The recent deadly heatwave in the Sahel and West Africa with temperatures of above 45°C would not have been possible without human-caused climate change, according to rapid analysis by an international team of leading climate scientists from the World Weather Attribution group.

In late March and early this April, extreme heat impacted countries in the Sahel and West Africa. The hottest temperature occurred on April 3, when Mali recorded 48.5°C.

In Bamako, the Gabriel-Toure Hospital announced a surge in deaths, with 102 deaths over the first four days of April. Around half were over the age of 60 and the hospital reports that heat likely played a role in many of the deaths.

A lack of data in the countries affected makes it impossible to know how many people were killed, however, it’s likely there were hundreds or possibly thousands of other heat-related deaths.

Climate change, caused by burning fossil fuels like oil, coal and gas, and other human activities, is making heatwaves more frequent, longer and hotter around the world.

“The early-April heat in the Sahel and West Africa was extraordinary – for nearly a week, daytime temperatures pushed well above 40°C, while nighttime temperatures in some regions reached 30°C,” said Clair Barnes, researcher at Grantham Institute - Climate Change and the Environment, Imperial College London.

“Our study joins a mountain of evidence linking dangerous heat with warming caused by fossil fuel emissions.”

Quantifying the human factor

To quantify the effect of human-caused warming on the extreme temperatures in the Sahel and West Africa, scientists analysed weather data and climate models to compare how these types of events have changed between today’s climate, with approximately 1.2°C of global warming, and the cooler pre-industrial climate using peer-reviewed methods.

The analysis looked at the five-day average of maximum daily temperatures in two areas: one that includes southern regions of Mali and Burkina Faso, where the heat was most extreme, and a larger area including regions of Niger, Nigeria, Benin, Togo, Ghana, Côte d'Ivoire, Mauritania, Senegal, Gambia, Guinea-Bissau and Guinea, where temperatures were widely above 40°C.

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Kiswendsida Guigma, Climate Scientist at the Red Cross Red Crescent Climate Centre in Burkina Faso, said “year-round heat is part of life in the Sahel and regions of West Africa. However, the extreme temperatures were unprecedented in many places and the surge in excess deaths reported by the Gabriel-Toure Hospital in Mali highlighted just how dangerous the heat was.

“For some, a heatwave being 1.4 or 1.5°C hotter because of climate change might not sound like a big increase.

“But this additional heat would have been the difference between life and death for many people.”

To investigate hot night time temperatures, which can be dangerous when the human body cannot rest and recover, the researchers also analysed the five-day average of minimum temperatures for the Mali and Burkina Faso region.

The scientists found that both the daytime and nighttime heatwaves, across both regions, would have been impossible if humans had not warmed the planet by burning fossil fuels like oil, coal and gas, and with other activities like deforestation.

Climate change made the maximum temperatures 1.5°C hotter and the nighttime temperatures 2°C hotter for the Burkina Faso and Mali region, and the five-day daytime temperatures for the wider region 1.4°C hotter.

Recent heatwave rare

A heatwave like the recent one is still relatively rare, even in today’s climate with 1.2°C of warming, the researchers found. Across the wider West Africa region, similarly high daytime temperatures can be expected about once every 30 years. However, daytime temperatures like those experienced in Mali and Burkina Faso, where heat-related fatalities were reported, are expected around once in every 200 years.

But events like these will become much more common, and even more dangerous, unless the world moves away from fossil fuels and countries rapidly reduce emissions to net zero. If global warming reaches 2°C, as is expected to occur in the 2040s or 2050s unless emissions are rapidly halted, similar events will occur 10 times more frequently.

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The researchers also quantified the possible influence of El Niño on the heat, but found that its effect was not significant when compared with the influence of human-caused climate change.

The study highlights factors that worsened the impacts of the heat across the region. The heat occurred at the end of Ramadan when many Muslim people fast during the day. The Sahel region has a large Muslim population and while high temperatures are common in April, the researchers say the relentless day and nighttime heat would have been overwhelming for many people who were abstaining from food and water.

They also note that conflict, poverty, limited access to safe drinking water, rapid urbanisation and strained health systems likely worsened the impacts.

Heat action plans that set out emergency responses to dangerous heat are extremely effective at reducing heat-related deaths during heatwaves. However, neither Burkina Faso or Mali have one in place.

Given the increasing risk of dangerous heat in the Sahel and West Africa, the researchers say developing heat action plans will help to save lives and lessen the burden of extreme heat on health systems.

Finally, the researchers say the Gabriel-Toure Hospital’s rapid reporting of heat-related deaths was a valuable illustration of the dangers of extreme heat that would have likely acted as an effective warning for people in the region.

“Attribution studies like this one clearly show that if the world continues to burn fossil fuels, the climate will continue to warm and vulnerable people will continue to die,” said Friederike Otto, Senior Lecturer in Climate Science at Grantham Institute - Climate Change and the Environment, Imperial College London.

“In the future, it’s likely this increasingly evident link between fossil fuel emissions and heat-related death will be used in litigation against fossil fuel companies.”

The study was conducted by 19 researchers as part of the World Weather Attribution group, including scientists from universities, organisations and meteorological agencies in Nigeria, Burkina Faso, Switzerland, Sweden, South Africa, The Netherlands, Germany, the United Kingdom and the United States.