Global Warming 2020

Global Warming News : Melting Greenland Ice Sheets May Threaten Northeast United States, Canada

Melting of the Greenland ice sheet this century may drive more water than previously thought toward the already threatened coastlines of New York, Boston, Halifax, and other cities in the northeastern United States and Canada, according to new research led by the National Center for Atmospheric Research (NCAR).

The study, which is being published May 29 in Geophysical Research Letters, finds that if Greenland’s ice melts at moderate to high rates, ocean circulation by 2100 may shift and cause sea levels off the northeast coast of North America to rise by about 12 to 20 inches (about 30 to 50 centimeters) more than in other coastal areas. The research builds on recent reports that have found that sea level rise associated with global warming could adversely affect North America, and its findings suggest that the situation is more threatening than previously believed.

“If the Greenland melt continues to accelerate, we could see significant impacts this century on the northeast U.S. coast from the resulting sea level rise,” says NCAR scientist Aixue Hu, the lead author. “Major northeastern cities are directly in the path of the greatest rise.”

A study in Nature Geoscience in March warned that warmer water temperatures could shift ocean currents in a way that would raise sea levels off the Northeast by about 8 inches (20 cm) more than the average global sea level rise. But it did not include the additional impact of Greenland’s ice, which at moderate to high melt rates would further accelerate changes in ocean circulation and drive an additional 4 to 12 inches (about 10 to 30 cm) of water toward heavily populated areas of northeastern North America on top of average global sea level rise. More remote areas in extreme northeastern Canada and Greenland could see even higher sea level rise.

Scientists have been cautious about estimating average sea level rise this century in part because of complex processes within ice sheets. The 2007 assessment of the Intergovernmental Panel on Climate Change projected that sea levels worldwide could rise by an average of 7 to 23 inches (18 to 59 cm) this century, but many researchers believe the rise will be greater because of dynamic factors in ice sheets that appear to have accelerated the melting rate in recent years.

The new research was funded by the U.S. Department of Energy and by NCAR’s sponsor, the National Science Foundation. It was conducted by scientists at NCAR, the University of Colorado at Boulder, and Florida State University.

How much meltwater?

To assess the impact of Greenland ice melt on ocean circulation, Hu and his coauthors used the Community Climate System Model, an NCAR-based computer model that simulates global climate. They considered three scenarios: the melt rate continuing to increase by 7 percent per year, as has been the case in recent years, or the melt rate slowing down to an increase of either 1 or 3 percent per year.

If Greenland’s melt rate slows down to a 3 percent annual increase, the study team’s computer simulations indicate that the runoff from its ice sheet could alter ocean circulation in a way that would direct about a foot of water toward the northeast coast of North America by 2100. This would be on top of the average global sea level rise expected as a result of global warming. Although the study team did not try to estimate that mean global sea level rise, their simulations indicated that melt from Greenland alone under the 3 percent scenario could raise worldwide sea levels by an average of 21 inches (54 cm).

If the annual increase in the melt rate dropped to 1 percent, the runoff would not raise northeastern sea levels by more than the 8 inches (20 cm) found in the earlier study in Nature Geoscience. But if the melt rate continued at its present 7 percent increase per year through 2050 and then leveled off, the study suggests that the northeast coast could see as much as 20 inches (50 cm) of sea level rise above a global average that could be several feet. However, Hu cautioned that other modeling studies have indicated that the 7 percent scenario is unlikely.

In addition to sea level rise, Hu and his co-authors found that if the Greenland melt rate were to defy expectations and continue its 7 percent increase, this would drain enough fresh water into the North Atlantic to weaken the oceanic circulation that pumps warm water to the Arctic. Ironically, this weakening of the meridional overturning circulation would help the Arctic avoid some of the impacts of global warming and lead to at least the temporary recovery of Arctic sea ice by the end of the century.

Why the Northeast?

The northeast coast of North America is especially vulnerable to the effects of Greenland ice melt because of the way the meridional overturning circulation acts like a conveyer belt transporting water through the Atlantic Ocean. The circulation carries warm Atlantic water from the tropics to the north, where it cools and descends to create a dense layer of cold water. As a result, sea level is currently about 28 inches (71 cm) lower in the North Atlantic than the North Pacific, which lacks such a dense layer.

If the melting of the Greenland Ice Sheet were to increase by 3 percent or 7 percent yearly, the additional fresh water could partially disrupt the northward conveyor belt. This would reduce the accumulation of deep, dense water. Instead, the deep water would be slightly warmer, expanding and elevating the surface across portions of the North Atlantic.

Unlike water in a bathtub, water in the oceans does not spread out evenly. Sea level can vary by several feet from one region to another, depending on such factors as ocean circulation and the extent to which water at lower depths is compressed.

“The oceans will not rise uniformly as the world warms,” says NCAR scientist Gerald Meehl, a co-author of the paper. “Ocean dynamics will push water in certain directions, so some locations will experience sea level rise that is larger than the global average.

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Journal reference:

Aixue Hu, Gerald Meehl, Weiqing Han, and Jianjun Yin. Transient Response of the MOC and Climate to Potential Melting of the Greenland Ice Sheet in the 21st Century. Geophysical Research Letters, May 29, 2009 DOI: 10.1029/2009GL037998

Adapted from materials provided by National Center for Atmospheric Research.

Source: Global Warming News, Greenhouse Gas Effects, Climate Change information at sciencedaily.com

Global Warming News : Greening Arctic Not Likely To Offset Permafrost Carbon Release

As the frozen soil in the Arctic thaws, bacteria will break down organic matter, releasing long-stored carbon into the warming atmosphere.

At the same time, plants will proliferate, nurtured by balmier temperatures, more nutrients from decomposing soil and the increasing abundance of the greenhouse gas they depend on for growth.

These connected but contrasting changes have raised a question for scientists who study the causes and consequences of global climate change: Will the shrubs and incipient forests spreading across the Arctic compensate for the permafrost’s rising release of carbon, blunting its impact on a warming planet? Or, with twice as much carbon locked up in the permafrost as now present in the atmosphere, will the lush growth become overwhelmed — like a kitchen sponge put down to stem a water main break?

Researchers led by a University of Florida ecologist may have an answer. In a paper set to appear May 28 in the journal Nature, the team reports experimental results suggesting tundra plant growth may keep up with rising carbon dioxide initially.

But if thawing continues in a warmer world, the permafrost will spew carbon for decades, and the plants will become overwhelmed — unable to sop up the excess carbon despite even the most vigorous growth.

“At first, with the plants offsetting the carbon dioxide, it will appear that everything is fine, but actually this conceals the initial destabilization of permafrost carbon,” said Ted Schuur, a UF associate professor of ecology and lead author of the paper. “But it doesn’t last, because there is so much carbon in the permafrost that eventually the plants can’t keep up.”

Schuur noted most of the 13 million square kilometers, or roughly 5 million square miles, of permafrost in Alaska, Canada, Siberia and parts of Europe remain frozen. However, thawing already occurring around its southern edges is expected to expand this century.

Should that occur, this study suggests the permafrost could lose in the range of 1 gigaton of carbon, or 1 billion tons, per year – about the same order of magnitude as being added by current deforestation of the tropics, another large biospheric source, Schuur said.

While burning fossil fuels contributes considerably more carbon, about 8.5 gigatons annually, that process can at least in theory be controlled – whereas once the permafrost thaw begins, it sets up a self-reinforcing loop far from human activity and potentially difficult to stop.

That highlights the urgent need to address human-caused emissions now, Schuur said.

“It is not an option to be putting insulation on top of the tundra,” he said. “If we address our own emissions, either by reducing deforestation or controlling emissions from fossil fuels, that’s the key to minimizing the changes in the permafrost carbon pool.”

Researchers from UF used hand-built, automated chambers to trap and measure carbon dioxide losses in Alaska year-round from 2004 through 2006. Thawing at the research sites near Denali National Park, in central Alaska, varies considerably, with some plots much more extensively thawed than others.

The researchers determined how long each spot had been thawing using long-term data from permafrost-monitoring instruments combined with historical aerial photographs. With a total of 18 of the automated chambers, they measured the release and uptake of carbon between the tundra and the atmosphere. This resulted in a measurement of net ecosystem carbon exchange – the total carbon each spot lost, or gained, due to thawing permafrost.

The results were clear.

Tundra sites that had thawed for the past 15 years gained net carbon, as increasingly verdant plant growth was greater than the permafrost’s carbon losses. However, radiocarbon dating of carbon dioxide showed that old carbon from the permafrost was already being released in higher amounts due to thaw – signifying that all was not well with the permafrost carbon even in that time period. The site that began thawing decades before gained net carbon emission to the atmosphere, revealing that more thaw caused significantly more old carbon loss — despite greening of the vegetation, including more shrubs.

Said Jason Vogel, a UF postdoctoral associate and author of the paper: “The plants are still growing faster in the extensively thawed area, but that’s not enough to keep up with the greater microbial activity releasing old carbon from deeper in the soil.”

As a result, even as the Arctic greens, its escalating old carbon loss “could make permafrost a large biospheric carbon source in a warmer world,” according to the paper.

The other authors are Kathryn Crummer, a UF lab technician; Hanna Lee, a UF doctoral student; James Sickman, of the University of California, Riverside; and T.E. Osterkamp of the University of Alaska, Fairbanks. The research was funded by the National Science Foundation, NASA and a cooperative agreement with the National Park Service.

Adapted from materials provided by University of Florida.

Source: Global Warming News, Climate Change, Greenhouse Gas Effect inormation at sciencedaily.com

Global Warming News : Bird Songs Change With Environment

Just as a changing radio landscape has made it tough for 1970’s bands like Foghat to get much airplay these days, so it is for birdsongs, according to new research.

Behavioral ecologist Elizabeth Derryberry (Louisiana State University) has found that the songs of white-crowned sparrows change over time in response to changing habitats. The research sheds light on the factors that drive the evolution of mating signals in birds.

Derryberry says she first noticed that sparrows seem to be changing their tunes while working on her doctoral research. She ran across some old recordings of classic sparrow songs from 1970, and noted that the old tunes seemed a little different from the ones the kids are singing today.

To evaluate how much the songs have changed—and what might be driving the change—Derryberry made new recordings in the same locations as the old ones. She then used aerial photographs to evaluate how vegetation had changed in each place. Using computer software to compare the songs then and now, she found that where vegetation had gotten thicker, the birdsongs had slowed down significantly in tempo.

“It’s pretty good evidence that vegetation density can influence birdsong over time,” Derryberry said.

Why would thicker vegetation cause slower songs?

Leaves create an echo. A slower tune, Derryberry says, is less apt to be garbled by reverberation.

“Young male sparrows learn to sing by listening to adult males nearby,” she explains. “Juveniles likely learn and repeat the songs they hear most clearly.” Since the slower songs come through loud and clear in leafy surroundings, those are the ones that are learned and passed on to the next generation. After a while, the slower songs dominate.

Derryberry’s study is the first to show that rapid habitat shifts can cause changes in birdsongs. She now plans to extend her research to investigate how habitat changes associated with global warming might cause birds to sing a different tune.

Journal reference:

Derryberry et al. Ecology Shapes Birdsong Evolution: Variation in Morphology and Habitat Explains Variation in White%u2010Crowned Sparrow Song. The American Naturalist, 2009; 090514093712063 DOI: 10.1086/599298
Adapted from materials provided by University of Chicago Press Journals, via EurekAlert!, a service of AAAS.

Source: Global Warming News, Climate Change, Greenhouse Effect information at sciencedaily.com

Global Warming News : Climate Change Odds Much Worse Than Thought

The most comprehensive modeling yet carried out on the likelihood of how much hotter the Earth’s climate will get in this century shows that without rapid and massive action, the problem will be about twice as severe as previously estimated six years ago – and could be even worse than that.

The study uses the MIT Integrated Global Systems Model, a detailed computer simulation of global economic activity and climate processes that has been developed and refined by the Joint Program on the Science and Policy of Global Change since the early 1990s. The new research involved 400 runs of the model with each run using slight variations in input parameters, selected so that each run has about an equal probability of being correct based on present observations and knowledge. Other research groups have estimated the probabilities of various outcomes, based on variations in the physical response of the climate system itself. But the MIT model is the only one that interactively includes detailed treatment of possible changes in human activities as well – such as the degree of economic growth, with its associated energy use, in different countries.

Study co-author Ronald Prinn, the co-director of the Joint Program and director of MIT’s Center for Global Change Science, says that, regarding global warming, it is important “to base our opinions and policies on the peer-reviewed science,” he says. And in the peer-reviewed literature, the MIT model, unlike any other, looks in great detail at the effects of economic activity coupled with the effects of atmospheric, oceanic and biological systems. “In that sense, our work is unique,” he says.

The new projections, published this month in the American Meteorological Society’s Journal of Climate, indicate a median probability of surface warming of 5.2 degrees Celsius by 2100, with a 90% probability range of 3.5 to 7.4 degrees. This can be compared to a median projected increase in the 2003 study of just 2.4 degrees. The difference is caused by several factors rather than any single big change. Among these are improved economic modeling and newer economic data showing less chance of low emissions than had been projected in the earlier scenarios. Other changes include accounting for the past masking of underlying warming by the cooling induced by 20th century volcanoes, and for emissions of soot, which can add to the warming effect. In addition, measurements of deep ocean temperature rises, which enable estimates of how fast heat and carbon dioxide are removed from the atmosphere and transferred to the ocean depths, imply lower transfer rates than previously estimated.

Prinn says these and a variety of other changes based on new measurements and new analyses changed the odds on what could be expected in this century in the “no policy” scenarios – that is, where there are no policies in place that specifically induce reductions in greenhouse gas emissions. Overall, the changes “unfortunately largely summed up all in the same direction,” he says. “Overall, they stacked up so they caused more projected global warming.”

While the outcomes in the “no policy” projections now look much worse than before, there is less change from previous work in the projected outcomes if strong policies are put in place now to drastically curb greenhouse gas emissions. Without action, “there is significantly more risk than we previously estimated,” Prinn says. “This increases the urgency for significant policy action.”

To illustrate the range of probabilities revealed by the 400 simulations, Prinn and the team produced a “roulette wheel” that reflects the latest relative odds of various levels of temperature rise. The wheel provides a very graphic representation of just how serious the potential climate impacts are.

“There’s no way the world can or should take these risks,” Prinn says. And the odds indicated by this modeling may actually understate the problem, because the model does not fully incorporate other positive feedbacks that can occur, for example, if increased temperatures caused a large-scale melting of permafrost in arctic regions and subsequent release of large quantities of methane, a very potent greenhouse gas. Including that feedback “is just going to make it worse,” Prinn says.

The lead author of the paper describing the new projections is Andrei Sokolov, research scientist in the Joint Program. Other authors, besides Sokolov and Prinn, include Peter H. Stone, Chris E. Forest, Sergey Paltsev, Adam Schlosser, Stephanie Dutkiewicz, John Reilly, Marcus Sarofim, Chien Wang and Henry D. Jacoby, all of the MIT Joint Program on the Science and Policy of Global Change, as well as Mort Webster of MIT’s Engineering Systems Division and D. Kicklighter, B. Felzer and J. Melillo of the Marine Biological Laboratory at Woods Hole.

Prinn stresses that the computer models are built to match the known conditions, processes and past history of the relevant human and natural systems, and the researchers are therefore dependent on the accuracy of this current knowledge. Beyond this, “we do the research, and let the results fall where they may,” he says. Since there are so many uncertainties, especially with regard to what human beings will choose to do and how large the climate response will be, “we don’t pretend we can do it accurately. Instead, we do these 400 runs and look at the spread of the odds.”

Because vehicles last for years, and buildings and powerplants last for decades, it is essential to start making major changes through adoption of significant national and international policies as soon as possible, Prinn says. “The least-cost option to lower the risk is to start now and steadily transform the global energy system over the coming decades to low or zero greenhouse gas-emitting technologies.”

This work was supported in part by grants from the Office of Science of the U.S. Dept. of Energy, and by the industrial and foundation sponsors of the MIT Joint Program on the Science and Policy of Global Change.

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Journal reference:

A.P. Sokolov, P.H. Stone, C.E. Forest, R. Prinn, M.C. Sarofim, M. Webster, S. Paltsev, C.A. Schlosser, D. Kicklighter, S. Dutkiewicz, J. Reilly, C. Wang, B Felzer, H.D. Jacoby. Probabilistic forecast for 21st century climate based on uncertainties in emissions (without policy) and climate parameters. Journal of Climate, 2007; preprint (2009): 1 DOI: 10.1175/2009JCLI2863.1
Adapted from materials provided by Massachusetts Institute of Technology.

Source: Global Warming News, Climate Change, Greenhouse Effects information at sciencedaily.com