Heat wave spread can be curbed with carbon cuts
Heat waves will become increasingly widespread and severe as the planet warms, a new study warns.
By 2040, exceptionally warm summer months will become commonplace for a fifth of the world, it says, with potentially serious effects for humans and the environment.
But how much heatwaves affect the planet after 2040 depends on whether greenhouse gas emissions can be aggressively curbed. Without carbon cuts, heat waves will continue to become more severe and widespread, the study says.
More heatwaves
One consequence of a warming planet is that heatwaves will become a more common. In the last decade alone there have been a number of record breaking heat waves. Some of them, like the European heatwave of 2003, have been made more likely by climate change.
The new research suggests that in the future more of the earth’s surface will be affected by heatwaves as temperatures continue to rise. To reach that conclusion, the scientists used climate models to look at how much of the world would experience exceptionally warm summer months, which are a useful proxy for the concept of a heatwave. Long-lasting heat waves, which are well captured by this measurement, are the ones which have the greatest impact on society too, making them important to study.
Professor Stefan Rahmstorf, a climate scientist who also works on temperature extremes, explained to us that it’s this focus on monthly temperatures which allows a consideration of how heatwave patterns are likely to change:
“Using monthly data is the right time scale when discussing heat waves, because heat that lasts for several weeks typically has the largest impacts in terms of human mortality or harvest losses – heat that lasts only a few days tends to have very little impact.”
Based on the modelling, the researchers were able to predict how much of the earth’s surface would would be affected by exceptionally high temperatures or heatwaves in the future as a result of global warming.
As there’s uncertainty over how much and how quickly earth will warm, the scientists modelled two scenarios – one where temperature rise was kept to two degrees Celsius by 2100 and one where temperatures rose five degrees above pre-industrial levels.
Extreme heat
Whichever scenario is used, heatwaves are projected to affect a much bigger area of the earth’s surface in the coming decades. By 2020, 10 per cent of land areas worldwide will be affected by heatwaves in summer months. By 2040, that figure will rise to 20 per cent.
Earth might also start to see very severe heatwaves which are almost absent at the moment, but by 2040 could affect three per cent of land areas worldwide.
But what happens from mid-century onwards depends on whether humans can curb their emissions, the modelling suggests. If emissions cuts halt the rise of greenhouse gases, heat waves are unlikely to become much more severe or widespread from 2040 onwards.
However, if emissions continue to rise unabated heatwaves could affect 85 per cent of land areas worldwide by the end of the century, and very severe heatwaves could affect up to 60 per cent of the world’s continents, the modelling suggests.
Who’s worst hit?
Summer temperatures fluctuate less in some parts of the world than others. This means that even modest rises in global temperatures will be enough to shift some regions beyond their normal temperature range, making extreme summer heat more common.
In the tropics for example, where temperatures don’t vary much, unusually hot conditions are expected to become the new norm by the end of the century and super-extreme heat waves become commonplace, whatever happens to emissions this century.
In places like Europe which have much bigger natural fluctuations in temperature, heatwaves will still be more widespread in the future, but the modelling suggests that after 2040 they don’t get much more common. Very severe heatwaves remain virtually absent – as they are today.
The impact of heatwaves on human society is also a lot about how well societies can adapt. Lead author, Dim Coumou, explained that the consequences of heat waves are often devastating:
“Heat extremes can be very damaging to society and ecosystems, often causing heat-related deaths, forest fires or losses to agricultural production.”
Some parts of the world may be able to adapt to impacts resulting from increasingly severe and widespread heat extremes, but others won’t.
Hotter, more often
Whatever happens to emissions in the next few years, this modelling suggests heat extremes will become more widespread in the first half of the 21st century. What happens then to some extent depends on whether we cut emissions now.
Met Office scientists we spoke to said the results of this study are consistent with scientific literature on this topic which points out that temperature extremes are expected to become more intense and frequent under climate change.
Coumou, D. & Robinson, A. (2013) Historic and Future Increase in the Frequency of Monthly Heat Extremes. Environmental Research Letters. DOI:10.1088/1748-9326/8/3/034018