Climate models confirm more moisture in atmosphere attributed to humans

Lawrence Livermore National Laboratory: When it comes to using climate models to assess the causes of the increased amount of moisture in the atmosphere, it doesn't much matter if one model is better than the other. They all come to the same conclusion: Humans are warming the planet, and this warming is increasing the amount of water vapor in the atmosphere.

In new research appearing in the Aug. 10 online issue of the Proceedings of the U.S. National Academy of Sciences, Lawrence Livermore National Laboratory scientists and a group of international researchers found that model quality does not affect the ability to identify human effects on atmospheric water vapor.

“Climate model quality didn't make much of a difference,” said Benjamin Santer, lead author from LLNL's Program for Climate Modeling and Intercomparison. “Even with the computer models that performed relatively poorly, we could still identify a human effect on climate. It was a bit surprising. The physics that drive changes in water vapor are very simple and are reasonably well portrayed in all climate models, bad or good.”

The atmosphere's water vapor content has increased by about 0.4 kilograms per square meter per decade since 1988, and natural variability alone can't explain this moisture change, according to Santer. “The most plausible explanation is that it's due to human-caused increases in greenhouse gases,” he said.

…“The issue of how we are going to deal with models of very different quality will probably become much more important in the next few years, when we look at the wide range of models that are going to be used in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change,” Santer said…..

Total amount of atmospheric water vapor over the oceans on July 4, 2009. These results are from operational weather forecasts of the European Centre for Medium-Range Weather Forecasting (ECMWF).