Earlier this week, University of Alabama in Huntsville (UAH) atmospheric scientist John Christy testified at a House Science Committee hearing on the Paris climate treaty. Christy’s testimony covers several important topics including the “low effectiveness” of surface temperature records for detecting anthropogenic global warming, the “curious” procedure NOAA scientist Tom Karl used in his “pause-busting” adjustment of sea-surface temperatures, the “tiny” impact the Paris Agreement is likely to have on global temperatures, and the insufficient empirical basis for claims that climate conditions are worsening.
Today’s post focuses on Christy’s rebuttal of a Yale Climate Connections video designed to discredit satellite data as a reality check on the models used by the UN Intergovernmental Panel on Climate Change (IPCC) to forecast global warming and the associated climate impacts.
What’s got the climate establishment in a tizzy is a chart–Figure 1 in Christy’s testimony–that shows a growing divergence between model predictions and observed temperatures in the mid-troposphere (the layer of air from the surface up to 50,000 feet).
Figure 1: Five-year averaged values of annual mean (1979-2015) global bulk (termed “mid-tropospheric” or “MT”) temperature as depicted by the average of 102 IPCC CMIP5 climate models (red), the average of 3 satellite datasets (green – UAH, RSS, NOAA) and 4 balloon datasets (blue, NOAA, UKMet, RICH, RAOBCORE)
Mid-troposphere (MT) data are a valid test of the models’ accuracy because the MT “overlaps with the region of the tropical atmosphere that has the largest anticipated signature of the greenhouse response by bulk mass – between 20,000 and 50,000 feet.”
Christy notes that in science, the test of whether we understand a natural system is whether we are able to predict its behavior. Thus, “If we are unable to make accurate predictions, then at least some of the factors in the system are not well defined or perhaps even missing.” Hind-casting is no substitute for prediction, because complex hypotheses such as climate models can be adjusted to produce results similar to what has already occurred. Yet Figure 1 shows that the models do not “even reproduce the past climate.”
Indeed, the models “clearly overcook the atmosphere,” overshooting observed warming in the MT by 250%. “The issue for congress here is that such demonstrably deficient model projections are being used to make policy.”
The remainder of this post excerpts Christy’s defense of the satellite data and summarizes his rebuttal of a common criticism of Figure 1.