Climate models

Stop using ‘too hot’ climate models, says Nature commentary

Too many climate researchers make unrealistic projections about the future consequences of human-induced climate change based on computer models that run too hotargues a new comment in Nature.

The authors of the commentary point out that the overheated models reported in the sixth phase of the Coupled Model Intercomparison Project (CMIP6) failed to reproduce historical climate trends, thus casting considerable doubt on their projections of an increase in temperature. more catastrophic temperature. Therefore, the researchers note that the old practice of “just taking an average” of all the models together leads to higher warming projections than warranted.

The Sixth Assessment Report (AR6) of the United Nations Intergovernmental Panel on Climate Change took this into account when evaluating the model results and lowered the projected temperatures from 0.2 to 0, 7 degrees Celsius for each greenhouse gas emissions scenario used in its AR6 analyses. “Results that show predicted climate change will be ‘worse than we thought’ are often attributable to warm CMIP6 models,” observe the commentary’s authors. The authors urge other researchers to avoid the mistake of simply averaging climate model results as they seek to identify how climate change will affect future global and regional temperatures, precipitation, sea levels, ecologies and the heat content of the oceans.

In addition to the model too hot problem, there is the extensive and common use of the highly implausible worst case Greenhouse gas emissions RCP/SSP5-8.5 scenario as a basis for making future climate projections. Other problems with this scenario include the fact that it assumes a six-fold increase in global coal consumption per capita by 2100. While coal use has seen a post-pandemic rebound, most analyzes expect a flattening of global consumption followed by a slump beginning later that decade.

The effects of this dubious combination – too hot models and unrealistic emissions scenarios – can be seen in the study”Avoid mass extinction of the oceans due to global warming,” Posted in Science Last week. Based on this study, The New York Times warned“Under the high emissions scenario that scientists have modelled, in which pollution from burning fossil fuels continues to rise, warming would lead to a loss of ocean species by 2300, comparable to the five extinctions. of Earth’s past. The last of these wiped out the dinosaurs.”

The two Princeton University researchers behind the ocean study compared their projections to the Permian extinction event that happened about 250 million years ago and killed more than 80% of marine species.

It turns out that the massive marine extinction projected by the researchers 300 years from now stems from their use of “intermodel means” that the Nature the comment warns of the implausibly high RCP/SSP5-8.5 emissions scenario. In this scenario, average global temperatures would increase by about 5 degrees Celsius by the end of this century and by 18 degrees Celsius by 2300. Considering that the difference between today and the the last ice age is 6 degrees Chumanity would have bigger problems than marine extinctions if temperatures rose to 18 degrees Celsius.

To be fair, the two Princeton researchers also sketched out a scenario in which an increase in global temperatures of about 2 degrees Celsius above the pre-industrial average led to the extinction of only about 4% of marine species due to of climate change by the end of this century. . The good news is that recent research suggests that, based on more likely greenhouse gas emissions trajectories, future human-induced warming is expected to match this scenario and increase by around 2 degrees C above the pre-industrial average by the end of this century.

Interestingly, the accompanying comment “A bleak future for marine life” in Science noted, “Fortunately, greenhouse gas emissions are not on the right track for the worst-case scenario given policies aimed at limiting greenhouse gas emissions and the slower-than-expected growth of global economies.”Marine animals face mass extinction due to climate change.”

Hopefully more climate change researchers will take the warnings to avoid inflated model projections and implausible emissions scenarios to heart. Overstating the real problem of human-caused climate change is not helpful in guiding the public and policy makers in their efforts to mitigate and adapt to rising global temperatures.