A few days ago, “Hurricane” Matthew weakened into a Category 1 storm by the time it made landfall in the U.S., which means its official title has been changed to “post-tropical storm Matthew.” Because it lost so much intensity and could no longer be considered a real hurricane as it made landfall, this development has further lengthened the more than 10-year long drought of major, intense (Category 3 and up) hurricanes that have failed to strike the U.S. coasts.
John Sutter, a CNN columnist who focuses on social justice and climate change in his op-ed essays, claimed a few days earlier that humans, by causing the ocean temperatures to increase, are simultaneously causing hurricanes (or, in this case, tropical storms) to get even more intense than they otherwise would. He called this claim a “truth,” and implored American readers to “rid the economy of fossil fuels” so as to reduce storm intensities.
CNN (John Sutter):
“[T]here’s an uncomfortable truth the rest of us should wrestle with: Hurricane Matthew looks a lot like future climate change. And if we want to stop storms like this from getting even more intense, we need to do everything we can to rid the economy of fossil fuels.”
To garner support for his opinions, Sutter quoted Dr. Michael Mann — the Penn State meteorologist made famous in the early 2000s by creating the hockey stick graph of the entire Northern Hemisphere with tree ring data from a few trees in North America — in the same opinion piece. Mann claims that (a) oceans are the warmest they’ve ever been, that (b) this apparently unprecedented warmth “intensifies” storms, and that, (c) within the last year (since 2015), we have “seen the strongest hurricane in both hemispheres.”
“Last year was the warmest our oceans have ever been on record. And that’s critical context. It’s thatwarmth that provides the energy that intensifies these storms. And it isn’t a coincidence that we’ve seen the strongest hurricane in both hemispheres within the last year.”
It’s understandable that Sutter, a columnist, would be unfamiliar with what the scientific literature has to say about a link between warming ocean waters (by hundredths to tenths of a degree C) and the intensification of hurricanes. He’s only taking the “experts” at their word when he calls it the “truth” that humans cause storms to become stormier. But Michael Mann, on the other hand …he should simply know better.
First of all, the Pacific Ocean (where most hurricanes form) is currently not the warmest it’s ever been. In fact, contrary to Mann’s hockey stick creations, the Pacific Ocean heat content is still cooler than it was just a few hundred years ago. For example, Rosenthal et al. (2013), publishing in the journal Science (the same journal that published Mann’s tree-ring hockey stick creation), points out that the Pacific Ocean is still much cooler (0.65°C) than it was during the Medieval Warm Period, and the paleoclimate graph of the Pacific reveals that today’s temperatures are still some of the coldest of the last 10,000 years.
Rosenthal et al., 2013 (Pacific Ocean Heat Content)
“We show that water masses linked to North Pacific and Antarctic intermediate waters were warmer by 2.1°C and 1.5°C, respectively, during the middle Holocene Thermal Maximum than over the past century. Both water masses were ~0.9°C warmer during the Medieval Warm period than during the Little Ice Age and ~0.65° warmer than in recent decades.”
But even more curious is Mann’s claim that this past year’s hurricanes are the strongest we have seen in both hemispheres. It is clear the scientific literature does not support Mann’s claims that hurricanes have been observed to become more intense with warming (however modest that warming may be relative to the rest of the Holocene). Even the IPCC (Chapter 2, WG1, AR5 2013) does not support Mann’s claims, citing low confidence in detecting a trend in increased hurricane intensities since 1900.
Simply put, the opposite of what Mann (and Sutter) claim to be “truth” about warming ocean temperatures and hurricane intensification is detailed in the peer-reviewed scientific literature. Namely, observations indicate that there has been no trend in increased hurricane intensity in recent decades (i.e., Category 3 and up), and many observations even show there has been a slight decline in overall hurricane intensities since the middle of the 20th century. Secondly, the frequency with which hurricanes make landfall have also been declining in recent decades. And finally, it has been determined from paleoclimate analyses that cooler ocean temperatures are associated with more tropical storms and major hurricanes than warmer ocean temperatures.
Below there are 30 peer-reviewed scientific papers that summarize the literature on the lack of connection between ocean temperatures and hurricane variability. Perhaps Sutter and Mann could find these educational.