New research indicates we should pay more attention to climate patterns that point to a warmer future and reject projections that indicate less warming.
The results, published on Wednesday in the review Naturesuggest that policymakers and international authorities rely on projections that underestimate global warming and, by extension, underestimate the reductions in greenhouse gas emissions needed to avoid the catastrophic effects of climate change climatic.
“The basic idea is that we have a range of future warming projections that come from these climate models, and for scientific interest and policy interest, we wanted to narrow that range,” said Patrick Brown, co. – author of the study. “We find that the models that do the best at simulating the recent past project more warming.”
Using this small group of models, the study found that if countries remain on a high emissions trajectory, there is a 93% chance that the planet will warm by more than 4 degrees Celsius by the end of the century. Previous studies put the odds at 62%.
Four degrees of warming would cause many severe impacts, drowning small islands, wiping out coral reefs and creating prolonged heat waves around the world, scientists say.
In the worst-case scenario, the study finds that global temperatures could rise 15% more than predicted by the Intergovernmental Panel on Climate Change (IPCC) – about half a degree Celsius more – in during the same period.
In the world of climate modeling, researchers rely on around 30 leading models to understand how the planet will warm in the future. These models say the planet will get warmer, but they vary in their projections of how much. The IPCC places the upper range of warming between 3.2 and 5.9 degrees Celsius by 2100 relative to pre-industrial levels by essentially weighing each model equally.
These discrepancies have long been the target of climate change deniers and haters of carbon regulation who say they mean the models are unreliable or inaccurate.
But Brown and his co-author, eminent climatologist Ken Caldeira, both of the Carnegie Institution for Science, wanted to see if there was a way to reduce uncertainty by determining which models were the best. To do this, they looked at how models predict recent weather conditions and compared them to what actually happened.
“The IPCC uses a model of democracy – one model, one vote – and that’s what they say, that’s the range,” Brown explained. “We say we can do better. We can try to distinguish between high-performing and low-performing models. We reduce the range of uncertainty.
“You’ll hear arguments before Congress: the models all predict warming, but they don’t do well at simulating the past,” he said. “But if you take the best models, they are the ones projecting the most warming into the future.”