SANTA ROSA (California), June 1: In a report that challenges conventional wisdom, Earth might become much rainier if planetary warming continues unabated, a team of experts on climate change announced on Friday.
Over the next 100 years, global rainfall could increase by about 20 per cent — three times as fast as the rate projected previously by global-warming scientists — if greenhouse gases in the atmosphere continue unabated, said physicist Frank Wentz and colleagues at Remote Sensing Systems in Santa Rosa. Their report appears in Friday’s issue of Science Express, an online publication associated with Science magazine.
Their study is not precise enough to forecast how increasing global warming will affect rainfall in specific regions such as California, Wentz said. Still, his team’s analysis of 19 years of planetary rainfall and humidity data hints that global warming might portend “a general tendency to make the wetter areas wetter and the drier areas drier — which, when it comes to climate change, is a pretty gloomy scenario,” he told The Chronicle on Thursday.
Kelly T Redmond, deputy director of the Western Regional Climate Centre at the Desert Research Institute in Reno, called the report a very interesting paper.
“It’s the kind of subject we need to be investigating,” said Redmond, who is not connected with the Santa Rosa team. “It’s a very fundamental issue: What is rainfall on Earth going to do (during) climate change?”
In the past, climate modellers have generally assumed that as global warming evaporates water and makes the planet more humid, the rainfall rate will rise more slowly. In other words, precipitation won’t intensify as fast as the humidity. Initially, the reason seems obvious: Warmer air can hold more water vapour, delaying its eventual cooling and falling back to Earth as raindrops, snow, sleet or hail.
However, when members of the Santa Rosa team analysed satellite measurements of planetary changes in humidity and rainfall from 1987 to 2006, they were surprised by what they found: Over that period, the global rainfall rate rose at almost exactly the same rate as humidity, like two race NASCAR drivers racing neck and neck. The difference between the rise in rainfall and the rise in humidity was about 1 per cent, Wentz said.
The implication, he said, is that as global warming continues, planetary rainfall — far from lagging behind the humidity rise — will increase at about the same rate and, thus, much faster than projected by earlier computer models.
