"Africa is one of the most vulnerable continents to climate change and the projected increase in heat waves can have severe consequences for the people living there," Simone Russo of the Institute for Environmental Protection and Research (ISPRA) told environmentalresearchweb. "Results show that across all seasons the percentage of African land area in heatwave has increased in recent years [compared to] the last two decades of the 20th century."

Russo and colleagues from the Institute for Environmental Protection and Research (ISPRA) in Italy, the University of Catania, Italy, and the Center for International Climate and Environmental Research (CICERO) in Norway found that by 2040 half their models simulated an unusual heatwave on a seasonal basis. By 2075, according to all the models, extreme heat waves "will become the ‘new normal’, occurring every season (four times per year)".

Earlier this year, Seneviratne et al showed that changes in regional extreme temperatures are likely to be greater than changes in the associated global mean.

"This can also be seen in our African heat wave study, where it is shown that extreme heat waves can be expected to occur much more frequently even under a modest increase in global average temperature (i.e. 2° temperature increase compared to current climate)," said Russo. "This means that the probability for regional extreme events such as heat waves will increase and could have severe impacts even if the COP21 (Paris agreement 2015) ambitions to limit the average rise in global temperatures well below 2°C are realized."

Russo believes we need a much better understanding of the consequences of 2° global warming for specific regions. "A 1.5 or 2 ° target is therefore not too ambitious, but may be able to prevent the worst," he said. "Even with ambitious mitigation action, we also need to put considerable effort in climate change adaptation to reduce the risk of increased probability in regional extreme events, such as heat waves, and strengthen resilience." That will need a better understanding of risk as a function of physical hazards and the exposure and vulnerability of the affected people, which varies substantially by region.

The researchers used the heat wave magnitude index daily (HWMId) metric in their models as it can compare heatwaves in different locations and seasons. "As an example, the most extreme African heat wave detected in our historical record in the Austral summer 2009–2010 was comparable in spatial extent and magnitude with the event in Russia in the boreal summer of 2010," said Russo.

There is a limitation to HWMId, however. As it’s based on temperature values, it only compares the physical aspect of heat waves. But heat waves occuring in regions with different climates – Finland, rather than Spain, for example – are likely to affect human mortality and crop growth differently, depending on the vulnerability of the people and environment.

"The heat wave in Finland in 1972 (see Russo et al 2015) was comparable in magnitude and spatial extent with that in Central Europe in 2003, however, the latter killed many more people than the Finland heat wave," said Russo.

Previously, Russo and colleagues have classified extreme heat waves in Europe and projected their future. "Differently from our previous study, here, the HWMId is used at seasonal scale in order to take into account the climatology of the Africa continent spanning between the two tropics," he said.

Now, the team, who reported the findings in Environmental Research Letters (ERL), is studying the impact of heat waves on human mortality and crop production.

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