Iceland rises as its glaciers melt from climate change

This global positioning satellite receiver is part of Iceland's network of 62 such receivers that geoscientists are using to detect movements of the Icelandic crust that are as small as one millimeter per year. Langjökull glacier can be seen in the background.

Earth's crust under Iceland is rebounding as global warming melts the island's great ice caps, a University of Arizona-led team reports in an upcoming issue of Geophysical Research Letters.

The paper is the first to show the current fast uplift of the Icelandic crust is a result of accelerated melting of the island's glaciers and coincides with the onset of warming that began about 30 years ago, the scientists said.

Some sites in south-central Iceland are moving upward as much as 1.4 inches (35 mm) per year -- a speed that surprised the researchers.

"Our research makes the connection between recent accelerated uplift and the accelerated melting of the Icelandic ice caps," said first author Kathleen Compton, a UA geosciences doctoral candidate.

Geologists have long known that as glaciers melt and become lighter, Earth rebounds as the weight of the ice decreases.

Whether the current rebound geologists detect is related to past deglaciation or modern ice loss has been an open question until now, said co-author Richard Bennett, a UA associate professor of geosciences.

"Iceland is the first place we can say accelerated uplift means accelerated ice mass loss," Bennett said.

To figure out how fast the crust was moving upward, the team used a network of 62 global positioning satellite receivers fastened to rocks throughout Iceland. By tracking the position of the GPS receivers year after year, the scientists "watch" the rocks move and can calculate how far they have traveled -- a technique called geodesy.

The new work shows that, at least for Iceland, the land's current accelerating uplift is directly related to the thinning of glaciers and to global warming.

"What we're observing is a climatically induced change in Earth's surface," Bennett said.

He added there is geological evidence that during the past deglaciation roughly 12,000 years ago, volcanic activity in some regions of Iceland increased thirtyfold.

Others have estimated the Icelandic crust's rebound from warming-induced ice loss could increase the frequency of volcanic eruptions such as the 2010 eruption of Eyjafjallajökull, which had negative economic consequences worldwide.

The article "Climate driven vertical acceleration of Icelandic crust measured by CGPS geodesy" by Compton, Bennett and their co-author Sigrun Hreinsdóttir of GNS Science in Avalon, New Zealand, was accepted for publication Jan. 14, 2015, and is soon to be published online. The National Science Foundation and the Icelandic Center for Research funded the research.

Some of Iceland's GPS receivers have been in place since 1995. Bennett, Hreinsdóttir and colleagues had installed 20 GPS receivers in Iceland in 2006 and 2009, thus boosting the coverage of the nation's geodesy network. In central and southern Iceland, where five of the largest ice caps are located, the receivers are 18 miles (30 km) or less apart on average.

The team primarily used the geodesy network to track geological activity such as earthquakes and volcanic eruptions.

In 2013, Bennett noticed one of long-running stations in the center of the country was showing that site was rebounding at an accelerated rate. He wondered about it, so he and his colleagues checked the nearby stations to see if they had recorded the same changes.

"The striking answer was, yes, they all do," he said. "We wondered what in the world could be causing this?"

The team began systematically analyzing years of signals from the entire network and found the fastest uplift was the region between several large ice caps. The rate of uplift slowed the farther the receiver was from the ice cap region.

Other researchers had been measuring ice loss and observed a notable uptick in the rate of melting since 1995. Temperature records for Iceland, some of which go back to the 1800s, show temperatures increasing since 1980.

To determine whether the same rate of ice loss year after year could cause such an acceleration in uplift, Compton tested that idea using mathematical models. The answer was no: The glaciers had to be melting faster and faster every year to be causing more and more uplift.

Compton found the onset of rising temperatures and the loss of ice corresponded tightly with her estimates of when uplift began.

"I was surprised how well everything lined up," she said.

Bennett said, "There's no way to explain that accelerated uplift unless the glacier is disappearing at an accelerated rate."

Estimating ice loss is laborious and difficult, he said. "Our hope is we can use current GPS measurements of uplift to more easily quantify ice loss."

The team's next step is to analyze the uplift data to reveal the seasonal variation as the ice caps grow during the winter snow season and melt during the summer.

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3-D view of Greenland Ice Sheet opens window on ice history

This is a cross-section of the age of the Greenland Ice Sheet. Layers determined to be from the Holocene period, formed during the past 11,700 years, are shown in green. Layers accumulated during the last ice age, from 11,700 to 115,000 years ago, are shown in blue. Layers from the Eemian period, more than 115,000 years old, are shown in red. Regions of unknown age are gray.

Scientists using ice-penetrating radar data collected by NASA's Operation IceBridge and earlier airborne campaigns have built the first comprehensive map of layers deep inside the Greenland Ice Sheet, opening a window on past climate conditions and the ice sheet's potentially perilous future.

This new map allows scientists to determine the age of large swaths of the second largest mass of ice on Earth, an area containing enough water to raise ocean levels by about 20 feet.

"This new, huge data volume records how the ice sheet evolved and how it's flowing today," said Joe MacGregor, the study's lead author, a glaciologist at The University of Texas at Austin Institute for Geophysics (UTIG), a unit of the Jackson School of Geosciences.

Greenland's ice sheet has been losing mass during the past two decades, a phenomenon accelerated by warming temperatures. Scientists are studying ice from different climate periods in the past to better understand how the ice sheet might respond in the future.

Ice cores offer one way of studying the distant past. These cylinders of ice drilled from the ice sheet hold evidence of past snow accumulation and temperature and contain impurities such as dust and volcanic ash compacted over hundreds of thousands of years. These layers are visible in ice cores and can be detected with ice-penetrating radar.

Ice-penetrating radar works by sending radar signals into the ice and recording the strength and return time of reflected signals. From those signals, scientists can detect the ice surface, sub-ice bedrock and layers within the ice.

New techniques used in this study allowed scientists to efficiently pick out these layers in radar data. Prior studies had mapped internal layers, but not at the scale made possible by these newer, faster methods.

Another major factor in this study was the scope of Operation IceBridge's measurements across Greenland, which included flights that covered distances of tens of thousands of kilometers across the ice sheet.

"IceBridge surveyed previously unexplored parts of the Greenland Ice Sheet and did it using state-of-the-art CReSIS radars," said study co-author Mark Fahnestock, an IceBridge science team member and glaciologist from the Geophysical Institute at the University of Alaska Fairbanks (UAF-GI).

CReSIS is the Center for Remote Sensing of Ice Sheets, a National Science Foundation science and technology center headquartered at the University of Kansas in Lawrence, Kansas.

IceBridge's flight lines often intersect ice core sites where other scientists have analyzed the ice's chemical composition to map and date layers in the ice. These core data provide a reference for radar measurements and provide a way to calculate how much ice from a given climate period exists across the ice sheet, something known as an age volume. Scientists are interested in knowing more about ice from the Eemian period, a time from 115,000 to 130,000 years ago that was about as warm as today. This new age volume provides the first data-driven estimate of where Eemian ice may remain.

Comparing this age volume to simple computer models helped the study's team better understand the ice sheet's history. Differences in the mapped and modeled age volumes point to past changes in ice flow or processes such as melting at the ice sheet's base. This information will be helpful for evaluating the more sophisticated ice sheet models that are crucial for projecting Greenland's future contribution to sea-level rise.

"Prior to this study, a good ice-sheet model was one that got its present thickness and surface speed right. Now, they'll also be able to work on getting its history right, which is important because ice sheets have very long memories," said MacGregor.

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NASA, NOAA find 2014 warmest year in modern record

This color-coded map displays global temperature anomaly data from 2014.

The year 2014 ranks as Earth's warmest since 1880, according to two separate analyses by NASA and National Oceanic and Atmospheric Administration (NOAA) scientists.

The 10 warmest years in the instrumental record, with the exception of 1998, have now occurred since 2000. This trend continues a long-term warming of the planet, according to an analysis of surface temperature measurements by scientists at NASA's Goddard Institute of Space Studies (GISS) in New York.

In an independent analysis of the raw data, also released Friday, NOAA scientists also found 2014 to be the warmest on record.

"NASA is at the forefront of the scientific investigation of the dynamics of the Earth's climate on a global scale," said John Grunsfeld, associate administrator for the Science Mission Directorate at NASA Headquarters in Washington. "The observed long-term warming trend and the ranking of 2014 as the warmest year on record reinforces the importance for NASA to study Earth as a complete system, and particularly to understand the role and impacts of human activity."

Since 1880, Earth's average surface temperature has warmed by about 1.4 degrees Fahrenheit (0.8 degrees Celsius), a trend that is largely driven by the increase in carbon dioxide and other human emissions into the planet's atmosphere. The majority of that warming has occurred in the past three decades.

"This is the latest in a series of warm years, in a series of warm decades. While the ranking of individual years can be affected by chaotic weather patterns, the long-term trends are attributable to drivers of climate change that right now are dominated by human emissions of greenhouse gases," said GISS Director Gavin Schmidt.

While 2014 temperatures continue the planet's long-term warming trend, scientists still expect to see year-to-year fluctuations in average global temperature caused by phenomena such as El Niño or La Niña. These phenomena warm or cool the tropical Pacific and are thought to have played a role in the flattening of the long-term warming trend over the past 15 years. However, 2014's record warmth occurred during an El Niño-neutral year.

"NOAA provides decision makers with timely and trusted science-based information about our changing world," said Richard Spinrad, NOAA chief scientist. "As we monitor changes in our climate, demand for the environmental intelligence NOAA provides is only growing. It's critical that we continue to work with our partners, like NASA, to observe these changes and to provide the information communities need to build resiliency."

Regional differences in temperature are more strongly affected by weather dynamics than the global mean. For example, in the U.S. in 2014, parts of the Midwest and East Coast were unusually cool, while Alaska and three western states -- California, Arizona and Nevada -- experienced their warmest year on record, according to NOAA.

The GISS analysis incorporates surface temperature measurements from 6,300 weather stations, ship- and buoy-based observations of sea surface temperatures, and temperature measurements from Antarctic research stations. This raw data is analyzed using an algorithm that takes into account the varied spacing of temperature stations around the globe and urban heating effects that could skew the calculation. The result is an estimate of the global average temperature difference from a baseline period of 1951 to 1980.

NOAA scientists used much of the same raw temperature data, but a different baseline period. They also employ their own methods to estimate global temperatures.

GISS is a NASA laboratory managed by the Earth Sciences Division of the agency's Goddard Space Flight Center, in Greenbelt, Maryland. The laboratory is affiliated with Columbia University's Earth Institute and School of Engineering and Applied Science in New York.

NASA monitors Earth's vital signs from land, air and space with a fleet of satellites, as well as airborne and ground-based observation campaigns. NASA develops new ways to observe and study Earth's interconnected natural systems with long-term data records and computer analysis tools to better see how our planet is changing. The agency shares this unique knowledge with the global community and works with institutions in the United States and around the world that contribute to understanding and protecting our home planet.

The data set of 2014 surface temperature measurements is available at:
http://data.giss nasa gov/ gistemp/

The methodology used to make the temperature calculation is available at:
http://data.giss.nasa gov/gistemp/sources v3/

For more information about NASA's Earth science activities, visit:
http://www nasa gov/ earthrightnow

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Correcting estimates of sea level rise

The acceleration in global sea level from the 20th century to the last two decades has been significantly larger than scientists previously thought, according to a new Harvard study.

The study, co-authored by Carling Hay, a post-doctoral fellow in the Department of Earth and Planetary Sciences (EPS), and Eric Morrow, a recent PhD graduate of EPS, shows that previous estimates of global sea-level rise from 1900-1990 had been over-estimated by as much as 30 percent. The report, however, confirms previous estimates of sea-level change since 1990, suggesting that the rate of sea-level change is increasing more quickly than previously believed. The new work is described in a January 14 paper published in Nature.

"What this paper shows is that sea-level acceleration over the past century has been greater than had been estimated by others," Morrow said. "It's a larger problem than we initially thought."

"Scientists now believe that most of the world's ice sheets and mountain glaciers are melting in response to rising temperatures." Hay added. "Melting ice sheets cause global mean sea level to rise. Understanding this contribution is critical in a warming world."

Previous estimates had placed sea-level rise at between 1.5 and 1.8 millimeters annually over the 20th century. Hay and Morrow, however, suggest that from 1901 until 1990, the figure was closer to 1.2 millimeters per year. But everyone agrees that global sea level has risen by about 3 millimeters annually since that time, and so the new study points to a larger acceleration in global sea level.

"Another concern with this is that many efforts to project sea-level change into the future use estimates of sea level over the time period from 1900 to 1990," Morrow said. "If we've been over-estimating the sea-level change during that period, it means that these models are not calibrated appropriately, and that calls into question the accuracy of projections out to the end of the 21st century."

To obtain their improved estimate of 20th century global sea level, Hay and Morrow approached the challenge of estimating sea-level rise from a completely new perspective.

Typically, Hay said, estimates of sea-level rise are created by dividing the world's oceans into sub-regions, and gathering records from tide gauges -- essentially yard-sticks used to measure ocean tides -- from each area. Using records that contain the most complete data, researchers average them together to create estimates of sea level for each region, then average those rates together to create a global estimate.

"But these simple averages aren't representative of a true global mean value" Hay explained. "Tide gauges are located along coasts, therefore large areas of the ocean aren't being included in these estimates. And the records that do exist commonly have large gaps."

"Part of the problem is related to the sparsity of these records, even along the coastlines," Morrow said. "It wasn't until the 1950s that there began to be more global coverage of these observations, and earlier estimates of global mean sea-level change across the 20th century were biased by that sparsity."

"We know the sea level is changing for a variety of reasons," Hay said. "There are ongoing effects due to the last ice age, heating and expansion of the ocean due to global warming, changes in ocean circulation, and present-day melting of land-ice, all of which result in unique patterns of sea-level change. These processes combine to produce the observed global mean sea-level rise."

The new estimates developed by Hay and Morrow grew out of a separate project aimed at modeling the physics that underpin sea-level "fingerprints" -- explainer from previous story.

"What we were interested in -- and remain interested in -- was whether we can detect the sea-level fingerprints we predicted in our computer simulations in sea-level records," Morrow said. "Using a global set of observations, our goal has been to infer how individual ice sheets are contributing to global sea-level rise."

The challenge, Hay said, is that doing so requires working with a "very noisy, sparse records."

"We have to account for ice age signals, and we have to understand how ocean circulation patterns are changing and how thermal expansion is contributing to both regional patterns and the global mean," she explained. "We try to correct for all those signals using our simulations and statistical methods, then look at what's left and see if it fits with the patterns we expect to see from different ice sheets."

"We are looking at all the available sea-level records and trying to say that Greenland has been melting at this rate, the Arctic at this rate, the Antarctic at this rate, etc." she continued. "We then sum these contributions and add in the rate that the oceans are changing due to thermal expansion to estimate a rate of global mean sea-level change."

To their surprise, Hay said, it quickly became clear that previous estimates of sea-level rise over most of the 20th century were too high.

"We expected that we would estimate the individual contributions, and that their sum would get us back to the 1.5 to 1.8 mm per year that other people had predicted," Hay said. "But the math doesn't work out that way. Unfortunately, our new lower rate of sea-level rise prior to 1990 means that the sea-level acceleration that resulted in higher rates over the last 20 years is really much larger than anyone thought."

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Climate policy pledges are an important step forward but fall short of 2°C

Pledges to reduce emissions in China, Europe and the US provide an important step forward for climate change action, but a more comprehensive effort is needed to stabilize the climate below critical thresholds. Climate finance can cover investment gaps and alleviate distributional tensions, a new study shows.

Researchers have released one of the most comprehensive assessments of the timing and amount of greenhouse gas emissions that each of the world's major economies could produce under different scenarios, i.e. without new climate policies, for the currently discussed pledges, and under a scenario that limits future temperature rise to 2°C. The study looks into several key negotiation issues on the road from the climate summit in Lima to the one in Paris 2015.

"The pledges made so far lead to earlier emission peaking in many countries, with 1-1.5 °C less total warming than without these policies, but not sufficient to meet the 2^°C target. Under the proposed commitments, cumulative CO₂ emissions in China would be reduced by half. Yet, together with those of the other Asian economies they would exceed the total emission budget compatible with 2°C--about 1000 Gt CO₂," says Massimo Tavoni (Fondazione Eni Enrico Mattei and Politecnico di Milano) who coordinated the project in press in the journal Nature Climate Change.

"Reducing emissions while limiting costs requires a significant contribution from developing countries. This could create unfair distribution of costs. Compensatory measures could address these" Tavoni adds. The study finds that financial support in the order of 100-150 billion USD /year by 2030 could achieve efficiency and cover the total investments in low carbon technologies needed in developing countries for the 2°C target. Fiscal revenues from instruments such as carbon taxes could also cover the clean energy investment gaps.

An international effort

The study was conducted by a team of six European research institutions, using six different modeling tools. "The IPCC AR5 report has clearly highlighted the level of global effort needed to stabilize the climate," says Tavoni. "But a quantitative assessment of the regional implications of post 2020 climate policies, which brings together different modeling tools was missing. This is what the paper has achieved."

The study is directly linked to the ongoing climate negotiation process and highlights the challenges on the road from Lima to Paris.

"In our 2^oC scenarios, global emissions peak around 2020. This is in clear contrast to our other scenarios projecting forward the pledges currently discussed by the major economies. They lead to a peaking of global emissions around or after 2040" says Elmar Kriegler, senior scientist at the Potsdam Institute for Climate Impact Research and co-leader of the study. "A large part of the emission reductions, if to be realized at lowest cost, would come from emerging economies such as China or India. The implication is clear. If a future climate agreement aims to tap into these abatement potentials, it would likely need to include mechanisms to compensate developing countries for part of their abatement effort."

Keywan Riahi, director of the Energy program at the International Institute for Applied Systems Analysis (IIASA) and a co-leader of the project, says, "This was the first study to examine regional climate mitigation potentials and needs in a real-life scenario, where the countries in the world start to transition from the currently fragmented climate policy regime towards global cooperative action. As a result, our study provides critical information for setting regional emission targets for the time period beyond 2020. We find that equitable solutions, which balance the costs across regions, would provide more "emission allowances" to the currently emerging economies. Yet even in these scenarios, countries like China will have to cut emissions to about half in 2050 to keep the 2^oC target within reach."

Detlef van Vuuren, senior researcher at PBL Netherlands Environmental Assessment agency and co-leader of the project emphasizes the importance of the study for the international negotiations. "Our scenarios show the importance of a near-term peak in all global regions to avoid rapid and expensive emission reductions later. They also clearly show how different sectors can contribute to the overall emission reductions. Emission reductions need to come from changing energy supply, reducing energy demand -- but also from changes in agricultural practices targeted at reducing non-CO₂ emissions and deforestation."

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Massive study provides first detailed look at how Greenland's ice is vanishing

This NASA visualization shows the change in the surface elevation of the southeast region of the Greenland ice sheet between 2003 and 2012. Thinning near coastal regions is shown in green, blue and purple. In addition, blue/white flows indicate the direction and speed of the ice movement. In the new study, University at Buffalo geophysicist Beata Csatho and her team found areas of rapid shrinkage in southeast Greenland that current climate models don’t address, which suggests that the ice sheet may lose ice more rapidly in the near future than previously thought.

The Greenland Ice Sheet is the second-largest body of ice on Earth. It covers an area about five times the size of New York State and Kansas combined, and if it melts completely, oceans could rise by 20 feet. Coastal communities from Florida to Bangladesh would suffer extensive damage.

Now, a new study is revealing just how little we understand this northern behemoth.

Led by geophysicist Beata Csatho, PhD, an associate professor of geology at the University at Buffalo, the research provides what the authors think is the first comprehensive picture of how Greenland's ice is vanishing. It suggests that current ice sheet modeling studies are too simplistic to accurately predict the future contributions of the entire Greenland Ice Sheet to sea level rise, and that Greenland may lose ice more rapidly in the near future than previously thought.

"The great importance of our data is that for the first time, we have a comprehensive picture of how all of Greenland's glaciers have changed over the past decade," Csatho says.

"This information is crucial for developing and validating numerical models that predict how the ice sheet may change and contribute to global sea level over the next few hundred years," says Cornelis J. van der Veen, PhD, professor in the Department of Geography at the University of Kansas, who played a key role in interpreting glaciological changes.

The project was a massive undertaking, using satellite and aerial data from NASA's ICESat spacecraft and Operation IceBridge field campaign to reconstruct how the height of the Greenland Ice Sheet changed at nearly 100,000 locations from 1993 to 2012.

Ice loss takes place in a complex manner, with the ice sheet both melting and calving ice into the ocean.

The study had two major findings:

• First, the scientists were able to provide new estimates of annual ice loss at high spatial resolution.

• Second, the research revealed that current models fail to accurately capture how the entire Greenland Ice Sheet is changing and contributing to rising oceans.

The second point is crucial to climate change modelers.

Today's simulations use the activity of four well-studied glaciers -- Jakobshavn, Helheim, Kangerlussuaq and Petermann -- to forecast how the entire ice sheet will dump ice into the oceans.

But the new research shows that activity at these four locations may not be representative of what is happening with glaciers across the ice sheet. In fact, glaciers undergo patterns of thinning and thickening that current climate change simulations fail to address, Csatho says.

"There are 242 outlet glaciers wider than 1.5 km on the Greenland Ice Sheet, and what we see is that their behavior is complex in space and time," Csatho says. "The local climate and geological conditions, the local hydrology -- all of these factors have an effect. The current models do not address this complexity."

The team identified areas of rapid shrinkage in southeast Greenland that today's models don't acknowledge. This leads Csatho to believe that the ice sheet could lose ice faster in the future than today's simulations would suggest.

The results will be published on Dec. 15 in the Proceedings of the National Academy of Sciences.

How much ice is the Greenland Ice Sheet losing?

To analyze how the height of the ice sheet was changing, Csatho and UB research professor and photogrammetrist Anton Schenk, PhD, developed a computational technique called Surface Elevation Reconstruction And Change detection to fuse together data from NASA satellite and aerial missions.

The analysis found that the Greenland Ice Sheet lost about 243 metric gigatons of ice annually -- equivalent to about 277 cubic kilometers of ice per year -- from 2003-09, the period for which the team had the most comprehensive data. This loss is estimated to have added about 0.68 millimeters of water to the oceans annually.

The figures are averages, and ice loss varied from year to year, and from region to region.

Why are today's projections of sea level rise flawed, and how can we fix them?

Glaciers don't just gradually lose mass when the temperature rises. That's one reason it's difficult to predict their response to global warming.

In the study, scientists found that some of Greenland's glaciers thickened even when the temperature rose. Others exhibited accelerated thinning. Some displayed both thinning and thickening, with sudden reversals.

As a step toward building better models of sea level rise, the research team divided Greenland's 242 glaciers into 7 major groups based on their behavior from 2003-09.

"Understanding the groupings will help us pick out examples of glaciers that are representative of the whole," Csatho says. "We can then use data from these representative glaciers in models to provide a more complete picture of what is happening."

In a new project, she and colleagues are investigating why different glaciers respond differently to warming. Factors could include the temperature of the surrounding ocean; the level of friction between a glacier and the bedrock below; the amount of water under a glacier; and the geometry of the fjord.

"The physics of these processes are not well understood," Csatho says.

The NASA missions: A colossal undertaking

The study combined data from various NASA missions, including:

• NASA's Ice, Cloud and Land Elevation Satellite (ICESat), which measured the ice sheet's elevation multiple times a year at each of the nearly 100,000 locations from 2003-09.

• NASA's, massive aerial survey that employs highly specialized research aircrafts to collect data at less frequent intervals than ICESat. These missions began measuring the Greenland Ice Sheet's elevation in 1993. Operation IceBridge was started in 2009 to bridge the time between ICESat-1 and ICESat-2, and will continue until at least 2017, when NASA's next generation ICESat-2 satellite is expected to come online.

Csatho says the new study shows why careful monitoring is critical: Given the complex nature of glacier behavior, good data is crucial to building better models.

Collaborators

Besides Csatho, Schenk and van der Veen, the project included additional researchers from the University at Buffalo, Utrecht University in The Netherlands, the Technical University of Denmark and Florida Atlantic University.

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Global warming's influence on extreme weather

Understanding the cause-and-effect relationship between global warming and record-breaking weather requires asking precisely the right questions.

Extreme climate and weather events such as record high temperatures, intense downpours and severe storm surges are becoming more common in many parts of the world. But because high-quality weather records go back only about 100 years, most scientists have been reluctant to say if global warming affected particular extreme events.

On Wednesday, Dec. 17, at the American Geophysical Union's Fall Meeting in San Francisco, Noah Diffenbaugh, an associate professor of environmental Earth system science at the Stanford School of Earth Sciences, will discuss approaches to this challenge in a talk titled "Quantifying the Influence of Observed Global Warming on the Probability of Unprecedented Extreme Climate Events." He will focus on weather events that -- at the time they occur -- are more extreme than any other event in the historical record.

Diffenbaugh emphasizes that asking precisely the right question is critical for finding the correct answer.

"The media are often focused on whether global warming caused a particular event," said Diffenbaugh, who is a senior fellow at the Stanford Woods Institute for the Environment. "The more useful question for real-world decisions is: 'Is the probability of a particular event statistically different now compared with a climate without human influence?'"

Diffenbaugh said the research requires three elements: a long record of climate observations; a large collection of climate model experiments that accurately simulate the observed variations in climate; and advanced statistical techniques to analyze both the observations and the climate models.

One research challenge involves having just a few decades or a century of high-quality weather data with which to make sense of events that might occur once every 1,000 or 10,000 years in a theoretical climate without human influence.

But decision makers need to appreciate the influence of global warming on extreme climate and weather events.

"If we look over the last decade in the United States, there have been more than 70 events that have each caused at least $1 billion in damage, and a number of those have been considerably more costly," said Diffenbaugh. "Understanding whether the probability of those high-impact events has changed can help us to plan for future extreme events, and to value the costs and benefits of avoiding future global warming."

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How pace of climate change will challenge ectotherms

Animals that regulate their body temperature through the external environment may be resilient to some climate change but not keep pace with rapid change, leading to potentially disastrous outcomes for biodiversity.

A study by the University of Sydney and University of Queensland showed many animals can modify the function of their cells and organs to compensate for changes in the climate and have done so in the past, but the researchers warn that the current rate of climate change will outpace animals' capacity for compensation (or acclimation).

The research has just been published in Nature Climate Change (Letters), written by Professor Frank Seebacher School of Biological Sciences and Professor Craig Franklin and Associate Professor Craig White from the University of Queensland.

Adapting to climate change will not just require animals to cope with higher temperatures. The predicted increase to fluctuations in temperature as well as to overall temperature would require animals to function across a broader range of conditions. This is particularly important for ectotherms, animals that rely on external sources of heat to control body temperature, and are therefore more influenced by environmental temperatures.

The research showed that many groups of ectotherms, which make up more than 90 percent of all animals, are able to change their physiological function to cope with an altered environment, but the rapid pace and fluctuations of human-induced climate change present serious challenges.

The researchers studied 40 years of published data to assess how biological functions change in response to a sudden fluctuations in environmental temperatures. They found that the physiological rates of ectothermic animals, such as heart rate, metabolism and locomotion, had already increased over the past 20 years with increasing average temperatures.

"It is important that animals maintain the right balance between the large number of physiological functions despite environmental fluctuations. An increase in temperature that leads to changed reaction rates can upset that balance and cause the decline of individuals and species," said Professor Seebacher. "For example, movement requires energy and oxygen to be delivered to muscles. However, if metabolism or the cardiovascular system can't cope with increased temperatures, animals can no longer move to forage, migrate or interact with each other.

"The overall trend in the last 20 years has been to increased physiological rates, and we predict that this would continue to increase with increasing temperature. "Even if animals are able to maintain the balance of their physiological functions in a warmer climate, increased metabolism leads to increases in the food resources needed and could upset the balance in ecosystems, particularly if predator and prey populations respond very differently to the environmental temperature change."

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Abandoned wells can be 'super-emitters' of greenhouse gas

Princeton University researchers have uncovered a previously unknown, and possibly substantial, source of the greenhouse gas methane to Earth's atmosphere.

After testing a sample of abandoned oil and natural gas wells in northwestern Pennsylvania, the researchers found that many of the old wells leaked substantial quantities of methane. Because there are so many abandoned wells nationwide (a recent study from Stanford University concluded there were roughly 3 million abandoned wells in the United States) the researchers believe the overall contribution of leaking wells could be significant.

The researchers said their findings identify a need to make measurements across a wide variety of regions in Pennsylvania but also in other states with a long history of oil and gas development such as California and Texas.

"The research indicates that this is a source of methane that should not be ignored," said Michael Celia, the Theodore Shelton Pitney Professor of Environmental Studies and professor of civil and environmental engineering at Princeton. "We need to determine how significant it is on a wider basis."

Methane is the unprocessed form of natural gas. Scientists say that after carbon dioxide, methane is the most important contributor to the greenhouse effect, in which gases in the atmosphere trap heat that would otherwise radiate from Earth. Pound for pound, methane has about 20 times the heat-trapping effect as carbon dioxide. Methane is produced naturally, by processes including decomposition, and by human activity such as landfills and oil and gas production.

While oil and gas companies work to minimize the amount of methane emitted by their operations, almost no attention has been paid to wells that were drilled decades ago. These wells, some of which date back to the 19th century, are typically abandoned and not recorded on official records.

Mary Kang, then a doctoral candidate at Princeton, originally began looking into methane emissions from old wells after researching techniques to store carbon dioxide by injecting it deep underground. While examining ways that carbon dioxide could escape underground storage, Kang wondered about the effect of old wells on methane emissions.

"I was looking for data, but it didn't exist," said Kang, now a postdoctoral researcher at Stanford.

In a paper published Dec. 8 in the Proceedings of the National Academy of Sciences, the researchers describe how they chose 19 wells in the adjacent McKean and Potter counties in northwestern Pennsylvania. The wells chosen were all abandoned, and records about the origin of the wells and their conditions did not exist. Only one of the wells was on the state's list of abandoned wells. Some of the wells, which can look like a pipe emerging from the ground, are located in forests and others in people's yards. Kang said the lack of documentation made it hard to tell when the wells were originally drilled or whether any attempt had been made to plug them.

"What surprised me was that every well we measured had some methane coming out," said Celia.

To conduct the research, the team placed enclosures called flux chambers over the tops of the wells. They also placed flux chambers nearby to measure the background emissions from the terrain and make sure the methane was emitted from the wells and not the surrounding area.

Although all the wells registered some level of methane, about 15 percent emitted the gas at a markedly higher level -- thousands of times greater than the lower-level wells. Denise Mauzerall, a Princeton professor and a member of the research team, said a critical task is to discover the characteristics of these super-emitting wells.

Mauzerall said the relatively low number of high-emitting wells could offer a workable solution: while trying to plug every abandoned well in the country might be too costly to be realistic, dealing with the smaller number of high emitters could be possible.

"The fact that most of the methane is coming out of a small number of wells should make it easier to address if we can identify the high-emitting wells," said Mauzerall, who has a joint appointment as a professor of civil and environmental engineering and as a professor of public and international affairs at the Woodrow Wilson School.

The researchers have used their results to extrapolate total methane emissions from abandoned wells in Pennsylvania, although they stress that the results are preliminary because of the relatively small sample. But based on that data, they estimate that emissions from abandoned wells represents as much as 10 percent of methane from human activities in Pennsylvania -- about the same amount as caused by current oil and gas production. Also, unlike working wells, which have productive lifetimes of 10 to 15 years, abandoned wells can continue to leak methane for decades.

"This may be a significant source," Mauzerall said. "There is no single silver bullet but if it turns out that we can cap or capture the methane coming off these really big emitters, that would make a substantial difference."

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