Hot weather and heat extremes: health risks

High ambient temperatures and the associated heat stress can increase morbidity and mortality, and increase adverse pregnancy outcomes, illnesses in very young children and physically active adults, and have negative consequences for mental health. Evidence suggests that high temperatures also can impair productivity and elevate the risk of disease in occupational workers. Almost half of the global population and more than one billion workers are exposed to high heat episodes and about one-third of all exposed workers experience negative health effects. However, excess deaths and many heat-related health risks are preventable with appropriate heat action plans involving behavioral strategies and bio-physical solutions. Extreme heat events are becoming permanent features of summers worldwide, causing large numbers of excess deaths. Heat-related morbidity and mortality are projected to further increase as climate change progresses, with greater risk associated with higher degrees of warming. Particularly in tropical regions, increased warming may mean that physiological limits related to heat tolerance will be reached regularly/more often in coming decades. Climate change is interacting with other trends, such as population growth and aging, urbanization, and socioeconomic development, that can either exacerbate or ameliorate heatrelated hazards. Urban temperatures are further enhanced by anthropogenic heat from vehicular transport and heat wasted from buildings. 3 Although there is some evidence of recent adaptation to increasing temperatures in high-income countries, projections of a hotter future suggest that without investment in research and risk management actions, heat-related morbidity and mortality will likely increase.