Wednesday, April 9, 2014

Changing climate creates pervasive risks, but opportunities exist for effective responses: IPCC report

Date:
March 31, 2014 - SCIENCE DAILY
Source:
Intergovernmental Panel on Climate Change

The United Nations' Intergovernmental Panel on Climate Change (IPCC) issued a report today that says the effects of climate change are already occurring on all continents and across the oceans. The world, in many cases, is ill-prepared for risks from a changing climate. The report also concludes that there are opportunities to respond to such risks, though the risks will be difficult to manage with high levels of warming. 

The report, titled Climate Change 2014: Impacts, Adaptation, and Vulnerability, from Working Group II of the IPCC, details the impacts of climate change to date, the future risks from a changing climate, and the opportunities for effective action to reduce risks. A total of 309 coordinating lead authors, lead authors, and review editors, drawn from 70 countries, were selected to produce the report. They enlisted the help of 436 contributing authors, and a total of 1,729 expert and government reviewers.
The report concludes that responding to climate change involves making choices about risks in a changing world. The nature of the risks of climate change is increasingly clear, though climate change will also continue to produce surprises. The report identifies vulnerable people, industries, and ecosystems around the world. It finds that risk from a changing climate comes from vulnerability (lack of preparedness) and exposure (people or assets in harm's way) overlapping with hazards (triggering climate events or trends). Each of these three components can be a target for smart actions to decrease risk.
"We live in an era of man-made climate change," said Vicente Barros, Co-Chair of Working Group II. "In many cases, we are not prepared for the climate-related risks that we already face. Investments in better preparation can pay dividends both for the present and for the future."
Adaptation to reduce the risks from a changing climate is now starting to occur, but with a stronger focus on reacting to past events than on preparing for a changing future, according to Chris Field, Co-Chair of Working Group II.
"Climate-change adaptation is not an exotic agenda that has never been tried. Governments, firms, and communities around the world are building experience with adaptation," Field said. "This experience forms a starting point for bolder, more ambitious adaptations that will be important as climate and society continue to change."
Future risks from a changing climate depend strongly on  the amount of future climate change. Increasing magnitudes of warming increase the likelihood of severe and pervasive impacts that may be surprising or irreversible.
"With high levels of warming that result from continued growth in greenhouse gas emissions, risks will be challenging to manage, and even serious, sustained investments in adaptation will face limits," said Field.
Observed impacts of climate change have already affected agriculture, human health, ecosystems on land and in the oceans, water supplies, and some people's livelihoods. The striking feature of observed impacts is that they are occurring from the tropics to the poles, from small islands to large continents, and from the wealthiest countries to the poorest.
"The report concludes that people, societies, and ecosystems are vulnerable around the world, but with different vulnerability in different places. Climate change often interacts with other stresses to increase risk," Field said.
Adaptation can play a key role in decreasing these risks, Barros noted. "Part of the reason adaptation is so important is that the world faces a host of risks from climate change already baked into the climate system, due to past emissions and existing infrastructure," said Barros.
Field added: "Understanding that climate change is a challenge in managing risk opens a wide range of opportunities for integrating adaptation with economic and social development and with initiatives to limit future warming. We definitely face challenges, but understanding those challenges and tackling them creatively can make climate-change adaptation an important way to help build a more vibrant world in the near-term and beyond."
Rajendra Pachauri, Chair of the IPCC, said: "The Working Group II report is another important step forward in our understanding of how to reduce and manage the risks of climate change. Along with the reports from Working Group I and Working Group III, it provides a conceptual map of not only the essential features of the climate challenge but the options for solutions."
The Working Group I report was released in September 2013, and the Working Group III report will be released in April 2014. The IPCC Fifth Assessment Report cycle concludes with the publication of its Synthesis Report in October 2014.
"None of this would be possible without the dedication of the Co-Chairs of Working Group II and the hundreds of scientists and experts who volunteered their time to produce this report, as well as the more than 1,700 expert reviewers worldwide who contributed their invaluable oversight," Pachauri said. "The IPCC's reports are some of the most ambitious scientific undertakings in human history, and I am humbled by and grateful for the contributions of everyone who make them possible."
The Working Group II contribution to the IPCC Fifth Assessment Report (WGII AR5) is available at www.ipcc-wg2.gov/AR5 and www.ipcc.ch.
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The above story is based on materials provided by Intergovernmental Panel on Climate Change. Note: Materials may be edited for content and length.
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Intergovernmental Panel on Climate Change. "Changing climate creates pervasive risks, but opportunities exist for effective responses: IPCC report." ScienceDaily. ScienceDaily, 31 March 2014. .
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What will climate policy mean for coal?

Date:
March 31, 2014
Source:
International Institute for Applied Systems Analysis

Limiting climate change to 2°C means shutting down coal power plants -- an unpopular proposition for coal power companies. But a new study shows that delaying climate policies could prove even worse for power plant owners.
Coal power plants are a major source of greenhouse gas emissions, and new plants are planned around the world, particularly in India and China. These new power plants are built to run for 30-50 years, paying off only after years of operation. But stringent climate policies could make the cost of emission so high that coal power generation is no longer competitive, leaving new power plants sitting idle and their owners and investors with huge losses -- a problem known as stranded capacity.
"If we are serious about meeting climate targets, then the reality is that eventually we will have to start shutting down coal-fired power plants. But the longer we delay climate action, the more stranded capacity we'll have," says IIASA researcher Nils Johnson, who led the new study, published today in the journal Technological Forecasting and Social Change. "Delaying action encourages utilities to build more coal-fired power plants in the near-term. Then, when policies are finally introduced, we have to phase out coal even more quickly and more investments go to waste," he says.
The new study finds that as much as 37% of global investment in coal power plants over the next 40 years could be stranded if action is delayed, with China and India bearing most of these costs. The study explored strategies to reduce stranded capacity in coal power plants, while limiting future climate change to the internationally agreed 2°C target.
It shows that one key is to avoid new coal power plant construction. Potential options include shifting to other kinds of power plants, keeping old coal plants running, and improving energy efficiency. By reducing the amount of energy used, efficiency improvements also reduce the amount of energy that must be generated and, therefore, the need for new power plants.
"The best strategy would be to stop building new coal power plants starting today," says Johnson. However, the researchers also explored what would happen in a perhaps more realistic case, if governments are not yet willing to limit new plant construction. Johnson and colleagues in IIASA's Energy Program also examined two additional strategies with this limitation: grandfathering existing plants so that they are exempt from future climate policies, or retrofitting plants with Carbon Capture and Storage (CCS), a yet unproven technology that would capture greenhouse gas emissions and store them underground.
However, both of these strategies create a major risk that average temperatures will rise above the 2°C goal -- a target set by international agreement in order to avoid the most dire consequences of climate change. While the grandfathering strategy would allow power plant operators to keep the old ones running, it would lead to greater emissions and reduced chances of limiting climate change to the 2°C target.
And while CCS could theoretically be used to retrofit coal power plants, the study shows that hundreds of power plants would need retrofitting in a short period of time -- a lot of pressure on a technology that as yet remains both technically and politically uncertain. "CCS could buy us time, but what if it doesn't work? It's a risky strategy," says Volker Krey, a co-author on the paper.
Story Source:
The above story is based on materials provided by International Institute for Applied Systems Analysis. Note: Materials may be edited for content and length.
Journal Reference:
  1. Nils Johnson, Volker Krey, David L. McCollum, Shilpa Rao, Keywan Riahi, Joeri Rogelj. Stranded on a low-carbon planet: Implications of climate policy for the phase-out of coal-based power plants. Technological Forecasting and Social Change, 2014; DOI: 10.1016/j.techfore.2014.02.028
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International Institute for Applied Systems Analysis. "What will climate policy mean for coal?." ScienceDaily. ScienceDaily, 31 March 2014. .

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Warming climate may spread drying to a third of earth: Heat, not just rainfall, plays into new projections

Date:
March 31, 2014 - SCIENCE DAILY
Source:
The Earth Institute at Columbia University
Summary:
A new study estimates that 12 percent of land will be subject to drought by 2100 through rainfall changes alone; but the drying will spread to 30 percent of land if higher evaporation rates are considered. An increase in evaporative drying means that even regions expected to get more rain, including important wheat, corn and rice belts in the western United States and southeastern China, will be at risk of drought.

Increasing heat is expected to extend dry conditions to far more farmland and cities by the end of the century than changes in rainfall alone, says a new study. Much of the concern about future drought under global warming has focused on rainfall projections, but higher evaporation rates may also play an important role as warmer temperatures wring more moisture from the soil, even in some places where rainfall is forecasted to increase, say the researchers.

The study is one of the first to use the latest climate simulations to model the effects of both changing rainfall and evaporation rates on future drought. Published this month in the journal Climate Dynamics, the study estimates that 12 percent of land will be subject to drought by 2100 through rainfall changes alone; but the drying will spread to 30 percent of land if higher evaporation rates from the added energy and humidity in the atmosphere is considered. An increase in evaporative drying means that even regions expected to get more rain, including important wheat, corn and rice belts in the western United States and southeastern China, will be at risk of drought. The study excludes Antarctica.
"We know from basic physics that warmer temperatures will help to dry things out," said the study's lead author, Benjamin Cook, a climate scientist with joint appointments at Columbia University's Lamont-Doherty Earth Observatory and the NASA Goddard Institute for Space Studies. "Even if precipitation changes in the future are uncertain, there are good reasons to be concerned about water resources."
In its latest climate report, the International Panel on Climate Change (IPCC) warns that soil moisture is expected to decline globally and that already dry regions will be at greater risk of agricultural drought. The IPCC also predicts a strong chance of soil moisture drying in the Mediterranean, southwestern United States and southern African regions, consistent with the Climate Dynamics study.
Using two drought metric formulations, the study authors analyze projections of both rainfall and evaporative demand from the collection of climate model simulations completed for the IPCC's 2013 climate report. Both metrics agree that increased evaporative drying will probably tip marginally wet regions at mid-latitudes like the U.S. Great Plains and a swath of southeastern China into aridity. If precipitation were the only consideration, these great agricultural centers would not be considered at risk of drought. The researchers also say that dry zones in Central America, the Amazon and southern Africa will grow larger. In Europe, the summer aridity of Greece, Turkey, Italy and Spain is expected to extend farther north into continental Europe.
"For agriculture, the moisture balance in the soil is what really matters," said study coauthor Jason Smerdon, a climate scientist at Lamont-Doherty. "If rain increases slightly but temperatures also increase, drought is a potential consequence."
Today, while bad weather periodically lowers crop yields in some places, other regions are typically able to compensate to avert food shortages. In the warmer weather of the future, however, crops in multiple regions could wither simultaneously, the authors suggest. "Food-price shocks could become far more common," said study coauthor Richard Seager, a climate scientist at Lamont-Doherty. Large cities, especially in arid regions, will need to carefully manage their water supplies, he added.
The study builds on an emerging body of research looking at how evaporative demand influences hydroclimate. "It confirms something we've suspected for a long time," said Toby Ault, a climate scientist at Cornell University, who was not involved in the study. "Temperature alone can make drought more widespread. Studies like this give us a few new powerful tools to plan for and adapt to climate change."
Rainfall changes do not tell the whole story, agrees University of New South Wales researcher Steven Sherwood, in a recent Perspectives piece in the leading journalScience. "Many regions will get more rain, but it appears that few will get enough to keep pace with the growing evaporative demand."
Story Source:
The above story is based on materials provided by The Earth Institute at Columbia University. Note: Materials may be edited for content and length.
Journal Reference:
  1. Benjamin I. Cook, Jason E. Smerdon, Richard Seager, Sloan Coats. Global warming and 21st century drying. Climate Dynamics, 2014; DOI:10.1007/s00382-014-2075-y
Cite This Page:
The Earth Institute at Columbia University. "Warming climate may spread drying to a third of earth: Heat, not just rainfall, plays into new projections." ScienceDaily. ScienceDaily, 31 March 2014. .
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New evidence linking fruit and vegetable consumption with lower mortality

Date:
March 31, 2014 - SCIENCE DAILY
Source:
University College London
Summary:
Eating seven or more portions of fruit and vegetables a day reduces your risk of death at any point in time by 42 percent compared to eating less than one portion, reports a new study. This is the first study to link fruit and vegetable consumption with all-cause, cancer and heart disease deaths in a nationally-representative population, the first to quantify health benefits per-portion, and the first to identify the types of fruit and vegetable with the most benefit.
This table summarizes the main effects of fruit and vegetable consumption on risk of death, expressed as percentage decreases.
Credit: UCL
Eating seven or more portions of fruit and vegetables a day reduces your risk of death at any point in time by 42% compared to eating less than one portion, reports a new UCL study.

This is the first study to link fruit and vegetable consumption with all-cause, cancer and heart disease deaths in a nationally-representative population, the first to quantify health benefits per-portion, and the first to identify the types of fruit and vegetable with the most benefit.
Compared to eating less than one portion of fruit and vegetables, the risk of death by any cause is reduced by 14% by eating one to three portions, 29% for three to five portions, 36% for five to seven portions and 42% for seven or more. These figures are adjusted for sex, age, cigarette smoking, social class, Body Mass Index, education, physical activity and alcohol intake, and exclude deaths within a year of the food survey.
The study, published in the Journal of Epidemiology & Community Health, found that fresh vegetables had the strongest protective effect, with each daily portion reducing overall risk of death by 16%. Salad contributed to a 13% risk reduction per portion, and each portion of fresh fruit was associated with a smaller but still significant 4% reduction.
"We all know that eating fruit and vegetables is healthy, but the size of the effect is staggering," says Dr Oyinlola Oyebode of UCL's Department of Epidemiology & Public Health, lead author of the study. "The clear message here is that the more fruit and vegetables you eat, the less likely you are to die at any age. Vegetables have a larger effect than fruit, but fruit still makes a real difference. If you're happy to snack on carrots or other vegetables, then that is a great choice but if you fancy something sweeter, a banana or any fruit will also do you good."
The findings lend support to the Australian government's 'Go for 2 + 5' guidelines, which recommend eating two portions of fruit and five of vegetables. The UK Department of Health recommends '5 a day', while 'Fruit and Veggies -- More Matters' is the key message in the USA.
"Our study shows that people following Australia's 'Go for 2 + 5' advice will reap huge health benefits," says Dr Oyebode. "However, people shouldn't feel daunted by a big target like seven. Whatever your starting point, it is always worth eating more fruit and vegetables. In our study even those eating one to three portions had a significantly lower risk than those eating less than one"
The researchers found no evidence of significant benefit from fruit juice, and canned and frozen fruit appeared to increase risk of death by 17% per portion. The survey did not distinguish between canned and frozen fruit so this finding is difficult to interpret. Canned fruit products are almost four times more popular than frozen fruit in Europe*, so it is likely that canned fruit dominated this effect.
"Most canned fruit contains high sugar levels and cheaper varieties are packed in syrup rather than fruit juice," explains Dr Oyebode. "The negative health impacts of the sugar may well outweigh any benefits. Another possibility is that there are confounding factors that we could not control for, such as poor access to fresh groceries among people who have pre-existing health conditions, hectic lifestyles or who live in deprived areas."
*Note: 13.0m tons of canned fruit and vegetables were sold in the EU in 2008 compared to 3.7m for frozen fruit and vegetables.
Story Source:
The above story is based on materials provided by University College London. Note: Materials may be edited for content and length.
Journal Reference:
  1. Oyinlola Oyebode, Vanessa Gordon-Dseagu, Alice Walker, Jennifer S Mindell.Fruit and vegetable consumption and all-cause, cancer and CVD mortality: analysis of Health Survey for England data. J Epidemiol Community Health, 31 March 2014 DOI: 10.1136/jech-2013-203500
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University College London. "New evidence linking fruit and vegetable consumption with lower mortality." ScienceDaily. ScienceDaily, 31 March 2014. .



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Health costs of air pollution from agriculture clarified

Date:
March 28, 2014 - SCIENCE DAILY
Source:
NASA/Goddard Space Flight Center
Summary:
Ammonia pollution from agricultural sources poses larger health costs than previously estimated, according to research. Computer models, including a NASA model of chemical reactions in the atmosphere, were used to better represent how ammonia interacts in the atmosphere to form harmful particulate matter. The improved simulation helped the scientists narrow in on the estimated health costs from air pollution associated with food produced for export -- a growing sector of agriculture and a source of trade surplus.

Ammonia pollution from agricultural sources poses larger health costs than previously estimated, according to NASA-funded research.

Harvard University researchers Fabien Paulot and Daniel Jacob used computer models including a NASA model of chemical reactions in the atmosphere to better represent how ammonia interacts in the atmosphere to form harmful particulate matter. The improved simulation helped the scientists narrow in on the estimated health costs from air pollution associated with food produced for export -- a growing sector of agriculture and a source of trade surplus.
"The 'cost' is an economic concept to measure how much people are willing to pay to avoid a risk," Paulot said. "This is used to quantify the cost for society but also to evaluate the benefits of mitigation."
The new research by Paulot and Jacob calculate the health cost associated with the ammonia emissions from agriculture exports to be $36 billion a year -- equal to about half of the revenue generated by those same exports -- or $100 per kilogram of ammonia. The study was published December 2013 in Environmental Science & Technology.
The new estimate is about double the current estimate by the U.S. Environmental Protection Agency, which suggests a cost of $47 per kilogram of ammonia. The scientists say the new estimate is on the high end of the spectrum, which reflects the need for more research into characterizing the relationship between agricultural ammonia emissions and the formation of the harmful fine particulate matter -- a relationship that's not as straightforward as previous estimates assumed.
"The effect of ammonia on fine particulate is complex, and we believe that the models previously used in the United States to price ammonia emissions have not captured this well," Paulot said.
Manure from livestock and fertilizer for crops release ammonia to the atmosphere. In the air, ammonia mixes with other emissions to form microscopic airborne particles, or particulates. The particulates that pose the greatest health risk are those that measure no more than 2.5 micrometers across, or about 1/30 the width of a human hair, which when inhaled can become lodged deep within the lungs. Long-term exposure has been linked to heart and lung diseases and even death. As such, the particles are on the list of six common air pollutants regulated by EPA's National Ambient Air Quality Standards.
An increase in ammonia, however, does not translate to an equal increase in particulates. The relationship depends on meteorology as well as the concentration of other precursors to particulate formation, such as sulfate and nitric acid.
To clarify the effect of ammonia on fine particulates, Paulot and Jacob first modeled the agricultural sources of ammonia emissions utilizing a relatively new ammonia emissions inventory. Next they used the NASA GEOS-Chem model of atmospheric composition to simulate the complex chemistry that converts agricultural emissions -- in this case ammonia -- into fine particulate matter.
This information was then combined with food export data from the U.S. Department of Agriculture and the United Nations Food and Agriculture Organization, averaged from 2000 to 2009. Results show that U.S. food exports account for 11 percent of the total U.S. emissions of ammonia.
"Our study suggests controls on ammonia emissions from agriculture could help reduce particulate matter and provide significant societal benefits," Paulot said.
The impact, however, is not equal everywhere. Areas downwind of large agricultural regions often set the stage for more mixing of ammonia with human-made emissions from combustion, such as from traffic and power plants. More mixing means the formation of more fine particulate matter. For this reason, the largest health costs are most often carried by the more populated states in the Northeast and Great Lakes region.
Story Source:
The above story is based on materials provided by NASA/Goddard Space Flight Center. Note: Materials may be edited for content and length.
Journal Reference:
  1. Fabien Paulot, Daniel J. Jacob. Hidden Cost of U.S. Agricultural Exports: Particulate Matter from Ammonia Emissions. Environmental Science & Technology, 2014; 48 (2): 903 DOI: 10.1021/es4034793
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NASA/Goddard Space Flight Center. "Health costs of air pollution from agriculture clarified." ScienceDaily. ScienceDaily, 28 March 2014. .







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Eating fruits, vegetables linked to healthier arteries later in life

Date:
March 28, 2014 - SCIENCE DAILY 
Source:
American College of Cardiology

Women who ate a diet high in fresh fruits and vegetables as young adults were much less likely to have plaque build-up in their arteries 20 years later compared with those who consumed lower amounts of these foods, according to research to be presented at the American College of Cardiology's 63rd Annual Scientific Session. This new finding reinforces the importance of developing healthy eating habits early in life.
Previous studies have found that middle-aged adults whose diet consists of a high proportion of fruits and vegetables are less likely to have a heart attack or stroke, but the relationship between fruit and vegetable consumption during young adulthood and heart disease later in life was less clear. To study this concept, researchers evaluated the association between dietary intake of fruits and vegetables in young adults and the presence of coronary artery calcification (CAC) 20 years later. CAC scores, which were obtained using a CT scan, provide a direct estimate of the amount of plaque in the coronary arteries.
"It's an important question because lifestyle behaviors, such as a heart healthy diet, are the foundation of cardiovascular prevention and we need to know what dietary components are most important," said Michael D. Miedema, M.D., M.P.H., a cardiologist at the Minneapolis Heart Institute, and the lead investigator of the study.
Specifically, women who reported consuming the most fruits and vegetables (eight to nine servings a day for a 2,000-calorie diet) in their 20s were 40 percent less likely to have calcified plaque in their arteries in their 40s compared with those who ate the least amount (three to four servings a day) during the same time period. This association persisted even after researchers accounted for other lifestyle behaviors, as well as for their current-day diets, further demonstrating the role dietary patterns at younger ages may play.
"These findings confirm the concept that plaque development is a lifelong process, and that process can be slowed down with a healthy diet at a young age," Miedema said. "This is often when dietary habits are established, so there is value in knowing how the choices we make in early life have lifelong benefits."
Surprisingly, the same benefit did not hold true for men, which warrants further investigation.
"Several other studies have also suggested that a diet high in fruits and vegetables is less protective in men, but we do not have a good biological reason for this lack of association," Miedema said, adding that the study had less power to evaluate men (62.7 percent were female vs. 37.3 percent male).
The study included 2,508 participants from the ongoing government-sponsored Coronary Artery Risk Development in Young Adults (CARDIA) study, which is evaluating how heart disease develops throughout adulthood. CARDIA began in the mid-1980s with a group of men and women 18-30 years of age and has collected extensive data on medical, socioeconomic, psychosocial and behavioral characteristics.
At the start of CARDIA (1985-1986), women and men were asked about their consumption of different fruits and vegetables and the number of servings they had eaten in the past month using a semi-quantitative interview food-frequency questionnaire. Researchers then calculated the average number of servings of fruits and vegetables per day and adjusted them to a 2,000-calorie diet. People were divided into three groups based on self-reported fruit and vegetable intake: high, moderate and low. CAC was measured at year 20 (2005-2006) using electron-beam computed tomography. The average age at baseline and the 20-year follow-up was 25 and 45 years, respectively.
"CAC scoring is currently the best predictor we have for future heart attacks," Miedema said. Calcium build-up in the walls of the coronary arteries is an early sign of heart disease, and the presence of CAC substantially raises an individual's risk for a future heart attack.
In their analysis, researchers controlled for smoking, exercise, consumption of red meat, sugar-sweetened beverages and other dietary and cardiovascular risk factors that correlate with atherosclerosis. Participants with extreme high or low caloric intake/day or those missing CAC scores were excluded from the analysis.
The current findings are in line with the 2011 U.S. Department of Agriculture Dietary Guidelines that advise Americans to fill half of their plates with colorful fruits and vegetables at each meal or snack. Based on these recommendations, adults who consume a 2,000-calorie a day diet should be consuming 2.5 cups of vegetables and two cups of fruit a day -- a big jump from what the average American usually gets from their diet, according to government figures.
Fruits and vegetables are packed with vitamins, minerals, fiber, antioxidants and other things that are known to promote good health. Plant-based diets in general have also been linked to greater longevity, less cancer, lower cholesterol, lower blood pressure and healthier body weight.
Miedema emphasized that more studies are needed to further define the relationship between fruits, vegetables and cardiovascular disease in men and women, in addition to determining the best ways to increase compliance with a diet high in fruits and vegetables in the U.S. population.
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The above story is based on materials provided by American College of Cardiology.Note: Materials may be edited for content and length.
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American College of Cardiology. "Eating fruits, vegetables linked to healthier arteries later in life." ScienceDaily. ScienceDaily, 28 March 2014. .
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A more potent greenhouse gas than carbon dioxide, methane emissions will leap as Earth warms

Date:
March 27, 2014 - SCIENCE DAILY 

Source:
Princeton University
Summary:
New research indicates that for each degree that the Earth's temperature rises, the amount of methane entering the atmosphere from microorganisms dwelling in lake sediment and freshwater wetlands -- the primary sources of the gas -- will increase several times.

While carbon dioxide is typically painted as the bad boy of greenhouse gases, methane is roughly 30 times more potent as a heat-trapping gas. New research in the journal Nature indicates that for each degree that  Earth's temperature rises, the amount of methane entering the atmosphere from microorganisms dwelling in lake sediment and freshwater wetlands -- the primary sources of the gas -- will increase several times. As temperatures rise, the relative increase of methane emissions will outpace that of carbon dioxide from these sources, the researchers report.

The findings condense the complex and varied process by which methane -- currently the third most prevalent greenhouse gas after carbon dioxide and water vapor -- enters the atmosphere into a measurement scientists can use, explained co-author Cristian Gudasz, a visiting postdoctoral research associate in Princeton's Department of Ecology and Evolutionary Biology. In freshwater systems, methane is produced as microorganisms digest organic matter, a process known as "methanogenesis." This process hinges on a slew of temperature, chemical, physical and ecological factors that can bedevil scientists working to model how Earth's systems will contribute, and respond, to a hotter future.
The researchers' findings suggest that methane emissions from freshwater systems will likely rise with the global temperature, Gudasz said. But to not know the extent of methane contribution from such a widely dispersed ecosystem that includes lakes, swamps, marshes and rice paddies leaves a glaring hole in climate projections.
"The freshwater systems we talk about in our paper are an important component to the climate system," Gudasz said. "There is more and more evidence that they have a contribution to the methane emissions. Methane produced from natural or humanmade freshwater systems will increase with temperature."
To provide a simple and accurate way for climate modelers to account for methanogenesis, Gudasz and his co-authors analyzed nearly 1,600 measurements of temperature and methane emissions from 127 freshwater ecosystems across the globe.
"The freshwater systems we talk about in our paper are an important component to the climate system," Gudasz said. "There is more and more evidence that they have a contribution to the methane emissions. Methane produced from natural or humanmade freshwater systems will increase with temperature."
To provide a simple and accurate way for climate modelers to account for methanogenesis, Gudasz and his co-authors analyzed nearly 1,600 measurements of temperature and methane emissions from 127 freshwater ecosystems across the globe.
The researchers found that a common effect emerged from those studies: freshwater methane generation very much thrives on high temperatures. Methane emissions at 0 degrees Celsius would rise 57 times higher when the temperature reached 30 degrees Celsius, the researchers report. For those inclined to model it, the researchers' results translated to a temperature dependence of 0.96 electron volts (eV), an indication of the temperature-sensitivity of the methane-emitting ecosystems.
"We all want to make predictions about greenhouse gas emissions and their impact on global warming," Gudasz said. "Looking across these scales and constraining them as we have in this paper will allow us to make better predictions."
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The above story is based on materials provided by Princeton University. Note: Materials may be edited for content and length.
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Princeton University. "A more potent greenhouse gas than carbon dioxide, methane emissions will leap as Earth warms." ScienceDaily. ScienceDaily, 27 March 2014. .
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