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Recovery has begun in the Bahamas after massive devastation from Hurricane Dorian, a Category 5 monster of historic intensity. The U.S. southeast coast and Canadian Maritimes are keeping a watchful eye on Dorian, still a powerful storm. However, even though Dorian is still churning in the Atlantic, questions are understandably being raised about the possible effects of human-caused climate change and hurricane behavior.


Such questions are not just scientific, but have a strong overlay of politics. Claims of the effects (or lack thereof) of accumulating greenhouse gases in the atmosphere on hurricanes are often a proxy for calls for more (or less) aggressive policy action on climate change. Fortunately, recent scientific assessments provide the latest understandings of hurricanes and climate change. Unfortunately, much of what you read in the media often ignores these assessments, in favor of more sensationalized and less accurate coverage.


Before proceeding, let me make a few things perfectly clear: Human-caused climate change, driven by accumulating greenhouse gases, is real and poses significant risks. Aggressive action is needed to decarbonize the global economy and to improve adaptation to climate. But none of that justifies departing from scientific integrity. Playing things straight is always the best course of action.

On hurricanes – and more generally, tropical cyclones -- we are fortunate that there have been two recent consensus statements of experts produced by the World Meteorological Organization (WMO, Part 1 and Part 2) and the National Oceanic and Atmospheric Administration (NOAA). These statements, along with the work of the Intergovernmental Panel on Climate Change (IPCC) and U.S. National Climate Assessment (USNCA) provide a robust and reliable guide to the current views of relevant experts on the science of hurricanes and climate change.


Let’s start with the obvious and uncontested. Humans have fundamentally altered the climate system. This means that all weather on planet earth is influenced by climate change. The important question thus is not the trivial one as to whether climate change exists and has effects, but how this influence manifests itself, the magnitude of the effects and their significance for life on Earth.


So it is a truism to say that hurricanes are – linked with, influenced by, associated with, connected to, impacted by – climate change. In addition, such effects can occur in many ways as scientists are studying many different metrics associated with tropical cyclones, here is just a partial list: global and ocean basin frequency and intensity, poleward migration, propagation speed, regional occurrence, intensity distribution (across storms and within regions), storm track locations, inland precipitation, coastal storm surge and global, regional, and sub-regional landfall frequency.


Commenting on Hurricane Dorian, Kevin Trenberth of the U.S. National Center for Atmospheric Research exemplified how to connect a hurricane with climate change, while actually conveying no substance: “The environment for all such storms has changed because of climate change. The case can be readily made that all storms are affected, but each responds differently.” This is not science, but an inkblot.


It is well understood that there have not been upwards trends in hurricane landfalls along the continental United States (over more than a century) or globally (since at least 1970). Florida experienced 18 major hurricane landfalls from 1900 to 1959 (60 years), but only 11 in the 59 years from 1960 to 2018. Those opposed to action on climate change will often point solely to such numbers to minimize climate change. Of course, a lack of upward trend in landfalls (or any other metric for that matter) does not disprove a human role in climate change or on hurricanes, now or in the future.


It is common to see claims that hurricane-related inland rainfall and flooding has increased due to climate change. This is not the view presented in recent assessments. NOAA concludes “an anthropogenic influence has not been formally detected for hurricane precipitation,” but finds it likely that increases will occur this century. Similarly, the WMO concluded, “no observational studies have provided convincing evidence of a detectable anthropogenic influence specifically on hurricane-related precipitation,” but also that an increase should be expected this century. The U.S. National Climate Assessment concurred, explaining that there is agreement on predictions for a future increase in hurricane-related rainfall, but “a limiting factor for confidence in the results is the lack of a supporting detectable anthropogenic contribution in observed tropical cyclone data.”


These consensus assessments went unmentioned by the New York Times in its discussion yesterday of how Hurricane Dorian was linked to climate change. Instead of referencing the assessments of the WMO, NOAA or USNCA the Times instead relied on a climate scientist who does not research hurricanes and who apparently invented a fictional consensus on rainfall and hurricanes: “some attributes of storms, particularly the increasing amount of rainfall associated with many of them, has reached a very strong consensus.” This is simply wrong. No wonder there is confusion.


It is essential to understand what a scientific consensus is and is not. A scientific consensus is not a catechism representing the only allowed view. Rather, a scientific consensus represents a distribution of views, often – but not always - with an identifiable central tendency. It is perfectly reasonable and expected that some experts will have legitimate views that lie at the fringes of any such consensus.


For instance, climate scientists Michael Mann of Penn State and Katherine Hayhoe of Texas Tech have expressed views on the relationship of hurricane-related rainfall and climate change that are far more bullish than those expressed in the NOAA, WMO and USNCA consensus assessments. Because their views are not consistent with these consensus views does not make them wrong or illegitimate. Science thrives because of disciplinary and methodological diversity and open debate. It is not uncommon for a consensus to shift in the direction of what were once minority views.


However, anyone – whether advocate, journalist or politician – who relies solely on outlier views while ignoring a well-established consensus perspective is cherry-picking at best, and being misleading at worst. It would be the same as highlighting those few legitimate voices who claim that human effects on the climate system are minimal while ignoring the consensus expressed by the Intergovernmental Panel on Climate Change (IPCC).


There is of course a tendency in the media to highlight positively those who are on the bullish fringe of consensus positions related to climate, while denigrating those who are on the bearish fringe. This is politics, not science. Both fringes are at odds with central-tendency consensus views, and care must be taken to distinguish where scientific claims sit with respect to that consensus from the worth of the causes being advocated for by those making the claims. Advocating for climate action does not provide a Teflon shield against having one’s scientific claims examined, tested and placed in relation to a broader consensus view.


It has also become common to see claims that sea level rise – again, undoubtedly true and caused by accumulating greenhouse gases – has led to increasing storm surges. While it is simple logic that an increasing sea level will alter inundation patterns, the WMO assessment notes, “our expectation is that a widespread worsening of total inundation levels during storms is occurring due to the global mean sea level rise associated with anthropogenic warming, assuming all other factors equal, although we note that no TC climate change signal has been convincingly detected in sea level extremes data.” It is happening, but the effect is not yet so large that we can observe it.


This highlights another source of potential confusion, that between what is expected for the future and what is observed today. The characteristics of any particular tropical cyclone today – such as its speed, intensification, rainfall, intensity, track – will necessarily be consistent with some scenarios of projected tropical cyclone behavior in late 21st century. Claiming that a storm today is consistent with a scenario of the distant future is simply another truism, and says little about the role of climate change in a storm today or the future. As the WMO assessment concludes: “anthropogenic signals are not yet clearly detectable in observations for most TC metrics.” The USNCA agrees: “A key uncertainty in tropical cyclones (TCs) is the lack of a supporting detectable anthropogenic signal in the historical data to add further confidence to these projections [of the future].”


A final confusion is an assumption that climate change means that everything is getting worse. As Hurricane Dorian was bearing down on the Bahamas, Hayhoe argued that the right question to ask of hurricanes and climate change is: “how much worse did climate change make it?" Again, we can expect that on balance, climate change will intensify some extreme weather now and in the future, but there is no expectation that every single hurricane will be made “worse.” That is just hyperbole.


In some cases, climate projections show human-caused climate change will not make things worse. For instance, earlier this year Cyclone Idai made landfall in southern Africa, causing extensive damage in Mozambique, Malawai and Zimbabwe. As typically happens, the storm was quickly linked to climate change. Paulo Ceppi, of Grantham Institute at Imperial College London, explained of Cyclone Idai, “there is a direct link between global warming and cyclone intensity. We need to make every effort to follow the Paris agreement target of remaining below 1.5C of global warming in order to minimise future increases in the severity of tropical storms.”


Not only does this comment illustrate the close link of science and politics, but Ceppi’s comment is both misleading and ironic. It is misleading because the region has seen no increase in tropical cyclone landfall frequency or intensity -- such storms are common in the region. It is ironic because one of the only climate modeling studies of future tropical cyclone landfalls in the region finds, “the number of tropical cyclones making landfalls over southern Africa under global warming will decrease” with continued greenhouse gas emissions. The study projects there would be more storms at 1.5 deg C than at 2 deg C. Not every storm should be enlisted in political advocacy.


Sometimes the peer-reviewed literature does not support the claims that activists wish to make. That is fine and expected, as science does not perform based on political demands. The good news for climate advocacy is that justifications for aggressive mitigation and adaptation are not dependent on establishing a close association of every disaster with climate change.


So how should the non-expert evaluate the various claims about hurricanes and climate change that accompany every storm that forms nowadays?


Here are three questions to ask when evaluating claims:

  1. Does the claim quote directly and accurately the conclusions of authoritative assessments such as the IPCC, WMO, NOAA or USNCA?
  2. Does the claim place individual voices into the context of the distribution of views reflected in that consensus? That is, are the views representative of that consensus or at odds with it?
  3. Are claims made by individual voices, even if at odds with consensus views, consistent with peer-reviewed literature?

Expect three yeses, anything less is problematic. As one moves from 1 to 3 ,the challenges for the non-expert become greater in evaluating claims. Of course, when it comes to scientific claims, don’t take my word for it or anyone else’s, you can access the consensus assessments directly. The good news is that the scientific community has over the past 20 years developed a robust consensus on hurricanes and climate change. Now it is up to all of us to put it to good use in support of both climate action and scientific integrity.


Original story from Forbes


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