Extreme heat raises error rate.

What this means

Extreme heat is indoor or outdoor air temperature that climbs well past the comfort range, roughly above the mid-20s °C, into the 30s and beyond. It raises the rate at which people make mistakes on tasks that need attention, memory and quick reactions. Office workers, students in classrooms and drivers all feel it. As a room warms past comfortable levels, accuracy on cognitive tasks slips, reactions slow and errors on the road grow more likely.

What the research shows

Yeganeh (2018) pooled the evidence and found cognitive performance falling as air temperature rose, with an overall decline of −7.97 % at a temperature increase of +26.68 °C, across both speed and accuracy. Laurent (2018) measured heatwave conditions and found reaction time on the STROOP test rising 13.4 % and throughput dropping 9.9 % among people without air conditioning relative to those with it.

Kim (2020) saw learning performance fall about 7.0 % once indoor temperature reached 33 °C. Tian (2020) found accuracy on cognitive tests dropping sharply as temperature climbed from 26 °C to 39 °C at 70 % relative humidity. Yin (2024) tracked longer exposure and linked a −9.87 % cognitive change to each 10 percentage points more hours above 32 °C over two years, tying both acute and sustained heat to decline. On the road, Basagaña (2015) found the risk of crashes with driver performance factors rising 1.1 % for each 1 °C increase in maximum temperature.

How certain this is

Two syntheses stand behind the link, Yeganeh (2018) and Martin (2019), and the primary studies under them span controlled chambers, learning tasks and real crash records, which lets the same direction show up across very different measures. Yeganeh (2018) supports the link across ten studies while two qualify it. The certainty holds at solid because the effect appears in field data such as Basagaña (2015) as well as lab work, and because the dose-response pattern is consistent rather than scattered. The remaining looseness sits in how much the size of the drop depends on task type and how long the heat lasts.

In practice

A room that drifts from the low-20s °C into the 30s is not a comfort problem alone but an accuracy problem, and the size of the drop tracks the size of the rise, as Yeganeh (2018) shows across +4.34 °C, +10.04 °C and +26.68 °C. Where a task depends on sustained attention, quick reaction or STROOP-type interference, that is where the losses in Laurent (2018) and Tian (2020) show up, so heat matters most for exactly the work that already needs concentration. Kim (2020) marks 33 °C as a point past which learning performance has already fallen, which gives a concrete line to check indoor readings against before assuming a warm spell is harmless. Yin (2024) adds that hours spent above 32 °C accumulate over time, so a space that runs hot on and off over weeks or months carries a cost even if no single day feels extreme. Before treating a warm space as a fixed loss, it is worth checking whether occupants have had sustained prior exposure to heat, since Martin (2019) ties habituation to how far cognition actually drops, and whether the task at hand is short-term memory in the mild 26–30 °C band, where Yang (2021) found no measurable effect.

Dose and thresholds

Yeganeh (2018) shows the decline scaling with heat: −0.40 % at +4.34 °C, −5.37 % at +10.04 °C and −7.97 % at +26.68 °C, so the loss grows with the size of the rise. Laurent (2018) places the optimum for the STROOP test at 22–23 °C, with performance worsening on either side of that band. Kim (2020) marks 33 °C as a point where learning performance has clearly fallen, and Yin (2024) counts hours above 32 °C as the threshold that drives longer-term decline.

Where it is contested

Yang (2021) tested short-term memory across 26–30 °C and found no significant effect of temperature, which suggests the memory task is less sensitive than reaction-time and accuracy tasks in that milder band. Zhang (2017) found cognitive performance staying stable or even improving slightly under mild heat intensity and short exposure from temperature cycles. Strong, sustained heat is what brings the losses; brief or mild warming in the high-20s °C can leave performance untouched.

Why it happens

People adapt to a warm setting over time, so someone used to heat holds performance better than someone freshly exposed. Martin (2019) notes that the skill and familiarity of the person, along with how long and how severe the exposure is, shape how far cognition drops. This habituation is why short temperature cycles in Zhang (2017) left performance intact while the sustained heat in Yin (2024) tracked with decline.