FSF: Emerging “Extreme Heat Belt” Will Impact over 107M Americans by 2053

FSF is the First Street Foundation in this context. They're a 501(c)(3) non-profit that aims to produce accurate models of the effects and risks caused by climate change. I personally use them as a source at work when dealing with questions raised by climate change. Anecdotally, I've found their models to be shockingly thorough, specifically their flooding model.

I chose to link to the press release, because at the bottom of the page there's two links. One to their more detailed methodology article and one to the 'highlights' article. Both are quite interesting, but the press release isn't a bad place to start for some context.

The full report is available from this link: https://report.firststreet.org/heat which requires an email submission unfortunately, but there are worse places to give your contact information to IMHO.

If you're interested in using their data they have quite an extensive free access program. https://firststreet.org/data-access/