The thermometer & the mind · public dossier
RO EN
Heat · brain · evidence from six disciplines

A threshold for the body,
none for the mind.

For every degree above normal we get icons, thresholds and advice, all for the body. Sleep, mood, learning, decisions and aggression climb the same temperature scale, with no public message naming them. The relationship is a measured slope that begins at ordinary temperatures.

+1,3% youth suicidality presentations / °C · NSW, 55,000+ cases
−1% learning / yr per +1°F, no air-conditioning · 10M students
+2,4% interpersonal conflict / 1σ of heat · 60 studies
68 countries where heat shortens sleep · 7M nights
01

Move the degrees. See what rises with them.

The same thermal load discharges into five outputs. Drag from a mild day toward a hot one. The bar shows direction and relative magnitude.

22°C
daily mean temperature
15°NSW mean 21.9°40°
Body: heat illness, heart, kidney public alert threshold
Pediatrics 2025 · Sydney cost study 2021
moderaterelative risk
Sleep: delayed onset, short nights
Minor et al. 2022 · One Earth · 68 countries
lowindex
Mood: youth suicidality presentations, 12–24
Dey et al. 2024 · ANZ J Psychiatry · NSW
±0%vs. baseline
Decisions: judgement and impulsivity under heat
Almås et al. 2025 · Economic Journal
lowindex
Aggression: interpersonal violence
Hsiang, Burke & Miguel 2013 · Science
±0≈ / 1σ

Only the first line has an alert threshold. The other four climb the same scale without one.

The figures are illustrative: they apply published slopes (where they exist, e.g. +1.3%/°C for NSW presentations) from a 22°C baseline to show direction and relative magnitude, not to predict any individual's absolute risk. Sleep, decision and body appear as an index because their effect doesn't reduce to a single per-degree slope.

02

Not only heatwaves

Risk seems tied to extreme peaks. The NSW study shows a single hot day loading as much as a heatwave day, with the slope starting at moderate temperatures. It's the signature of a physiological mechanism.

4045 5055 presentations / day 15°22° 28°38° daily mean temperature baseline 21.9°: 45.7 presentations single hot day ≈ heatwave day
youth suicidality presentations (NSW, Nov–Mar 2012–2019)

At 21.9°C, the period mean, the state saw about 45.7 presentations a day. Each extra degree adds around 1.3%, and the effect grows from mild temperatures up. The lead author puts it plainly: "this is about hot weather itself, not climate change."

03

What air-conditioning moves

The strongest known moderator is cooling. Across 10 million U.S. students who retook the PSAT, a school year 1°F hotter cuts 1% of that year's learning, but only in schools without air-conditioning. Turn the AC on and the slope flattens, here and across the page.

100%94% learning retained cool hotter school year hot with AC: almost flat no AC: -1% / °F
≈ 73% of heat's effect on learning offset by classroom air-conditioning
~5% of the racial achievement gap comes from hot days; the burden falls on poorer and minority students, who less often have AC
$25.000 future earnings lost per classroom per year that AC would offset, passing a cost-benefit test

The detail that isolates the mechanism: only school-day heat lowers scores, while hot summers and weekends have no effect. Heat disrupts instruction and sleep time. Cooling becomes cognitive infrastructure, and its unequal distribution shifts the burden onto those without access: sleep is eroded most in poorer countries, in older adults and in women.

04

One slope, seen from six disciplines

What gives the thesis weight is the convergence. Psychiatry, sleep science, education economics, behavioural economics, conflict research and public health arrive separately at the same monotonic relationship between degrees and the brain.

Psychiatry solid
+13% MH hospital visits in heat
A global meta-analysis in children and adolescents: high temperature is linked to 13% added risk of mental-health hospitalization, 18% for depression, 14% for psychosis. "720,000" is the pooled sample size for one outcome, not a single cohort and not a doubling.
Lai, Bauermeister & Sarkar, npj Mental Health Research 5:7 (2026) · n=720.512 · RR 1,13 (1,08–1,19)
Sleep science solid
68 countries, one direction
Seven million tracked nights via sleep wristbands: heat shortens sleep through delayed onset and raises the odds of insufficient sleep. The effect is larger in poorer countries, in older adults and in women, with no sign of short-term adaptation.
Minor et al., One Earth 5:534 (2022) · n=47.628 · 68 countries
Education economics solid
10M students, lower scores after a hot year
Only school-day heat lowers scores, while summers and weekends don't. The sign that it's lost instruction time. Air-conditioning offsets almost all of it.
Goodman, Hurwitz, Park & Smith, AEJ: Economic Policy 12(2):306 (2020)
Conflict and aggression robust, heterogeneous
+2,4% violence / 1σ of heat
A meta-analysis of 60 studies, from archaeology to criminology: each standard deviation toward hotter raises interpersonal violence about 2.4% and group conflict far more. The mechanism stays debated; the convergence, less so.
Hsiang, Burke & Miguel, Science (2013) · Burke, Hsiang & Miguel, Annu. Rev. Econ. (2015)
Economy and decisions emerging
13°C productivity peak
Economic productivity is non-linear in temperature: it rises to about 13°C annual mean and falls sharply above. At the individual level, thermal stress degrades judgement and economic decision-making, from the classroom to the courtroom.
Burke, Hsiang & Miguel, Nature (2015) · Almås et al., Economic Journal 135 (2025)
Public health policy gap
0 full assessments of mind inclusion
Extreme heat is tied to suicide, anxiety and substance use, yet mental health's integration into heat-health action plans stays limited. No comprehensive assessment of its inclusion exists, exactly the gap this page names.
Current Environmental Health Reports 12:23 (2025)
05

What is fact, what is reading

Measured fact

  • NSW youth suicidality presentations rise about 1.3% per degree, from moderate temperatures up.
  • Heat objectively shortens measured sleep across 68 countries.
  • Without AC, a hotter school year lowers scores; with AC, the effect nearly vanishes.
  • Interpersonal violence rises, on average, with heat across dozens of studies.

Reading and hypothesis

  • A shared biological mechanism, through thermoregulation, sleep and mood, plausibly links these outputs.
  • If heat messaging included the mind, prevention could act at the same thresholds.
  • Cooling could be treated as mental-health infrastructure.
  • The burden falls unequally, on those without access to cooling.
06

What this page does not say

Rigour here also means marking the limits hard, especially on a subject that touches suicidality.

Correlation, not simple causation

The associations are real and replicated, but heterogeneous. We don't claim a degree causes an outcome in a person. These are population slopes, with uncertainty.

Physical heat, not climate distress

The measured effect comes from physical body temperature, not from anxiety about climate change. These are different things; this page addresses only the first.

A health signal, not an alarm

We follow responsible-reporting guidelines. No methods, no sensational language, no acts framed as a response to a trigger.

Magnitudes differ widely

1.3% per degree and 13% in extreme heat are different numbers, and neither is a doubling. Every figure stays tied to its source and unit.

If you or someone close needs support now

  • Romania: DepreHUB, 0800 801 200 (24/7)
  • Romania, youth: Child Helpline, 116 111
  • UK and Ireland: Samaritans, 116 123
  • EU: emergency 112
07

Questions this page opens

Why does a heat warning tell you to drink water and avoid exertion, but nothing about sleep, mood or irritability?

If cooling is the strongest known moderator, should school air-conditioning be treated as public-health infrastructure?

Who absorbs the thermal load on the mind, and what does the map of cooling access look like in your city?

What would a mental-health alert threshold, calibrated on the same scale as the body alert, look like?

08

Sources

PsychiatryLai KY, Bauermeister S, Sarkar C. Associations of heat exposure with mental health and suicide in children and adolescents. npj Mental Health Research 5:7 (2026). nature.com
Psychiatry · NSWDey C et al. Rise in youth suicidality presentations linked to hotter temperatures. ANZ Journal of Psychiatry (2024). unsw.edu.au
SleepMinor K et al. Rising temperatures erode human sleep globally. One Earth 5(5):534 (2022). cell.com
EducationGoodman J, Hurwitz M, Park RJ, Smith J. Heat and Learning. AEJ: Economic Policy 12(2):306 (2020). aeaweb.org
ConflictHsiang SM, Burke M, Miguel E. Quantifying the Influence of Climate on Human Conflict. Science (2013). science.org
EconomyBurke M, Hsiang SM, Miguel E. Global non-linear effect of temperature on economic production. Nature (2015). · Almås I et al. Economic Journal 135 (2025).
Children · NSWExtreme Heat Stress and Unplanned Hospital Admissions. Pediatrics 155(1) (2025). aap.org
PolicyA Critical Gap in Addressing Mental Health in Heat-Health Action Plans. Current Environmental Health Reports 12:23 (2025). ncbi.nlm.nih.gov