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 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 that warmth 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 its 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.
No Trend Or Reduced Intensity Of Landfalling Hurricanes With Warming
“The impact of climate change is seen in slightly decreased intensities in landfalling cyclones.”
“[T]be global frequency of category 4 and 5 hurricanes has shown a small, insignificant downward trend [1990-2014].”
“The various SST measures only have a weak influence on TMLGP [tropical cyclones making landfall, South China] intensities. Despite the long-term warming trend in SST in the WNP, no long-term trend is observed in either the frequency or intensities of TMLGP [tropical cyclones making landfall, South China].”
“A long-term (five decade) downward trend continues to be evident primarily in the frequency of intense hurricanes. In addition, the mean maximum intensity (i.e., averaged over all cyclones in a season) has decreased, while the maximum intensity attained by the strongest hurricane each year has not shown a significant change.”
“All of the counts, lifespans, and accumulated cyclone energy of the late-season typhoons during the 1995–2011 epoch decreased significantly, compared with typhoons that occurred during the 1979–94 epoch.”
“There has been no trend towards an increase in the number of categories 3–5 cyclones over the last 30 years.”
“Extratropical cyclones cause much of the high impact weather over the mid-latitudes. With increasing greenhouse gases, enhanced high-latitude warming will lead to weaker cyclone activity. Here we show that between 1979 and 2014, the number of strong cyclones in Northern Hemisphere in summer has decreased at a rate of 4% per decade, with even larger decrease found near northeastern North America.”
“[D]ata show a decrease in the proportion of category 4-5 typhoons from 18% to 8% between the two periods of 1977-1989 and 1990-2004 (Table 1; intensity estimates in terms of sustained maximum winds first became available in RSMC-Tokyo best track data in 1977).”
“No significant correlation was found between the typhoon activity parameters and local SST [during 1960-2003]. In other words, an increase in local SST [sea surface temperatures] does not lead to a significant change of the number of intense TCs [tropical cyclones] in the NWP, which is contrary to the results produced by many of the numerical climate models.”
“Multi-member ensembles show that the overall number of TCs [tropical cyclones] generated by the model is reduced by 5-9% when allowing for two-way air-sea interactions. TC [tropical cyclones] intensity is greatly impacted; the strongest 1% of all TCs are 20-30 hPa (4-8 m s−1) weaker and the number of simulated Category 4 and 5 TCs [tropical cyclones] are reduced by 65% in slab ocean configurations. Reductions in [tropical cyclone] intensity are in line with published thermodynamic theory.”
“[D]uring the 40-year period 1961-2000 both the number and intensity of landfalling U.S. hurricanes decreased sharply. Based on 1901-1960 statistics, the expected number of hurricanes and major hurricanes during the period 1961-2000 would have been 77 and 30, respectively. However, only 55 (or 71%) of the expected number of hurricanes struck the U.S. with only 19 major hurricanes (or 63% of that expected number).”
“[D]uring 1970−2010 … SST in the MDR [along Mexican coasts] showed a statistically significant increase of 0.57°C over the whole period, but the frequency of HUR4−5 [intense hurricanes, Category 4 and 5] did not show a significant trend, while the frequency of HUR1−5 [weak and intense hurricanes] significantly decreased (−0.95% yr−1).”
“Long-term changes in the intensity of tropical cyclones are of considerable interest because of concern that greenhouse warming may increase storm damage. The PI [potential intensity of tropical cyclones] calculated using radiosonde data at 14 tropical island locations shows only small, statistically insignificant trends from 1980 to 1995 and from 1975 to 1995. … Between 1975 and 1980, however, while SSTs rose, PI [potential intensity] decreased, illustrating the hazards of predicting changes in hurricane intensity from projected SST changes alone.”
“Our estimate of the frequency of such ‘super-cyclones’ [wind speeds in excess of 182 kilometers per hour] is an order of magnitude higher than that previously estimated. … [The Great Barrier Reef] experienced at least five such storms over the past 200 years, with the area now occupied by Cairns experiencing two super-cyclones between 1800 and 1870. The 20th century, however, was totally devoid of such [super-cyclone] storms, with only one such event (1899) since European settlement in the mid-nineteenth century.”
“In summary, confidence in large scale changes in the intensity of extreme extratropical cyclones since 1900 is low”
Reduced Frequency Of Landfalling Hurricanes With Warming
“Here we assess, in our model system, the changes in large-scale climate that are projected to occur by the end of the twenty-first century by an ensemble of global climate models, and find that Atlantic hurricane and tropical storm frequencies are reduced. At the same time, near-storm rainfall rates increase substantially. Our results do not support the notion of large increasing trends in either tropical storm or hurricane frequency driven by increases in atmospheric greenhouse-gas concentrations.”
“Our record of tropical cyclone activity reveals no significant trends in the total number of tropical cyclones (tropical storms and hurricanes) in the best sampled regions for the past 318 years. However, the total number of hurricanes in the 20th century is ∼20% lower than in previous centuries. … Long-term variations in the number of tropical cyclones do not show any evidence of increasing storm frequency and have declined a nonstatistically significant amount.”
Australian tropical cyclone activity lower than at any time over the past 550–1,500 years
“The assessment of changes in tropical cyclone activity within the context of anthropogenically influenced climate change has been limited by the short temporal resolution of the instrumental tropical cyclone record (less than 50 years). Furthermore, controversy exists regarding the robustness of the observational record, especially before 1990. Here we show, on the basis of a new tropical cyclone activity index (CAI), that the present low levels of storm activity on the mid west and northeast coasts of Australia are unprecedented over the past 550 to 1,500 years.”
“We conducted 228-year long, three-member ensemble simulations using a high resolution (60 km grid size) global atmosphere model, MRI-AGCM3.2, with prescribed sea surface temperature and greenhouse gases and aerosols from 1872 to 2099. We found a clear decreasing trend of global tropical cyclone (TC) frequency throughout the 228 years of the simulation.”
“As of the end of the 2014 hurricane season, the US has experienced no major hurricane landfall since Hurricane Wilma in 2005, a drought that currently stands at nine years. Here, we use a stochastic tropical-cyclone model to calculate the mean waiting time for multi-year landfall droughts. We estimate that the mean time to wait for a nine-year drought is 177 years. We also find that the average probability of ending the drought with a major landfall in the next year is 0.39, and is independent of the drought duration, as one would expect for a Bernoulli process.”
“Here we use observational data to show that global warming of the sea surface is associated with a secular increase of tropospheric vertical wind shear in the main development region (MDR) for Atlantic hurricanes. The increased wind shear coincides with a weak but robust downward trend in U.S. landfalling hurricanes.”
“Results show that the SCS TC [South China Sea tropical cyclone] activity experienced an abrupt decadal decrease at around 2002/2003. Compared to the TC [tropical cyclone] activities from the early 1990s to 2002, the number of TCs [tropical cyclones] formed in the SCS markedly decreased from 2003 through the early 2010s.”
“The linear trend in the number of severe TCs [tropical cyclones] making land-fall over eastern Australia declined from about 0.45 TCs/year in the early 1870s to about 0.17 TCs/year in recent times—a 62% decline.”
“Tropical cyclone (TC) activity over the western North Pacific (WNP) exhibits a significant interdecadal variation during 1960-2011, with two distinct active and inactive periods each. This study examines changes in TC [tropical cyclone] activity and atmospheric conditions in the recent inactive period (1998-2011). The overall TC [tropical cyclone] activity shows a significant decrease [1960-2011], which is partly related to the decadal variation of TC genesis frequency in the southeastern part of the WNP and the downward trend of TC genesis frequency in the main development region.”
“Bayesian age–depth models, derived from eight AMS radiocarbon dates, suggest that the frequency of typhoon strikes was 2–5 times greater from 3900 to 7800 cal. yr. BP compared to 0–3900 cal. yr. BP [calendar years before present]. Possible explanations for this variability in the typhoon record are that typhoons were more frequent and/or more intense in Southeast Asia in the mid-Holocene because of climatic changes associated with the Mid-Holocene Warm Period or that the record reflects site sensitivity changes resulting from a mid-Holocene sea-level highstand.”
“Storms and tsunamis, which may seriously endanger human society, are amongst the most devastating marine catastrophes that can occur in coastal areas. Many such events are known and have been reported for the Mediterranean, a region where high-frequency occurrences of these extreme events coincides with some of the most densely populated coastal areas in the world. In a sediment core from the Mar Menor (SE Spain), we discovered eight coarse-grained layers which document marine incursions during periods of intense storm activity or tsunami events. Based on radiocarbon dating, these extreme events occurred around 5250, 4000, 3600, 3010, 2300, 1350, 650, and 80 years cal BP. No comparable events have been observed during the 20th and 21st centuries.”
“Current datasets indicate no significant observed trends in global tropical cyclone frequency over the past century … No robust trends in annual numbers of tropical storms, hurricanes and major hurricanes counts have been identified over the past 100 years in the North Atlantic basin.”
Cooler (Not Warmer) Sea Surface Temps Produce More Frequent, Intense Hurricanes
More tropical cyclones in a cooler climate?
“Recent review papers reported that many high-resolution global climate models consistently projected a reduction of global tropical cyclone (TC) frequency in a future warmer climate, although the mechanism of the reduction is not yet fully understood. Here we present a result of 4K-cooler climate experiment. The global TC [tropical cyclone] frequency significantly increases in the 4K-cooler climate compared to the present climate. This is consistent with a significant decrease in TC frequency in the 4K-warmer climate.“
“Our record demonstrates that the frequency variability of intense landfalling cyclones is greatest at centennial scale compared to seasonal and decadal oscillations. [T]he period between AD 1600 to 1800 [Little Ice Age] had many more intense or hazardous cyclones impacting the site than the post AD 1800 period.”
“A comparison with North Atlantic and Western Mediterranean paleoclimate proxies shows that the phases of high storm activity occurred during cold periods, suggesting a climatically-controlled mechanism for the occurrence of these storm periods. … Periods of low storm activity occurred from 560 cal yr BC to 140 cal yr AD (SP9 and SP8, Roman Warm Period) and from 820 to 1230 cal yr AD (SP4, Medieval Warm Period).”
“Our work illustrates a major constraint on the large-scale global atmospheric engine: As the climate warms, the system may be unable to increase its total entropy production enough to offset the moistening inefficiencies associated with phase transitions. … On a warming Earth, the increase in perceptible water has been identified as a reason for the tropical overturning to slow down, and studies over a wide range of climates suggest that global atmospheric motions are reduced in extremely warm climates.“