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Is Global Warming Causing More Hurricanes?

In the wake of Hurricanes Harvey and Irma, and with strengthening storms Jose and Maria moving through the Atlantic and Caribbean this week, concern about future damaging storms in the U.S. is high. And as with almost every dramatic weather event these days, alarmists have been quick to claim that increasing carbon dioxide emissions—and the resulting manmade climate change—are the cause. 

Public figures like former Vice President Al Gore have been doing this for years, suggesting that the devastation wrought by Hurricane Katrina, for example, would be best countered with a carbon tax or a new United Nations climate treaty rather than resiliency measures like better infrastructure and improved disaster preparedness. But are this year’s round of hurricanes, after a decade or so of absence from the U.S. mainland, evidence that we’re entering an age of climate catastrophe? Recent commentary and analysis from CEI experts suggests not.

Myron Ebell, Director of CEI’s Center for Energy and Environment, and research associate Roger O’Neill wrote an op-ed for The Hill on Friday, criticizing recent “loose talk” about hurricanes and global warming from people who should know better:

The chapter on severe weather events in the UN Intergovernmental Panel on Climate Change’s Fifth Assessment Report assigns a rating of “low confidence” to attributing any human contributions (that is, increasing greenhouse gas emissions) to changes in tropical cyclone activity. Harvey and Irma are the first two Category 3 or above storms to make landfall in the United States since Katrina in 2005. That’s 12 years without a major storm.

[…]

Some researchers have claimed that there has been an uptick in Atlantic hurricane activity, but the uptick is almost certainly an artifact of improved weather-monitoring capabilities, as Chris Landsea at the National Hurricane Center has documented. Since the mid-1960s, weather satellites have collected information about temperature and some imagery, but it wasn’t until the late 1970s when NASA established Geostationary Operational Environmental Satellites that scientists have been able to consistently monitor hurricane activity. Additionally, the U.S. Coast Guard began its National Data Buoy Center in 1966, which dramatically expanded data collection capacity. Today, hundreds of buoys monitor wind speed and direction, air temperature and barometric pressure.

Myron, writing earlier in the week on his own at USA Today, countered the paper’s lead editorial about the alleged climate change proof supplied by recent hurricanes:

The notion that Hurricanes Harvey and Irma should cause President Trump to reconsider withdrawing from the Paris climate treaty and dismantling the Obama climate agenda is preposterous. Did the fact that no hurricanes of Category 3 or above made landfall in the United States from 2006 until this year cause global warming alarmists to reconsider their ruinously expensive and utterly ineffectual policies?

[…]

Although improvements in forecasting, infrastructure, emergency response and building methods have cut fatalities from hurricanes dramatically since more than 6,000 people died from the hurricane in Galveston, Texas, in 1900, many more people are at risk. And the costs of property destruction have gone up exponentially as beach shacks have been replaced in many areas by large housing tracts.

Rather than wasting hundreds of billions of dollars on reducing greenhouse gas emissions, much smaller amounts should be spent on improving the infrastructure that protects the Gulf and Atlantic coasts.

My colleague Marlo Lewis has long been a critic of thinly-sourced climate impact claims, whether it’s the theory that increasing temperatures are killing more people in traffic accidents, or the idea that hundreds of thousands of additional people will die heat-induced deaths in future decades because of greenhouse gas accumulations. He’s also been a long-time critic of Mr. Gore’s activism, writing an exhaustive rebuttal to the documentary An Inconvenient Truth in the form of a 154-page study titled Al Gore’s Science Fiction (shorter version here).

Marlo weighed in last year to revisit what he termed Gore’s “Katrina innuendo.” In the book version of An Inconvenient Truth, Gore suggested that there was an “emerging consensus linking global warming to the increasing destructive power of hurricanes,” which, given his frequent references to the then-recent destruction of Hurricane Katrina, formed an unmistakable implication that anthropogenic global warming was responsible. That claim was based largely on a controversial 2005 study by Prof. Peter Webster at Georgia Tech and his co-authors. Those conclusions have since been re-evaluated:

[The January 2016] edition of CO2Science.Org reviews “Extremely Intense Hurricanes: Revisiting Webster et al. (2005) after 10 Years,” a study by Phil Klotzbach of Colorado State University and Christopher Landsea of NOAA/NWS/National Hurricane Center.

Klotzbach and Landsea examine whether the “trends” found by Webster et al. continue after an additional 10 years of data. The two researchers find that “the global frequency of category 4 and 5 hurricanes has shown a small, insignificant downward trend while the percentage of category 4 and 5 hurricanes has shown a small, insignificant upward trend between 1990 and 2014.” They further report that “Accumulated cyclone energy globally has experienced a large and significant downward trend during the same period.” In other words, there has been a large decrease in the overall destructive power of hurricanes based on an assessment of the number, strength, and duration of all individual hurricanes worldwide.

Klotzbach and Landsea conclude that the intense-hurricane trends observed by Webster et al. were primarily due to “observational improvements at the various global tropical cyclone warning centers, primarily in the first two decades of that study.”

So not only can we not say that any particular hurricane or the intensity of any particular storm is the result of recent climatic changes, the supposed evidence that hurricanes are becoming more frequent or intense at all seems not to hold up to scrutiny. Marlo provided more context in another post yesterday:

…there has been no trend since 1900 in the frequency, strength, and destructiveness of U.S. land-falling hurricanes. That may change. However, neither one hurricane season nor even several active seasons is long enough to detect a greenhouse “signal” in the noise of natural inter-decadal variability.  

Harvey and Irma were the first major (Category 3+) hurricanes to strike the United States since Wilma in 2005. That 12-year major hurricane “drought” beats the previous record holder, an eight-year period (1861-1868) with no major U.S. hurricane strikes, in a record going back to 1851. Since 1970, five hurricanes of Category 4 or 5 strength struck the United States. “In the previous 47 years, the country was struck by 14 such storms,” notes University of Colorado professor Roger Pielke, Jr. All we can reasonably infer about the climate system from Harvey and Irma is that our luck ran out.

Several facts weigh against claims that global warming caused or intensified Harvey and Irma:

  • There is no correlation between all major hurricane strikes in Texas since 1870 and sea surface temperature variations over the western Gulf of Mexico, according to University of Alabama in Huntsville atmospheric scientist Roy Spencer. For spawning major hurricanes, it really doesn’t matter whether Gulf water temperature is above average or below average.
  • Harvey produced extraordinary flooding because it stalled over Houston, dumping nearly all its rain on a relatively compact area. University of Pennsylvania professor Michael Mann claims global warming slowed Harvey’s movement by pushing the jet stream farther north. Weather data conflict with that hypothesis, Spencer contends: “We didn’t have a warm August” such as might shift the jet stream northward.
  • Meteorologist Cliff Mass similarly finds “no change in zonal winds over the Gulf of Mexico for the past 50 years” such as might account for Harvey’s meander after making landfall. He also reports there has been no trend in hurricane season precipitation around Houston during the past 50 years.
  • Climatologist Judith Curry reports that Irma developed into a major hurricane “over relatively cool waters in the Atlantic—26.5°C—the rule of thumb is 28.5°C for a major hurricane (and that threshold has been inching higher in recent years).”

Read more on how the news media tend to employ misleadingly specific statistics when reporting on major weather events, from Roger O’Neill, here.

Hurricanes and tropical storms can have terrible, deadly impacts—which is why we need a rational, clear-eyed assessment of what the real risks are. Spending billions of dollars of taxpayers’ money (and lost GDP value) on decarbonizing the world’s ecoonmy would be a tragic mistake when we can save more lives and make more communities safer with a wiser set of priorities.