A United Nations agency warned of an increased risk of heart attacks and deaths as the northern hemisphere reeled from heat waves Tuesday.

The World Meteorological Organization (WMO), the U.N.’s authority on weather and climate, said global temperatures have reached “unprecedented” levels within the last few weeks in a post on its website.

According to the agency, multiple regions around the world including “North America, parts of Asia and across North Africa and the Mediterranean,” have seen temperatures above 40 degrees Celsius (104 degrees Fahrenheit) for a “prolonged” period of time this week.

“Heat is a rapidly growing health risk, due to burgeoning urbanization, an increase in high temperature extremes, and demographic changes in countries with aging populations,” the WMO said in the post on its website. “Hundreds of thousands of people die from preventable heat-related causes each year.”

The agency said that because of increased overnight temperatures worldwide, human bodies have trouble recovering from the higher temperatures of the day. This then creates a larger risk during the daytime heat.

The WMO said this lack of recovery time leads to “increased cases of heart attack and death.”

The WMO also cited a recent study that showed Europe saw 60,000 additional deaths last summer from “extreme heat.” The agency said this calculation is considered a “conservative estimate” among experts and governments.