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Atmospheric methane levels remain flat for seven years

rice field

Scientists at the University of California, Irvine, have determined that levels of atmospheric methane, an important greenhouse gas, have stayed nearly flat for the past seven years, following a rise that spanned at least two decades. This finding indicates that methane may no longer be as large a global warming threat as previously thought, and it provides evidence that methane levels can be controlled.

Scientists also found that pulses of increased methane were paralleled by increases of ethane, a gas known to be emitted during fires. This is further indication that methane is formed during biomass burning and that large-scale fires can be a big source of atmospheric methane.

The methane research was published in the 23 November issue of Geophysical Research Letters. It was funded by NASA and the Gary Comer Abrupt Climate Change Fellowship.

The researchers (Isobel Simpson, Sherwood Rowland, Simone Meinardi, and Donald Blake) believe one reason for the slowdown in methane concentration growth may be repairs made to oil and gas lines and storage facilities, which can release methane into the atmosphere if they leak. Other reasons may include a slower growth or decrease in methane emissions from coal mining, rice paddies, and natural gas production.

There is no reason to believe that methane levels will remain stable in the future, the scientists point out, but the fact that leveling off is occurring now indicates that society can do something about global warming.

"If one really tightens emissions, the amount of methane in the atmosphere 10 years from now could be less than it is today. We will gain some ground on global warming if methane is not as large a contributor in the future as it has been in the past century," said Rowland.

The researchers examined data from sea-level air collected in locations from northern Alaska to southern New Zealand to obtain a global average. From 1978 to 1987, the amount of methane in the global troposphere increased by 11%, that is, more than 1% per year. In the late 1980s, the growth rate slowed to 0.3–0.6% per year. It continued to decline into the 1990s, but with a few sharp upward fluctuations, which scientists have linked to non-cyclical events such as the eruption of Mt. Pinatubo in 1991 and the Indonesian and boreal wildfires in 1997 and 1998.

From 1998 to 2005, the samples showed a near-zero growth of methane.

University of California, Irvine

Latitude isn't the only concern when species respond to climate change

wave rock

According to a recent study in Ecological Monographs, predicting the impact of climate change on organisms is much more complicated than simply looking at species' northern and southern range limits. Studying the ecologically important California sea mussel (Mytilus californianus), scientists from four universities measured body temperatures of this mussel along most of its range, from Washington to southern California. They found that differences in water temperature and other factors can turn what would seem to be an ideal environment for a species into one that's decidedly different.

As global climate changes occur, the role of an organism's internal temperature in driving species distribution becomes more important. "In many cases, science has a poor understanding of how the physiologically relevant environmental factors vary in space and time. We know little of how climate is translated into patterns of body temperature," said author Brian Helmuth (University of South Carolina).

Over five years and across almost 2,000 kilometers (1,200 miles), the scientists explored how mussel body temperatures changed across latitudes, and how waves affected the mussels. Using sensors placed in several regions throughout the organisms' territory, the scientists were able to study the temperature changes the mussels experienced diurnally as well as annually. They found that tides as well as wave action affect the temperature ranges the species experience.

Helmuth and his colleagues found several "hot spots"—areas where the mussel temperatures ran warmer than expected—and "cold spots"—sites where daily minimum temperatures ran lower than at other sites at about the same latitude. This produced a pattern of complex thermal mosaics rather than simple latitudinal gradients. Importantly, they found that animal temperatures were as hot at sites well within the species' range as they were at sites far to the south, suggesting that climate change may cause damage not just at range edges, where scientists usually look for such effects, but at locations well within the range.

University of South Carolina
University of California, Santa Barbara
University of British Columbia, Vancouver
Oregon State University

Icelandic volcano linked to historic famine in Egypt


An environmental drama played out on the world stage in the late 18th century when a volcanic eruption that killed 9,000 Icelanders also helped produce a famine in Egypt that reduced the population of the Nile Valley by a sixth.

A study by three scientists from Rutgers University and a collaborator from the University of Edinburgh demonstrates a connection between these two widely separated events. The investigators used a computer model developed by NASA's Goddard Institute for Space Studies to trace atmospheric changes that followed the 1783 eruption of Laki in southern Iceland back to their point of origin.

The study is the first to conclusively establish the link between high-latitude eruptions and the water supply in North Africa. Eruptions of volcanoes in the tropics are known to produce warmer winters in the Northern Hemisphere; however, the new study shows that volcanic influences also can flow north to south, generating an array of repercussions, including both hot and cold weather.

The authors present new evidence, from observations as well as climate model simulations, that high-latitude eruptions have altered Northern Hemisphere atmospheric circulation in the summer following the eruption, with impacts extending deep into the tropics.

In June 1783, the Laki volcano began a series of eruptions, regarded as the largest at a high latitude in the last millennium.

The eruptions produced around 12 cubic kilometers of lava and more than 90 million metric tons of sulfur
dioxide and toxic gases, killing vegetation, livestock, and people. These eruptions were followed by a drought in a swath across northern Africa, producing a very low flow in the Nile.

Laki's far-flung effects were chronicled by Benjamin Franklin and other scientists of the time. In both 1783 and 1784, the annual Nile inundations were insufficient for agriculture, leading to widespread famine throughout Egypt by the end of 1784.

In the Northern Hemisphere, the summer of 1783 was chilly—the coldest in at least 500 years in some locations, according to tree ring data. While the model linked these lowered Northern Hemisphere temperatures to Laki, it also connected the dots to a monsoon—the seasonal winds that bring annual rains to southern Asia and northern Africa. The unusual cold in the north lessened the temperature contrast between land and oceans upon which the monsoon winds rely for their development and strength.

The modeling showed significant warming that occurred from west to east across Africa to the southern Arabian Peninsula and on to India during the summer of 1783. With little or no monsoon, there were no clouds to bring rain for the rivers or shield the surface from evaporation.

The research was funded by NSF and NASA. The study, by Luke Oman (Rutgers) and colleagues, was published on 30 September 2006 in Geophysical Research Letters.

The Laki volcanic eruption, which emerged in 1783 from the Grimsvoetn caldera (below), apparently led to famine in the Nile Valley of Egypt (left) through a chain of climate events. (Iceland image by Roger McLassus; satellite composite of Nile Valley courtesy NASA.)


Rutgers, The State University of New Jersey
University of Edinburgh

Humans' effect on climate shown at the mesoscale


Research has demonstrated that the warming temperatures in central England over the past 40 years can be attributed to human factors and not nature – the first time a significant human influence on climate change has been identified at such a small scale.

Since the 1950s, central England's temperature has risen by 1°C (1.8°F). David Karoly (University of Oklahoma) and Peter Stott (Hadley Centre for Climate Prediction and Research) used modeled and observed temperatures to study whether the rise is part of a natural cycle or caused by anthropogenic factors. The temperature observations they used were made at several sites in central England as far back as 1659—the longest continuous data set on surface air temperature in the world.

The scientists found that the probability that a natural cycle caused the rise in temperature is less than 1%. Their research was published in Atmospheric Science Letters.

"This warming in central England is already affecting many aspects of life, leading to the recent record temperatures and the much earlier onset of spring," Karoly said.

According to Stott, "Sharp spikes in warming have been recorded in regions across the world, but because we in the UK hold this unique temperature record we are able to say that background climate noise can't reasonably be held responsible for what's happening in central England."

He added: "This is the first time anywhere in the world that climate scientist have been able to look at a small geographical area, identify significant warming and say humans have very likely played a part."

Earlier this year the UK Met Office announced that the extended summer period (May-September 2006) was the warmest on record in the central England temperature record.

University of Oklahoma
Hadley Centre for Climate Prediction and Research

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