Large parts of the world could experience dramatic increases in heat-related deaths under scenarios of greater climate change, according to a new paper published September 13 in the journal Climate Change. Researchers argue that the world needs to keep global temperatures in check by meeting the goals set out in the Paris Agreement.

“Under more extreme climate scenarios, most regions are expected to experience considerably larger heat-mortality risks that would not be counter-balanced by decreases in cold-related excess mortality,” said study co-author Kristie Ebi, professor of global health and environmental and occupational health sciences at the University of Washington. The Department of Global Health bridges the Schools of Public Health and Medicine.

The Paris Agreement binds nations to hold warming well below 2 degrees Celsius in global mean surface temperature, relative to pre-industrial levels. It also urges countries to make additional efforts to limit warming to 1.5 degrees Celsius.

Led by the London School of Hygiene & Tropical Medicine, this is the first study that projects global temperature-related health impacts under scenarios consistent with the Paris Agreement. Researchers first analyzed historical data on temperature-related deaths from 451 locations in 23 countries with different socioeconomic and climatic conditions. They then projected changes in mortality for a range of temperature increases, either compatible with the Paris thresholds or higher. These projections accounted for how increases in heat-related deaths might be offset by a decrease in cold-related deaths as global temperatures increase.

Results showed dramatic increases of heat-related deaths under extreme warming (3 and 4 degrees Celsius) compared to the mildest change (1.5 degrees Celsius). In a 4-degree-warmer world, central and southern regions of America, Europe and East Asia could experience anywhere from 3.5 to 8.9 percent more heat-related deaths than a 1.5-degree-warmer world. The net difference remained positive and high in most areas, even when potential decreases in cold-related deaths were considered.

The picture was more complex when comparing a warming of 2 degrees Celsius to 1.5 degrees Celsius. A net increase in deaths was projected for warmer regions such as South America, South Europe and Southeast Asia, while in cooler regions the excess mortality was projected to stay stable or drop slightly.

"Efforts to limit the increase in global temperature to below 1.5°C could provide additional benefits in tropical or arid regions, including the most populous and often poorest countries,” said the study’s first author Ana Maria Vicedo-Cabrera, assistant professor in environmental epidemiology and statistics at the London School of Hygiene & Tropical Medicine.