Days of extreme heat raise the odds of hospitalization for infants and expecting mothers, especially black women.

These findings from a new National Bureau of Economic Research paper highlight additional ways that climate change could impair human health and exacerbate racial health disparities.

The results: An additional day of unusually high temperatures during a pregnancy increases the chances of hospitalization by around 2.6% for white women and 5% for black women, according to the analysis of discharge records in Arizona, New York, and Washington state. Another hot day during the second trimester also raises the likelihood that babies will be born dehydrated by 31% and the odds that they’ll be readmitted to the hospital before their first birthday by 3.4%.

The study notes that black women are more likely to be exposed to extreme heat because they tend to live in hotter areas and have less access to air conditioning or other ways of avoiding the heat. 

Other heat risks: The dangers of extreme heat to humans are well known, if not fully understood.

Earlier studies have found that extreme temperatures during gestation and early life result in lower birth rates, higher infant mortality, and impaired cognitive function. Maya Rossin-Slater, an economist at Stanford’s School of Medicine and coauthor of the new study, also worked on a 2017 paper finding that early exposure to high temperatures could affect a person’s earnings three decades later.

That study notes that still-developing fetuses and infants may be especially susceptible to high temperatures. But heat waves also harm adults, increasing violence, suicide rates, hospital visits, deaths, and global inequality.

Worse to come: This is all bad news, because the US is set to experience many more hot days as global warming increases. An earlier United Nations study estimated that the number of days with mean temperatures above 32 ˚C (89.6 ˚F) could climb from one per year in the average US county now to more than 40 by about 2070.