The projection of global heating by climate models was accurate for the past 50 years, a study has found.
Since as early as 1970, fundamental understanding of the Earth’s climate system and the ability to project its response to continued increases in the greenhouse effect has been solid in climate scientists, the findings confirm. So far, climate models have accurately anticipated global temperature changes; therefore, we can easily rely on their projections of future warming as well.
The accuracy of 17 models that were published over the past 50 years examined in the study. Beginning with a 1970 study, it included 1981 and 1988 models led by James Hansen. James was the former NASA climatologist, who testified to the US Senate in 1988 about the anthropogenic global heating impacts. The first 4 reports by the UN’s Intergovernmental Panel on Climate Change (IPCC) were also included in the study.
“We found that climate models – even those published back in the 1970s – did remarkably well, with 14 out of the 17 model projections indistinguishable from what actually occurred,” said Zeke Hausfather, of the University of California, Berkeley, and lead author of the paper, published in the journal Geophysical Research Letters.
As per the current climate model projections, the planet is on track for about 3C of warming above pre-industrial temperatures by 2100 if nations go by the current climate policies and pledges. The situation would be catastrophic as the IPCC and others predict.
The challenge in the evaluation of climate model accuracy is that simulations are only run for a few specific scenarios of future greenhouse gas emissions due to limitations in computing power. Even if there are an infinite number of such possible scenarios, real-world emissions will follow only one path, which will never precisely match the few scenarios input into climate models. Therefore in case, Earth warms less than in a climate model projection, it is not that the model was inaccurate.
It is not the job of climate scientists to predict human fossil fuel consumption, but they can attempt to accurately simulate how the climate will change with a given rise in greenhouse gas emissions.
“Future emissions depend on human behaviour, not physical systems, and climate models should be evaluated on their physics rather than the future emission projections,” said Hausfather.
In around half of the model projections that were examined in the paper, the input scenarios were importantly different from the real-world changes in greenhouse gas emissions. This is why, in 10 out of the 17 models projected, temperature changes were only consistent with observed global warming. While four models found to project more warming, three of them projected less than that subsequently occurred.
However, the inconsistencies have been addressed by the study authors by evaluating the change in temperature for every change in “radiative forcing,” which is the global energy imbalance caused by the increased greenhouse effect and other factors in models against what happened in the real world. Whether the climate models are producing the temperature response accurately to a given emission change means if these are accurately simulating the physical response of Earth’s climate system, this metric reveals. With this factored in, 14 models were found accurate out of the 17.
“The rate of warming we are experiencing today is pretty much exactly what past climate models projected it would be,” said Hausfather.
The credibility of climate models is undermined by the people who oppose policies for limiting the impacts of global heating. In case the model projections are considered unreliable, they argue, that we do not know how urgent slowing global warming is. The result is, “climate models are unreliable” has become a popular myth propagated by climate deniers.
The most recent study adds to the body of evidence supporting the accuracy of climate models. Those who are arguing for the requirement of more aggressive climate policies to avoid dangerous levels of global warming welcomed it. The UN climate summit in Glasgow in 2020 will play a crucial role where countries will be expected to commit to scaling up the reductions in emissions that were pledged in the 2015 Paris agreement on climate change.
