By Paul Homewood
h/t Joe Public
You may recall all sorts of ridiculous claims about the effect of global warming on Hurricane Florence, when it hit in 2018.
The attribution study below was typical, claiming that rainfall was 50% more than it would have been without climate change, and that it was bigger and longer lasting to boot:
Naturally such claims were widely reported in the media.
Lo and behold, a year and a half later, exactly the same authors have now published their full study:
https://advances.sciencemag.org/content/6/1/eaaw9253.full
As it turns out, according to their modelling, rainfall was only 3.8% greater because of global warming, and allowing for error margins may actually have been less! And instead of being 80km in diameter larger, it was only 1 to 2%.
In other words, statistically global warming made no difference at all to Hurricane Florence.
Roger Pielke Jr is scathing about this tendency to rush out attribution studies, in order to blame climate change for every bad weather event.
He writes at Forbes:
In September 2018, as Hurricane Florence was heading towards a landfall in North Carolina, a team of researchers announced that the storm would be 80 kilometers larger and drop 50% more rainfall due to “human induced climate change.” In a study published last week the researchers shared that their initial numbers were wildly off base.
The new study explained: “The quantitative aspects of our forecasted attribution statements fall outside broad confidence intervals of our hindcasted statements and are quite different from the hindcasted best estimates.” In plain English that means: “We were really, really wrong.”
Both studies of Hurricane Florence reflect a recently developed approach that seeks to quantify the influence of human-caused climate change on individual weather events. Such “event attribution” studies typically use models to produce results under two different conditions: the real world and a counterfactual world in which climate change is not present. The differences between the two worlds are used to make statements about the connection of climate change and the specific event.
Such studies are increasingly easy to do, extremely media friendly and as a consequence, have now become commonplace. The major error in the initial attribution study of Hurricane Florence provides an opportunity to offer some guidance on how to interpret such studies. Here I offer three rules to guide the production and interpretation of such event attribution studies.
Before proceeding it is necessary to state the obvious: Human caused climate change is real and has undoubtedly influenced all global weather events. The world has evolved differently than it would have otherwise due to the significant human influence, which notably includes the emission of carbon dioxide from the burning of fossil fuels, but through other influences as well, such as changes to the land surface.
We should therefore be cautious when climate change is associated with individual extreme events through weasel words that imply a connection but in a trivial non-specific way. Such weasel words include claims that a particular extreme event has been — linked or connected or cited (I’m sure you can think of other examples) – in connection with human-caused climate change.
Of course, the prevalence of weasel words reflects intense political overlay on the association of extreme weather events and climate change. For instance, one of the scientists who performed the initial Hurricane Florence analysis, Michael Wehner of Lawrence Berkeley National Laboratory, openly expressed his desire to get the initial analysis in the news. According to Buzzfeed, “Wehner admitted that he and his colleagues are sticking their necks out in making an estimate of the effect of climate change before the storm makes landfall. But he said that it’s important to provide answers when a hurricane is in the news, not months later when most people are thinking about other issues.” Wehner also expressed a political motivation: “This kind of study really brings home the point that dangerous climate change is here now.”
The publicity campaign was enormously successful. Many news outlets ran with the sensational story. For instance, the Guardian proclaimed: “Climate change means Hurricane Florence will dump 50% more rain.” Newsweek announced: “How Global Warming Is Turbocharging Monster Storms Like Hurricane Florence.” Wehner was contrasted with President Trump by the Center for American Progress and he told them: “The most important message from this (and previous) analyses is that “Dangerous climate change is here now!” It is not a distant threat in the future but today’s reality” (emphasis in original).
Apart from media sensationalism and efforts to shape public and policy maker opinion on climate change, the attribution of extreme weather to causal factors (including the emission of greenhouse gases) is important for actual decision making related to disaster planning and climate adaptation. In such contexts, science should be more than just a symbol. Here scientific quality actually matters.
To ensure rigor in its work, the Intergovernmental Panel on Climate Change (IPCC) has employed a statistical framework for concluding that extreme weather phenomena had actually increased (or decreased) and the factors responsible for such changes. The detection of changes required quantifying a change in the statistics of weather extremes over climate time scales of 30 years or even longer. Once detection was achieved, then scientists seek to attribute those changes to particular causes, including the accumulation of carbon dioxide in the atmosphere.
When it comes to many types of extreme events the IPCC has for decades been unable to conclusively detect changes in their frequency or intensity. For instance, the IPCC has reported increases in heat waves and in heavy precipitation, but not tropical cyclones (including hurricanes), floods, tornadoes or drought.
The rise of individual “event attribution” studies coincides with frustration that the IPCC has not definitively concluded that many types of extreme weather had become more common. Elizabeth Lloyd, a philosopher of biology, and Naomi Oreskes, a science historian, expressed this frustration in a 2018 paper in the journal Reviews of Geophysics:
“The traditional risk‐based approach to extreme events [detection and attribution under the IPCC] may lead to a challenge in communication, and to the impression that climate science is less epistemically secure than it actually is.. . . Because no event can be attributed to climate change without an attribution study, this effectively means that scientists following community norms will nearly always convey the message that individual events are not related to climate change—or at least, that we cannot say if they are. In short, it conveys the impression that we just do not know, which feeds into both contrarian claims that climate science is in a state of high uncertainty, doubt, or incompleteness, and the general tendency of humans to discount threats that are not imminent.”
The rise of “event attribution” studies offers comfort and support to those focused on climate advocacy by establishing the linkage (weasel word) of specific extreme events and climate change. It it is not clear however that such studies offer much in the way of empirical rigor, particularly as compared to the conventional IPCC detection and attribution framework. As one climate scientist observes of the event attribution methods, “it is important to appreciate that being quantitative is not necessarily the same thing as being rigorous.”
With a focus on scientific rigor, here are three rules for accepting the coming avalanche of “event attribution” studies that will without a doubt connect (weasel word) most every extreme weather event with climate change.
He goes on to list the three rules, but the first is in my view the really critical one:
Rule Number One: Any model used in an event attribution study to quantify a linkage (weasel word) between climate change a specific extreme event should also produce accurate historical climate trends associated with the relevant phenomena. The claim that rainfall from Hurricane Florence was boosted 50% by climate change should have raised immediate doubts because observations have not shown an increase in rainfall related to landfalling hurricanes. Any event attribution study that cannot accurately replicate historical trends using the same model and methods is clearly fatally flawed. A comparison of observations and modelled climate history with respect to the extreme weather phenomena under study should always be included in event attribution results.
In short, if the model does not fit with the facts, then the model is wrong!
via NOT A LOT OF PEOPLE KNOW THAT
January 9, 2020 at 04:46AM
Iowa Climate Science Education 
Reblogged this on Climate- Science.press.
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