Exceeding human heat tolerance in a warming, ageing world: a global projection modelling study.
Older adults are at significantly greater risk of heat limit exceedances due to climate change, with projections indicating that many will face intolerable heat for extended periods.
Where it sits
this study against the rest of the slu-pp-332 (exercise mimetic) corpusSummary and findings
This study examined heat tolerance limits across different age groups in the context of global warming. It specifically assessed how accounting for age-specific heat tolerance affects projections of heat limit exceedances. The findings indicate that older adults are at greater risk of exceeding heat limits compared to younger populations.
Abstract
<h4>Background</h4>In a warming world, understanding where, when, and to what extent human heat tolerance limits will be breached has become increasingly important. Previous projections applied heat limits for healthy young adults to all age groups, overlooking greater vulnerability in older ages. With global ageing, this oversight could seriously underestimate future heat risks. In this study, we aimed to examine the extent to which accounting for age-specific heat tolerance alters global projections of heat limit exceedances.<h4>Methods</h4>We integrated experimentally derived heat limits for young (18-39 years), middle-aged (40-59 years), and older adults (≥60 years) with climate projections and age-stratified population projections to assess where and to what extent these limits could be breached across age groups under 1-4°C of global warming above preindustrial levels. The climate projections include bias-corrected projections of dry-bulb temperature and wet-bulb temperature from 14 Coupled Model Intercomparison Project Phase 6 climate models under the shared socioeconomic pathway 5-8·5 scenario. We also highlighted countries with high exposure risk and low adaptive capacity.<h4>Findings</h4>More widespread and imminent breaches of heat limits were estimated among older adult populations than among other populations. Older adults faced more frequent and spatially extensive exceedances under the 1·5°C global warming scenario relative to the preindustrial period than young adults did under 4°C. Using age-specific thresholds more than doubled the global population having 180 h or more of exceedance annually as compared with previous estimates. Older adults in south Asia and the Persian Gulf could face sustained, day-and-night exposure for three consecutive months at 3°C or more warming. We also identified 13 countries under 3°C global warming above the preindustrial period where poverty rates exceed 50% and either at least 10 million older adults or at least 80% of the older adult population experiences 180 h or more of heat limit exceedance annually. India, Pakistan, Bangladesh, Myanmar, and Niger exceed both the absolute (10 million older adults) and proportional (80% of older adults) exposure thresholds.<h4>Interpretation</h4>Our results suggest accounting for age stratified vulnerability, intolerable heat will be experienced at much larger scales and for longer durations, affecting far more people than previously estimated. By identifying who and where people are exposed, our findings can inform targeted heat action plans and guide resource allocation and response planning.<h4>Funding</h4>US National Institutes of Health; US National Science Foundation; US National Aeronautics and Space Administration; Yale Institute for Biospheric Studies; The Rockefeller Foundation.
Background
This paper addresses the clinical question of how age-specific heat tolerance affects projections of heat limit exceedances in a warming world. Previous studies applied uniform heat limits across all age groups, potentially underestimating risks for older adults. Understanding these dynamics is crucial as global temperatures rise and populations age.
Methods
The study integrated experimentally derived heat limits for young (18-39 years), middle-aged (40-59 years), and older adults (≥60 years) with climate projections and age-stratified population projections. The analysis assessed exceedances under 1-4°C of global warming using data from 14 Coupled Model Intercomparison Project Phase 6 climate models under the shared socioeconomic pathway 5-8·5 scenario.
Results
The study found that older adults faced more frequent and extensive heat limit exceedances, particularly under the 1·5°C scenario. The use of age-specific thresholds resulted in a more than twofold increase in the global population exceeding 180 hours annually compared to previous estimates.
Interpretation
These findings indicate that accounting for age-specific vulnerabilities reveals a more severe impact of heat exposure than previously understood. While the statistical significance of the findings is clear, the clinical relevance may vary based on local conditions and adaptive capacities. Confounding factors include reliance on model projections and potential biases from funding sources.
Key findings
- Older adults faced more frequent and spatially extensive exceedances under the 1·5°C global warming scenario relative to the preindustrial period than young adults did under 4°C.
- Using age-specific thresholds more than doubled the global population having 180 h or more of exceedance annually as compared with previous estimates.
- Older adults in south Asia and the Persian Gulf could face sustained, day-and-night exposure for three consecutive months at 3°C or more warming.
- 13 countries under 3°C global warming above the preindustrial period have poverty rates exceeding 50% and either at least 10 million older adults or at least 80% of the older adult population experiences 180 h or more of heat limit exceedance annually.
- India, Pakistan, Bangladesh, Myanmar, and Niger exceed both the absolute (10 million older adults) and proportional (80% of older adults) exposure thresholds.
Limitations
- Relies on projections and models, which may not capture real-world variability.
- Funding sources could introduce bias in interpretation.
- Does not report specific sample sizes or detailed methodology.