Although it might be hard to directly blame climate change for Hurricane Harvey, which has wreaked havoc in the U.S. state of Texas, human-caused global warming has enhanced some of the impacts of the tropic storm, climate scientists say.
EXTREME RAINFALL EXACERBATED BY CLIMATE CHANGE
"It's hard to put a figure on the amount that climate change has contributed to Harvey's impacts but we've definitely exacerbated the flooding impacts in particular," Andrew King, climate extremes research fellow at School of Earth Sciences, University of Melbourne, told Xinhua via email late Tuesday.
"Limiting the future damage from this kind of event could definitely be seen as an incentive to follow the Paris Accord and attempt to keep global warming below the 2C (2 degrees Celsius) level," King said.
Harvey's biggest effect is through its intense and prolonged rainfall, the scholar noted, a low pressure system to the north is keeping Harvey over southern Texas, resulting in greater rainfall totals.
"We know that climate change is enhancing extreme rainfall. As the atmosphere is getting warmer, it can hold more moisture -- roughly 7 percent more for every 1 degree Celsius rise in temperature," King explained.
"This means that when we get the right circumstances for very extreme rainfall to occur, climate change is likely to make these events even worse than they would have been otherwise."
"Without a full analysis, it is hard to put exact numbers on this effect, but on a basic level, wetter skies mean more intense rain," he added.
According to local media reports, Harvey's rainfall total reached 49.32 inches (125.27 cm) in Friendswood, Texas, in less than a week. That is about as much rain as the metropolitan region normally sees in a year.
Harvey is "unusual" because it "continued to strengthen in the Gulf of Mexico until it made landfall...This is almost definitely linked to the anomalously high sea surface temperatures there as it developed," noted Sir Brian Hoskins, chairman of the Grantham Institute for Climate Change at Imperial College London and professor of Meteorology at the University of Reading.
DAMAGE WORSENED BY HUMAN ACTIVITIES
Many scientists have pointed to Hurricane Harvey as further evidence of the dangers of climate change.
"Climate change due to increased greenhouse gases in the atmosphere makes the occurrence of the warm waters in the Gulf of Mexico (and elsewhere) more likely, and so it has increased the chances of occurrence of a hurricane like Harvey, and the devastating impacts that go with it," Hoskins said.
"Whether we can attribute Harvey to global warming, as with any individual weather event, is a questionable proposition," said Dr. Jeffrey Kargel, Department of Hydrology & Atmospheric Sciences at the University of Arizona.
"But it is very likely that many more storms like Harvey and Katrina and bigger ones yet are on the way. The expected higher frequency of such storms is "an effect of global climate change" brought on mainly by burning of fossil fuels," Kargel said.
One cannot say climate change "caused" Hurricane Harvey but the severity of the storm and associated damage were "worsened" by human activities, particularly the substantial emissions of greenhouse gases that are warming the oceans and the air above, said Richard Allan, professor of climate processes at the University of Reading.
A warmer ocean and the air above were able to inject greater quantities of moisture into the storm leading to an intensification of the already extreme rainfall, he said.
