Extreme heat is growing threat to harvests

By Tim Radford | 17 April 2019
Climate News Network

Parched crops will become a commoner sight as the heat rises. (Photo by Irina Iriser on Unsplash)

A warmer world means more chance of extreme heat in more than one continent at the same time, and a rising threat to global food security.

Ever-higher average global temperatures mean more intense extreme heat over ever-wider regions.

When the planet becomes on average 1.5°C warmer than it was for most of human history, then for two out of every three years, one-fourth of the northern hemisphere will experience the kind of blistering heat waves recorded in 2018.

And should planetary average temperatures creep up by 2°C – the maximum proposed by 195 nations at the global climate conference in Paris in 2015 – then the probability rises to 100%. That is, extreme heat over a large area of the hemisphere will be guaranteed every summer.

Heat extremes are all too often accompanied by devastating thunderstorms or extended drought and massive outbreaks of wildfire, with potentially disastrous consequences for harvests in the blighted regions.

In 2018, people died of heatstroke, roads and even rails started to melt, forests went up in flames, and power generation systems sometimes failed, not just in one region but in a number in the temperate zones and the Arctic at the same time.

Between May and July, 22% of agricultural land and crowded cities of the northern half of the globe were hit simultaneously by extended periods of extreme heat. In all, 17 countries were affected, from Canada and the US across the Atlantic and Pacific to Russia, Japan and South Korea. In Europe, temperatures in the rivers Rhine and Elbe reached such heights that fish suffocated; there were wildfires in Sweden, Latvia and Greece and record temperatures in Germany.

“Without climate change that can be explained by human activity, we wouldn’t have such a large area being simultaneously affected by heat as we did in 2018,” said Martha Vogel, of the Swiss Federal Institute of Technology, known as ETH Zurich, who presented her findings at a press conference held by the European Geosciences Union in Vienna.

Serious impacts

The reasoning and methodology have yet to be published, but the authors say their paper is in review for the journal Earth’s Future. “If in future more and more key agricultural regions and densely populated areas are affected by simultaneous heatwaves, this would have severe consequences.”

Other research teams have already warned that global warming could bring a repeat of the simultaneous drought and heat outbreaks across the world that triggered calamitous famines in Asia and Africa between 1875 and 1878.

They have repeatedly warned of potentially catastrophic levels of heat that could arrive with increasing frequency to claim greater numbers of lives especially when accompanied by extreme levels of humidity.

The Swiss scientists focussed on data from agricultural regions and busy urban areas above latitude 30° for the years 1958 to 2018 to find occasions of heat extremes in more than one region and then used computer modelling to simulate probabilities as average planetary temperatures continued to grow.

Poor are hardest-hit

The choice of agricultural areas was purposeful: in such scenarios where more than one region suffers harvest failures, food prices begin to soar. In the 2010 heatwave, Russia ended all its wheat exports and prices in Pakistan rose by 16%, with harsh consequences for the poorest. Governments, agriculture ministries and international aid agencies need to be prepared.

“Such incidents cannot be resolved by individual countries acting on their own. Ultimately, extreme events affecting large areas of the planet could threaten food supply elsewhere, even in Switzerland,” said Sonia Seneviratne, an ETH climate scientist who has also shared in the study.

“We are already clearly feeling the effects just from the one degree that global average temperature has risen since the pre-industrial era.”

Tim Radford, a founding editor of Climate News Network, worked for The Guardian for 32 years, for most of that time as science editor. He has been covering climate change since 1988.

Climate change: How half a degree could change the world forever | BBC Ideas

How climate change is making food insecurity worse

David Attenborough’s Witness Statement (A Life on Our Planet)

World Scientists’ Warning of a Climate Emergency

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