Washington, August 12 : Climate models have confirmed that as a result of human-induced global warming, the amount of water vapor in the atmosphere is increasing.

The research was done by scientists from Lawrence Livermore National Laboratory (LLNL) scientists and a group of international researchers.

They 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,” he added.

The atmosphere’s water vapor content has increased by about 0.4 kilograms per cubic meter (kg/m) 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.

In the recent study, the scientists first took each model and tested it individually, calculating 70 different measures of model performance.

These “metrics” provided insights into how well the models simulated today’s average climate and its seasonal changes, as well as on the size and geographical patterns of climate variability.

This information was used to divide the original 22 models into various sets of “top ten” and “bottom ten” models.

“When we tried to come up with a David Letterman type ‘top ten’ list of models, we found that it’s extremely difficult to do this in practice, because each model has its own individual strengths and weaknesses,” Santer said.

Then, the group repeated their fingerprint analysis, but now using only “top ten” or “bottom ten” models rather than the full 22 models.

They did this more than 100 times, grading and ranking the models in many different ways.

In every case, a water vapor fingerprint arising from human influences could be clearly identified in the satellite data.

“One criticism of our first study was that we were only able to find a human fingerprint because we included inferior models in our analysis,” said Karl Taylor, another LLNL co-author.

“We’ve now shown that whether we use the best or the worst models, they don’t have much impact on our ability to identify a human effect on water vapor,” he added. (ANI)