In another major finding, scientists using AIRS data have removed most of the uncertainty about the role of water vapor in atmospheric models. The data are the strongest observational evidence to date for how water vapor responds to a warming climate.
"AIRS temperature and water vapor observations have corroborated climate model predictions that the warming of our climate produced as carbon dioxide levels rise will be greatly exacerbated -- in fact, more than doubled -- by water vapor," said Andrew Dessler, a climate scientist at Texas A&M University, College Station, Texas.
Dessler explained that most of the warming caused by carbon dioxide does not come directly from carbon dioxide, but from effects known as feedbacks. Water vapor is a particularly important feedback. As the climate warms, the atmosphere becomes more humid. Since water is a greenhouse gas, it serves as a powerful positive feedback to the climate system, amplifying the initial warming. AIRS measurements of water vapor reveal that water greatly amplifies warming caused by increased levels of carbon dioxide. Comparisons of AIRS data with models and re-analyses are in excellent agreement.
"The implication of these studies is that, should greenhouse gas emissions continue on their current course of increase, we are virtually certain to see Earth's climate warm by several degrees Celsius in the next century, unless some strong negative feedback mechanism emerges elsewhere in Earth's climate system," Dessler said.