About 1 billion people now face extreme heat stress each year. Far fewer once did.

A research analysis published in Nature Climate Change and summarized this month in JAMA quantifies something climate scientists have been describing qualitatively for years: a rapidly expanding share of the world's population is now experiencing dangerous heat stress on a regular basis, using temperature data stretching back to 1950 [s1].

What the analysis measured

The underlying research examined human heat stress exposure globally from 1950 through 2024, tracking how often people around the world experience "feels-like" temperatures — a measure that accounts for humidity alongside raw air temperature — at levels associated with health risk [s1]. JAMA's summary, published July 2, frames the analysis around two specific exposure thresholds: a moderate heat-stress threshold of 90°F (32°C) feels-like temperature, and an extreme heat-stress threshold of 115°F (46°C) [s1].

The numbers

Exposure to at least 90 days a year of 90°F feels-like heat rose from 55% of the global population in the 1970s to 70% today [s1] — meaning roughly seven in ten people on Earth now spend a substantial chunk of the year under conditions that meet this heat-stress threshold, up from roughly half that experienced it fifty years ago.

The extreme threshold moved too, in both share and raw numbers: exposure to feels-like temperatures of 115°F rose from 16% to 22% of the global population over the same period [s1] — an increase JAMA's summary describes as equivalent to roughly 1 billion additional people now facing that level of extreme heat stress [s1].

Why this framing matters

The analysis identifies global heat stress as the leading cause of weather-related mortality [s1] — a designation that puts heat ahead of more visually dramatic weather disasters like hurricanes, floods, or tornadoes in terms of actual death toll, a pattern consistent with other heat-mortality research published in recent years. The specific contribution of this analysis is longitudinal: rather than a snapshot of a single year or a single heat wave, it traces the trajectory of global heat-stress exposure across more than seven decades, and finds that trajectory has been climbing steadily since roughly the 1970s [s1].

What the numbers don't tell us

The figures reported here are global aggregates — worldwide shares and totals — rather than a regional breakdown identifying which specific countries or populations are driving the increase, and the JAMA summary does not report accompanying mortality or illness figures tied directly to these exposure numbers [s1]. A rising share of the population experiencing heat-stress thresholds is not the same as a directly counted rise in heat deaths, though the two are closely related in the broader heat-health literature: more frequent, more widespread exposure to dangerous heat thresholds generally translates into a larger population at risk, even before accounting for factors like air conditioning access, urban heat island effects, or age that shape how that exposure turns into actual harm for any specific person or place.

Sources

• Heat Stress From Climate Change Surges Globally — JAMA, 2026-07-02
• Global heat stress intensification and its expanding footprint on the human population — Nature Climate Change, 2026-06-22