Katrina, Sandy, Harvey, Irma and Maria: This is what global warming and climate change looks like!
Hurricanes are not caused by global warming, but they are made more powerful and destructive. Basic physics indicate a warming planet will have more energy in the atmosphere and in the ocean, and this increased heat content feeds and strengthens hurricanes.
This energy increases evaporation, changes atmospheric circulation, and causes thermal expansion of the ocean. A warmer atmosphere will hold more moisture, resulting in heavier downpours and more flooding. Sea level rise extends the storm surge farther inland. Changes in atmospheric circulation, like that which stalled Harvey over Texas, can greatly worsen flooding.
The stalling of Harvey over Texas resulted from very weak prevailing winds, which in turn resulted from a greatly expanded high pressure system over much of the U.S. at the time. A recent article in the journal Nature by Michael Mann, director of Penn State Earth System Science Center, discusses how nearly “stationary” summer weather patterns … appear to be favored by human-caused climate change.
The Washington Post on Sept. 15 stated: “The back-to-back landfalls of two harrowing storms (Harvey) in Texas and (Irma) in Florida have reignited both the scientific debate over the link between hurricanes and global warming and the political debate over what, if anything, to do to address climate change.”
Don’t expect any action to mitigate climate change from this White House. Scott Pruitt, EPA administrator, said “it’s insensitive to discuss the cause and effect of these storms” in the midst of the dual disasters of Hurricanes Harvey and Irma. And in an interview with Breitbart News, Pruitt said it was “opportunistic” and “misplaced” to tie Hurricane Harvey to climate change. What? If not now, when?
President Trump, who has consistently dismissed climate change as a “hoax,” earlier stated Irma was “perhaps bigger than we have ever seen.” Then when questioned if he had changed his opinion, said, “If you go back into the 1930s and the 1940s, and you take a look, we’ve had bigger storms than this.”
Kerry Emanuel, MIT hurricane expert, stated, “That’s just not correct.” Hurricane Harvey dumped more rainfall than any other hurricane in the continental United States; Hurricane Irma maintained category 5 winds longer than any other hurricane in the satellite record; Hurricane Katrina produced the largest storm surge observed in the U.S.; and Hurricane Sandy was the largest diameter of any Atlantic hurricane. Exactly what does Trump mean by “bigger storms than this?”
The University of Wisconsin’s Space Science and Engineering Center determined that Harvey was a “1,000 year flood event.” A 1,000 year event means there is a 1 in 1,000 chance of an event occurring in any particular year. The UW researcher stated, “There is nothing in the historical record that rivals this. In looking at many of these events (in the United States), I’ve never seen anything of this magnitude or size. This is something that hasn’t happened in our modern era of observations.”
Gabriel Vecchi, a Princeton hurricane scientist, has stated, “The president may have been referring to the fact that the 1930s to 1950s were an unusually active phase for hurricane activity in the Atlantic.” But MIT hurricane expert Kerry Emanuel says, “The real anomaly is that the ’70s and ’80s were unusually quiet. It’s not that the ’30s and ’40s were unusually active.”
Temperatures in the Atlantic are affected by a natural phenomenon called the Atlantic Multidecadal Oscillation (AMO), which results partly from a change in ocean currents. From the 1970s to the early 1990s, the AMO kept Atlantic temperatures relatively cool. Since then, the Atlantic has been generally warmer, coinciding with rising greenhouse gases and elevated global temperatures.
According to NOAA, “Recent studies have shown a link between ocean surface temperatures and tropical storm intensity — warmer waters fuel more energetic storms.” To analyze what is occurring, scientists at the National Center for Atmospheric Research (NCAR) have developed climate models based on temperatures recorded over the last century. According to Kevin Trenberth, head of climate analysis at NCAR, those models show the Atlantic has warmed beyond the impact of natural oscillations (AMO) and there is also strong evidence that global warming contributed to the intensification of Hurricane Harvey. Trenberth says during this period, surface temperatures in the Gulf were above average, with “record levels” of heat deep into the water column and dense air-moisture above. “The conditions were ripe” for the hurricane to intensify and later unleash record rainfall.
So, who do you believe, Trump and Pruitt or the scientists who actually know what they are talking about? As long as Trump, Pruitt and other deniers continue to believe that we have no control over the earth’s climate, this debate will continue. But when magical/mythical thinking collides with science, either science wins or we all lose.
William Gran, now retired, was an adjunct instructor at Greenfield Community College on global warming and climate change. He can be reached at whgran@gmail.com