Limiting global warming to 1.5 degrees C could prevent thousands of deaths in the U.S.

Having the world meet a more stringent goal to limit global warming may prevent thousands of heat-related deaths in 15 major U.S. cities, a study shows. The projections illustrate the high risk from climate change faced by urban populations.

Under the Paris Agreement, participating countries have pledged to curb greenhouse gas emissions with the aim of limiting warming to no more than 2 degrees Celsius over preindustrial times by 2100 (SN: 1/9/16, p. 6). Keeping warming to 2 degrees C could mean 75 to 1,980 fewer deaths in an especially warm year in these 15 cities, compared with a scenario in which the world warms by 3 degrees, researchers report online June 5 in Science Advances.

Limiting warming to a more stringent 1.5 degrees, however, could spare 114 to 2,716 more U.S. city-dwellers from death in an especially warm year than the 3 degree scenario, the team reports.

The study is the latest to suggest that, without additional efforts to help people adapt to hotter temperatures, “heat-related mortality is likely to increase in the coming decades,” says climatologist David Hondula of Arizona State University in Tempe, who was not involved in the research.

The 2-degree goal doesn’t go far enough in many respects, according to the Intergovernmental Panel on Climate Change, or IPCC. Holding warming to 1.5 degrees would further reduce the risk of extreme heat waves, droughts, sea level rise and habitat loss for species (SN: 10/27/18, p. 7).

Excessive heat can kill (SN: 4/14/18, p. 18), most directly via heat stroke. Heat is risky for everyone, but some groups are more vulnerable than others, especially older adults, outdoor laborers and people in low-income neighborhoods lacking air conditioning.

In the new study, climate scientist Eunice Lo at the University of Bristol in England and colleagues explored how various possible warming scenarios might impact heat-related deaths.

The researchers used mortality and temperature data from 1987 to 2000 for 15 U.S. cities, combined with computer modeling to simulate conditions in different warming scenarios. The group projected heat-related deaths during an especially warm year — one expected to occur once in 30 years under each of the scenarios. Among the cities studied were New York, Chicago, Miami, Houston, Phoenix and Los Angeles.

Limiting warming to 1.5 degrees “makes a huge difference in terms of human lives across cities” in the United States, Lo says. “Immediate and drastic emission cuts would be substantially beneficial to public health.”