News and Commentary

Climate Scientists: Climate Models Have Overestimated Global Warming

A new report published by a team of prominent climate scientists confirms what many skeptics have pointed out for years: the climate models have overestimated the amount of global warming and failed to predict what climatologists call the warming “hiatus,” over 20 years of almost no change in temperatures.

The report, published in the journal Nature Geoscience on September 18, acknowledges that most of the models of warming trends failed to predict the “slowdown” in warming post-2000, resulting in less pronounced warming than predicted and thus more room in the CO2 “emissions budget” for the coming decades. The report in part intends to “reset” the estimations for the new predictions on when the earth will hit what the U.N. has determined to be dangerous warming levels.

The team of climate scientists notes that in failing to predict the warming “hiatus” in the beginning of the 21st century, the Intergovernmental Panel on Climate Change (IPCC) models overestimated temperature increases, consequently setting key benchmarks for warming earlier than they need to be, given the actual numbers.

“The models end up with a warming which is larger than the observed warming for the current emissions,” University of Exerter’s Pierre Friedlingstein, one of the study’s authors, told The Washington Post. “So, therefore, they derive a budget which is much lower,” he added.

Another co-author, the International Institute for Applied Systems Analysis’ Joeir Rogelj, explained to the Post that the models used by the IPCC have made two mistakes: “slightly overestimat[ing] historical warming” and “underestimat[ing] compatible historical CO2 emissions”

“These two small discrepancies accumulate over time and lead to an slight underestimation of the remaining carbon budget,” said Rogelj. The new study, he said, attempts to “reset the uncertainties, starting from where we are today.”

The report follows a study by another team of climate scientists published in June 2017 that likewise determined that the actual increases in warming post-2000 was “generally smaller than trends estimated” from the models. Here’s the abstract of the study:

In the early twenty-first century, satellite-derived tropospheric warming trends were generally smaller than trends estimated from a large multi-model ensemble. Because observations and coupled model simulations do not have the same phasing of natural internal variability, such decadal differences in simulated and observed warming rates invariably occur. Here we analyse global-mean tropospheric temperatures from satellites and climate model simulations to examine whether warming rate differences over the satellite era can be explained by internal climate variability alone. We find that in the last two decades of the twentieth century, differences between modelled and observed tropospheric temperature trends are broadly consistent with internal variability. Over most of the early twenty-first century, however, model tropospheric warming is substantially larger than observed; warming rate differences are generally outside the range of trends arising from internal variability. The probability that multi-decadal internal variability fully explains the asymmetry between the late twentieth and early twenty-first century results is low (between zero and about 9%). It is also unlikely that this asymmetry is due to the combined effects of internal variability and a model error in climate sensitivity. We conclude that model overestimation of tropospheric warming in the early twenty-first century is partly due to systematic deficiencies in some of the post-2000 external forcings used in the model simulations.

The Daily Caller notes a few other reports by climate scientists in the last few years that have likewise underscored the climate models’ overestimation of warming, with one determining that the models have predicted 2.5 times more warming than has actually been observed:

Cato Institute scientists Patrick Michaels and Chip Knappenberger have noted the climate models have been over-hyping warming for decades. Scientist John Christy of the University of Alabama-Huntsville has testified before Congress on the matter.

Christy’s research has shown climate models show 2.5 times more warming in the bulk atmosphere than has been observed.

[The] author and atmospheric scientist Ryan Maue wrote about the new “consensus” on global warming in the wake of a June study by prominent climate scientists.

That study found “satellite-derived tropospheric warming trends were generally smaller than trends estimated from a large multi-model ensemble.”

Read the full report here.