Global warming added at least 15pc to Hurricane Harvey’s rain, studies find
UNITED STATES: There’s a theme lurking under the giant science meeting in New Orleans along the Mississippi River: Extreme weather really is getting more extreme because of climate change. The human influence on hurricanes and wildfires is increasingly obvious. For years this has been a subject clouded in uncertainties. But now scientists say they have hard numbers.
Yesterday, two independent research teams, one based in the Netherlands and the other in California, reported that the deluge from Hurricane Harvey was significantly heavier than it would have been before the era of humancaused global warming.
One paper put the best estimate of the increase in rain at 15 per cent. The other said climate change increased rainfall by 19 per cent at least – with a best estimate of 37 per cent.
Meanwhile another team of scientists released a blockbuster report on extreme weather in 2016, saying that for the first time they could declare that three separate weather events – the weirdly warm ‘‘blob’’ of water off the Alaska coast, a heat wave in Asia and the highest global temperature – would have been impossible without human-caused climate change.
‘‘This is the first time we’ve ever had statements like that,’’ said Stephanie Herring, a climate scientist with the National Oceanic and Atmospheric Administration who spoke to the American Geophysical Union yesterday. And about that ‘‘blob’’: ‘‘The blob is an ongoing phenomenon. It’s still sitting there.’’
‘‘Attribution’’ research, as it’s known, seeks to find and quantify the influence of climate change on a weather event, which has always been problematic. There’s a truism: Climate is what you expect and weather is what you get. Weather events emerge from chaotic forces and elements, and there is variability from place to place and year to year.
The result has been an ongoing issue for scientists studying extreme weather and journalists reporting on the subject. Definitive statements about causality, or the magnitude of an effect, are hard to come by. The discussion gets mired in caveats, because extreme events can happen with or without a changed climate.
That’s changing.
‘‘There is a large, new body of literature about attributing human influence on individual extreme events,’’ said Michael Wehner, senior staff scientist at the Lawrence Berkeley National Laboratory and co-author of one of the two papers on Hurricane Harvey published yesterday.
‘‘It’s no longer appropriate to say scientists can’t say anything about these individual events.’’
Extreme weather is a familiar topic in the Crescent City. At one panel yesterday a city planner warned that the flood control infrastructure is nowhere near adequate for the perils ahead. Many scientists have urged that the government improve flood maps to capture the new reality of the warmer world.
‘‘They have not been improving the maps as they should. They’re treating that as static,’’ said Columbia University research professor Suzana Camargo, an expert on extreme weather.
And flood maps are just maps, by the way: ‘‘I’ve never met a molecule of floodwater that could read a flood map,’’ said George Homewood, a planning director for the city of Norfolk.
The meeting had numerous sessions yesterday devoted to latebreaking research on hurricanes Harvey, Irma and Maria.
Scientific research usually takes longer to cohere, but 2017 was an astonishing year of natural disasters and many people dropped what they were doing to tease out early findings about the hurricanes and other tumult, including western US wildfires.
– Washington Post