In the aftermath of Hurricane Dorian’s catastrophic impacts on the Bahamas, we have been reminded of the inevitability that some aspect of any damaging hurricane will be blamed on man-made climate change.
We first saw this after Hurricane Katrina in 2005, with the publication of two papers linking an increase in the strongest hurricanes to increasing sea-surface temperatures. As co-author of one these papers, I was astonished to see the outsize media and public attention that they garnered. Katrina was the first time people realized that a small amount of warming could have substantial adverse impacts. Since then, each hurricane has been viewed as an opportunity by activists to emphasize the urgent need to reduce fossil-fuel emissions.
Katrina also touched off an intense and publicly acrimonious debate among hurricane scientists about the quality of hurricane-intensity data and the effect of man-made climate change. “We anticipate that it may take another decade for observations to clarify the situation,” I wrote of the controversy in 2006. Since then, research on the climate dynamics of hurricanes has grown in leaps and bounds. But there remains substantial scientific debate surrounding the issue of hurricanes and climate change.
In 2013, the UN Intergovernmental Panel on Climate Change (IPCC) concluded that:
Globally, there is low confidence in attribution of changes in tropical cyclone activity to human influence. This is due to insufficient observational evidence, lack of physical understanding of the links between anthropogenic drivers of climate and tropical cyclone activity, and the low level of agreement between studies as to the relative importance of [natural variability and man-made forcing].
Last month, the World Meteorological Organization (WMO) Task Force, consisting of eleven international experts on hurricanes and climate change, published two assessment reports. Unlike the IPCC’s, which focus on consensus statements, the WMO reports discussed disagreement among the authors, distinguishing the issues on which there was substantial agreement among the authors from those on which there was substantial disagreement owing in part to limited evidence.
Any convincing claim that man-made climate change has altered hurricane activity requires identifying a change in hurricane characteristics that can’t be explained by natural climate variability. The only conclusion on which there was high agreement among the WMO Task Team members was that there is low-to-medium confidence that the location of typhoons in the North Pacific has changed as a result of climate change. The team members disagreed as to whether any other observed alterations in hurricane activity could be said to have been discernibly influenced by man-made climate change.
The WMO reports discussed a number of more speculative statements about the relationship between hurricane behavior and climate change, which could very well be false and overstate the influence of man-made climate change. There is some evidence suggesting contributions from man-made climate change to: an increase in the average intensity of the strongest hurricanes since the early 1980s; an increase in the proportion of hurricanes reaching Category 4 or 5 in recent decades; and the increased frequency of Hurricane Harvey–like extreme precipitation events in the Texas region. There is also evidence suggesting a decrease in how fast hurricanes move, but that has not been attributed to man-made climate change with any confidence. The WMO Report states that there is disagreement among the authors about whether these trends reflect the influence of man-made climate change.
Why, then, is there so much hype about man-made climate change in the news media after every catastrophic hurricane? Rather than referencing these assessment reports, sensationalized news coverage of the issue tends to lean on activist climate scientists with little or no expertise in hurricanes, implying that their speculative perspective represents the “consensus.”
Insofar as there is any such “consensus,” it is a weak one. Climate and hurricane scientists continue to have a range of perspectives on the impact of man-made climate change on hurricanes. The frequent disagreements among them help move the debate forward, adding to our collective scientific knowledge of the issues involved for everyone’s benefit.
My own perspective is described in a comprehensive Special Report on Hurricanes and Climate Change that was prepared for the clients of my company, Climate Forecast Applications Network (CFAN). My report is broadly consistent with the WMO’s assessment reports, but maintains a greater focus on aspects of hurricanes that contribute to landfall impacts and on the role of natural climate variability in explaining the observed variability of hurricanes and their impacts.
All measures of Atlantic hurricane activity have increased since 1970, although comparably high levels of activity occurred during the 1950s and 1960s, and higher levels of activity were seen in the first decades of the 20th century. Of the 13 strongest recorded hurricanes to hit the U.S. mainland, only three have occurred since 1970: Andrew (1992), Charley (2004), and Michael (2018). Four of these 13 hurricanes — including the strongest, the Labor Day hurricane that hit Florida in 1935 — occurred between 1926 and 1935, when sea-surface temperatures were substantially cooler than they’ve been in recent decades. Hence it is difficult to support an argument that man-made climate change, which has been significant only since 1970, is making hurricanes worse.
Predictions of future hurricane activity are even more uncertain. Possible scenarios in which hurricanes could incrementally worsen over the course of the 21st century are described in the WMO Report. But they don’t change the fundamental fact that hurricanes become catastrophes through a combination of large populations, land-use practices and coastal-ecosystem degradation.
My recent testimony to the House Government Oversight and Reform Committee described ways that we can reduce vulnerability to hurricanes. Rapidly escalating hurricane damage in recent decades owes much to government policies that subsidize risk. The most politically important hurricane that you have probably never heard of is the Category 3 Hurricane Frederic, which struck Alabama and Mississippi in 1979. Its landfall occurred shortly after FEMA was established, and prompted almost $250 million in federal aid for recovery. In 1992, following Hurricane Andrew, Robert Sheets, the then-director of the National Hurricane Center, testified to Congress that the aid for Frederic’s recovery had spurred development in the hurricane-prone regions of the Gulf Coast. Federal disaster policies provide humanitarian benefits, but also encourage the growth of regions vulnerable to hurricanes, which can make the damage from future storms worse. The political pressure on state insurance regulators that often holds down insurance premiums in risky coastal areas contributes to the problem, as well.
It does no one any good to proceed on the assumption that reducing fossil-fuel emissions will mitigate damage from future hurricanes in a meaningful way. The hype that links today’s hurricanes to man-made climate change is diverting our attention from implementing policies that can reduce our vulnerability to hurricanes, which by some measures were worse prior to 1970. These policies include fixing our federal disaster policies and state insurance policies, making better land-use decisions, improving building codes and coastal engineering, hardening infrastructure, and protecting coastal wetlands.
Overselling the possible effect of man-made climate change on hurricane impacts not only risks eroding scientific credibility, but also distracts from addressing our vulnerability to the storms themselves.