Dissimilar global record-breaking heatwave exposure driven by divergent population projections within shared socioeconomic pathways

Exposure to record-breaking heatwaves represents a significant and growing challenge for human health and societal well-being in a changing climate. Comprehending the risks of future exposure to record-breaking heatwaves is vital for devising effective mitigation strategies. However, population data, a key determinant in projecting future exposure risks, has rarely been scrutinized for the uncertainty it introduces into these projections. This study investigates population exposure risks to record-breaking heatwaves from 2020 to 2 100 using four population datasets (ECNU, Lund, NASA SEDAC, and Tsinghua) under various IPCC AR6 shared socioeconomic pathways (SSPs: 1–2.6, 2–4.5, 3–7.0, and 5–8.5). Results indicate that by the 2090s, approximately 0.9 billion, 2 billion, 4.8 billion, and 4 billion people per year will be exposed to record-breaking heatwaves under SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5, accounting for about 10 %, 21 %, 42 %, and 50 % of the total population, respectively. Key risk areas include East Asia, South Asia, Western and Central Europe, the Mediterranean coast, West and East Africa, and the Northeastern United States. Our results also demonstrate good consistency in global population estimates across the datasets under different SSPs, except for Lund, which tends to predict a higher global population than the other datasets by about 8 % in SSP2 and SSP3. The Kappa test results reveal that, in the context of global population distribution, while the datasets of ECNU and Tsinghua, as well as Lund and Tsinghua, display a strong degree of spatial consistency, other dataset combinations show only a moderate level of agreement. Notably, at the subcontinental level, significant disparities emerge in the projected population sizes and distributions across different population projections, and over time, this gap is widening. This will have a significant impact on the estimation of future population exposure. For example, in the Northern Hemisphere mid-to-high latitudes and the Australian region, the ECNU dataset forecasts a higher population growth rate than the other datasets. Subsequently, a similar trend is observed in the projections of population exposure to record-breaking heatwaves. These findings highlight the variability in regional risk projections across different population datasets, providing valuable insights for future population-related risk assessments and informing targeted mitigation efforts. • Global population estimates are generally consistent but significant subcontinental disparities persist. • By 2090s, 10−50 % of global population may face record-breaking heatwaves annually, varying by the climate scenario and dataset. • The study finds higher spatial consistency in record-breaking heatwave exposure assessments than in population distribution.