Out-of-hospital cardiac arrest (OHCA) remains a critical public health concern, with low survival rates despite emergency care advances. Extremes in high and low ambient temperatures are important triggers of OHCA. To highlight the importance of the relation between OHCA and temperatures associated with climate change, we evaluated temperature effects during the high temperature period (June to September) and low temperature period (December to March) in Korea and projected future temperature-attributable OHCA burdens using climate change scenarios.

A time-stratified case-crossover study examined the association between ambient temperature and OHCA incidence across 250 administrative districts in Korea from 2013 to 2020. Data from the Korean OHCA registry and Google Earth Engine were analyzed using distributed lag non-linear models. Observed OHCA risk was projected to future temperatures using Shared Socio-economic Pathway (SSP) scenarios: SSP1–2.6 (low-emission) and SSP5–8.5 (high-emission).

A total of 110,172 OHCA cases were analyzed. The temperature-attributable burden of OHCA increased during both high and low temperatures. Future projections under SSP1–2.6 and SSP5–8.5 showed a continued increase in heat-related OHCA burden, with attributable fractions ranging from 5.5%–9.2% under SSP1–2.6 and 6.3%–16.8% under SSP5–8.5. Cold-related attributable burden decreased over time in both scenarios, declining from 33.0% to 30.2% under SSP1–2.6 and from 33.0% to 21.6% under SSP5–8.5.

In point estimates, the projected reduction in cold-related OHCA exceeded the increase in heat-related OHCA across the study period. However, heat-related OHCA burden is expected to increase substantially—particularly under the high-emission SSP5–8.5 scenario—highlighting the need to strengthen early warning systems, optimize emergency medical preparedness, and implement targeted cardiovascular health interventions for vulnerable populations.