LLNL: Increase in Atmospheric Moisture Tied to Human Activities

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, researchers said.

The findings of the 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 (LLNL) Program for Climate Modeling and Intercomparison. "The atmosphere's water vapor content has increased by about 0.41 kilograms per cubic 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."

The researchers said that more water vapor 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.

According to the researchers, 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.

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."

Benjamin Santer: http://www-pcmdi.llnl.gov/about/staff/Santer/index.php

Check out the archives of Environmental Protection magazine Web site for additional articles related to atmospheric moisture, including: "Research: Storing Carbon To Combat Global Warming May Cause Other Environmental Problems."

This article originally appeared in the 09/01/2007 issue of Environmental Protection.

Download Center

  • Waste Management in 2021: Accelerate Your Success with Technology

    Join waste management experts on February 23rd for a live best practice session webinar. You’ll learn how to take your waste program to the next level with visual location, barcoding, and mobility. Register now.

  • Green Quadrant EHS Software 2021

    Reserve your copy of the new report by independent analyst firm, Verdantix, to get a detailed, fact-based comparison of the 22 most prominent EHS software vendors in the industry.

  • Your Guide to Environmental Metrics that Drive Performance

    Translating sustainability into action starts with implementing the right metrics to assess your environmental risk and performance. Learn how to design metrics that improve your decision-making process and drive enterprise performance.

  • 5 Keys to Best-in-Class Chemical Management

    Running a safe chemical program is challenging and complex: from knowing what's on-site to proper handling and disposal - all while navigating regulatory changes. Learn the best ways to mitigate chemical risk, get the most value out of your data, and gain buy-in for a chemical management solution.

  • Unpacking ESG: 6 Questions You Were Too Afraid to Ask

    Environmental and Sustainability experts from Arcadis and Cority answer 6 of the most pressing questions EHS professionals have about getting started with Environmental, Social, and Governance (ESG) reporting.

  • Industry Safe