Climate models

News – Climate models overestimate the impact of carbon dioxide on temperature, study confirms

A new study shows that climate models consistently overestimate the warming effect of rising carbon dioxide concentrations on climate.

Researchers have long known that there are significant discrepancies between climate model projections, based on assumptions about the effect of anthropogenic greenhouse gas emissions on global temperatures, and actual climate observations. , but modellers and those who rely on them have not acted to correct problems with the models, the study says.

“[T]Models are heating up 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 at Huntsville, in the study.

Degree difference

The models’ assumptions about the climate’s response to the emission of additional greenhouse gases resulting from the burning of fossil fuels are at issue. The goal is to know the climate impact of the extra carbon dioxide we’ve added to the atmosphere, Christy writes.

In the early 1990s, most climate modellers developed models projecting a temperature increase of 0.35 degrees Celsius per decade.

Christy says he and his colleague Dick McNider, Ph.D. were skeptical of this screening. They did not trust 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 way temperatures were recorded. and discrepancies with the locations where they were recorded over time.

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

Confirms the previous conclusion

In 2017, Christy and McNider repeated the exercise, using 37.5 years of satellite measurements. After accounting for volcanic eruptions and the effects of El Niño, their latest projection was a warming of 0.095 degrees C per decade, almost exactly what they found in 1994.

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

Models still do not indicate warming

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

The Russian model assumes much lower sensitivity to carbon dioxide than other models, so its temperature projections at the end of the century are closer to those made by Christy and much lower than those made by other models. climatic.

“The rest of them [climate models] are already falsified and their predictions for 2100 are unreliable,” writes Christy.

That models do not accurately reflect actual temperature measurements has been known for years, Christy writes, citing a 2001 report from the National Academy of Sciences that states, “A more definitive reconciliation of temperature change modeling observed expects improvements in models used to simulate atmospheric responses to natural and human-induced forces.

Those improvements haven’t happened, says Christy, and the 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 gets worse over time, says David Wojick, Ph.D., senior science policy adviser at the Committee for a Constructive Future (CFACT).

“Unfortunately the new models are even hotter than the old ones, so the obvious flaws that 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 modified to match 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 question of whether models exaggerate the increase in the global mean temperature anomaly has been around for quite a long time,” Lindzen said. “The models are modified to reproduce this [actual temperatures] afterwards.

“It ignores the many other issues with the models, many of which are much 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 at CFACT.


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