Suicide is the second leading cause of death among youth, with growing evidence linking higher ambient temperatures to increased suicidality – a concerning trend as global temperatures rise. Sleep disruption is a theorized mechanism, though clinical evidence is lacking.

We performed a cross-sectional analysis of 5,590 pediatric patients (3–18 years) presenting to a psychiatric emergency department with and without suicidality (December 2018-March 2023). Seven-day averages of mean and minimum daily ambient temperatures and precipitation were obtained at home addresses from the PRISM Climate Group dataset. Logistic regression assessed insomnia as a moderator and mediator of the temperature-suicidality relationship, controlling for sociodemographic, diagnostic, and environmental variables. Negative controls included modeling suicidality using hypersomnia-temperature and insomnia-precipitation interactions.

Mean and minimum daily temperatures moderated the temperature-suicidality relationship only in those with insomnia (Mean Temperature: RR: 1.06 per 5°C [95% CI 1.01–1.06], p = 0.015; Minimum Temperature: RR: 1.06 per 5°C [95% CI 1.01–1.06], p = 0.010). Minimum temperature, a proxy for nighttime temperature, was associated with suicidality through insomnia in a mediation model (Indirect Pathway: OR: 1.05 [95% CI 1.00–1.11], p = 0.045), though mean temperature was not. No significant moderation occurred modeling suicidality with hypersomnia-temperature or insomnia-precipitation interactions.

This is the first clinical evidence that insomnia influences the heat-suicidality relationship in youth. Limitations include cross-sectional data that cannot establish temporal directionality of associations, heterogeneous suicidality outcomes, self-reported sleep data, and pandemic-era data collection. Larger mechanistic analyses of temperature, sleep, and suicidality are needed to understand climatic mental health impacts and develop interventions.