Global warming amplifier: Rising water vapor in upper troposphere to intensify climate change

"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 human-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 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 Earth's temperature.

The paper, titled "Upper Tropospheric Moistening in response to Anthropogenic Warming," was published in the July 28th, 2014 Early Addition on-line of the journal Proceedings of the National Academy of Sciences (PNAS). The paper's authors include Chung, Soden, B.J. Sohn of Seoul National University, and Lei Shi of NOAA's National Climatic Data Center in Ashville, North Carolina.