Showing posts with label Susan Solomon. Show all posts

Written by fatih al-farahat in , ,


Real Climate: The Wisdom of Solomon

The wisdom of Solomon

Filed under:  Climate Science — gavin @ 29 January 2010 
 
A quick post for commentary on the new Solomon et al paper in Science Express. We’ll try and get around to discussing this over the weekend, but in the meantime I’ve moved some comments over. There is some commentary on this at DotEarth, and some media reports on the story – some good, some not so good. It seems like a topic that is ripe for confusion, and so here are a few quick clarifications that are worth making.
First of all, this is a paper about internal variability of the climate system in the last decade, not on additional factors that drive climate. Second, this is a discussion about stratospheric water vapour (10–15 km above the surface), not water vapour in general. Stratospheric water vapour comes from two sources – the uplift of tropospheric water through the very cold tropical tropopause (both as vapour and as condensate), and the oxidation of methane in the upper stratosphere (CH4+2O2 –> CO2 + 2H2O; NB: this is just a schematic, the actual chemical pathways are more complicated). There isn’t very much of it (between 3 and 6 ppmv), and so small changes (~0.5 ppmv) are noticeable.

The decreases seen in this study are in the lower stratosphere and are likely dominated by a change in the flux of water through the tropopause. A change in stratospheric water vapour because of the increase in methane over the industrial period would be a forcing of the climate (and is one of the indirect effects of methane we discussed last year), but a change in the tropopause flux is a response to other factors in the climate system. These might include El Nino–La Nina events, increases in Asian aerosols, or solar impacts on near-tropopause ozone – but this is not addressed in the paper and will take a little more work to figure out.

The study includes an estimate of the effect of the observed stratospheric water decadal decrease by calculating the radiation flux with and without the change, and comparing this to the increase in CO2 forcing over the same period. This implicitly assumes that the change can be regarded as a forcing. However, whether that is an appropriate calculation or not needs some careful consideration. Finally, no-one has yet looked at whether climate models (which have plenty of decadal variability too) have phenomena that resemble these observations that might provide some insight into the causes.

Link: http://www.realclimate.org/index.php/archives/2010/01/the-wisdom-of-solomon/

Written by fatih al-farahat in ,


Susan Solomon: Water vapor caused one-third of global warming in 1990s

Water vapour caused one-third of global warming in 1990s, study reveals

Experts say their research does not undermine the scientific consensus on man-made climate change, but call for 'closer examination' of the way computer models consider water vapour
Cloud
A 10% drop in water vapour, 10 miles up has had an effect on global warming over the last 10 years, scientists say. Photograph: Getty

Scientists have underestimated the role that water vapour plays in determining global temperature changes, according to a new study that could fuel further attacks on the science of climate change.

The research, led by one of the world's top climate scientists, suggests that almost one-third of the global warming recorded during the 1990s was due to an increase in water vapour in the high atmosphere, not human emissions of greenhouse gases. A subsequent decline in water vapour after 2000 could explain a recent slowdown in global temperature rise, the scientists add.

The experts say their research does not undermine the scientific consensus that emissions of greenhouse gases from human activity drive global warming, but they call for "closer examination" of the way climate computer models consider water vapour.

The new research comes at a difficult time for climate scientists, who have been forced to defend their predictions in the face of an embarrassing mistake in the 2007 report of the Intergovernmental Panel on Climate Change (IPCC), which included false claims that Himalayan glaciers could melt away by 2035. There has also been heavy criticism over the way climate scientists at the University of East Anglia apparently tried to prevent the release of data requested under Freedom of Information laws.

The new research, led by Susan Solomon, at the US National Oceanic and Atmospheric Administration, who co-chaired the 2007 IPCC report on the science of global warming, is published today in the journal Science, one of the most respected in the world.

Solomon said the new finding does not challenge the conclusion that human activity drives climate change. "Not to my mind it doesn't," she said. "It shows that we shouldn't over-interpret the results from a few years one way or another."

She would not comment on the mistake in the IPCC report -- which was published in a separate section on likely impacts -- or on calls for Rajendra Pachauri, the IPCC chairman, to step down.

"What I will say, is that this [new study] shows there are climate scientists round the world who are trying very hard to understand and to explain to people openly and honestly what has happened over the last decade."

The new study analysed water vapour in the stratosphere, about 10 miles up, where it acts as a potent greenhouse gas and traps heat at the Earth's surface.

Satellite measurements were used to show that water vapour levels in the stratosphere have dropped about 10% since 2000. When the scientists fed this change into a climate model, they found it could have reduced, by about 25% over the last decade, the amount of warming expected to be caused by carbon dioxide and other greenhouse gases.

They conclude: "The decline in stratospheric water vapour after 2000 should be expected to have significantly contributed to the flattening of the global warming trend in the last decade."

Solomon said: "We call this the 10, 10, 10 problem. A 10% drop in water vapour, 10 miles up has had an effect on global warming over the last 10 years." Until now, scientists have struggled to explain the temperature slowdown in the years since 2000, a problem climate sceptics have exploited.

The scientists also looked at the earlier period, from 1980 to 2000, though cautioned this was based on observations of the atmosphere made by a single weather balloon. They found likely increases in water vapour in the stratosphere, enough to enhance the rate of global warming by about 30% above what would have been expected.

"These findings show that stratospheric water vapour represents an important driver of decadal global surface climate change," the scientists say. They say it should lead to a "closer examination of the representation of stratospheric water vapour changes in climate models."

Solomon said it was not clear why the water vapour levels had swung up and down, but suggested it could be down to changes in sea surface temperature, which drives convection currents and can move air around in the high atmosphere.

She said it was not clear if the water vapour decrease after 2000 reflects a natural shift, or if it was a consequence of a warming world. If the latter is true, then more warming could see greater decreases in water vapour, acting as a negative feedback to apply the brakes on future temperature rise.

Link:  http://www.guardian.co.uk/environment/2010/jan/29/water-vapour-climate-change

Written by fatih al-farahat in , ,


S. Solomon et al., 10% decrease in water vapor in the stratosphere over the last 10 years has slowed Earth’s warming trends, researchers say

Ten percent decrease water vapor in the stratosphere slows Earth’s warming trends, researchers say





by Sindya N. Bhandoo, New York Times, January 28, 2010 
A decrease in water vapor concentrations in parts of the middle atmosphere has contributed to a slowing of Earth’s warming, researchers are reporting. The finding, they said, offers part of the explanation for a string of years with relatively stable global surface temperatures.

Despite the decrease in water vapor, the study’s authors said, the overall trend is still toward a warming climate, primarily caused by a buildup in emissions of carbon dioxide and other heat-trapping gases from human sources.

“This doesn’t alter the fundamental conclusion that the world has warmed and that most of that warming has to do with greenhouse gas emissions caused by man," said Susan Solomon, a climate scientist at the National Oceanic and Atmospheric Administration and the lead author of the report, which appears in the January 29, 2010, issue of the journal Science.

Water vapor, a potent heat-trapping gas, absorbs sunlight and re-emits heat into Earth’s atmosphere. Its concentrations in the stratosphere, the second of three layers in the atmosphere, appear to have decreased in the last 10 years, according to the study.

This has slowed the rate of Earth’s warming by about 25 percent, Dr. Solomon said.

“We use the 10-10-10 to describe it,” she said. “That is, a 10 percent change in water vapor, 10 miles above our head, over the past 10 years.”

The study also found that from 1980 to 2000, an increase in water vapor sped the rate of warming — the result of an increase in emissions of methane, another greenhouse gas, during the industrial period. Methane, when oxidized, produces water vapor. Why a decrease in water vapor has occurred in the last 10 years is still unknown.

Dr. Solomon emphasized that the study focused on the atmosphere’s middle layer, not to be confused with the troposphere, Earth’s first layer. It has been known for years that water vapor in the troposphere amplifies the effect of greenhouse gas emissions.

Some climate skeptics have claimed that a spate of years with relatively stable temperatures indicates that the threat of global warming has been overblown.

Last week, the National Aeronautics and Space Administration released figures indicating that the decade ending in 2009 was the warmest on record.

Link:  http://www.nytimes.com/2010/01/29/science/earth/29vapor.html

Written by fatih al-farahat in ,


S. Solomon et al., Science, Contributions of stratospheric water vapor to decadal changes in the rate of global warming

Science, published online January 28, 2010; DOI: 10.1126/science.1182488

Contributions of stratospheric water vapor to decadal changes in the rate of global warming

Susan Solomon,1 Karen Rosenlof,1 Robert Portmann,1 John Daniel,1 Sean Davis,1,2 Todd Sanford,1,2 and Gian-Kasper Plattner3

1 NOAA Earth System Research Laboratory, Chemical Sciences Division, Boulder, CO, U.S.A.
2 Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, U.S.A.
3 Climate and Environmental Physics, Physics Institute, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland.  


Abstract

Stratospheric water vapor concentrations decreased by about 10% after the year 2000. Here, we show that this acted to slow the rate of increase in global surface temperature over 2000-2009 by about 25% compared to that which would have occurred due only to carbon dioxide and other greenhouse gases. More limited data suggest that stratospheric water vapor probably increased between 1980 and 2000, which would have enhanced the decadal rate of surface warming during the 1990s by about 30% compared to estimates neglecting this change. These findings show that stratospheric water vapor represents an important driver of decadal global surface climate change.

Link:  http://www.sciencemag.org/cgi/content/abstract/science.1182488