Five degrees off New York's heat-alert trigger tracked a drop of more than half in heat-stroke admissions

A trigger threshold is a scheduling rule. Move it down five degrees and the same list of city actions runs on days that used to be treated as ordinary summer ^[20]. New York's reason for moving it was clinical: officials had noticed people getting heat stroke below the National Weather Service line of a 105 F heat index ^[2][3].

The reduction is a correlation. Live Science describes the threshold change as part of a wider effort, so the alert and the services it switched on moved together, and the published account does not include a baseline count of hospitalizations or a comparison city ^[4][6]. Live Science calls New York one of the clearest examples of an intervention that worked against deadly heat, and says most solutions do not offer that level of clarity ^[22][23].

One component of the New York package has thin evidence of its own. The same review found limited evidence that cooling centers, an intuitive measure, are effective at a societal level ^[10]. "The strongest evidence is where these approaches reduce illness, hospital visits or death," Charles Leonard, an associate professor of epidemiology at the University of Pennsylvania, told Live Science, "not just heat exposure, pollution levels or other intermediate markers" ^[9]. Some interventions have shown reductions in death or disease at the population level; others rest on modeling or proxy measures ^[8].

Air conditioning is the measure the review graded as strong ^[11]. During a heat wave in Portugal, patients admitted to an AC-supported hospital had a 40% lower risk of dying than those in wards without it ^[13]. AC has also been tied to fewer hospital admissions in California and fewer heat-related deaths in Texas prisons ^[12]. The equipment is mostly in place: 90% of US households used AC in 2020, the latest year of energy survey data, leaving roughly one household in ten that did not ^[14][21]. Analyses of US household data have consistently shown families limiting food purchases, the "heat or eat" dilemma ^[16].

"One of the most important lessons emerging from heat adaptation research is that no single intervention is sufficient on its own," said Shweta Arya, senior project manager for smart surfaces at the American Public Health Association's Center for Climate, Health and Equity ^[17]. Emissions set the size of the problem the rest of the measures manage. Live Science reports the scientific consensus that slowing warming is the most effective way to avoid the worst health outcomes of climate change, and that holding warming to 1.5 C instead of 3 C would mean 11,600 fewer US deaths a year from wildfire smoke exposure ^[18][19].