In his tweeted warning about Hurricane Florence Wednesday, President Trump said, “bad things can happen when you’re talking about a storm this size. It’s called Mother Nature.”
The authors of a bombshell new analysis, “The human influence on Hurricane Florence,” disagree. They find that human-caused global warming has supercharged the atmosphere so much that it is boosting the very worst of the projected rainfall totals by more than 50 percent.
ThinkProgress asked coauthor Dr. Michael Wehner of Lawrence Berkeley National Laboratory (LBNL) whether “your analysis allows us to say the storm is more than just Mother Nature.” He replied in an email:
Indeed. The most important message from this (and previous) analyses is that “Dangerous climate change is here now!” It is not a distant threat in the future but today’s reality. Event attribution has shown this for heat waves, floods, certain kind of droughts and tropical cyclones.
Scientists have been warning for decades that global warming means more intense deluges since there’s more water vapor in the atmosphere and because warmer ocean temperatures are the engine that drives stronger hurricanes. And scientists have now observed that the most extreme rainfall events have been rising rapidly, especially on the East Coast.
In response, scientists have started doing “after-the-fact” analyses of how much climate change has contributed to worsening the rainfall of major storms.
For instance, a December 2017 study (coauthored by Wehner) found that climate change boosted Harvey’s rainfall in the worst hit area by 38 percent. A 2018 study found that “post-1980 warming” boosted Harvey’s total precipitation by 20 percent.
The new study on Florence published Thursday is the first to look at the impact of human-caused climate change on a hurricane before it makes landfall.
Lead by Dr. Kevin Reed of the Climate Extremes Modeling (CEM) Group at Stony Brook University, the researchers found that because of human-caused climate change, “rainfall will be significantly increased by over 50% in the heaviest precipitating parts of the storm.”
Because the analysis was done in real time, before Florence hit, it was not formally peer-reviewed. The state of the art of attribution analysis has been improving rapidly, allowing this kind of quick analysis. But as Dr. Wehner pointed out to ThinkProgress, the main finding of a 50 percent rain increase for Florence in the hardest hit region isn’t that dissimilar to his peer-reviewed paper on Harvey, which found a 38% increase in the hardest hit region.
The chart below compares two forecasts by the scientists. The Standard Forecast (left) uses an ensemble of existing climate models to create an actual forecast of Florence’s rainfall on September 11. The “Modified Forecast” (right) uses a model that has been “modified to remove the estimated climate change signal from the temperature, moisture, and SST fields to represent a world without climate change.”
In the real world, where humans have dramatically changed the climate through emissions of heat trapping carbon pollution, large parts of North Carolina will be hit by 18 or more inches of rain — a devastating deluge.
In a world without climate change, Florence is still a very destructive storm, but the worst hit region is much smaller and these areas would have much less rain.
Note that this study does not attempt to look at how some of the larger scale impacts of climate change on the jet stream are impacting the storm — and are potentially responsible for the storm hitting the coast in the first place.
Dr. Wehner offered some final words of advice: “The most important thing is to heed the warnings from the National Hurricane Center. Be safe!”