It was inevitable that global warming alarmists like Al Gore would blame mankind for Hurricanes Harvey and Irma.
Well, with folks saying global warming causes over 600 other things—from longer plane flights to summer frost in Africa, from a beer shortage to beetle infestation, from struggling brothels to declining rates of circumcision, from early marriages to the 2015 Nepal earthquake—the more intuitively plausible connection just couldn’t escape the minds of such great scientists as “Stevie Wonder, Beyoncé, Jennifer Lawrence, Mark Ruffalo, Bill Nye the Science Guy, Neil deGrasse Tyson, Pope Francis, Eric Holthaus at Politico, Bill McKibben in The Guardian, and Naomi Klein.”
That’s climatologist and hurricane expert Dr. Roy W. Spencer’s partial list (he later adds Gore and Nation editor Mark Hertsgaard), in his new e-book Inevitable Disaster: Why Hurricanes Can’t be Blamed on Global Warming, of folks who blame the two recent hurricanes on global warming. There are plenty more.
Strangely enough, though, they don’t tend to be climate scientists, hurricane experts, or even scientists of any sort.
The Geophysical Fluid Dynamics Laboratory (GFDL) of the National Oceanic and Atmospheric Administration (NOAA) says:
It is premature to conclude that human activities–and particularly greenhouse gas emissions that cause global warming—have already had a detectable impact on Atlantic hurricane or global tropical cyclone activity. That said, human activities may have already caused changes that are not yet detectable due to the small magnitude of the changes or observational limitations, or are not yet confidently modeled (e.g., aerosol effects on regional climate).
The Intergovernmental Panel on Climate Change says:
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.
Someone might object that the GFDL goes on to say:
Anthropogenic warming by the end of the 21st century will likely cause tropical cyclones globally to be more intense on average (by 2 to 11% according to model projections [emphasis added] for an IPCC A1B scenario). This change would imply an even larger percentage increase in the destructive potential per storm, assuming no reduction in storm size.
There are better than even odds that anthropogenic warming over the next century will lead to an increase in the occurrence of very intense tropical cyclone in some basins—an increase that would be substantially larger in percentage terms than the 2–11% increase in the average storm intensity. This increase in intense storm occurrence is projected despite a likely decrease (or little change) in the global numbers of all tropical cyclones.
Anthropogenic warming by the end of the 21st century will likely cause tropical cyclones to have substantially higher rainfall rates than present-day ones, with a model-projected [emphasis added] increase of about 10–15% for rainfall rates averaged within about 100 km of the storm center.
The trouble with this, of course, is in the words I’ve emphasized. These are the climate models that, on average, predict 2 to 3 times as much warming as actually observed over the period already observed. That suggests that they exaggerate anthropogenic global warming’s influence on tropical cyclone frequency and intensity by 2 to 3 times as well. So perhaps AGW is more likely to increase average storm intensity by 1/3–5.5% than 2–11%.
Even assuming the models get it right for the end of the century, though, the implication for 2017 is quite different. The GFDL doesn’t specify the starting point from which tropical cyclone strength is projected to increase by 2–11%, but let’s assume it’s the start of the century. That means 1/6 of the time has passed so far. So on GFDL’s reasoning, AGW could have increased Harvey and Irma’s strength by 0.33–1.83%. And if the models’ projections for cyclone intensity are as far off as those for warming itself, we can divide those by 2 or 3, leaving a range of 0.11–0.92%.
Apply that to Irma’s 185 mph maximum sustained winds, and it follows that 183.3–184.8 mph would have occurred naturally—too little difference to measure accurately or to have significantly different consequences. Apply it to Harvey’s ~53 inches of maximum rainfall in a single location, and it follows that 52.5–52.9 inches would have occurred naturally.
As Spencer, a Senior Fellow of the Cornwall Alliance as well as Principal Research Scientist in climatology in the Earth Systems Science Center at the University of Alabama, Huntsville, points out in An Inevitable Disaster, “… catastrophic hurricanes have occurred long before our greenhouse gas emissions could have been blamed. Some decades are busy with hurricane activity, while others are relatively quiet. … [M]ajor hurricanes have always been a risk, and always will be a risk to Atlantic and Gulf coastal residents of the United States. … [T]here is little if any evidence that tropical cyclone activity is increasing, even as our climate system has warmed modestly.”
While it was widely, and accurately, reported that Irma was the strongest hurricane measured (something we’ve been able to do for a comparatively short time, generally not before the 1960s) in the Atlantic outside the Caribbean Sea and the Gulf of Mexico, it was mistakenly thought that global warming accounted for that. But Spencer reports that “Unusually warm sea surface temperatures were not present as Irma became a major Category 3 hurricane long before it reached the warmest sea surface temperatures around the Bahamas, northern Caribbean islands, and the straits of Florida.” So it wasn’t exceptional warmth that made Irma as strong as she was.
Just as major hurricanes can develop without exceptional warmth, exceptional warmth doesn’t guarantee the development of major hurricanes, either. “In fact, the Gulf of Mexico and area around the Bahamas are warm enough every summer to support a catastrophic hurricane. That such hurricanes almost never develop is not due to a lack of warm surface waters. It is more often the result of too much wind shear, or the absence of a preexisting cyclonic circulation in the lower atmosphere to kick-start cyclone formation.”
Further, Spencer explains, lake sediment studies in Florida show “that catastrophic hurricane strikes were more frequent 1,000 to 2,000 years ago than in the most recent 1,000 years. This means that, at least for hurricane activity, natural climate variability and climate change does indeed exist. But since our carbon dioxide emissions were virtually nonexistent before the 1940s, we can assume humanity’s role in millennium time scale variations was also non-existent.”
Does all this mean there’s no reason to be concerned about possible major damage from future hurricanes? Certainly not. Spencer offers a history of reported major hurricanes (Category 3 or higher) making landfall in the United States running back to colonial times. He discusses 13 in the 1600s and 1700s; 23 from 1800–1850; 24 from 1850–1899; 57 from 1900–1999; and 9 from 2000–2017 (so far). Don’t let the rising numbers fool you—it’s likely that at least until the 1970s most hurricanes were simply never reported because there were too few people around to observe them. (E.g., Miami wasn’t incorporated until 1900, with a population of 300.)
Note that the 21 year period from 1941 to 1961 was particularly active for landfalling major hurricanes, with nearly one per year on average. Then the 1980s were fairly inactive, averaging one every two years. A large upswing in activity occurred when a total of seven major hurricanes were experienced in 2004 and 2005, but then nearly 12 years passed before major Hurricane Harvey hit Houston in 2017. That most recent major hurricane ‘drought’ is believed to be something that happens only once every 250 to 300 years.
This illustrates just how variable major hurricane strikes in the United States can be. Some years and decades are very active, while others are relatively quiet. This isn’t what human-caused climate change looks like. It’s what weather looks like.
Of particular interest are the only three Category 5 hurricanes to hit the United States in modern times, in 1935, 1969, and 1992.
He reports that the National Hurricane Center estimates that a major “hurricane has made landfall as frequently as every 15 years in the Miami area, to a[s] little as once every 200–300 years in Maine.”
The probability of a major hurricane strike is one thing and seems to be overwhelmingly, if not entirely, determined by natural forces. But the amount of damage a hurricane will do depends also on what’s in its path—how many people, and how much (and what quality of) property.
The areas of Miami-Dade and Broward counties in Florida have grown from a population of a few hundred people around 1900 to over 6 million today. Consequently, there are nearly 6 million more people in the path of a major hurricane that strikes the area. And those people have far more property, too. As a result, the value of property destroyed by hurricanes hitting such locations rises regardless whether the storms get stronger.
Based upon the history of numerous major hurricane strikes combined with massive coastal development, it is only a matter of time before the U.S. will experience a hurricane disaster of catastrophic proportions, worse than Katrina, Harvey, and Irma combined. I predict it will be a “trillion dollar hurricane,” and it will eventually happen as long as people insist on flocking to our nation’s coastlines and building there.
But it’s all part of what Mother Nature does, without any help from humans.
Yet there is an upside to this. As buildings are constructed to higher standards and infrastructure improves, losses from hurricanes switch from lives to property.
To illustrate, the Category-3 San Marcos hurricane of October 5–14, 1870, struck Cuba, Florida, and the Bahamas, and killed 800–2,000 people out of a combined population of about 1.5 million (a death rate of ~53–133/100,000). Hurricane Irma, which was Category 5 through much of the Caribbean including a prolonged passage along the northern coast of Cuba and Category 4 when it made landfall in southwestern Florida, killed 68 people out of a combined population of over 33 million (a death rate of ~0.2/100,000). I.e., the death rate from Irma was ~98.5% lower than that from the San Marcos hurricane.
This is why continuing economic development, combined with policies that discourage rather than encourage dwelling along hurricane-prone coastlines, is a far more effective means of reducing future harm from hurricanes than anything we can do to control global temperature. The latter has next to nothing to do with the risks we face. The former, everything.