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Tuesday, October 19, 2021

Hurricane Ida and Global Warming: Unsupported Claims


From the Cliff Mass Weather Blog

It didn’t take long before the media “connected the dots” and made full-throated claims that Hurricane Ida was the stepchild of global warming.

Even well-known TV weather personality Al Roker (who I very much admire) got into the act:“We are looking at the results of climate change … that’s what created this monster storm”

But it is easy to demonstrate that real data shows that these claims are without basis, and that National Public Radio, the Seattle Times, and others are publishing stories that are contradictory to the best science and observations.

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The hypothesis in all these stories is that human-caused climate change war,ed the temperatures of the sea surface (e.g., the Gulf of Mexico, tropical Atlantic) and thus “supercharged” Hurricane Ida.
Now the first thing that a responsible journalist would do regarding Ida would be to determine whether the Gulf of Mexico, where Ida developed, had significantly above-normal temperatures last week.
If that was true, then a reasonable journalist would check whether the warming was the result of a long-term trend–something required if human-caused global warming was significant.
Apparently (as demonstrated below), most journalists did not take these basic steps before they wrote the stories.    But I will do so here!
Temperatures of the Gulf of Mexico
Keep in mind the track of Hurricane Ida, as illustrated by the official NOAA track information below.  The shading shows you the locations of tropical storm and hurricane-force winds.  The storm revved up to hurricane strength south of Cuba and really started to rev up north of 25N.

152146 wind history

To get hurricane formation, one needs sea surface temperatures of at least approximately 27 °C, and virtually the whole Gulf of Mexico was at that level, which is typical for this time of the year.
Below are the sea surface temperatures for the seven days immediately before Ida revved up and made landfall.  Temperatures of the whole route of the storm were way above the necessary threshold.  Warm water was no problem for development if Ida (29C and more pretty much the whole way).

oisst 7d gulf 2021082800


Now, the million-dollar question:

How unusual were the Gulf sea surface temperatures during the strengthening of Hurricane Ida?   The figure below shows you the anomaly (or difference) from climatology (normal)  of the sea surface temperatures before Ida strengthened (Courtesy of Ryan Maue, previously NOAA Chief Scientist).
Wow. The water temperatures were actually COOLER than normal where Ida started to intensify (south of Cuba).  Interestingly, this is due to the vertical mixing due to previous Hurricane Grace.   And for much the route north of Cuba, where Ida rapidly strengthened, temperatures were normal or slightly above normal (less than 1°C above normal).  Only near the coast, for the shallow waters of the Gulf shelf, did the temperatures climbed more than 1°C above normal.

oisst anom 7d gulf 2021082800


The bottom line:  warmer than normal water was not the key to the development and intensification of Hurricane Ida. The Gulf of Mexico is pretty much always warm enough to support the rapid strengthening of tropical disturbances.
For Ida, there were some very favorable elements:  little vertical wind shear (which tears the storms apart) and a plume of very moist air that got ingested into the storm (see a map of integrated water vapor transport, IVT, below).

Sea Surface Temperature Trends
Even though the sea surface temperatures were not significantly warmer than normal for Ida, one might ask, has there been a significant upward trend in sea surface temperatures in the Gulf, one that might be indicative of a major global warming trend?
To give you some insight into this issue, here is a plot of August sea surface temperatures over the Gulf from 1983 to this year (click to expand).   Yes, there has been some warming over nearly 40 years….and yes, human-caused global warming could have been the cause…. but the warming is quite small–less than 1°C.

I independently secured some NOAA sea surface temperature data over the Gulf of Mexico for a longer period (1948 to now) for the month of July and plotted it up below.  Not much a trend, with July 2021 being RELATIVELY COOL.

A responsible journalist investigating the potential impact of global warming on Hurricane Ida SHOULD have examined the information noted above and would have found that the connection was very weak:  the sea surface temperatures were not very anomalous (warmer than normal) along the path of the hurricane and that there has been only a very minor upward trend in sea surface temperatures in the Gulf of Mexico.
And a competent journalist should have also asked:  is there much evidence of an increasing trend of hurricanes reaching U.S. shores?  Something that should have occurred if global warming was significant.
Below is a plot of the number of landfilling hurricanes that have struck the continental U.S. (Courtesy Roger Pielke Jr). The trendline is down.

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Major hurricanes  (category 4 and 5)…the same thing.  No increase.

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What a responsible journalist would conclude
A competent journalist doing a story on the relationship of global warming and Hurricane Ida would quickly have learned that:

  • Hurricane Ida did not develop over unusually warm water.
  • That the Gulf of Mexico is always warm enough to support major hurricanes in late summer.
  • There is only a very small warming trend of the Gulf of Mexico over the past half-century
  • There is no upward trend in the number of hurricanes striking the U.S.
  • There is no upward trend in the number of major hurricanes striking the U.S.

And the clear conclusion that would have been reached: there is little reason to expect that global warming had much to do with the rapid intensification of the hurricane over the Gulf of Mexico.
Unfortunately, journalists at major media outlets from the NY Times, to the Washington Post, to the Seattle Times did not take the time to do the research needed to determine the truth.  And they published stories that seriously misinformed their readership.
Global warming is now used by incurious, politically oriented media to explain almost everything.  Don’t believe me?  Check out this recent headline in the Seattle Times, based on a NY Times article.  Profoundly disappointing.

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