By Paul Homewood
NOAA’s leading hurricane scientist, Chris Landsea, has recently published an analysis of Hurricane Harvey, and concludes that it is totally misleading to blame global warming for the record rainfall.
Michael Bastasch has the story at Climate Change Dispatch:
It’s “misleading” to blame Hurricane Harvey’s record rainfall, or hurricane rainfall in general, on man-made global warming, according to a National Oceanic and Atmospheric Administration (NOAA) scientist.
“Linking hurricane rainfall to global warming today (and even decades from now) based upon such a tiny contribution is misleading,” Christopher Landsea of the National Hurricane Center wrote in an analysis of the potential links between warming and Harvey.
“Moreover, such a fixation can delay steps that can be taken now to better mitigate the effects of extreme flooding from hurricanes,” wrote Landsea, a veteran hurricane expert.
Hurricane Harvey brought record levels of rainfall to southeastern Texas when it made landfall in late August. Much of Texas was covered in at least two feet of rain, with areas east of Texas seeing more than five feet. The storm is estimated to have caused $125 billion worth of damage and directly responsible for nearly 70 deaths.
Almost immediately, some scientists and activists linked the deluge to man-made global warming. At least three studies have come out blaming warming for Harvey’s record rainfall, but Landsea came to a different conclusion.
Landsea examined the data surrounding theoretical and climate model-based arguments linking man-made warming to hurricane rainfall. What he found was global warming played, at most, a “tiny” role in the storm.
“Scaling the results from both theories as well as climate model projections suggest, then, that roughly 3% of hurricane rainfall today can be reasonably attributed to manmade global warming,” Landsea wrote.
“This value is a rather tiny contribution,” Landsea wrote. “Thus only about 2” (50 mm) of Hurricane Harvey’s peak amount of 60” (1525 mm) can be linked to man-made global warming.”
But even then, Landsea noted that any “interpretation of Harvey’s rainfall is also made more uncertain because the source of much of the rainfall was due to the interaction of the very slow moving tropical storm with a stationary frontal boundary along the Texas/Louisiana coast.”
Harvey made landfall in Texas as a Category 4 hurricane, but most of the rainfall came while Harvey was just a tropical storm. But what made the rainfall particularly bad was Harvey stalled over Houston, therefore more rainfall was concentrated in a smaller area.
That’s a major problem for studies attempting to link Harvey’s rainfall to man-made global warming. Two Harvey studies did not actually look at the storm itself, rather relying on climate model simulations.
Another study from the Lawrence Berkeley National Laboratory admitted that “precipitation rates were not particularly unusual for a hurricane of this magnitude.”
Landsea did not address every study linking Harvey to global warming, instead focusing on just one of them written by Massachusetts Institute of Technology climate scientist Kerry Emanuel.
Emanuel concluded global warming led to “a sixfold increase” in the odds of Harvey-level rainfall pummeling Houston in any given year and an 18 percent chance of such rainfall by the end of the 21st Century.
“These projections appear, in my view, to be extremely inconsistent with current theoretical rainfall projections as well as explicit dynamical model forecasts from climate models as detailed above,” Landsea wrote.
“Bottom line is that there has not been a meaningful change in U.S. tropical storm and hurricane rain over the last century, but that there have been few studies to address the topic lately,” Landsea wrote about long-term trends in hurricane rainfall.
Landsea makes several pertinent remarks:
1) Theory suggests that the amount of rainfall in the tropical latitudes would go up about 4% per degree F sea surface temperature (7% per degree C).
The tropical North Atlantic Ocean, Caribbean Sea, and Gulf of Mexico have warmed up about 0.7 F (0.4 C) in the last few decades, much of which appears to be due to anthropogenic climate change (increased greenhouse gases)xix. Scaling the results from both theory as well as climate model projections suggest, then, that roughly 3% of hurricane rainfall today can be reasonably attributed to manmade global warming. This value is a rather tiny contribution. Thus only about 2” (50 mm) of Hurricane Harvey’s peak amount of 60” (1525 mm) can be linked to manmade global warming.
This is a point I have made in the past about extreme UK rainfall. For instance, rainfall in England during the record winter of 2013/14 was 401mm. Even assuming that the theory is right, a warmer atmosphere would only account for maybe only 12mm of this, barely noticeable.
2) Landsea mentions Amelia, Claudette and Allison, in 1979, 1979 and 2001 respectively. He also mentions Hurricane Easy, which hit Florida in 1950.
All had similar intensity, or greater. What made Harvey’s rainfall much greater was the fact that the storm stalled.
3) He mentions a study from 2004, by Pavel Groisman, which could not identify any significant upward trend in rainfall from tropical storms in the Southeastern United States, between 1900 and 2000. The study did, however, find multidecadal variations.
What is particularly noticeabe is the big increase in the number of stations (red curve). When you are looking for “extreme events”, the more stations you use, the more events you will find.
As we have seen with Harvey, most of the rainfall fell over a very small area.
Landsea concludes by declaring Emmanuel’s findings as unreliable.
He finishes by asking what lessons can be learned:
What lessons can be learned from Harvey’s catastrophic flooding?
There are several important points that should be recognized in the aftermath of Harvey’s impact:
1. Hurricanes (and Tropical Storms) have been associated for millenniums with extreme rainfall and freshwater flooding. There is nothing that one can do to prevent these storms from occurring, hitting land, and impacting people;
2. Massive flooding and catastrophic impact from tropical storms and hurricanes occurs when the system moves slowly over a major city. This is precisely what happened because of Harvey as a tropical storm over Texas;
3. Flooding is made worse when extreme rainfall occurs over impervious land (such as roads and buildings) and the rain cannot soak in. Land use decisions should better consider allowing building (or rebuilding) in flood prone areas;
4. Studies should be made to see if evacuating people in advance of extreme flooding rain is feasible. (Currently, only evacuations from hurricanes are primarily issued from possible storm surge – salt-water – flooding. However, because the skill of in day-to-day rainfall amounts and locations continues to improve, it might be feasible to call for limited evacuations in the most vulnerable locations.);
5. Linking hurricane rainfall to global warming today (and even decades from now) based upon such a tiny contribution is misleading. Moreover, such a fixation can delay steps that can be taken now to better mitigate the effects of extreme flooding from hurricanes. See the following sites for more action today that can be taken: the Federal Emergency Management Agency (FEMA), the Insurance Institute for Business and Home Safety (IIBHS), the Environmental Protection Agency (EPA), and academia
They are all commonsense conclusions. But the last one is particularly important.
How often do we hear global warming blamed for all sorts of bad weather? Pretending that we can solve the problem by building lots of wind mills and solar farms simply distracts attention from the practical things which really could make a difference.
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February 6, 2018 at 01:12PM