Study Shows Anthropogenic Climate Change is Responsible for Large-Scale Heatwaves Across the World

A majority of people will be able to recall the previous summer, both in Switzerland and in huge swathes throughout the rest of Europe, and also in Asia and North America.

Withered meadow near Kaarst, Germany at the beginning of July: The 2018 heat wave lasted from May to July and covered large parts of the northern hemisphere.(image credit: Mimikry11, CC BY-SA 3.0,

Concurrent heatwaves would not have affected such a huge area without the climate change induced by human activity. This was the conclusion reached by ETH Zurich researchers based on model and observational data.

Globally, many places experienced so much heat that a number of people died of heatstroke, roads and rails began to melt, power generation had to be reduced, and forest areas started to burn. This heatwave not only impacted a single area like the Mediterranean region but also affected several other regions across the Arctic and the temperate zones at the same time, which was indeed sobering.

According to the conclusion reached by the ETH researchers, anthropogenic climate change was responsible for causing heatwave in many regions over a number of months. These are the results of the latest study that was presented at the European Geosciences Union press conference in Vienna by ETH climate researcher Martha Vogel. Vogel is a member of ETH Professor Sonia Seneviratne’s team. The paper ensuing from this latest study is being reviewed for an academic publication.

Analyzing models and observations

In the analysis, Vogel studied the regions of the Northern Hemisphere north of the 30th latitude that faced severe heat concurrently from May to July 2018. Along with her fellow researchers, Vogel focused on major agricultural areas and thickly populated regions. The team also looked into how heatwaves on a massive scale are estimated to change as a result of global warming.

In order to investigate these occurrences, the scientists examined observation-based data between 1958 and 2018, and they looked into sophisticated model simulations to estimate the geographic extent that heatwaves can possibly reach toward the century end if temperatures continue to soar.

Massive increase in the areas affected by intense heat

An assessment of the data taken from the previous year’s hot summer has shown that, on an average day between May and July, 22% of populated areas and agricultural land in the Northern Hemisphere were concurrently affected by very high temperatures. At least 17 countries, from the United States and Canada to Russia, South Korea, and Japan were hit by the heatwave.

When the researchers examined the measurement data, they came to know that such extreme heatwaves initially emerged in the northern hemisphere in 2010, subsequently in 2012, and again in 2018. However, before 2010, the researchers did not find any occurrences of such massive areas being concurrently affected by heat.

Widespread heat extremes ever more likely

This trend was confirmed by model calculations. As the planet becomes warmer, there are increased chances of widespread heat extremes. In fact, as per the model projections, each degree of global warming will cause the land area in major agricultural regions or thickly populated regions in the Northern Hemisphere that is concurrently hit by extreme heat to increase by 16%. If global temperatures increase to 1.5 °C above pre-industrial levels, then a summer as hot as the 2018 summer will be experienced in one-quarter of the northern hemisphere every two out of three years. Similarly, if global warming rises to 2 °C, the chances of such a period of large-scale heat increase to nearly 100%. Simply put, each year, severe heat will impact a region just as large as the 2018 heatwave did.

Without the 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. If in future more and more key agricultural regions and densely populated areas are affected by simultaneous heatwaves, this would have severe consequences.

Dr Martha Vogel, Climate Researcher, ETH Zurich.

Increased global temperatures (for example, 2 °C) will increase the probability of severe heat affecting an area as huge as it did in 2018 every year—a fact that is indeed alarming to Vogel.

Heat puts food security in jeopardy

If multiple countries are affected by such natural disasters at the same time, they have no way to help one another.

Dr Sonia Seneviratne, Professor, Department of Environmental Systems Science, ETH Zurich.

This was shown in 2018 by the forest fires that occurred in Sweden: during that time, a number of countries were able to assist with firefighting infrastructure, but if multiple countries are fighting extensive fires simultaneously, then they would not be able to help other affected countries.

Moreover, the food supply situation may become crucial—if huge swathes of areas critical to agriculture are hit by a heatwave, harvests could experience huge losses, causing food prices to increase phenomenally. For those who believe that these assumptions are highly pessimistic, then they should recall the heatwave that hit across Ukraine and Russia in 2010. Extreme heatwave forced Russia to stop all its wheat exports completely, which increased the cost of wheat on the international market. The price of wheat in Pakistan—one of the largest importers of Russian wheat—increased by as much as 16%. And when the Pakistani government cut food subsidies during the same period, poverty increased by 1.6%, revealed a report from an aid organization, Oxfam.

Such incidents cannot be resolved by individual countries acting on their own. Ultimately, extreme events affecting large areas of the planet could threaten the food supply elsewhere, even in Switzerland.

Dr Sonia Seneviratne, Professor, Department of Environmental Systems Science, ETH Zurich.

She also pointed out that if people don’t try harder, then climate change will never stabilize. Currently, individuals are on course for a temperature increase of 3 °C. The Paris Agreement targets for a maximum temperature of 1.5 °C.

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

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