Record-breaking climate events, such as Canada’s highest temperature on record being exceeded by almost 5°C last month, will be increasingly likely in the coming decades, suggests new research. It comes as the ability of climate models to predict such extremes has been called into question following a string of intense weather events around the world.
Erich Fischer at ETH Zurich, Switzerland, and his colleagues ran computer models to simulate the average maximum temperature of the hottest week of the year in parts of North America and Europe to see if they could yield temperatures that broke records by large margins. They could – under some emissions scenarios, records were smashed by more than a degree by 2030, not the 0.1°C or 0.2°C usually predicted.
The researchers conclude that the likelihood of such record-breaking events is largely down to the speed at which Earth is warming, not just the amount it has warmed, which is 1.1°C so far and continues to rise. “It’s really the rate of change,” says Fischer.
Geert Jan van Oldenborgh at the Royal Netherlands Meteorological Institute, who linked North America’s recent heatwave to climate change, says it is worrying that some statistical models indicated the region’s records were impossible. Such models have a theoretical distribution of extreme values, which gives an upper bound for temperatures in an area. That limit usually moves smoothly up in line with climate change.
“Then this heatwave came and it was way above the upper bound [for the region]. It’s rather surprising and shaking that our theoretical picture of how heatwaves behave was broken so roughly,” says van Oldenborgh.
The heatwave isn’t the only event that has rattled climate scientists of late. Germany has been hit by fatal floods while Henan in China has seen its heaviest rainfall in a millennium, with people killed in flooded subways. “It has shocked me,” says Tim Palmer at the University of Oxford.
So what of future events? At a broad level, climate models have done a good job of predicting large-scale shifts from climate change, says Peter Stott at the UK’s Met Office. “Not just the global average temperature rise, but the increase in extreme temperatures and rainfall. That’s been very clearly signalled, and is indeed what’s happening.”
However, older models weren’t capturing the intensity of some regional extremes like those seen in Canada, says Stott. The good news, he says, is that some new climate models have a higher level of spatial detail more akin to weather models, down to a grid of boxes 2 kilometres across, which will be better at predicting local extremes. Modellers are also getting better at understanding the processes behind short but intense rainfall, like that seen in Germany and China.
However, the higher resolution required for some models generally needs more computing power – and resolution isn’t the only issue for projecting extremes: another significant one is timescales. Much climate modelling works on centennial timescales, but some scientists have now turned to decadal predictions, which could roughly be described as weather forecasts spun out to predict the next few years. These have already been shown to predict Atlantic hurricanes.
“There’s definitely a move towards these decadal predictions. They are not for predicting what climate change will do, but what climate change is doing now,” says Ted Shepherd at the University of Reading, UK.
While many modellers say greater computing power alone isn’t a silver bullet for projecting extremes, it should help. One example is the computing needed to yield numbers from the complex calculations of the Navier-Stokes equations, which can be used to model motion in the atmosphere.
More processing power would give more accurate figures, says Palmer. “It does basically come down to computing.” He has called for a “CERN for climate change”, a supercomputing project he believes could be run for about €200 million a year. That hasn’t yet come to pass, but there are initiatives afoot that could help climate models, such as an EU-backed project to build a “digital twin” of Earth.
And it is worth remembering climate models are always improving, says Tim Osborn at the University of East Anglia, UK. He says it is possible that models can’t simulate records like those for North America’s heat because they are failing to pick up a complex combination of processes, such as an interaction between clear skies, low soil moisture and wind direction, but the truth is we simply don’t know yet.
Better climate models will be vital for adapting to climate change and informing early warning systems to avoid deaths. But it isn’t as though we need them to act on mitigating the cause of climate change: humanity’s greenhouse gas emissions. “I don’t think it’s the models,” says Shepherd. “I think people are not just taking action on climate change for other reasons. They put their head in the sand. It’s hard to imagine things that haven’t happened.”
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