But the models so far suggest that such extreme rain events can now be expected to occur in the region about every 30 years on average, whereas in 1900, it was more like once every 50 years.
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It’s worth noting that the study is still undergoing peer-review, so we need to bear that in mind when considering the researcher’s calculations.
The climate model experiments involved altering the climate based on levels of greenhouse gases in the atmosphere, aerosols such as soot and dust, ozone and natural changes in the sun’s radiation and from volcanic eruptions for various periods of time to assess how extreme rainfall events respond to climate changes.
Historically, scientists are reluctant to link any particular weather event to climate change because of the dangers inherent in drawing a scientific conclusion when the “experiment” in question has no control member – for instance, you can not “re-run” the flooding event without climate change and see what would have happened, then compare the two.
For their assessment, these scientists conducted a statistical analysis of rainfall observations and used two climate models to understand how the odds have changed for such three-day events between the early 20th century and the early 21st century.
Karin van der Wiel, a research associate at NOAA’s Geophysical Fluid Dynamics Laboratory is the study’s lead author.
While we concluded that 40 percent is the minimum increase in the chances of such rains, we found that the most likely impact of climate change is a near doubling of the odds of such a storm. “We can say that the change (in rainfall rates) is because of greenhouse gases”.
The burning of fossil fuels such as oil, gas and coal releases “greenhouse” gases such as carbon dioxide into the Earth’s atmosphere, which has warmed to levels that can not be explained by natural variability, scientists say.
“They trap heat in the atmosphere, and by warming the atmosphere, they make the atmosphere hold moisture”, said Vecchi. For the recent devastating flooding in south Louisiana (mid-August, 2016), a team of scientists from NOAA and the World Weather Attribution (WWA) has now said that human-caused climate warming increased the chances of the torrential rains that caused the foods by at least 40 percent, and possibly more.
The study describes how the National Hurricane Center began tracking a low pressure system as it threatened to become a tropical depression on August 5 while off the Florida coast, and then slowly moved west, becoming near stationary over Louisiana on August 12, allowing the continuous development of thunderstorms to the south and southeast of its center. The flooding caused at least 13 deaths, and Gov. John Bel Edwards on Tuesday estimated the damage toll would be at least $8.7 billion. This is because the U.S. Geological Survey has had teams out measuring floodwater heights and the data is still being compiled.
They also point out that their rainfall estimates are for the region, rather than for individual locations around Baton Rouge.
The new study is part of a “rapid climate attribution” push by many climate scientists to speed up the time it takes to inform the public and policymakers about the role that global warming may have played in a newsworthy extreme weather event. Illustration via NOAA Climate.gov, based on Van der Wiel, et al., 2016.
Rain started falling in central parts of Louisiana around August 10, with areas around Baton Rouge among the hardest hit.
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And Vecchi pointed out that the 1 in 30 year chance doesn’t really mean once every 30 years; the same 1 in 30 chance occurs every year. With extra heat helping to nourish storms, scientists expect global warming to help produce more intense downpours. “We cancelled everything for two weeks and just did this”.
