With rising temperatures, California is experiencing fewer deaths from cold weather while seeing a greater number of heat-related emergency department visits. Although overall mortality from extreme heat has not increased, the health impacts are shifting and could place more burden on the healthcare system.
Researchers from University of California San Diego and Stanford University analyzed data from 2006 to 2017, finding that both hot and cold temperatures impact illness and deaths differently. Their study was published in Science Advances.
Science Advances"Even when heat doesn't lead to deaths, it can still harm health," said Carlos F. Gould, Ph.D., an assistant professor at the Herbert Wertheim School of Public Health at UC San Diego. "Warmer temperatures are consistently linked with more emergency department visits, so focusing solely on mortality overlooks a significant part of the problem."
The study revealed that emergency room visits surge during hotter days across various age groups for conditions like injuries, mental health issues, and poisonings—factors often missed in studies focusing only on mortality.
"Age is a critical factor in temperature-related health risks," noted Gould. "Older adults are more vulnerable to cold temperatures, whereas younger adults and children face greater heat challenges."
While fewer extreme cold days may result in reduced cold-related deaths in California, this benefit will be counterbalanced by increased emergency room visits due to extreme heat. Experts recommend that health policies address the varying impacts of temperature on different population segments, especially as climate change progresses.
"Understanding who faces these risks at what temperatures is essential for implementing appropriate protective measures," said co-author Marshall Burke, Ph.D., associate professor of environmental social sciences at Stanford's Doerr School of Sustainability. "This becomes even more important in a warming climate."
According to the National Health Expenditure Accounts, annual spending on chronic diseases alone in the U.S. exceeds $3 trillion, comprising 17.6% of the U.S. GDP.
Using moderate climate change projections through 2050, researchers estimate California will see around 53,500 fewer deaths due to reduced cold weather—saving about $30 billion annually. However, this gain is partially offset by an estimated 1.5 million more heat-driven emergency department visits, adding approximately $52 million annually in healthcare costs.
"We must consider the full range of health impacts from heat waves—not just deaths," said Alexandra K. Heaney, Ph.D., co-author and assistant professor at UC San Diego. "This includes injuries, digestive issues, and endocrine disorders."
Co-authors include Carlos F. Gould and Alexandra K. Heaney from UC San Diego; Sam Heft-Neal, Eran Bendavid, Christopher W. Callahan, Mathew V. Kiang, and Marshall Burke from Stanford University; as well as Josh Graff Zivin, UC San Diego and the National Bureau of Economic Research.