The health impacts of climate change
Climate Change and Extreme Heat Events

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Abstract

The association between climate change and the frequency and intensity of extreme heat events is now well established. General circulation models of climate change predict that heatwaves will become more frequent and intense, especially in the higher latitudes, affecting large metropolitan areas that are not well adapted to them. Exposure to extreme heat is already a significant public health problem and the primary cause of weather-related mortality in the U.S. This article reviews major epidemiologic risk factors associated with mortality from extreme heat exposure and discusses future drivers of heat-related mortality, including a warming climate, the urban heat island effect, and an aging population. In addition, it considers critical areas of an effective public health response including heat response plans, the use of remote sensing and GIS methodologies, and the importance of effective communications strategies.

Introduction

Extreme heat events, characterized by stagnant, warm air masses and consecutive nights with high minimum temperatures, are a significant public health problem in the U.S. that will be exacerbated by the synergistic effects of a warming climate, urbanization, and an aging population. In fact, extreme heat events (EHE), or heatwaves, are the most prominent cause of weather-related human mortality in the U.S.,1 responsible for more deaths annually than hurricanes, lightning, tornadoes, floods, and earthquakes combined.

Although all heat-related deaths and illness are preventable, many people succumb to extreme heat every year. Over a 5-year period, from 1999 to 2003, a total of 3442 heat-related deaths were reported in the U.S. (an annual average of 688).2 Extreme heatwaves, such as that witnessed across Europe in 2003, can result in a significantly higher mortality.3

Despite the high mortality associated with EHE and projections of a warming climate, there is a lack of public recognition of the hazard of extreme heat exposure,4 and U.S. metropolitan areas generally lack preparedness measures such as heatwave-response plans.5, 6 Part of the problem lies in the fact that heatwaves are silent killers—natural disasters that do not leave a trail of destruction in their wake. Like other natural disasters they are sporadic phenomena, but unlike hurricanes, which leave lasting reminders of the devastation, memories of the heatwave disappear once cooler weather arrives.

This article reviews the clinical and epidemiologic features of heat-related deaths in the U.S. and discusses the potential impacts of climate change, urbanization, and demographic trends on EHE-related mortality. It also discusses individual- and community-level approaches to preventing heat-related illness and death, as well as the application of new methodologies for identifying locations and populations at greatest risk of exposure to extreme heat stress and their contribution to efforts to bolster public health preparedness for heatwaves.

Section snippets

Heat-Related Illness: Clinical and Epidemiologic Aspects

Prolonged exposure to high temperatures can cause heat-related illnesses, including heat cramps, heat syncope, heat exhaustion, heat stroke, and death.7 Heat exhaustion is the most common heat-related illness.8 Signs and symptoms include intense thirst, heavy sweating, weakness, paleness, discomfort, anxiety, dizziness, fatigue, fainting, nausea or vomiting, and headache. Core body temperature can be normal, below normal, or slightly elevated, and the skin can be cool and moist.1, 7, 9 If

Climate Change

Mounting evidence that the earth's climate is changing has led the UN Intergovernmental Panel on Climate Change (IPCC) to conclude that “warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising of global average sea level.”27 In fact, climate model simulations project that, for the first half of the twenty-first century, year-round temperatures across North America

The Public Health Response and Adaptation Measures

Public health efforts to prevent heat-related illness during EHEs require attention to both individual- and community-level risk factors. During heatwaves, elderly, disabled, or homebound people should be checked frequently for sign of heat-related illnesses, or transported to emergency cooling shelters for respite. Even a few hours spent daily in an air-conditioned environment has been shown to be a strong protective measure in reducing heat-related illnesses and death.10

If exposure to heat

Conclusion

Heatwaves are a significant public health threat in the U.S. Although climate change, urbanization, and demographic trends will continue to contribute to risk, preventive approaches can help reduce the morbidity and mortality associated with these events. Public health practitioners can play an active role in developing adaptation measures such as city-specific heat response plans. The development and implementation of these plans should be guided by the best evidence, generated by

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