The comment period for the U.S. Global Change Research Program’s (USGCRP) Fourth National Climate Assessment closed on January 31, 2018. The 477-page tome contains an estimated 118 distinct message points. With so many trees, it can be hard to see the forest. Fortunately, Cato Institute scientist Patrick Michaels spotlights the big picture. He identifies two methodological flaws that permeate the entire work, rendering the Fourth Assessment biased, misleading, and unscientific.
When meteorologists want to know which model to trust for forecasting the weather, they “look out of the window.” They compare predictions to observations and determine which model or mix of models provides the most reliable guidance. Rarely if ever do the average up every available model regardless of each model’s demonstrated forecasting skill (or lack thereof).
Yet that is typically how climate impact assessments are done. The USGCRP and Intergovernmental Panel on Climate Change (IPCC) run ensembles of numerous models regardless of their accuracy, develop ranges and averages of model-based temperature projections, and infer additional climate change impacts from those projections.
Since the vast majority of models project more warming than actually observed, the assessments always end up somewhere between dire and catastrophic. That generates headlines, fuels activism, and puts pressure on policy makers to suppress fossil fuels. However, the scary-sounding results are not scientific verities but artifacts of a ridiculous methodology.
The proper approach is to find models that accurately forecast changes in global temperature, and use only those to inform speculation about other potential climate change impacts. Turns out, only one model, known as INM-CM4, does not project more warming than has actually occurred at the surface and the bulk atmosphere. Since INM-CM4 is the only model that works, it should be the basic model for official climate change assessments.
The other key flaw is the USGCRP’s assumption that an “emissions concentration pathway” called RCP8.5 is a genuine business-as-usual scenario that reasonably projects how fast greenhouse gas emissions will accumulate in the atmosphere absent policies like the Clean Power Plan and Paris Climate Treaty. In fact, RCP8.5 projects higher emission levels by 2100 than about 90 percent of other baseline scenarios. The core problem can be summed up in two words: natural gas. Despite the fracking revolution, RCP8.5 projects a future in which coal grows more rapidly than gas as an electricity fuel.
If one assumes, as the International Energy Agency does, that natural gas is going to continue to replace large amounts of coal energy, 21st century warming predicted by INM-CM4 is approximately 1.5⁰C, a value so low that the social costs of carbon become the social benefits of lukewarming.
In summary, the USGCRP must hit the reset button now. It should use a methodology that works—i.e. a model that works—rather than a family of failures that tout a future of unwarranted gloom and doom. It would also be wise to rely more heavily on a concentration pathway that recognizes the massive worldwide switch from coal to natural gas for both electrical generation and manufacturing. That’s the right way, and the only way to produce a credible Assessment.