Stayin' alive: heatwave makes searing case for 1.5°C

Date
15 August 2018

Written by
Claire Fyson, Fahad Saeed, Robert Brecha, Peter Pfleiderer, Quentin Lejeune, Carl-Friedrich Schleussner

This year’s extreme summer, still scorching central and northern Europe, is a stark illustration of the kind of climate change impacts we could see if nothing is done to reduce greenhouse gas emissions. Heat waves, droughts and other extremes will only increase in severity and frequency as the Earth continues to warm. Limiting warming to 1.5°C, as governments around the world pledged by signing the Paris Agreement, can help avoid the worst impacts of climate change.

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Unprecedented high temperatures during the 2018 heatwave have caught hundreds of millions of people in the northern hemisphere off-guard. Tragic stories from the Japanese and Canadian heat waves, which resulted in the death of over 100 individuals were not over when Europe came into the grip of some of the most extreme temperatures in its history.

The countries affected are some of the richest in the world, with the highest capacities to adapt. However, the intensity of the heat wave was so high that in UK alone it has resulted in the death of over 600 individuals, and still counting. Large swathes of Europe are expecting reduced harvests, freshwater fish are dying, and deadly forest fires have occurred in Scandinavia. 

The 2018 extreme summer in central and northern Europe is characterised by persistent warm conditions (according to NASA’s GISSTEMP temperature record, European April-June have been 2°C above the 1951-1980 average) as well as a prolonged and intense drought period already since April. Heat and drought conditions are found to amplify each other over Europe, and it is the compound natureof these extremes that contributes to the impacts observed. Under prolonged conditions of high temperatures, soil loses more moisture than normal, and as the drought intensifies, heat bakes the earth, resulting in agricultural losses.

These feedbacks between drought and extreme heat conditions will intensify with increasing warming. This will lead to hot extremes over central Europe increasing substantially faster than global mean temperature. Drought conditions are found to increase with more warming, in particular in the Mediterranean region and continental Europe.What would be a 1-in-1200 years drought in terms of area affected in today’s climate is projected to become a 1-in-60 years event under 3°C of warming. This is a sobering projection, given that current level of climate action globally puts us on a path to around 3.5°C warming by 2100. If warming is limited to 1.5°C, such drought would be a 1-in-300 years event.

Recent scientific advances have revealed that climate change also affects large-scale atmospheric circulation patternsin the northern hemisphere, and specifically its prominent feature called the jet stream. It is found that climate change increases the odds that the movement of the jet stream stalls, causing weather patterns to persist for weeks on end rather than shifting onwards to a new location – exactly what has been happening during the summer of 2018. A ridge of warm air has been sitting over Europe, Japan and Western North America for prolonged periods during this summer, causing persistent dry, hot cloud-free conditions. A similar blocking event in 2010 caused a deadly heat wave in Russia. A stream of peer-reviewed literature published afterwards linked this behavior of the jet stream to climate change. 

The 2018 heatwave is a sign of things to come. The similar extreme 2003 heat wave in Central Europe has been studied in detail. While it would have been very unlikely without climate change, it is assessed to be a 1-in-4 years event under present day warming of around 1°C. In this regard, the 2018 heatwave is not an outlier, but in line with our expectations as a result of present day climate change. Climate models project that if the planet warms by 1.5°C, such heatwaves would occur in 4 out of 10 summers, and 6 out of 10, if it warms by 2°C.

While northern latitudes are struggling with the dry heat of 2018, tropical regions face even greater challenges. According to a recent study, around 14% of the world population will be exposed to severe heat waves at least once every 5 years already in a 1.5°C world. Tropical regions in South America, South Asia and Africa are most affected. This fraction becomes nearly three times larger under 2°C warming, a difference of around 1.7 billion people. Under a 2°C warming, heatwaves currently considered unusual, would become the new normal for Africa.The differences in climate impacts between 1.5 and 2°C warming will be felt unequally around the world, with tropical regions – where the majority of poorer, developing countries are – bearing the brunt of the additional impacts.

The extreme weather of 2018 is a glaring reminder of the need to keep to the Paris Agreement’s temperature limit of 1.5°C to avoid the worst impacts of climate change. But if warming surpasses the 1.5°C limit the pace of change will become much more difficult – if not impossible – to adapt to both in wealthy countries and particularly in the most vulnerable regions.