Climate models have accurately predicted global heating for the past 50 years, a study by climate scientists from the University of California, Berkeley, the Massachusetts Institute of Technology and NASA has found.
The study found that computer models dating back to 1970, which were used to simulate what heat-trapping gases will do to global temperatures, were reliable in forecasting the physical response of the climate system to continued increases in the greenhouse effect.
Zeke Hausfather, lead author of the study which was published in the journal Geophysical Research Letters Wednesday, considered 17 models used between 1970 and 2007 and found that the majority of them predicted results that were "indistinguishable from what actually occurred."
Recent climate model projections have found that even if countries follow through with current and anticipated climate policies, the world is still on track to reach about 3C above pre-industrial figures by 2100, a situation the UN’s intergovernmental panel on climate change has warned against.
Dr Hausfather decided to evaluate the models’ accuracy after years of hearing critics voice scepticism about them. “Climate models are a really important way for us to understand how the climate could change in the future, and now that we have taken a detailed look at how well past climate models have held up in terms of their projections, we are far more confident that our current generation of models are getting it right,” he said.
Carbon Dioxide levels in the last 20yrs
Ten of the 17 the models the team examined came close to the temperatures that actually occurred, Dr Hausfather said. However the input scenarios in nearly half of those examined was significantly different from the real-life greenhouse gas emissions that occurred.
But scientists actually got the physics right in the majority of the models, Dr Hausfather added.
Creating models to forecast changes in the climate is so difficult because it relies on two main assumption of what will happen in the future – one is the physics of the atmosphere and how it reacts to heat-trapping gases, the other is the amount of greenhouse gases emitted.
“We did not focus on how well their crystal ball predicted future emissions of greenhouse gases, because that is a question for economists and energy modelers, not climate scientists,” Dr Hausfather said. “It is impossible to know exactly what human emissions will be in the future. Physics we can understand, it is a deterministic system; future emissions depend on human systems, which are not necessarily deterministic.”
So Dr Hausfather and his colleagues, including NASA climate scientist Gavin Schmidt, also looked at how well the models did on just the pure science, taking out the emissions factor.
On that count, 14 of the 17 computer models accurately predicted the future.
The scientists also gave each computer simulation a "skill score" that essentially gave a percentage grade to each one. The average grade was a 69 per cent.
University of Illinois climate scientist Donald Wuebbles, who was not part of the study, said climate change "deniers do a lot of weird things to misrepresent models. None of those analyses have been valid and they should be ignored. We should no longer be debating the basic science of climate change."
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