When a federal agency announced this week that global warming increased by 40 percent the chances of the torrential rains that caused last month’s devastating Louisiana flood, climate activists quickly spread the word.
So did University of Colorado Boulder senior climate scientist Roger Pielke Sr. — for a very different reason.
Pielke said the National Oceanic and Atmospheric Administration should be “embarrassed” by its rush to release the research before conducting a peer review, accusing the agency of “bias” and calling the study a “dismaying example of manipulation of science for political reasons.”
“The models being used in the study have not shown the skill needed to make these definitive forecasts of changes in extreme rainfall statistics,” said Mr. Pielke in an email. “Also, the article is still under peer review and it was premature for NOAA to have done a press release.”
The heated reaction to the NOAA study reflects an increasingly contentious split in the scientific community over the connection, if any, between extreme weather events such as flooding and rising levels of carbon dioxide in the atmosphere.
Climate change activists argue that such research is needed to prepare policymakers, emergency agencies and insurers for the catastrophic consequences of human-caused global warming, while skeptics have expressed concern that the attribution research is often scientifically suspect and politically motivated.
Despite the divide, the NOAA study has already had an impact after being cited extensively by news outlets such as The New York Times as well as advocacy publications and websites like Climate Central, InsideClimate News, Mother Jones and Carbon Brief.
“That’s why the attribution studies now being done by NOAA and others are so critical,” said a Wednesday report in Gizmodo. “They are building a foundation that legitimizes the connection between extreme weather and climate change through statistics.”
Using climate models and observational data, the NOAA rapid assessment concluded that human-caused global warming “increased the chances of the torrential rains that unleashed devastating floods in south Louisiana in mid-August by at least 40 percent.”
“We found human-caused, heat-trapping greenhouse gases can play a measurable role in events such as the August rains that resulted in such devastating floods, affecting so many people,” said Karin van der Wiel, a research associate at NOAA’s Geophysical Fluid Dynamics Laboratory and the lead author.
She added that 40 percent is the “minimum increase,” and that “the most likely impact of climate change is a near doubling of the odds of such a storm.”
Not everyone is sold. Louisiana State University climatologist Barry Keim said it’s possible that climate change had a significant impact on the tropical wave that dumped 21 inches in some areas of south Louisiana from Aug. 11-13, but so far the research doesn’t prove that.
“I really don’t believe any single event really tells us a whole lot about climate change,” said Mr. Keim, who is also the state of Louisiana climatologist. “I know some of these efforts to try to find attribution to climate change like this, they use a lot of models, and there’s certain assumptions that go into those models. And there is some logic behind all that.
“But we have a long, long history of extreme events, not only in Louisiana but across the entire United States, and some of these really big, extraordinary events date back many decades, back to the turn of the 20th century, back to the 1800s,” Mr. Keim said. “So I’m just not real quick to point the finger and say that this event would not have happened if it were not for climate change.”
One of the scientists behind the NOAA study, Heidi Cullen, works for Climate Central, an advocacy climate science and news organization that leads the World Weather Attribution, which was also involved with the study.
“This is not just a case of being unlucky, climate change is increasing our risk,” Ms. Cullen told Carbon Brief.
Her involvement came as a red flag for Georgia Tech climate scientist Judith A. Curry, who also raised questions about releasing the study before a peer review.
“This study involves several scientists from NOAA, along with a scientist that works for an advocacy group,” said Ms. Curry in an email. “NOAA has a team in Boulder, Colorado (led by Marty Hoerling) that typically conducts quite sensible analyses of such extreme events. So I don’t know why NOAA issued such a press release about a new publication without checking with this other team at NOAA.”
Meanwhile, there is no shortage of criticism from climate skeptics, who argue the study flies in the face of evidence showing that flooding disasters are actually on the downswing.
They cite the 2013 testimony of University of Colorado environmental studies professor Roger Pielke Jr., who told a Senate committee, “Floods have not increased in the U.S. in frequency or intensity since at least 1950. Flood losses as a percentage of US GDP have dropped by about 75 percent since 1940.”
Climate Depot’s Marc Morano accused NOAA of twisting the facts to “make it appear the invisible hand of ‘global warming’ has a role in almost every weather event,” while Real Science’s Tony Heller said the agency had engaged in “man-made modeling abuse.”
Monica Allen, a NOAA spokeswoman, refuted the charges of political bias, saying that the scientists “would have provided the results of the rapid assessment regardless of the findings.”
“The rapid assessment was submitted to the open access journal, Hydrology and Earth System Sciences Discussions, which has an open online peer review process,” said Ms. Allen in an email. “The rapid response research provides useful information about a severe event nearly immediately to help scientists analyzing the event. The research also goes through a more lengthy open comment period and peer review. The robust findings from that process will advance our knowledge on the topic.”
The 2016 Louisiana flood dropped as much as 25 inches of rain in 48 hours over some areas of south Louisiana after a low-pressure system stalled above the Baton Rouge area. Thirteen people died in the rapid flooding, which resulted in nearly $9 billion in damage.
The torrential downpour was unusual in that it resulted from a tropical wave and not a named hurricane or weather front, said Mr. Keim.
“Was that just a fluke occurrence or did the warm sea surface temperatures over the Gulf play some role there? And was the Gulf running warm because of global warming, or was that just warm because it happened to be warm for a whole variety of other reasons?” asked Mr. Keim. “These are the things we’re trying to pick apart and trying to better understand as we move forward.”