Global Climate Change Science News (Pt. 2)

[MacDoc]

Particulate Pollution Combined With Airborne Soot Adds To Global Warming



Los Angeles. Particulate pollution thought to be holding climate change in check by reflecting sunlight instead enhances warming when combined with airborne soot, a new study has found. (Credit: iStockphoto/Daniel Stein)

ScienceDaily (June 30, 2009) — Particulate pollution thought to be holding climate change in check by reflecting sunlight instead enhances warming when combined with airborne soot, a new study has found.

Like a black car on a bright summer day, soot absorbs solar energy. Recent atmospheric models have ranked soot, also called black carbon, second only to carbon dioxide in potential for atmospheric warming. But particles, or aerosols, such as soot mix with other chemicals in the atmosphere, complicating estimates of their role in changing climate.

"Until now, scientists have had to assume how soot is mixed with other chemical species in individual particles and estimate how that ultimately impacts their warming potential," said Kimberly Prather, professor in the Department of Chemistry and Biochemistry and the Scripps Institution of Oceanography at the University of California, San Diego. "Our measurements show that soot is most commonly mixed with other chemicals such as sulfate and this mixing happens very quickly in the atmosphere. These are the first direct measurements of the optical properties of atmospheric soot and allow us to better understand the role of soot in climate change."

Prather and Ryan Moffet, a former graduate student at UC San Diego who is now at the Lawrence Berkeley National Laboratory, measured atmospheric aerosols over Riverside, California and Mexico City. Using an instrument that measures the size, chemical composition and optical properties of aerosols in real time, they showed that jagged bits of fresh soot quickly become coated with a spherical shell of other chemicals, particularly sulfate, nitrate, and organic carbon, through light-driven chemical reactions.

Within several hours of sunrise, most of the atmospheric carbon they measured had been altered in this way, they report in the Proceedings of the National Academy of Sciences online the week of June 29.

Particles of sulfate or nitrate alone reflect light, and some have proposed pumping sulfate aerosols into the atmosphere to slow climate change. But these chemicals play a different role when they mix with soot.

"The coating acts like a lens and focuses the light into the center of the particle, enhancing warming," Prather said. "Many people think sulfate aerosols are a good thing because they are highly reflective and cool our planet. However we are seeing that sulfate is commonly mixed with soot in the same particles, which means in some regions sulfate could lead to more warming as opposed to more cooling as one would expect for a pure sulfate aerosol."

Their measurements showed that in the atmosphere the lens-like shell of sufate and nitrate enhances absorption of light by coated soot particles 1.6 times over pure soot particles.

Soot comes from fires, including those used to cook food and clear agricultural fields, as well as burning of diesel fuel in trucks and ships. Simple measures such as providing better cook stoves with more complete combustion to those in developing countries would help reduce atmospheric soot levels.

Efforts to reduce soot would pay off soon. Unlike carbon dioxide, which lingers in the atmosphere for centuries, soot falls from the sky in a matter of days to weeks, making the reduction of soot a quicker option for slowing down climate change.

"While reducing CO2 concentrations is extremely important, changes we make today will not be felt for quite a while, whereas changes we make today on soot and sulfate could affect our planet on timescales of months," Prather said. "This could buy us time while we grapple with the problems of reducing carbon dioxide and other greenhouse gases."
_{Adapted from materials provided by University of California - San Diego, via EurekAlert!, a service of AAAS.}

http://www.sciencedaily.com/releases/20 ... 200808.htm

[RichardPrins]

Plants put limit on ice ages

Palo Alto, CA— When glaciers advanced over much of the Earth's surface during the last ice age, what kept the planet from freezing over entirely? This has been a puzzle to climate scientists because leading models have indicated that over the past 24 million years geological conditions should have caused carbon dioxide levels in the atmosphere to plummet, possibly leading to runaway "icehouse" conditions. Now researchers writing in the July 2, 2009, Nature report on the missing piece of the puzzle – plants.

"Atmospheric CO2 concentrations have been remarkably stable over the last 20 or 25 million years despite other changes in the environment," says co-author Ken Caldeira of the Carnegie Institution's Department of Global Ecology. "We can look to land plants as the primary buffering agent that's held CO2 in such a narrow range during this time."

The research team, led by Mark Pagani of Yale University, found that the critical role of plants in the chemical breakdown and weathering of rocks and soil gave them a strong influence on carbon dioxide levels. It was a link that earlier studies had missed.

Over geologic time, large volumes of carbon dioxide have been released into the atmosphere by volcanoes. This would cause CO2 to build up in the atmosphere were it not for countervailing geologic processes of sedimentation, which bury carbon-containing minerals in the crust, sequestering it from the atmosphere. The overall rate of sedimentation is controlled by the upthrust of mountains and the erosion and chemical breakdown of their rocks. The rise of the Andes, Himalayas, Tibetan Plateau, and mountain ranges in western North America over the past 25 million years would have been expected to have cause faster weathering and erosion, and therefore a faster burial of carbon drawn from the atmosphere. But the stability of carbon dioxide levels indicate that this didn't happen. Why not?

This is where the plants come in. "The rates of weathering reactions are largely controlled by plants. Their roots secrete acids that dissolve minerals, they hold soils, and they increase the amount of carbon dissolved in groundwater," says Caldeira. "But when levels of carbon dioxide get too low, the plants basically suffocate and the weathering slows down. That means less sediment is eroded from the uplands and less carbon can be buried. It's a negative feedback on the system that has kept carbon dioxide levels from dropping too low."

Extremely low carbon dioxide levels would have reduced the atmosphere's ability to retain heat, putting the planet into a deep freeze. "So you could say that by limiting the drawdown of CO2 by chemical weathering and sedimentation, plants saved the planet from freezing over," says Caldeira.

Could plants save us from rising carbon dioxide from human emissions and harmful greenhouse warming? No, says Caldeira. "We are releasing CO2 to the atmosphere about 100 times faster than all the volcanoes in the world put together. While these weathering processes will eventually remove the CO2 we are adding to the atmosphere, they act too slowly to help us avoid dangerous climate change. It will take hundreds of thousands of years for these rock weathering processes to remove our fossil fuel emissions from the atmosphere."

The Carnegie Institution (http://www.CIW.edu) has been a pioneering force in basic scientific research since 1902. It is a private, nonprofit organization with six research departments throughout the U.S. Carnegie scientists are leaders in plant biology, developmental biology, astronomy, materials science, global ecology, and Earth and planetary science. The Department of Global Ecology, located in Stanford, California, was established in 2002 to help build the scientific foundations for a sustainable future. Its scientists conduct basic research on a wide range of large-scale environmental issues, including climate change, ocean acidification, biological invasions, and changes in biodiversity.

Plants save the earth from an icy doom

New Haven, Conn. — Fifty million years ago, the North and South Poles were ice-free and crocodiles roamed the Arctic. Since then, a long-term decrease in the amount of CO2 in the atmosphere has cooled the Earth. Researchers at Yale University, the Carnegie Institution of Washington and the University of Sheffield now show that land plants saved the Earth from a deep frozen fate by buffering the removal of atmospheric CO2 over the past 24 million years.

While the upper limit for atmospheric CO2 levels has been a focus for discussions of global warming and the quality of life on Earth, this study points to the dynamics that maintain the lower sustainable limits of atmospheric CO2.

Volcanic gases naturally add CO2 to the atmosphere, and over millions of years CO2 is removed by the weathering of silica-based rocks like granite and then locked up in carbonates on the floor of the world's oceans. The more these rocks are weathered, the more CO2 is removed from the atmosphere.


As plants become starved for CO2, rock weathering diminishes. Credit: David Beerling

"Mountain building in places like Tibet and South America during the past 25 million years created conditions that should have sucked nearly all the CO2 out of the atmosphere, throwing the Earth into a deep freeze," said senior author Mark Pagani, associate professor of geology and geophysics and a member of the Yale Climate and Energy Institute's executive committee. "But as the CO2 concentration of Earth's atmosphere decreased to about 200 to 250 parts per million, CO2 levels stabilized."


Mark Pagani is a researcher at Yale University. Credit: Pagani.

The study, published in the XX issue of Nature, looked for a possible explanation. They used simulations of the global carbon cycle and observations from plant growth experiments to show that as atmospheric CO2 concentrations began to drop towards near-starvation levels for land plants, the capacity of plants and vegetation to weather silicate rocks greatly diminished, slowing the draw-down of atmospheric CO2.

"When CO2 levels become suffocatingly low, plant growth is compromised and the health of forest ecosystems suffer," said Pagani. "When this happens, plants can no longer help remove CO2 from the atmosphere faster than volcanoes and other sources can supply it."

"Ultimately, we owe another large debt to plants" said co-author Ken Caldeira from the Carnegie Institution of Washington at Stanford University. "Aside from providing zesty dishes like eggplant parmesan, plants have also stabilized Earth's climate by inhibiting critically low levels of CO2 that would have thrown Earth spinning into space like a frozen ice ball."

Co-author David Beerling from Sheffield University adds, "Our research supports the emerging view that plants should be recognized as a geologic force of nature, with important consequences for all life on Earth"

Robert Berner, professor emeritus of geology and geophysics at Yale, is also an author on the study. The Yale Climate and Energy Institute; the National Science Foundation; the Department of Energy; the Leverhulme Trust and a Royal Society-Wolfson Research Merit Award supported the research.

The Yale Climate and Energy Institute (YCEI) is a newly established interdisciplinary institute focused on bridging research and policy around climate and energy issues so that practical solutions can be implemented in both the developing and developed world.

An interview with Mark Pagani is available at http://tinyurl.com/yale-pagani-052909

Citation: Nature, (doi:10.1038/nature08133)

[RichardPrins]

The least sea ice in 800 years

New research, which reconstructs the extent of ice in the sea between Greenland and Svalbard from the 13th century to the present indicates that there has never been so little sea ice as there is now. The research results from the Niels Bohr Institute, among others, are published in the scientific journal, Climate Dynamics.

There are of course neither satellite images nor instrumental records of the climate all the way back to the 13th century, but nature has its own 'archive' of the climate in both ice cores and the annual growth rings of trees and we humans have made records of a great many things over the years - such as observations in the log books of ships and in harbour records. Piece all of the information together and you get a picture of how much sea ice there has been throughout time.


There has never been so little sea ice in the area between Svalbard and Greenland in the last 800 years. Credit: NASA/GSFC.

Modern research and historic records
"We have combined information about the climate found in ice cores from an ice cap on Svalbard and from the annual growth rings of trees in Finland and this gave us a curve of the past climate" explains Aslak Grinsted, geophysicist with the Centre for Ice and Climate at the Niels Bohr Institute at the University of Copenhagen.

In order to determine how much sea ice there has been, the researchers needed to turn to data from the logbooks of ships, which whalers and fisherman kept of their expeditions to the boundary of the sea ice. The ship logbooks are very precise and go all the way back to the 16th century. They relate at which geographical position the ice was found. Another source of information about the ice are records from harbours in Iceland, where the severity of the winters have been recorded since the end of the 18th century.

By combining the curve of the climate with the actual historical records of the distribution of the ice, researchers have been able to reconstruct the extent of the sea ice all the way back to the 13th century. Even though the 13th century was a warm period, the calculations show that there has never been so little sea ice as in the 20th century.

In the middle of the 17th century there was also a sharp decline in sea ice, but it lasted only a very brief period. The greatest cover of sea ice was in a period around 1700-1800, which is also called the 'Little Ice Age'.

"There was a sharp change in the ice cover at the start of the 20th century," explains Aslak Grinsted. He explains, that the ice shrank by 300.000 km2 in the space of ten years from 1910-1920. So you can see that there have been sudden changes throughout time, but here during the last few years we have had some record years with very little ice extent.

"We see that the sea ice is shrinking to a level which has not been seen in more than 800 years", concludes Aslak Grinsted.

Link: http://dx.doi.org/10.1007/s00382-009-0610-z

[MacDoc]

New Type Of El Nino Could Mean More Hurricanes Make Landfall


The 2008 hurricane season was one of the most active on record. In this image, taken on August 28, 2008, three storms can be seen in various stages: Fay, Gustav and Hannah. (Credit: National Oceanic and Atmospheric Administration)

ScienceDaily (July 3, 2009) — El Niño years typically result in fewer hurricanes forming in the Atlantic Ocean. But a new study suggests that the form of El Niño may be changing potentially causing not only a greater number of hurricanes than in average years, but also a greater chance of hurricanes making landfall, according to climatologists at the Georgia Institute of Technology. The study appears in the July 3, 2009, edition of the journal Science.

"Normally, El Niño results in diminished hurricanes in the Atlantic, but this new type is resulting in a greater number of hurricanes with greater frequency and more potential to make landfall," said Peter Webster, professor at Georgia Tech's School of Earth and Atmospheric Sciences.

That's because this new type of El Niño, known as El Niño Modoki (from the Japanese meaning "similar, but different"), forms in the Central Pacific, rather than the Eastern Pacific as the typical El Niño event does. Warming in the Central Pacific is associated with a higher storm frequency and a greater potential for making landfall along the Gulf coast and the coast of Central America.

Even though the oceanic circulation pattern of warm water known as El Niño forms in the Pacific, it affects the circulation patterns across the globe, changing the number of hurricanes in the Atlantic. This regular type of El Niño (from the Spanish meaning "little boy" or "Christ child") is more difficult to forecast, with predictions of the December circulation pattern not coming until May. At first glance, that may seem like plenty of time. However, the summer before El Niño occurs, the storm patterns change, meaning that predictions of El Niño come only one month before the start of hurricane season in June. But El Niño Modoki follows a different prediction pattern.

"This new type of El Niño is more predictable," said Webster. "We're not sure why, but this could mean that we get greater warning of hurricanes, probably by a number of months."

As to why the form of El Niño is changing to El Niño Modoki, that's not entirely clear yet, said Webster.

"This could be part of a natural oscillation of El Niño," he said. "Or it could be El Niño's response to a warming atmosphere. There are hints that the trade winds of the Pacific have become weaker with time and this may lead to the warming occurring further to the west. We need more data before we know for sure."

In the study, Webster, along with Earth and Atmospheric Sciences Chair Judy Curry and research scientist Hye-Mi Kim used satellite data along with historical tropical storm records and climate models.

The research team is currently looking at La Niña, the cooling of the surface waters in the Eastern and Central Pacific.

"In the past, La Nina has been associated with a greater than average number of North Atlantic hurricanes and La Nina seems to be changing its structure as well," said Webster. "We're vitally interested in understanding why El Niño-La Niña has changed. To determine this we need to run a series of numerical experiments with climate models."

_{Adapted from materials provided by Georgia Institute of Technology, via EurekAlert!, a service of AAAS.}

http://www.sciencedaily.com/releases/20 ... 140835.htm

[MacDoc]

Super-size deposits of frozen carbon threat to climate change
June 30th, 2009 in Space & Earth / Earth Sciences

The vast amount of carbon stored in the arctic and boreal regions of the world is more than double that previously estimated, according to a study published this week.

The amount of carbon in frozen soils, sediments and river deltas (permafrost) raises new concerns over the role of the northern regions as future sources of greenhouse gases.

"We now estimate the deposits contain over 1.5 trillion tons of frozen carbon, about twice as much carbon as contained in the atmosphere", said Dr. Charles Tarnocai, Agriculture and Agri-Food Canada, Ottawa, and lead author.

Dr. Pep Canadell, Executive Director of the Global Carbon Project at CSIRO, Australia, and co-author of the study says that the existence of these super-sized deposits of frozen carbon means that any thawing of permafrost due to global warming may lead to significant emissions of the greenhouse gases carbon dioxide and methane.

Carbon deposits frozen thousands of years ago can easily break down when permafrost thaws releasing greenhouse gases to the atmosphere, according to another recent study by some of the same authors.

"Radioactive carbon dating shows that most of the carbon dioxide currently emitted by thawing soils in Alaska was formed and frozen thousands of years ago. The carbon dating demonstrates how easily carbon decomposes when soils thaw under warmer conditions," said Professor Ted Schuur, University of Florida and co-author of the paper.

The authors point out the large uncertainties surrounding the extent to which permafrost carbon thawing could further accelerate climate change.

"Permafrost carbon is a bit of a wildcard in the efforts to predict future climate change," said Dr Canadell. "All evidence to date shows that carbon in permafrost is likely to play a significant role in the 21st century climate given the large carbon deposits, the readiness of its organic matter to release greenhouse gases when thawed, and the fact that high latitudes will experience the largest increase in air temperature of all regions."

Carbon in permafrost is found largely in northern regions including Canada, Greenland, Kazakhstan, Mongolia, Russia, Scandinavia and USA.

The carbon assessment is published this week in the journal of "Global Biogeochemical Cycles" of the American Geophysical Union, and the radiocarbon study was recently published in the journal of Nature.

Source: Global Carbon Project

http://www.physorg.com/print165588881.html

[Foxy13]

http://news.yahoo.com/s/afp/20090707/sc ... NhdGVsbGl0

NASA Satellite Shows 'Dramatically Thinned' Arctic Ice

WASHINGTON (AFP) – Arctic sea ice thinned dramatically between the winters of 2004 and 2008, with thick older ice shrinking by the equivalent of Alaska's land area, a study using data from a NASA satellite showed Tuesday.

Using information from NASA's Ice, Cloud and Land Satellite (ICESat), scientists from the US space agency and the University of Washington in Seattle estimated both the thickness and volume of the Arctic Ocean's ice cover.

ICESat allows scientists to measure changes in the thickness and volume of Arctic ice, whereas previously scientists relied only on measurements of area to determine how much of the Arctic Ocean is covered in ice.

Scientists found that Arctic sea ice thinned some seven inches (17.8 centimeters) a year, or 2.2 feet (67 centimeters) over four winters, according to the study by NASA and the University of Washington, published in the Journal of Geophysical Research-Oceans.

They also found that thicker, older ice, which has survived one or more summers, shrank by 42 percent.

"Between 2004 and 2008, multi-year ice cover shrank 595,000 square miles (1.5 million square kilometers) -- nearly the size of Alaska's land area," a report of the study's findings said.

The Arctic ice cap grows each winter, when the northerly region grows intensely cold as the sun sets for several months.

Then, in the summer, wind and ocean currents cause some of the ice to flow out of the Arctic, while warmer temperatures make much of it melt in place.

Thicker, older ice is less vulnerable than thinner ice to melting in the summer months.

But in recent years, the amount of ice replaced in the winter has not been sufficient to offset summer ice losses, the ICESat study showed.

That makes for more open water in summer, which absorbs more heat, warming the ocean and further melting the ice, the report of the scientists' findings said.

The research team attributed the changes in the overall thickness and volume of Arctic Ocean sea ice to recent warming and anomalies in patterns of sea ice circulation.

"The near-zero replenishment of the multi-year ice cover, combined with unusual exports of ice out of the Arctic after the summers of 2005 and 2007, have both played significant roles in the loss of Arctic sea ice volume," said Ron Kwok of NASA's Jet Propulsion Laboratory in California who led the study.

Data from the study will help scientists to better understand how fast the volume of Arctic ice is decreasing and how soon the region might be "nearly ice-free in the summer," said Kwok.

A study published in April by the Colorado-based National Snow and Ice Data Center (NSIDC) also showed that the Arctic ice cap is thinner than ever and the maximum extent of Arctic ice was at an all-time low.

The same month, US researchers warned that the Arctic could be almost ice-free within 30 years, not 90 as scientists had previously estimated.

[MacDoc]

Warming Arctic could teem with life by 2030

* 19:01 08 July 2009 by Catherine Brahic



"Teeming with life" may not be the description that springs to mind when thinking of the Arctic Ocean, but that could soon change as global warming removes the region's icy lid.

A study of what the Arctic looked like just before dinosaurs were wiped off the planet has provided a glimpse of what could be to come within decades.

Alan Kemp of the UK National Oceanography Centre in Southampton and colleagues used powerful microscopes to inspect cores of mud extracted from the bottom of the Arctic Ocean. They found successive layers of tiny algae called diatoms. The pattern of the layers and the distribution of the diatoms provides strong evidence that the Arctic was free of ice during the summer and, contrary to recent studies, frequently covered in ice during the winter.
Hot summer

Ice-free summers and icy winters are precisely what glaciologists fear could happen in the Arctic within decades. Over the past few years, wind pattern and warm temperatures have been gradually thinning Arctic sea ice, making it less and less likely to survive the summer. Some believe the Arctic could be ice-free during the summer as soon as 2030.

The researchers say that the sheer number of diatoms locked in the mud suggests that when the dinosaurs roamed the Earth the Arctic Ocean was biologically very rich during the summer, on a par with the most productive regions of the Southern Ocean today. Since diatoms are at the very bottom of the food chain, waters rich in diatoms can support a lot of larger life forms as well.

"On the basis of our findings, we can say that it is likely that a future Arctic Ocean free of summer sea ice will also be highly productive," says Kemp. Arctic fauna today is limited by the region's harsh conditions. The ocean is home to very few species of fish – such as the Arctic cod – which in turn support seals, whales and polar bears.
Summer migration

While more diatoms during the summer does not mean that larger animals will spontaneously appear in the Arctic over the coming decades, it could give species that currently live further south an incentive to move into the region by providing them with food. The most likely scenario is one in which larger species migrate to the Arctic in the summer to feed on the enriched summer food chain, then move back south during the dark winters.

"The outcome would depend on organisms at all levels of the food chain moving in to exploit this potential," says Kemp. "What is unpredictable is what species from elsewhere may migrate in to fill the new ecological niches."

A study of fossils and fossilised faeces carried out around Devon Island in the Canadian Arctic, suggested last year that the regions may once have been home to a rich gathering of larger fish and possibly even sharks during the late Cretaceous (Proceedings of the Royal Society B, DOI: 10.1098/rspb.2008.0801). Presumably, these animals would have been supported by Kemp's diatoms.

Journal reference: Nature (DOI: 10.1038/nature08141)

[MacDoc]

Arctic glacier to lose Manhattan-sized 'tongue'

* 17:34 14 July 2009 by Catherine Brahic


http://brightcove.newscientist.com/serv ... 9419261001

Video: Researcher Alun Hubbard discusses the break up of the ice

The biggest glacier in the Arctic is on the verge of losing a chunk of ice the size of Manhattan. A group of scientists and climate change activists who are closely monitoring the Petermann glacier's ice tongue believe the rapid flow of ice is in part due to warm ocean currents moving up along the coast of Greenland, fuelled by global warming.

During the summer of last year, Jason Box of Ohio State University in Columbus noticed a huge crack in the glacier's floating ice tongue, which acts as a conveyor belt, pushing the glacier's ice through a fjord and out to sea. The crack extended almost completely from one side of the fjord to the other, 16 kilometres away.

This prompted Box and colleagues to return this year on the Arctic Sunrise, a Greenpeace vessel. The researchers are equipped with an arsenal of cameras and sensors, which they have been setting up on surrounding cliffs as well as on the ice itself.
Break imminent

Stitched together, the pictures they are taking will provide a blow-by-blow animation of the event. "We're looking on a minute by minute basis at what it's doing, how it's moving in relation to the rest of the glacier, and looking for that critical point where it fractures and breaks off," says Alun Hubbard, a glaciologist at the University Of Wales, UK.

The team believes this will happen within weeks. Only yesterday, a 3-square-kilometre chunk broke away. There are now more than 10 cracks in the ice, some 500 metres wide. The researchers expect the ice tongue to break up within the coming weeks.

When this happens, an island of ice the size of Manhattan, spanning 100 km2 holding 5 billion tonnes of ice, will break free and drift out to sea.
Melt concerns

As with all glaciers that terminate over water, big chunks of ice regularly break off the Petermann ice tongue, a process which is normally compensated for by the snow that falls on the upper reaches of the glacier. But the sheer amount of ice that could break away in a single event is concerning the scientists – five billion tonnes of ice is equivalent to nearly half of the glacier's usual annual flow.

The researchers are unsure what exactly is causing the break-up. A chunk of 1 million tonnes of ice broke off last year and there has been an acceleration in the flow of ice over the past few years. They think a number of factors are involved including warmer ocean currents that are melting the ice from below and warmer air temperatures that are melting it from above.

"Ocean warming currents are circulating around the fjord and eroding the underbelly of Petermann glacier at an incredible rate," says Hubbard.
Driller thriller

Melting at the surface of the ice forms huge whirlpools of relatively warm fresh water that bore holes into the floating sheet. The scientists believe this process is accelerating the ice's demise.

In places, the meltwater bores holes through the ice right down to the bottom of the ice tongue. Surfacing seals are proof that some of the holes – called moulins – pierce to bottom of the ice.

Box, who in addition to posting his instruments on the ground is surveying the ice by helicopter, says the view from above is one of "innumerable turquoise pools, from puddles to lakes – thousands of them".

When the huge section of ice breaks off, it could be like uncorking a bottle. A smaller ice tongue will provide less resistance for the glacier as it flows out to sea, which ultimately will accelerate sea level rise.

http://www.newscientist.com/article/dn1 ... ongue.html

[MacDoc]

Indian Ocean: Gatekeeper to climate extremes?

Some glacial periods in the Earth’s more recent geological past have been cooler and more severe than others, despite very similar greenhouse gas concentrations and orbital parameters. What is it that decouples global temperature from carbon dioxide levels and the solar heat?

Changes in ocean circulation, particularly in the climatically crucial North Atlantic region, are the most likely candidate. A paper in Nature (subscription required) now suggests that some of these changes originate more than 10,000 kilometres away in the subtropical Indian Ocean.



Edouard Bard and Rosalind Rickaby analysed an 800,000-year record of sea surface temperature and ocean productivity from an ocean sediment core retrieved off the southeastern coast of South Africa (Editor's summary). This is the region where a portion of the warm and salty water carried southwards by the Agulhas current, the Indian Ocean equivalent to the Gulf Stream, leaks into the South Atlantic. The inflow compensates for the export of cold Atlantic deep water to other ocean basins. More importantly, it fuels the Atlantic overturning circulation which carries warm tropical surface water towards the poles, and cold deep water back towards the equator.

The strength of this heat conveyor depends on the position of ocean fronts, boundaries between water masses of different temperature and salinity, which are known to intermittently shift northwards and southwards.

Bard and Rickaby suggest that the Agulhas current between Madagascar and the African coast has almost come to a halt during times when the subtropical front in the Indian Ocean migrated northwards by up to 1,000 kilometres. Isotopic data from the sediment record suggest this has happened at least twice, namely during glacial stadials around 340,000 and 420,000 years ago. The closure of the Agulhas ‘valve’ might explain why these glacial periods have been severely colder than most others before and thereafter.

The “persuasive” study makes “a compelling case that, at times in the past, severely reduced water transport between the Indian and Atlantic oceans may have caused climate to cool beyond typical ice-age conditions,” writes Barcelona-based oceanographer Rainer Zahn in a News & Views piece (subscription required).

There’s a tempting afterthought: If in warm climates such as ours more Indian Ocean water leaks into the Atlantic it could help stabilize the Atlantic overturning circulation, safeguarding us against drastic climate disruptions caused by the heat conveyor’s hypothesized failure.

But as is often the case in Earth system studies, it is hard to distinguish the forces that push from those that pull on the causal chain to mode shifts. It is not quite clear, for example, what might have caused the subtropical Indian Ocean front to move this far northwards in the first place.

How the Agulhas current might behave if temperatures continue to rise is even more uncertain. “Let’s keep an eye on what the leakage does next,” says Zahn.

<sub>Quirin Schiermeier

Image: The Agulhas current carries warm Indian Ocean water around the Cape of Good Hope.
Credit: SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE</sub>

http://blogs.nature.com/climatefeedback ... to_cl.html

[MacDoc]

Scientists Expect Wildfires To Increase As Climate Warms In Coming Decades


This graph shows the percentage increase in area burned by wildfires, from the present-day to the 2050s, as calculated by the model of Spracklen et al. [2009] for the May-October fire season. The model follows a scenario of moderately increasing emissions of greenhouse gas emissions and leads to average global warming of 1.6 degrees Celsius (3 degrees Fahrenheit) by 2050. Warmer temperatures can dry out underbrush, leading to more serious conflagrations in the future climate. (Credit: Loretta Mickley, Harvard School of Engineering and Applied Sciences)

ScienceDaily (July 29, 2009) — As the climate warms in the coming decades, atmospheric scientists at Harvard's School of Engineering and Applied Sciences (SEAS) and their colleagues expect that the frequency of wildfires will increase in many regions. The spike in the number of fires could also adversely affect air quality due to the greater presence of smoke.

The study, led by SEAS Senior Research Fellow Jennifer Logan, was published in the June 18th issue of Journal of Geophysical Research. In their pioneering work, Logan and her collaborators investigated the consequences of climate change on future forest fires and on air quality in the western United States. Previous studies have probed the links between climate change and fire severity in the West and elsewhere. The Harvard study represents the first attempt to quantify the impact of future wildfires on the air we breathe.

"Warmer temperatures can dry out underbrush, leading to a more serious conflagration once a fire is started by lightening or human activity," says Logan. "Because smoke and other particles from fires adversely affect air quality, an increase in wildfires could have large impacts on human health."

Using a series of models, the scientists predict that the geographic area typically burned by wildfires in the western United States could increase by about 50% by the 2050s due mainly to rising temperatures. The greatest increases in area burned (75-175%) would occur in the forests of the Pacific Northwest and the Rocky Mountains. In addition, because of extra burning throughout the western U.S., one important type of smoke particle, organic carbon aerosols, would increase, on average, by about 40 percent during the roughly half-century period.

To conduct the research, the team first examined a 25-year record of observed meteorology and fire statistics to identify those meteorological factors that could best predict area burned for each ecosystem in the western United States. To see how these meteorological factors would change in the future, they then next ran a global climate model out to 2055, following the A1B scenario in greenhouse gas emissions. This scenario, one of several devised by the Intergovernmental Panel on Climate Change, describes a future world with rapid economic growth and balanced energy generation from fossil and alternative fuels. Relative to the other scenarios, it leads to a moderate warming of the earth's average surface temperature, about 3oF (1.6 oC) by 2050.

"By hypothesizing that the same relationships between meteorology and area burned still hold in the future, we then could predict wildfire activity and emissions from 2000 to the 2050's," explains Logan.

As a last step, the researchers used an atmospheric chemistry model to understand how the change in wildfire activity would affect air quality. This model, combining their predictions of areas burned with 2050's meteorology data, shows the emissions and fate of the smoke and other particles emitted by the future wildfires. The resulting diminished air quality could lead to smoggier skies and adversely affect those suffering from lung and heart conditions such as asthma and chronic bronchitis.

The authors expect the work will help policymakers gauge the "climate penalty" related to ongoing efforts to reduce air pollution across the United States. In addition, the study underscores the need for a vigorous fire management plan.

The team next plans to focus on future wildfires and air quality over the densely populated areas in California and in the southwest United States.

_{Logan's collaborators included SEAS Research Associate Loretta Mickley and former postdocs Dominick Spracklen (now at University of Leeds), Rynda Hudman, and Rosemarie Yevich; Michael D. Flannigan, Canadian Forest Service; and Anthony. L. Westerling, University of California, Merced. The authors acknowledge the support of a STAR (Science to Achieve Results) grant from National Center for Environmental Research of the U.S. Environmental Protection Agency and a grant from the National Aeronautics and Space Administration.}

http://www.sciencedaily.com/releases/20 ... 123047.htm