Water Vapor May Be Biggest Contributor to Higher Global Temperatures, Researcher Says
GENEVA An unexpected greenhouse gas -- water vapor -- may be the biggest factor contributing to higher global air temperatures, a Swiss researcher said Wednesday.
Other greenhouse gases heat the ground, which causes more water evaporation that in turn further increases ground and then air temperatures, said Rolf Philipona of the World Radiation Center in Davos, Switzerland.
"Water vapor is a greenhouse gas," said Philipona. "Wherever you have an increase in water vapor, you have an increase in temperature."
A study led by Philipona found that temperatures in the Alps increased by 1.3 to 1.4 degrees Celsius since 1980, but rose much more rapidly after 1995 -- jumping up almost a full degree at the same time that water vapor levels there rose by relatively high 4 percent.
Manmade greenhouse gases such as carbon dioxide, methane and ozone had a direct contribution of only about 30 percent to this rapid increase in temperature, Philipona said.
The major cause of temperature change in this region -- the other 70 percent -- was increased levels of water vapor, according to the study, which was published by the U.S. journal Geophysical Research Letters.
"There has been a lot of speculation over why temperatures go up," Philipona said in a telephone interview. "In this study, we were able to distinguish between the effects of water vapor and the effects of aerosols and other factors."
Over the same period of time, temperatures in relatively arid Spain hardly rose at all because the dry landscape did not release a significant amount of water vapor, Philipona said.
Most water vapor in the air occurs naturally, but humans can help restrict the problem by limiting carbon dioxide emissions, which heat the earth's surface and cause greater water evaporation, he said.
"We cannot reduce water vapor, but we can enhance it marginally," Philipona said. "We have to strongly reduce the CO2 which we put into the atmosphere."
Previously, global warming skeptics have claimed that rising surface temperatures would cause a lack of water vapor, potentially cooling the planet.
"We are the first to measure the water vapor feedback and its effect on temperatures," Philipona said.
Source: Associated Press