New study confirms water vapor as global warming amplifier

A press release from the Rosenstiel School of Marine and Atmospheric Science at the University of Miami: A new study from scientists at the University of Miami Rosenstiel School of Marine and Atmospheric Science and colleagues confirms rising levels of water vapor in the upper troposphere – a key amplifier of global warming – will intensify climate change impacts over the next decades. The new study is the first to show that increased water vapor concentrations in the atmosphere are a direct result of human activities.

“The study is the first to confirm that human activities have increased water vapor in the upper troposphere,” said Brian Soden, professor of atmospheric sciences at the UM Rosenstiel School and co-author of the study.

To investigate the potential causes of a 30-year moistening trend in the upper troposphere, a region 3- 7 miles above Earth’s surface, Soden, UM Rosenstiel School researcher Eui-Seok Chung and colleagues measured water vapor in the upper troposphere collected by NOAA satellites and compared them to climate model predictions of water circulation between the ocean and atmosphere to determine whether observed changes in atmospheric water vapor could be explained by natural or man-made causes. Using the set of climate model experiments, the researchers showed that rising water vapor in the upper troposphere cannot be explained by natural forces, such as volcanoes and changes in solar activity, but can be explained by increased greenhouse gases, such as CO2.

Greenhouse gases raise temperatures by trapping the Earth’s radiant heat inside the atmosphere. This warming also increases the accumulation of atmospheric water vapor, the most abundant greenhouse gas. The atmospheric moistening traps additional radiant heat and further increases temperatures. Climate models predict that as the climate warms from the burning of fossil fuels, the concentrations of water vapor will also increase in response to that warming. This moistening of the atmosphere, in turn, absorbs more heat and further raises the Earth's temperature....

A NASA color-enhanced image of upper tropospheric water vapor

Water vapor in stratosphere plays role in climate

Newswise via Texas A&M University: Water vapor changes in the stratosphere contribute to warmer temperatures and likely play an important role in the evolution of Earth’s climate, says a research team led by a Texas A&M University professor.

Andrew Dessler, a Texas A&M atmospheric sciences professor, and colleagues from the University of Colorado, NOAA (National Oceanic and Atmospheric Administration) and the Science and Technology Corp. have had their findings published in the Proceedings of the National Academy of Sciences.

The researchers found that increased surface temperatures, such as from the addition of carbon dioxide to the atmosphere, leads to increased humidity in the stratosphere. Because stratospheric water vapor is a greenhouse gas, this leads to additional warming, they said. This cycle is frequently called a climate feedback.

“We find that this stratospheric water vapor feedback is probably responsible for 5-10 percent of the total warming you get from adding carbon dioxide to the climate,” Dessler explained. “While it’s not really surprising that this process is going on, we were surprised at how important the process is for our climate system.”

Climate models already include this process, but unevenly. Some models predict large increases in stratospheric humidity, while others don’t, the researchers say.

“It’s clear to us that, if models want to make accurate predictions of climate change, they should get stratospheric water vapor right,” said Sean Davis, a research scientist at the Cooperative Institute for Research in Environmental Sciences at the University of Colorado at Boulder and study coauthor. He added, “A better understanding of the stratospheric water vapor feedback could help explain some of the spread among predictions of future climate change from different models,” referring to the projections made by the recently released 5th Assessment report of the Intergovernmental Panel on Climate Change (IPCC) last week....

Sunset from the International Space Station, shot by NASA