Increase in atmospheric moisture tied to human activities

September 18, 2007
Increase in atmospheric moisture tied to human activities
Estimates of the amount of atmospheric water vapor over oceans from the satellite-based Special Sensor Microwave Imager. Results are for August 28th (top panel) and August 29th, 2005 (bottom panel). Locations with high atmospheric moisture content are denoted by red and white colors. The highest water vapor values are associated with typhoons Talim and Nabi in the Pacific and with Hurricane Katrina in the Gulf of Mexico. Credit: Carl Mears and Frank Wentz/Remote Sensing Systems

Observations and climate model results confirm that human-induced warming of the planet is having a pronounced effect on the atmosphere’s total moisture content. Those are the findings of a new study appearing in the Sept. 17 online edition of the Proceedings of the National Academy of Sciences.

“When you heat the planet, you increase the ability of the atmosphere to hold moisture,” said Benjamin Santer, lead author from Lawrence Livermore National Laboratory’s Program for Climate Modeling and Intercomparison. “The atmosphere’s water vapor content has increased by about 0.41 kilograms per square meter (kg/m²) per decade since 1988, and natural variability in climate just can’t explain this moisture change. The most plausible explanation is that it’s due to the human-caused increase in greenhouse gases.”

More water vapor – which is itself a greenhouse gas – amplifies the warming effect of increased atmospheric levels of carbon dioxide. This is what scientists call a “positive feedback.”

Using 22 different computer models of the climate system and measurements from the satellite-based Special Sensor Microwave Imager (SSM/I), atmospheric scientists from LLNL and eight other international research centers have shown that the recent increase in moisture content over the bulk of the world’s oceans is not due to solar forcing or gradual recovery from the 1991 eruption of Mount Pinatubo. The primary driver of this ‘atmospheric moistening’ is the increase in carbon dioxide caused by the burning of fossil fuels.

“This is the first identification of a human fingerprint on the amount of water vapor in the atmosphere,” Santer said.

“Fingerprint” studies seek to identify the causes of recent climate change and involve rigorous comparisons of modeled and observed climate change patterns. To date, most fingerprint studies have focused on temperature changes at the Earth’s surface, in the free atmosphere, or in the oceans, or have considered variables whose behavior is directly related to changes in atmospheric temperature.

The water vapor feedback mechanism works in the following way: as the atmosphere warms due to human-caused increases in carbon dioxide, methane, nitrous oxide, and chlorofluorocarbons, water vapor increases, trapping more heat in the atmosphere, which in turn causes a further increase in water vapor.

Basic theory, observations and climate model results all show that the increase in water vapor is roughly 6 percent to 7.5 percent per degree Celsius warming of the lower atmosphere.

The authors note that their findings, when taken together with similar studies of continental-scale river runoff, zonal-mean rainfall, and surface specific humidity, point toward an emerging human-caused signal in the cycling of moisture between the atmosphere, land and ocean.

“This new work shows that the climate system is telling us a consistent story,” Santer said. “The observed changes in temperature, moisture, and atmospheric circulation fit together in an internally- and physically-consistent way.”

The Livermore authors included Karl Taylor, Peter Gleckler, Jim Boyle and Stephen Klein.

Other scientists contributing to this research were Carl Mears and Frank Wentz at Remote Sensing Systems in Santa Rosa, Calif.; Tom Wigley, Jerry Meehl, and Warren Washington at the National Center for Atmospheric Research in Boulder; Tim Barnett and Dave Pierce at Scripps Institution of Oceanography in La Jolla; Wolfgang Brüggemann at the University of Hamburg in Germany; Nathan Gillett at the University of East Anglia and Peter Stott at the Hadley Centre for Climate Prediction and Research (both in the U.K.); Toru Nozawa at the National Institute for Environmental Studies in Japan; and Mike Wehner at Lawrence Berkeley National Laboratory.

Source: Lawrence Livermore National Laboratory

Explore further: Scientists, tribe study shrinking Washington state glacier

Related Stories

Scientists, tribe study shrinking Washington state glacier

August 28, 2015

Mauri Pelto digs his crampons into the steep icy slope on Mount Baker in Washington state and watches as streams of water cascade off the thick mass of bare, bluish ice. Every 20 yards, the water carves vertical channels ...

A technique for reducing the salinity of brackish water

August 28, 2015

The Fource project created by Lodewijk Stuyt from Alterra and PhD candidate Melle Nikkels from Wageningen University has won first prize at Water Republic x SAIL 2015 Innovation Edition. In Pakhuis de Zwijger, situated on ...

Saving Louisiana's coast

August 27, 2015

It was Day Nine after Katrina struck in 2005 when Sarah Mack's bosses at the Sewerage and Water Board of New Orleans called her back to work.

Data backs limits on deep-sea fishing by depth

August 27, 2015

Researchers reporting in the Cell Press journal Current Biology on August 27 have evidence in support of a clearly defined depth limit for deep-sea fishing in Europe. The findings come just as the European Union considers ...

Recommended for you

Climate ups odds of 'grey swan' superstorms

August 31, 2015

Climate change will boost the odds up to 14-fold for extremely rare, hard-to-predict tropical cyclones for parts of Australia, the United States and Dubai by 2100, researchers said Monday.

Quantifying the impact of volcanic eruptions on climate

August 31, 2015

Large volcanic eruptions inject considerable amounts of sulphur in the stratosphere which, once converted into aerosols, block sun rays and tend to cool the surface of the Earth down for several years. An international team ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.