A central goal of the United Nations’ Paris climate agreement is to keep global temperature rise this century to well below 2 degrees Celsius, and to pursue efforts to limit the increase to only 1.5 degrees.

A new research paper shows that each pathway to achieve a 1.5-degree-warmer world would likely result in vastly different regional temperatures. Published June 7 in Nature, the report comes from an international collaboration that included Kristie L. Ebi from the University of Washington School of Public Health.

Regional differences arise from variations in the pace and location of climate change, as well as a society’s vulnerabilities and options for mitigation and adaptation.

“Continued emissions of greenhouse gases will change the world we live in, in many fundamental ways,” said Ebi, a professor of global health and of environment and occupational health sciences. “Climate change is changing the numbers of injuries, illnesses and deaths from a range of health outcomes affected by weather and climate. Fewer emissions will have less significant health impacts.”

The report shows that limiting global warming to 1.5 degrees Celsius would avoid risks of extreme changes that could appear if it increased to 2 degrees. Such changes include a five-degree temperature increase on the hottest days in the United States or a nine-degree increase on the coldest nights in the Arctic. The risk of the Mediterranean becoming significantly drier would also be avoidable. However, even the lower level of warming would involve substantial climate risks for ecosystems and societies.

Scientists say policy- and decision-makers should consider the magnitude of emerging regional risks. They should also consider how policies could increase the resilience of human and natural systems. According to Ebi, avoiding future risks will depend on how quickly communities, businesses and nations reduce their greenhouse gas emissions, and the effectiveness and timeliness of adaptation to manage the risks that will arise. Sonia Seneviratne of the Institute for Atmospheric and Climate Science in Switzerland was the report’s lead author.

In another study, published May 15 in Environmental Research Letters, Ebi led a comprehensive review of publications over the last decade that projected the health risks of climate change. Risks for adverse health outcomes were higher at 2 degrees Celsius compared to 1.5 degrees. There were regional variations due to differences in average temperatures, population acclimatization and vulnerability, the built environment, access to air conditioning and other factors.

“Each increase in global mean surface temperature increases most climate-sensitive health risks, so aiming for lower limits will benefit health and other sectors,” Ebi says. Risks were elevated for heat-related morbidity and mortality, heat stress, ground-level ozone and undernutrition. Risks for vector-borne diseases, such as malaria and dengue, depend on regional climate responses and disease ecology. Warmer temperatures may result in some regions becoming too hot or too dry for a vector.

At lower increases in global mean temperatures by 2050, “hotspots” of vulnerability in multiple sectors (e.g., water, energy, health, others) include communities in South and East Asia. At higher temperature increases, high vulnerability extends to Central America, West and East Africa, the Middle East, and the Mediterranean. This is based on new research, also published in Environmental Research Letters and co-authored by Ebi.

The research team, led by Edward Byers from the International Institute for Applied Systems Analysis in Austria, investigated the interactions between multiple climate change risks and socioeconomic development to identify vulnerability hotspots. The findings, published May 31, show that the number of people affected by multiple climate change risks could double if the global temperature rises by 2 degrees Celsius, compared to the number affected at a rise of 1.5 degrees.

Promoting socioeconomic development in these hotspots is particularly important for reducing vulnerability in regions where the impacts are projected to be most severe, Ebi says. Sustainable development in these areas could reduce the number of people exposed from 1.5 billion to 100 million.

“Increasing preparedness will reduce health impacts and will increase functioning of health care facilities during extreme weather and climate events,” Ebi says.