A Test of the Tropical 200‐ to 300‐hPa Warming Rate in Climate Models

Abstract

Overall climate sensitivity to CO2 doubling in a general circulation model results from a complex system of parameterizations in combination with the underlying model structure. We refer to this as the model's major hypothesis, and we assume it to be testable. We explain four criteria that a valid test should meet: measurability, specificity, independence, and uniqueness. We argue that temperature change in the tropical 200‐ to 300‐hPa layer meets these criteria. Comparing modeled to observed trends over the past 60 years using a persistence‐robust variance estimator shows that all models warm more rapidly than observations and in the majority of individual cases the discrepancy is statistically significant. We argue that this provides informative evidence against the major hypothesis in most current climate models.

Climate sensitivity, agricultural productivity and the social cost of carbon in FUND

“…The methodology of Christy and McNider (2017) provides an independent and model-free check on this approach. Also, while climate models with high ECS values can be made to fit the surface warming trend, they have shown demonstrably excess warming elsewhere, especially in the troposphere over the tropics (Fu et al 2011;McKitrick and Christy 2018). We therefore believe that the LC18 results in Table 2 are more credible than the ones conditioned on the Roe-Baker distribution.…”

Global Climate

“…When examining the time series of these three methods (radiosondes, satellites, reanalyses), the radiosondes display an increasing trend over the past 10 years relative to the other methods (see trend values in column Global LTT 1979 and Fig. A2.7) This may be related to a change in software installed after 2009 in many stations to improve the tropospheric humidity and temperature values (Christy et al 2018).…”

“…The median TTT trends from the available datasets since 1958 and 1979 are both +0.16°C decade -1 with ranges of +0.15 to +0.19 and +0.13 to +0.23°C decade -1 , respectively (Table A2.1). This layer in the tropics is a key area of interest due to its expected significant response to forcing, including that of increasing greenhouse gas concentrations (McKitrick and Christy 2018;see Fig. A2.8).…”

Climate change and agriculture

“…There is a great deal of uncertainty concerning climate change (Nordhaus 2013;van Kooten 2013;Tol 2014) regarding (1) the contribution to global warming of human activities (e.g., burning of fossil fuels, land-use changes) versus that of natural factors (e.g., CO2 release from oceans, changes in the sun's activities) (de Maurellis 2004, 2006;Michaels 2004, 2007; McKitrick and Nierenberg 2011); (2) the projected increase/decrease in average global temperatures (Hourdin et al 2017;Millar et al 2017; Lewis and Curry 2018;McKitrick and Christy 2018); and (3) the regional changes in climate that might be expected (Lomborg 2007;Pielke 2018a). The conclusions to be drawn from trends of past temperatures are controversial, as are the associated climate models, especially in projecting future temperatures and precipitation.…”

“…3 Scientists use the emission scenarios in computer models that then project increases in future global temperatures. When the outcomes of climate models are tested against observed data, however, they perform rather poorly -temperature predictions from climate models have been consistently too high (Santer et al 2017;McKitrick and Christy 2018). Nor are climate models calibrated to real-world data in any comprehensive fashion (Levitt and Dubner 2009, pp.177-186;Hourdin et al 2017).…”