Just as the Arctic air blasting across the mainland in recent days does not disprove the scientific evidence that the world’s climate is warming, so the hurricanes that ripped up the Caribbean and other areas in 2017 don’t prove it is.
But they look like pretty good circumstantial evidence for the case.
In speaking of Irma and Maria, the back-to-back Category 5 hurricanes that devastated Puerto Rico and the Virgin Islands in September, climate change expert William Gould said, “We were all surprised by the intensity of the storms, but maybe we shouldn’t have been.”
That’s because for years climate science has been predicting that the intensity of catastrophic events, such as tropical cyclones, will increase as global warming progresses.
As Caribbean residents know well, warm waters are a big driver when it comes to forming tropical cyclones. And for years the trend in the Caribbean and the Atlantic basin has been toward warmer sea temperatures. This year, there also was little wind shear to inhibit formation.
“A lot of things lined up in the wrong way,” said climate researcher Laverne Ragster, adding that the science has been predicting an uptick in storm intensity, though not necessarily in the number of storms.
Both Gould and Ragster are involved with the fourth National Climate Assessment, an extensively reviewed, comprehensive report sponsored by the U.S. Global Change Research Program and published ever four years. The 2018 report will be the first to contain a chapter on the U.S. Caribbean territories as well as information on each of the states.
A researcher with the U.S. Forest Service International Institute of Tropical Forestry in Puerto Rico, Gould is the coordinating lead author for the Caribbean chapter. Ragster, the former president of the University of the Virgin Islands, is one of its reviewers.
The 2018 report has been in the works for more than a year. The draft had already been reviewed and edited by a number of institutions and agencies before the 2017 hurricane season got into full swing. It must also go through a public review process before it is released at the end of the year.
Data from Irma, Maria and other 2017 storms is still being collected. There is no time to analyze it, and have the research subjected to the rigorous review process required for the National Climate Assessment in order for it to be a formal part of the report, Gould explained. At the same time, it shouldn’t be ignored.
“We will try to add whatever we have learned at this point,” he said. That probably means substantially “stating the obvious” – such as the fact that there was significant damage to communications, electrical power grids and other infrastructure.
Both Maria and Irma were unusually strong storms; Maria’s winds were well above the 157 mph threshold for the highest category hurricane, and Irma tied for second place as the strongest Atlantic hurricane on record – moreover, it maintained a sustained wind force of 185 mph for 37 hours, longer than any tropical storm ever anywhere.
But while the back-to-back storms made a big, ugly impression on the Caribbean region, they were not the only stand-outs in 2017.
For rain, you couldn’t beat Harvey, which caused flooding in much of Texas and several other states during a week in August, and set a record for rainfall in the continental U.S.: 51.88 inches in Cedar Bayou, Texas.
Before the unusual season ended there was one more surprise, this one in October. Hurricane Ophelia traveled further east than any other major hurricane in history, bringing heavy rains and deadly winds to Ireland and other parts of the United Kingdom and blanketing the skies over London with Sahara dust.
Climate scientists are being almost universally cautious about attributing the busy season to global warming.
As Gould and Ragster both point out, climate change is not about isolated events, but about trends over long periods of time. It will be a while before the 2017 hurricanes can be put into perspective, but Gould is confident they will be.
“There’s lots of good science going on here,” he said, speaking of the Caribbean. So far, much of it is “documenting trends that match fairly well with the predictions.”