the Earth’s climate history through ice core analysis. The specific technique that the Oregon State research team used requires large samples of pristine ice that date back to the desired time of study – in this case, between about 16,000 and 10,000 years ago.

The unusual way in which Taylor Glacier is configured allowed the scientists to extract ice samples from the surface of the glacier instead of drilling deep in the polar ice cap because older ice is transported upward near the glacier margins, said Brook, a professor in Oregon State’s College of Earth, Ocean, and Atmospheric Sciences.

The scientists were able to discern the contributions of marine and terrestrial nitrous oxide through analysis of isotopic ratios, which fingerprint the different sources of N2O in the atmosphere.

“The scientific community knew roughly what the N2O concentration trends were prior to this study,” Brook said, “but these findings confirm that and provide more exact details about changes in sources. As nitrous oxide in the atmosphere continues to increase – along with carbon dioxide and methane – we now will be able to more accurately assess where those contributions are coming from and the rate of the increase.”

Atmospheric N2O was roughly 200 parts per billion at the peak of the ice age about 20,000 years ago then rose to 260 ppb by 10,000 years ago. As of 2014, atmospheric N2Owas measured at about 327 ppb, an increase attributed primarily to agricultural influences.

Although the N2O increase at the end of the last ice age was almost equally attributable to marine and terrestrial sources, the scientists say, there were some differences.

“Our data showed that terrestrial emissions changed faster than marine emissions, which was highlighted by a fast increase of emissions on land that preceded the increase in marine emissions,” Schilt pointed out. “It appears to be a direct response to a rapid temperature change between 15,000 and 14,000 years ago.”

That finding underscores the complexity of analyzing how Earth responds to changing conditions that have to account for marine and terrestrial influences; natural variability; the influence of different greenhouse gases; and a host of other factors, Brook said.

“Natural sources of N2O are predicted to increase in the future and this study will help up test predictions on how the Earth will respond,” Brook said.

Technology-dependent emissions of gas extraction in the US

The KIT measurement instrument on board of a minivan directly measures atmospheric emissions on site with a high temporal resolution. -  Photo: F. Geiger/KIT
The KIT measurement instrument on board of a minivan directly measures atmospheric emissions on site with a high temporal resolution. – Photo: F. Geiger/KIT

Not all boreholes are the same. Scientists of the Karlsruhe Institute of Technology (KIT) used mobile measurement equipment to analyze gaseous compounds emitted by the extraction of oil and natural gas in the USA. For the first time, organic pollutants emitted during a fracking process were measured at a high temporal resolution. The highest values measured exceeded typical mean values in urban air by a factor of one thousand, as was reported in ACP journal. (DOI 10.5194/acp-14-10977-2014)

Emission of trace gases by oil and gas fields was studied by the KIT researchers in the USA (Utah and Colorado) together with US institutes. Background concentrations and the waste gas plumes of single extraction plants and fracking facilities were analyzed. The air quality measurements of several weeks duration took place under the “Uintah Basin Winter Ozone Study” coordinated by the National Oceanic and Atmospheric Administration (NOAA).

The KIT measurements focused on health-damaging aromatic hydrocarbons in air, such as carcinogenic benzene. Maximum concentrations were determined in the waste gas plumes of boreholes. Some extraction plants emitted up to about a hundred times more benzene than others. The highest values of some milligrams of benzene per cubic meter air were measured downstream of an open fracking facility, where returning drilling fluid is stored in open tanks and basins. Much better results were reached by oil and gas extraction plants and plants with closed production processes. In Germany, benzene concentration at the workplace is subject to strict limits: The Federal Emission Control Ordinance gives an annual benzene limit of five micrograms per cubic meter for the protection of human health, which is smaller than the values now measured at the open fracking facility in the US by a factor of about one thousand. The researchers published the results measured in the journal Atmospheric Chemistry and Physics ACP.

“Characteristic emissions of trace gases are encountered everywhere. These are symptomatic of gas and gas extraction. But the values measured for different technologies differ considerably,” Felix Geiger of the Institute of Meteorology and Climate Research (IMK) of KIT explains. He is one of the first authors of the study. By means of closed collection tanks and so-called vapor capture systems, for instance, the gases released during operation can be collected and reduced significantly.

“The gas fields in the sparsely populated areas of North America are a good showcase for estimating the range of impacts of different extraction and fracking technologies,” explains Professor Johannes Orphal, Head of IMK. “In the densely populated Germany, framework conditions are much stricter and much more attention is paid to reducing and monitoring emissions.”

Fracking is increasingly discussed as a technology to extract fossil resources from unconventional deposits. Hydraulic breaking of suitable shale stone layers opens up the fossil fuels stored there and makes them accessible for economically efficient use. For this purpose, boreholes are drilled into these rock formations. Then, they are subjected to high pressure using large amounts of water and auxiliary materials, such as sand, cement, and chemicals. The oil or gas can flow to the surface through the opened microstructures in the rock. Typically, the return flow of the aqueous fracking liquid with the dissolved oil and gas constituents to the surface lasts several days until the production phase proper of purer oil or natural gas. This return flow is collected and then reused until it finally has to be disposed of. Air pollution mainly depends on the treatment of this return flow at the extraction plant. In this respect, currently practiced fracking technologies differ considerably. For the first time now, the resulting local atmospheric emissions were studied at a high temporary resolution. Based on the results, emissions can be assigned directly to the different plant sections of an extraction plant. For measurement, the newly developed, compact, and highly sensitive instrument, a so-called proton transfer reaction mass spectrometer (PTR-MS), of KIT was installed on board of a minivan and driven closer to the different extraction points, the distances being a few tens of meters. In this way, the waste gas plumes of individual extraction sources and fracking processes were studied in detail.

Warneke, C., Geiger, F., Edwards, P. M., Dube, W., Pétron, G., Kofler, J., Zahn, A., Brown, S. S., Graus, M., Gilman, J. B., Lerner, B. M., Peischl, J., Ryerson, T. B., de Gouw, J. A., and Roberts, J. M.: Volatile organic compound emissions from the oil and natural gas industry in the Uintah Basin, Utah: oil and gas well pad emissions compared to ambient air composition, Atmos. Chem. Phys., 14, 10977-10988, doi:10.5194/acp-14-10977-2014, 2014.

New research highlights the key role of ozone in climate change

Many of the complex computer models which are used to predict climate change could be missing an important ozone ‘feedback’ factor in their calculations of future global warming, according to new research led by the University of Cambridge and published today (1 December) in the journal Nature Climate Change.

Computer models play a crucial role in informing climate policy. They are used to assess the effect that carbon emissions have had on the Earth’s climate to date, and to predict possible pathways for the future of our climate.

Increasing computing power combined with increasing scientific knowledge has led to major advances in our understanding of the climate system during the past decades. However, the Earth’s inherent complexity, and the still limited computational power available, means that not every variable can be included in current models. Consequently, scientists have to make informed choices in order to build models which are fit for purpose.

“These models are the only tools we have in terms of predicting the future impacts of climate change, so it’s crucial that they are as accurate and as thorough as we can make them,” said the paper’s lead author Peer Nowack, a PhD student in the Centre for Atmospheric Science, part of Cambridge’s Department of Chemistry.

The new research has highlighted a key role that ozone, a major component of the stratosphere, plays in how climate change occurs, and the possible implications for predictions of global warming. Changes in ozone are often either not included, or are included a very simplified manner, in current climate models. This is due to the complexity and the sheer computational power it takes to calculate these changes, an important deficiency in some studies.

In addition to its role in protecting the Earth from the Sun’s harmful ultraviolet rays, ozone is also a greenhouse gas. The ozone layer is part of a vast chemical network, and changes in environmental conditions, such as changes in temperature or the atmospheric circulation, result in changes in ozone abundance. This process is known as an atmospheric chemical feedback.

Using a comprehensive atmosphere-ocean chemistry-climate model, the Cambridge team, working with researchers from the University of East Anglia, the National Centre for Atmospheric Science, the Met Office and the University of Reading, compared ozone at pre-industrial levels with how it evolves in response to a quadrupling of CO2 in the atmosphere, which is a standard climate change experiment.

What they discovered is a reduction in global surface warming of approximately 20% – equating to 1° Celsius – when compared with most models after 75 years. This difference is due to ozone changes in the lower stratosphere in the tropics, which are mainly caused by changes in the atmospheric circulation under climate change.

“This research has shown that ozone feedback can play a major role in global warming and that it should be included consistently in climate models,” said Nowack. “These models are incredibly complex, just as the Earth is, and there are an almost infinite number of different processes which we could include. Many different processes have to be simplified in order to make them run effectively within the model, but what this research shows is that ozone feedback plays a major role in climate change, and therefore should be included in models in order to make them as accurate as we can make them. However, this particular feedback is especially complex since it depends on many other climate processes that models still simulate differently. Therefore, the best option to represent this feedback consistently might be to calculate ozone changes in every model, in spite of the high computational costs of such a procedure.

“Climate change research is all about having the best data possible. Every climate model currently in use shows that warming is occurring and will continue to occur, but the difference is in how and when they predict warming will happen. Having the best models possible will help make the best climate policy.”

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For more information, or to speak with the researchers, contact:

Sarah Collins, Office of Communications University of Cambridge Tel: +44 (0)1223 765542, Mob: +44 (0)7525 337458 Email: sarah.collins@admin.cam.ac.uk

Notes for editors:

1.The paper, “A large ozone-circulation feedback and its implications for global warming assessments” is published in the journal Nature Climate Change. DOI: 10.1038/nclimate2451

2.The mission of the University of Cambridge is to contribute to society through the pursuit of education, learning and research at the highest international levels of excellence. To date, 90 affiliates of the University have won the Nobel Prize. http://www.cam.ac.uk

3.UEA’s school of Environmental Sciences is one of the longest established, largest and most fully developed of its kind in Europe. It was ranked 5th in the Guardian League Table 2015.In the last Research Assessment Exercise, 95 per cent of the school’s activity was classified as internationally excellent or world leading. http://www.uea.ac.uk/env

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Adjusting Earth’s thermostat, with caution

David Keith, Gordon McKay Professor of Applied Physics at Harvard SEAS and professor of public policy at Harvard Kennedy School, coauthored several papers on climate engineering with colleagues at Harvard and beyond. -  Eliza Grinnell, SEAS Communications.
David Keith, Gordon McKay Professor of Applied Physics at Harvard SEAS and professor of public policy at Harvard Kennedy School, coauthored several papers on climate engineering with colleagues at Harvard and beyond. – Eliza Grinnell, SEAS Communications.

A vast majority of scientists believe that the Earth is warming at an unprecedented rate and that human activity is almost certainly the dominant cause. But on the topics of response and mitigation, there is far less consensus.

One of the most controversial propositions for slowing the increase in temperatures here on Earth is to manipulate the atmosphere above. Specifically, some scientists believe it should be possible to offset the warming effect of greenhouses gases by reflecting more of the sun’s energy back into space.

The potential risks–and benefits–of solar radiation management (SRM) are substantial. So far, however, all of the serious testing has been confined to laboratory chambers and theoretical models. While those approaches are valuable, they do not capture the full range of interactions among chemicals, the impact of sunlight on these reactions, or multiscale variations in the atmosphere.

Now, a team of researchers from the Harvard School of Engineering and Applied Sciences (SEAS) has outlined how a small-scale “stratospheric perturbation experiment” could work. By proposing, in detail, a way to take the science of geoengineering to the skies, they hope to stimulate serious discussion of the practice by policymakers and scientists.

Ultimately, they say, informed decisions on climate policy will need to rely on the best information available from controlled and cautious field experiments.

The paper is among several published today in a special issue of the Philosophical Transactions of the Royal Society A that examine the nuances, the possible consequences, and the current state of scientific understanding of climate engineering. David Keith, whose work features prominently in the issue, is Gordon McKay Professor of Applied Physics at Harvard SEAS and a professor of public policy at Harvard Kennedy School. His coauthors on the topic of field experiments include James Anderson, Philip S. Weld Professor of Applied Chemistry at Harvard SEAS and in Harvard’s Department of Chemistry and Chemical Biology; and other colleagues at Harvard SEAS.

“The idea of conducting experiments to alter atmospheric processes is justifiably controversial, and our experiment, SCoPEx, is just a proposal,” Keith emphasizes. “It will continue to evolve until it is funded, and we will only move ahead if the funding is substantially public, with a formal approval process and independent risk assessment.”

With so much at stake, Keith believes transparency is essential. But the science of climate engineering is also widely misunderstood.

“People often claim that you cannot test geoengineering except by doing it at full scale,” says Keith. “This is nonsense. It is possible to do a small-scale test, with quite low risks, that measures key aspects of the risk of geoengineering–in this case the risk of ozone loss.”

Such controlled experiments, targeting key questions in atmospheric chemistry, Keith says, would reduce the number of “unknown unknowns” and help to inform science-based policy.

The experiment Keith and Anderson’s team is proposing would involve only a tiny amount of material–a few hundred grams of sulfuric acid, an amount Keith says is roughly equivalent to what a typical commercial aircraft releases in a few minutes while flying in the stratosphere. It would provide important insight into how much SRM would reduce radiative heating, the concentration of water vapor in the stratosphere, and the processes that determine water vapor transport–which affects the concentration of ozone.

In addition to the experiment proposed in that publication, another paper coauthored by Keith and collaborators at the California Institute of Technology (CalTech) collects and reviews a number of other experimental methods, to demonstrate the diversity of possible approaches.

“There is a wide range of experiments that could be done that would significantly reduce our uncertainty about the risks and effectiveness of solar geoengineering,” Keith says. “Many could be done with very small local risks.”

A third paper explores how solar geoengineering might actually be implemented, if an international consensus were reached, and suggests that a gradual implementation that aims to limit the rate of climate change would be a plausible strategy.

“Many people assume that solar geoengineering would be used to suddenly restore the Earth’s climate to preindustrial temperatures,” says Keith, “but it’s very unlikely that it would make any policy sense to try to do so.”

Keith also points to another paper in the Royal Society’s special issue–one by Andy Parker at the Belfer Center for Science and International Affairs at Harvard Kennedy School. Parker’s paper furthers the discussion of governance and good practices in geoengineering research in the absence of both national legislation and international agreement, a topic raised last year in Science by Keith and Edward Parson of UCLA.

“The scientific aspects of geoengineering research must, by necessity, advance in tandem with a thorough discussion of the social science and policy,” Keith warns. “Of course, these risks must also be weighed against the risk of doing nothing.”

For further information, see: “Stratospheric controlled perturbation experiment (SCoPEx): A small-scale experiment to improve understanding of the risks of solar geoengineering” doi: 10.1098/rsta.2014.0059

By John Dykema, project scientist at Harvard SEAS; David Keith, Gordon McKay Professor of Applied Physics at Harvard SEAS and professor of public policy at Harvard Kennedy School; James Anderson, Philip S. Weld Professor of Applied Chemistry at Harvard SEAS and in Harvard’s Department of Chemistry and Chemical Biology; and Debra Weisenstein, research management specialist at Harvard SEAS.

“Field experiments on solar geoengineering: Report of a workshop exploring a representative research portfolio”
doi: 10.1098/rsta.2014.0175

By David Keith; Riley Duren, chief systems engineer at the NASA Jet Propulsion Laboratory at CalTech; and Douglas MacMartin, senior research associate and lecturer at CalTech.

“Solar geoengineering to limit the rate of temperature change”
doi: 10.1098/rsta.2014.0134

By Douglas MacMartin; Ken Caldeira, senior scientist at the Carnegie Institute for Science and professor of environmental Earth system sciences at Stanford University; and David Keith.

“Governing solar geoengineering research as it leaves the laboratory”
doi: 10.1098/rsta.2014.0173

By Andy Parker, associate of the Belfer Center at Harvard Kennedy School.

Fracking’s environmental impacts scrutinized

Greenhouse gas emissions from the production and use of shale gas would be comparable to conventional natural gas, but the controversial energy source actually faired better than renewables on some environmental impacts, according to new research.

The UK holds enough shale gas to supply its entire gas demand for 470 years, promising to solve the country’s energy crisis and end its reliance on fossil-fuel imports from unstable markets. But for many, including climate scientists and environmental groups, shale gas exploitation is viewed as environmentally dangerous and would result in the UK reneging on its greenhouse gas reduction obligations under the Climate Change Act.

University of Manchester scientists have now conducted one of the most thorough examinations of the likely environmental impacts of shale gas exploitation in the UK in a bid to inform the debate. Their research has just been published in the leading academic journal Applied Energy and study lead author, Professor Adisa Azapagic, will outline the findings at the Labour Party Conference in Manchester, England, today (Monday, 22 September).

“While exploration is currently ongoing in the UK, commercial extraction of shale gas has not yet begun, yet its potential has stirred controversy over its environmental impacts, its safety and the difficulty of justifying its use to a nation conscious of climate change,” said Professor Azapagic.

“There are many unknowns in the debate surrounding shale gas, so we have attempted to address some of these unknowns by estimating its life cycle environmental impacts from ‘cradle to grave’. We looked at 11 different impacts from the extraction of shale gas using hydraulic fracturing – known as ‘fracking’- as well as from its processing and use to generate electricity.”

The researchers compared shale gas to other fossil-fuel alternatives, such as conventional natural gas and coal, as well as low-carbon options, including nuclear, offshore wind and solar power (solar photovoltaics).

The results of the research suggest that the average emissions of greenhouse gases from shale gas over its entire life cycle are about 460 grams of carbon dioxide-equivalent per kilowatt-hour of electricity generated. This, the authors say, is comparable to the emissions from conventional natural gas. For most of the other life-cycle environmental impacts considered by the team, shale gas was also comparable to conventional natural gas.

But the study also found that shale gas was better than offshore wind and solar for four out of 11 impacts: depletion of natural resources, toxicity to humans, as well as the impact on freshwater and marine organisms. Additionally, shale gas was better than solar (but not wind) for ozone layer depletion and eutrophication (the effect of nutrients such as phosphates, on natural ecosystems).

On the other hand, shale gas was worse than coal for three impacts: ozone layer depletion, summer smog and terrestrial eco-toxicity.

Professor Azapagic said: “Some of the impacts of solar power are actually relatively high, so it is not a complete surprise that shale gas is better in a few cases. This is mainly because manufacturing solar panels is very energy and resource-intensive, while their electrical output is quite low in a country like the UK, as we don’t have as much sunshine. However, our research shows that the environmental impacts of shale gas can vary widely, depending on the assumptions for various parameters, including the composition and volume of the fracking fluid used, disposal routes for the drilling waste and the amount of shale gas that can be recovered from a well.

“Assuming the worst case conditions, several of the environmental impacts from shale gas could be worse than from any other options considered in the research, including coal. But, under the best-case conditions, shale gas may be preferable to imported liquefied natural gas.”

The authors say their results highlight the need for tight regulation of shale gas exploration – weak regulation, they claim, may result in shale gas having higher impacts than coal power, resulting in a failure to meet climate change and sustainability imperatives and undermining the deployment of low-carbon technologies.

Professor Azapagic added: “Whether shale gas is an environmentally sound option depends on the perceived importance of different environmental impacts and the regulatory structure under which shale gas operates.

“From the government policy perspective – focusing mainly on economic growth and energy security – it appears likely that shale gas represents a good option for the UK energy sector, assuming that it can be extracted at reasonable cost.

“However, a wider view must also consider other aspects of widespread use of shale gas, including the impact on climate change, as well as many other environmental considerations addressed in our study. Ultimately, the environmental impacts from shale gas will depend on which options it is displacing and how tight the regulation is.”

Study co-author Dr Laurence Stamford, from Manchester’s School of Chemical Engineering and Analytical Science, said: “Appropriate regulation should introduce stringent controls on the emissions from shale gas extraction and disposal of drilling waste. It should also discourage extraction from sites where there is little shale gas in order to avoid the high emissions associated with a low-output well.

He continued: “If shale gas is extracted under tight regulations and is reasonably cheap, there is no obvious reason, as yet, why it should not make some contribution to our energy mix. However, regulation should also ensure that investment in sustainable technologies is not reduced at the expense of shale gas.”

Forest emissions, wildfires explain why ancient Earth was so hot

This photo shows Nadine Unger with Yale University's omega supercomputer. -  Photo by Matthew Garrett/Yale School of Forestry & Environmental Studies
This photo shows Nadine Unger with Yale University’s omega supercomputer. – Photo by Matthew Garrett/Yale School of Forestry & Environmental Studies

The release of volatile organic compounds from Earth’s forests and smoke from wildfires 3 million years ago had a far greater impact on global warming than ancient atmospheric levels of carbon dioxide, a new Yale study finds.

The research provides evidence that dynamic atmospheric chemistry played an important role in past warm climates, underscoring the complexity of climate change and the relevance of natural components, according to the authors. They do not address or dispute the significant role in climate change of human-generated CO2 emissions.

Using sophisticated Earth system modeling, a team led by Nadine Unger of the Yale School of Forestry & Environmental Studies (F&ES) calculated that concentrations of tropospheric ozone, aerosol particles, and methane during the mid-Pliocene epoch were twice the levels observed in the pre-industrial era – largely because so much more of the planet was covered in forest.

Those reactive compounds altered Earth’s radiation balance, contributing a net global warming as much as two to three times greater than the effect of carbon dioxide, according to the study, published in the journal Geophysical Research Letters.

These findings help explain why the Pliocene was two to three degrees C warmer than the pre-industrial era despite atmospheric levels of carbon dioxide that were approximately the same as today, Unger said.

“The discovery is important for better understanding climate change throughout Earth’s history, and has enormous implications for the impacts of deforestation and the role of forests in climate protection strategies,” said Unger, an assistant professor of atmospheric chemistry at F&ES.

“The traditional view,” she said, “is that forests affect climate through carbon storage and by altering the color of the planet’s surface, thus influencing the albedo effect. But as we are learning, there are other ways that forest ecosystems can impact the climate.”

The albedo effect refers to the amount of radiation reflected by the surface of the planet. Light-colored snowy surfaces, for instance, reflect more light and heat back into space than darker forests.

Climate scientists have suggested that the Pliocene epoch might provide a glimpse of the planet’s future if humankind is unable to curb carbon dioxide emissions. During the Pliocene, the two main factors believed to influence the climate – atmospheric CO2 concentrations and the geographic position of the continents – were nearly identical to modern times. But scientists have long wondered why the Pliocene’s global surface air temperatures were so much warmer than Earth’s pre-industrial climate.

The answer might be found in highly reactive compounds that existed long before humans lived on the planet, Unger says. Terrestrial vegetation naturally emits vast quantities of volatile organic compounds, for instance. These are critical precursors for organic aerosols and ozone, a potent greenhouse gas. Wildfires, meanwhile, are a major source of black carbon and primary organic carbon.

Forest cover was vastly greater during the Pliocene, a period marked not just by warmer temperatures but also by greater precipitation. At the time, most of the arid and semi-arid regions of Africa, Australia, and the Arabian peninsula were covered with savanna and grassland. Even the Arctic had extensive forests. Notably, Unger says, there were no humans to cut the forests down.

Using the NASA Goddard Institute for Space Studies Model-E2 global Earth system model, the researchers were able to simulate the terrestrial ecosystem emissions and atmospheric chemical composition of the Pliocene and the pre-industrial era.

According to their findings, the increase in global vegetation was the dominant driver of emissions during the Pliocene – and the subsequent effects on climate.

Previous studies have dismissed such feedbacks, suggesting that these compounds would have had limited impact since they would have been washed from the atmosphere by frequent rainfall in the warmer climate. The new study argues otherwise, saying that the particles lingered about the same length of time – one to two weeks – in the Pliocene atmosphere compared to the pre-industrial.

Unger says her findings imply a higher climate sensitivity than if the system was simply affected by CO2 levels and the albedo effect.

“We might do a lot of work to reduce air pollution from road vehicle and industrial emissions, but in a warmer future world the natural ecosystems are just going to bring the ozone and aerosol particles right back,” she said. “Reducing and preventing the accumulation of fossil-fuel CO2 is the only way to ensure a safe climate future now.”

The modeling calculations were performed on Yale University’s omega supercomputer, a 704-node cluster capable of processing more than 52 trillion calculations per second.

Rain as acidic as lemon juice may have contributed to ancient mass extinction

Rain as acidic as undiluted lemon juice may have played a part in killing off plants and organisms around the world during the most severe mass extinction in Earth’s history.

About 252 million years ago, the end of the Permian period brought about a worldwide collapse known as the Great Dying, during which a vast majority of species went extinct.

The cause of such a massive extinction is a matter of scientific debate, centering on several potential causes, including an asteroid collision, similar to what likely killed off the dinosaurs 186 million years later; a gradual, global loss of oxygen in the oceans; and a cascade of environmental events triggered by massive volcanic eruptions in a region known today as the Siberian Traps.

Now scientists at MIT and elsewhere have simulated this last possibility, creating global climate models of scenarios in which repeated bursts of volcanism spew gases, including sulfur, into the atmosphere. From their simulations, they found that sulfur emissions were significant enough to create widespread acid rain throughout the Northern Hemisphere, with pH levels reaching 2 – as acidic as undiluted lemon juice. They say such acidity may have been sufficient to disfigure plants and stunt their growth, contributing to their ultimate extinction.

“Imagine you’re a plant that’s growing happily in the latest Permian,” says Benjamin Black, a postdoc in MIT’s Department of Earth, Atmospheric and Planetary Sciences. “It’s been getting hotter and hotter, but perhaps your species has had time to adjust to that. But then quite suddenly, over the course of a few months, the rain begins to sizzle with sulfuric acid. It would be quite a shock if you were that plant.”

Black is lead author of a paper reporting the group’s results, which appears in the journal Geology. Co-authors include Jean-François Lamarque, Christine Shields, and Jeffrey Kiehl from the National Center for Atmospheric Research and Linda Elkins-Tanton of the Carnegie Institution for Science.

Lemon juice spike

Geologists who have examined the rock record in Siberia have observed evidence of immense volcanism that came in short bursts beginning near the end of the Permian period and continuing for another million years. The volume of magma totaled several million cubic kilometers – enough to completely blanket the continental United States. This boiling stew of magma likely released carbon dioxide and other gases into the atmosphere, leading to gradual but powerful global warming.

The eruptions may also have released large clouds of sulfur, which ultimately returned to Earth’s surface as acid rain. Black, who has spent several summers in Siberia collecting samples to measure sulfur and other chemicals preserved in igneous rocks, used these measurements, along with other evidence, to develop simulations of magmatic activity in the end-Permian world.

The group simulated 27 scenarios, each approximating the release of gases from a plausible volcanic episode, including medium eruptions, large eruptions, and magma erupted through explosive pipes in the Earth’s crust. The researchers included a wide range of gases in their simulations, based on estimates from chemical analyses and thermal modeling. They then tracked water in the atmosphere, and the interactions among various gases and aerosols, to calculate the pH of rain.

The results showed that both carbon dioxide and volcanic sulfur could have significantly affected the acidity of rain at the end of the Permian. Levels of carbon dioxide and other greenhouse gases may have risen rapidly at the time, in part because of Siberian volcanism. According to their simulations, the researchers found that this elevated carbon dioxide could have increased rain’s acidity by an order of magnitude.

Adding sulfur emissions to the mix, they found that acidity further spiked to a pH of 2 – as acidic as undiluted lemon juice – and that such acidic rain may have fallen over most of the Northern Hemisphere. After an eruption ended, the researchers found that pH levels in rain bounced back, becoming less acidic within one year. However, with repeated bursts of volcanic activity, Black says the resulting swings in acid rain could have greatly stressed terrestrial species.

“Plants and animals wouldn’t have much time to adapt to these changes in the pH of rain,” Black says. “I think it certainly contributed to the environmental stress which was making it difficult for plants and animals to survive. At a certain point you have to ask, ‘How much can a plant take?'”

Life as an end-Permian organism

In addition to acid rain, the researchers modeled ozone depletion resulting from volcanic activity. While ozone depletion is more difficult to model than acid rain, their results suggest that a mix of gases released into the atmosphere may have destroyed 5 to 65 percent of the ozone layer, substantially increasing species’ exposure to ultraviolet radiation. The greatest ozone depletion occurred near the poles.

Going forward, Black hopes paleontologists and geochemists will consider the results as a point of comparison for their own observations of the end-Permian mass extinction. In the meantime, he says he now has a much more vivid picture of that catastrophic time.

“It’s not just one thing that was unpleasant,” Black says. “It’s this whole host of really nasty atmospheric and environmental effects. These results really made me feel sorry for end-Permian organisms.”

Acid raid, ozone depletion contributed to ancient extinction

This photo taken along Kotuy River in Arctic Siberia shows the base of the Siberian Traps volcanic sequence. -  Benjamin Black
This photo taken along Kotuy River in Arctic Siberia shows the base of the Siberian Traps volcanic sequence. – Benjamin Black

Around 250 million years ago, at the end of the Permian period, there was a mass extinction so severe that it remains the most traumatic known species die-off in Earth’s history. Some researchers have suggested that this extinction was triggered by contemporaneous volcanic eruptions in Siberia. New results from a team including Director of Carnegie’s Department of Terrestrial Magnetism Linda Elkins-Tanton show that the atmospheric effects of these eruptions could have been devastating. Their work is published in Geology.

The mass extinction included the sudden loss of more than 90 percent of marine species and more than 70 percent of terrestrial species and set the stage for the rise of the dinosaurs. The fossil record suggests that ecological diversity did not fully recover until several million years after the main pulse of the extinction.One leading candidate for the cause of this event is gas released from a large swath of volcanic rock in Russia called the Siberian Traps. Using advanced 3-D modeling techniques, the team, led by Benjamin Black of the Massachusetts Institute of Technology, was able to predict the impacts of gas released from the Siberian Traps on the end-Permian atmosphere.

Their results indicate that volcanic releases of both carbon dioxide (CO2) and sulfur dioxide (SO2) could have created highly acidic rain, potentially leaching the soil of nutrients and damaging plants and other vulnerable terrestrial organisms. Releases of halogen-bearing compounds such as methyl chloride could also have resulted in global ozone collapse.

The volcanic activity was likely episodic, producing pulses of acid rain and ozone depletion. The team concluded that the resulting drastic fluctuations in pH and ultraviolet radiation, combined with an overall temperature increase from greenhouse gas emissions, could have contributed to the end-Permian mass extinction on land.

The team also included Jean-François Lamarque, Christine Shields, and Jeffrey Kiehl of the National Center for Atmospheric Research.

The biggest mass extinction and Pangea integration

Relationships between geosphere disturbances and mass extinction during the Late Permian and Early Triassic are shown. -  ©Science China Press
Relationships between geosphere disturbances and mass extinction during the Late Permian and Early Triassic are shown. – ©Science China Press

The mysterious relationship between Pangea integration and the biggest mass extinction happened 250 million years ago was tackled by Professor YIN Hongfu and Dr. SONG Haijun from State Key Laboratory of Geobiology and Environmental Geology, China University of Geosciences (Wuhan). Their study shows that Pangea integration resulted in environmental deterioration which further caused that extinction. Their work, entitled “Mass extinction and Pangea integration during the Paleozoic-Mesozoic transition”, was published in SCIENCE CHINA Earth Sciences.2013, Vol 56(7).

The Pangea was integrated at about the beginning of Permian, and reached its acme during Late Permian to Early Triassic. Formation of the Pangea means that the scattered continents of the world gathered into one integrated continent with an area of nearly 200 million km2. Average thickness of such a giant continental lithosphere should be remarkably greater than that of each scattered continent. Equilibrium principle implies that the thicker the lithosphere, the higher its portion over the equilibrium level, hence the average altitude of the Pangea should be much higher than the separated modern continents. Correspondingly, all oceans gathered to form the Panthalassa, which should be much deeper than modern oceans. The acme of Pangea and Panthalassa was thus a period of high continent and deep ocean, which should inevitably induce great regression and influence the earth’s surface system, especially climate.

The Tunguss Trap of Siberia, the Emeishan Basalt erupted during the Pangea integration. Such global-scale volcanism should be evoked by mantle plume and related with integration of the Pangea. Volcanic activities would result in a series of extinction effects, including emission of large volume of CO2, CH4, NO2 and cyanides which would have caused green house effects, pollution by poisonous gases, damage of the ozone layer in the stratosphere, and enhancement the ultra-violet radiation.

Increase of CO2 concentration and other green house gases would have led to global warming, oxygen depletion and carbon cycle anomaly; physical and chemical anomalies in ocean (acidification, euxinia, low sulfate concentration, isotopic anomaly of organic nitrogen) and great regression would have caused marine extinction due to unadaptable environments, selective death and hypercapnia; continental aridity, disappearance of monsoon system and wild fire would have devastated the land vegetation, esp. the tropical rain forest.

The great global changes and mass extinction were the results of interaction among earth’s spheres. Deteriorated relations among lithosphere, atmosphere, hydrosphere, and biosphere (including internal factors of organism evolution itself) accumulated until they exceeded the threshold, and exploded at the Permian-Triassic transition time. Interaction among bio- and geospheres is an important theme. However, the processes from inner geospheres to earth’s surface system and further to organism evolution necessitate retardation in time and yields many uncertainties in causation. Most of the processes are now at a hypothetic stage and need more scientific examinations.

Corn syrup model splits Yellowstone’s mantle plume in 2

A corn syrup mantle plume rises near the subducting plate, which induces fluid flow that distorts and deforms the plume as it rises toward the surface. -  Kelsey Druken
A corn syrup mantle plume rises near the subducting plate, which induces fluid flow that distorts and deforms the plume as it rises toward the surface. – Kelsey Druken

One of the greatest controversies in science is what’s underneath the Yellowstone supervolcano. The controversy surrounds a unique relationship between a mantle plume (like the one that powers Hawaiian volcanoes) and the subduction zone off the Washington-Oregon coast. Cutting-edge research using a common kitchen ingredient is explored in the latest issue of EARTH Magazine.

Recently published research explores this problem in 3-D, using a model created with corn syrup, fiberglass and a series of hydraulic pistons. What the scientists saw was a plume sliced in half by the subducting plate. Before this research, different scientific teams had only investigated the subducting tectonic plate or the mantle plume, but not both at the same time.

The resulting model of a bifurcated mantle plume potentially answers key questions about the Yellowstone supervolcano. Read about how these results impact volcano research in Washington, Oregon, Montana, Wyoming and the South Pacific in the July issue of EARTH Magazine: http://bit.ly/153lVat. For complete access – including to see the corn syrup apparatus subscribe to Earth Magazine at: http://www.earthmagazine.org/digital.

Don’t miss the other great articles in the July issue of EARTH Magazine. Uncover ancient earthquake damage in a Roman Mausoleum, Arctic ozone depletion, and plankton growth caused by Icelandic volcanoes, all in this month’s issue of EARTH, now available on the digital newsstand at http://www.earthmagazine.org/digital.