NPR spent 2 years tracking deaths from heat. We found a staggering hidden toll

Thousands of Americans die every year from a chronically underreported cause: heat.

As summer heat intensifies because of human-driven climate change, the United States' official tally of heat-related deaths does not come close to capturing the full human toll. The data feeding into nationwide death counts is collected inconsistently and rarely thoroughly.

The result is a vast undercount of the number of people who die because of heat. And experts say failing to recognize and address this may cost more people their lives.

So NPR set out to create a more comprehensive national count.

We partnered with Boston University to find the total number of deaths influenced by heat every year in the United States. The investigation took two years and involved building a statistical model that assessed nearly every county in the country. The full analysis will soon be published in a scientific journal.

An accurate assessment of the true scope — as well as understanding who is affected, where and why — is critical for developing lifesaving solutions, says Quinn Adams, a research scientist at Boston University's Center for Climate and Health and the lead partner in the joint NPR-BU investigation.

Beyond the statistical assessment, NPR set out to find people whose deaths slipped through the cracks — those who might not have died if heat hadn't pushed them beyond their breaking point — to understand exactly how heat could be missed as a factor. We will be bringing you their stories in the coming days.

But first, here are three key takeaways from our research — and why it matters.