The above images on hurricanes come via hurricane researcher @philklotzbach. The top graph shows US hurricane landfalls from 1878 to 2017 (through today). Within that data the trend is down and if you’d like to consider the data as a sample from a larger population, there is no trend. Either way you slice it, US hurricanes have not increased.
The bottom table shows summary statistics for the entire Northern Hemisphere for 2017. Even with the massive damage in Texas, Florida and the Caribbean, by the numbers 2017 is an average year. Lesson: Don’t confuse impact with climate. More on that below.
The US National Climate Assessment and Weather Extremes
- The 4th US National Climate Assessment was published a few weeks ago, and it is worth reviewing what it says about trends in extreme weather events. In short, the NCA supports arguments I’ve been making for many years.
- “Cold extremes have become less severe over the past century.”
- “Changes in warm extremes are more nuanced than changes in cold extremes.” (Yes, you read that correctly.)
- Here are trends in cold spells, warm spells and heat waves 1900 to present from the report:
- “The Intergovernmental Panel on Climate Change’s (IPCC’s) Fifth Assessment Report (AR5) concluded that it is very likely that human influence has contributed to the observed changes in frequency and intensity of temperature extremes on the global scale since the mid-20th century. . . In general, however, results for the contiguous United States are not as compelling as for global land areas . . .” (emphasis added, and yes, that means weak attribution).
- Hurricanes: “there is still low confidence that any reported long-term (multidecadal to centennial) increases in TC activity are robust”
- Tornadoes: “A particular challenge in quantifying the existence and intensity of these events arises from the data source”
- Winter storms: “Analysis of storm tracks indicates that there has been an increase in winter storm frequency and intensity since 1950”
- Drought: “drought statistics over the entire CONUS have declined … no detectable change in meteorological drought at the global scale” (One for John Holdren)
- “Western North America…. where determining if observed recent droughts were unusual compared to natural variability was particularly difficult” (Another for Dr. Holdren)
- “IPCC AR5 did not attribute changes in flooding to anthropogenic influence nor report detectable changes in flooding magnitude, duration, or frequency”
- In the US “”increasing & decreasing flooding magnitude but does not provide robust evidence that these trends are attributable to human influences… no formal attribution of observed flooding changes to anthropogenic forcing has been claimed”
- “a number of precipitation metrics over the continental United States has been examined; however trends identified for the U.S. regions have not been clearly attributed to anthropogenic forcing”
- The data says what it says. There is precious little evidence that extremes have become worse in the US since at least 1900, with the exception of more winter storms since 1950 and overall fewer cold spells. Attribution is weak to nonexistent.
- Despite the evidence there is a drumbeat of news stories and various claims that weather disasters are getting worse.
- For instance, the New York Times article on the release of the report contained this statement: “In the United States, the report finds that every part of the country has been touched by warming, from droughts in the Southeast to flooding in the Midwest …”
- Michael Mann, the same professor suing his critics for being wrong about scientific claims says this: “Whether we’re talking about unprecedented heat waves, increasingly destructive hurricanes, epic drought and inundation of our coastal cities, the impacts of climate change are no longer subtle“
- Both the NYT characterization of the report and Mann’s claims are irrefutably incorrect according to the report. These are just a few of many similar examples of claims that are contrary to the NCA related to extreme weather.
- Claiming that the weather has gotten worse is today an important cultural shibboleth related to climate science. It’s not supported by the evidence but it serves an important role in the political debate over climate. Another weakened norm, I suppose.
The Politics of Inconceivable Scenarios
- Last for this month, but perhaps most important, is a hugely significant paper published by Justin Ritchie and Hadi Dowlatabdi of the University of British Columbia titled Why do climate scenarios return to coal?
- The paper argues that the IPCC’s scenario for future emissions of carbon dioxide most often characterized as “business-as-usual” (technically called RCP 8.5) should be considered implausible.
- They explain: “RCP8.5 no longer offers a trajectory of 21st-century climate change with physically relevant information for continued emphasis in scientific studies or policy assessments.”
- Why does this matter? A “business as usual” scenario is frequently used as the basis for projections of how the future climate will evolve in the absence of climate policy that seeks to reduce emissions.
- The difference between BAU and a climate policy scenario in terms of climate outcomes is thus characterized as the consequences (and sometimes the costs) of not mitigating.
- Right away you can see that for those seeking to argue the case for mitigation action, there is every incentive for BAU to be as bad as possible. But what if BAU isn’t as bad as it used to be, under assumptions that may have made sense in the 1970s for a dramatic return-to-coal through the 21st century? Should today’s BAU baseline be made more realistic?
- Larry Kummer has done a great job documenting how RCP 8.5 has been frequently invoked as a “business-as-usual” scenario.
- In fact, once you start looking, you’ll see RCP 8.5 everywhere in the climate impacts literature. For instance, just yesterday, PNAS published a quick-turnaround study by Kerry Emanuel arguing that storms like Hurricane Harvey will become 6x more common by 2100 … under RCP 8.5. But if RCP 8.5 is implausible, then so too are Emanuel’s results (any other methodological issues aside).
- Revisiting BAU has profound significance. As Ritchie and Dowlatabadi explained in an earlier paper: “For the past quarter-century, high emission baselines have been the focus of research, explicitly or implicitly shaping national policy benchmarks, such as estimates for the social cost of carbon.” That innocuous sentence gets close to a third rail of the climate debate — the social cost of carbon (SCC).
- The more extreme the BAU scenario, the higher the SCC and the higher the cost of what those using the SCC would claim to be acceptable regulatory action. See the incentives at play here?
- The Ritchie and Dowlatabadi paper reveals a deeply problematic aspect of the climate issue: It depends almost entirely on competing visions of the future as codified in integrated assessment models. The costs of action and inaction are based on the assumptions used to build these models – not evidence, not data but assumptions.
- Policy arguments based on assumptions in highly speculative models are tailor-made for pathological politicization, appeals to authority and gatekeeping to protect from critical views. Based on this, in the real world of politics they also have very little weight in near-term policy decisions.
- A far better approach would be to focus on carbon-free energy as a proportion of global supply and to argue about what would actions would move that proportion from a current ~14% towards upwards of 90%.
- Richie says he has faced some difficulties getting his arguments published: “Despite getting over 30 peer reviews collected from all of these journals, no one has shot it down,” he said, adding that he still has detected a reluctance among some scholars to grapple with his observations. “Maybe I’m completely wrong about all of this, and here I’ve written all these papers and there’s some critical flaws in them. That’s great—tell me about it,” Ritchie said. “Please! Someone just read it!““
- Read it. It is important.