Climate Models Overstate Temperature Impact of Carbon Dioxide, Study Confirms

Published July 4, 2019

A new study demonstrates climate models consistently overstate the warming effect of increasing carbon dioxide concentrations on climate.

Researchers have long known there were significant discrepancies between the projections of climate models, based on assumptions about the effect of manmade emissions of greenhouse gases on global temperatures, when compared to actual climatological observations, yet modelers and those who rely on them have not acted to correct the problems with the models, the study states.

“[T]he models are warming too fast,” writes John Christy, Ph.D., director of the Earth System Science Center and distinguished professor of atmospheric sciences and Alabama State Climatologist at the University of Alabama in Huntsville, in the study.

Difference of Degrees

At issue are the models’ assumptions about the climate’s response to the emission of extra greenhouse gases as a result of combustion of fossil fuels. The goal is to know the impact on the climate of the extra carbon dioxide we have added to the atmosphere, Christy writes.

In the early 1990s, most climate modelers developed models projecting a 0.35 degree Celsius rise in temperature per decade.

Christy says he and colleague Dick McNider, Ph.D. were skeptical about that projection. They didn’t trust the surface temperature databases because there were no measurements for much of the Earth and because the measurements that had been taken had serious inconsistencies in the ways temperatures were recorded and discrepancies with the locations where they were recorded over time.

Using satellite readings, available since 1979, and after factoring in variables such as volcanic eruptions, in 1994 Christy and McNider projected the amount of carbon dioxide being added to the atmosphere should cause the Earth to warm, on average, by about 0.09 degrees Celsius per decade. That’s about one-quarter of the level projected by prevailing models used by the Intergovernmental Panel on Climate Change (IPCC) and government agencies such as NASA.

Confirms Earlier Conclusion

In 2017, Christy and McNider repeated the exercise, using 37 and a half years of satellite measurements. After allowing for volcanic eruptions and the effects of El Niño, their latest projection was a warming of 0.095 degree C per decade, almost exactly what they had found in 1994.

“The warming trend we found suggests that we are having a relatively minor impact on global temperatures,” Christy writes.

Models Still Misstate Warming

With the notable exception of a Russian model, almost all climate models still overstate carbon dioxide-induced warming, Christy says.

The Russian model assumes a much lower sensitivity to carbon dioxide than other models, with the result being its end-of-the-century temperature projections are closer to those made by Christy and much lower than those made by other climate models.

“The rest of them [climate models] are already falsified and their predictions for 2100 cannot be trusted,” writes Christy.

That models do not accurately reflect real-world temperature measurements has been known for years, Christy writes, citing a 2001 report by the National Academy of Sciences which states, “A more definitive reconciliation of modeling observed temperature changes awaits improvements of the models used to simulate the atmospheric responses to the natural and human induced forces.”

Those improvements have not taken place, Christy says, and IPCC has gone to extraordinary lengths to avoid drawing attention to the problem.

‘No Appetite for Correction’

The difference between actual temperatures and model projections is actually getting worse over time, says David Wojick, Ph.D., a senior science policy advisor with the Committee for a Constructive Tomorrow (CFACT).

“Unfortunately, the new models are even hotter than the old ones, so the clear failings Christy has—thankfully—identified are increasing, not decreasing,” Wojick said. “The modeling community has no appetite for correction.”

Because climate models have many weaknesses, they are constantly tweaked to correspond to actual temperatures, says Richard Lindzen, Ph.D., professor emeritus in the Department of Earth, Atmospheric, and Planetary Sciences at the Massachusetts Institute of Technology.

“The issue of whether the models are exaggerating the increase in global mean temperature anomaly has been around for quite a long while,” Lindzen said. “Models are modified to replicate this [actual temperatures] after the fact.

“This ignores the numerous other problems with the models—many of them far more relevant to practical projections,” Lindzen said.

Bonner R. Cohen, Ph.D. ([email protected]) is a senior fellow at the National Center for Public Policy Research and a senior policy analyst with CFACT.


John Christy, “The Tropical Skies: Falsifying Climate Alarm,” Global Warming Policy Forum, May 23, 2019: