November 1998

Overview

1. Introduction

   The assessment is intended to be a report that analyzes the potential effects of climate change and variability on the health of the United States population over the next twenty to one hundred years. The uncertainties about many future variables, including population, economic conditions, other possible health or societal priorities (e.g., an unanticipated epidemic, war, etc.), as well as the complexities of human behavior, must be acknowledged and addressed in the analysis. Possible positive, as well as negative, effects must be recognized.

   We intend throughout the report to try to answer four overarching questions (with subquestions):

   1. What is the current status of the nation's health, and what are current stresses on our health?
   2. How might climate change affect (exacerbate or ameliorate) the country's health and existing or predicted stresses on health?
   3. What is the country's capacity to adapt to climate change and variability, for example, through modifications to the health infrastructure, behavioral changes, or by adopting specific coping mechanisms?
      • What are the negative health impacts, if any, of adapting?
      • What are the co-benefits, if any?
      • What are the economic and social costs/benefits?
   4. What essential research gaps must be filled?

2. Context: Current Health Status in the United States

   In this section, we plan to identify trends in morbidity and mortality in the United States population generally, and in certain subpopulations that may be particularly susceptible to variations in climate, such as the very young and the elderly. In addition to identifying the leading causes of morbidity and mortality, we also hope to identify and examine morbidity and mortality data that might be environmentally-related (e.g., respiratory illnesses).

   We also plan to identify ways in which socioeconomic changes expected over the next 100 years-the aging of the current population, immigration trends, and economic changes-might affect the health status of the country.

   In addition to looking at disease and death patterns in this country, we will also examine the current levels of and recent trends in vaccine coverage, health care utilization, and health insurance.

   Finally, we will also look at current trends in environmental conditions in the United States that could be weather or climate sensitive, and identify the ways in which those trends might affect health in the future. For example, water resource depletion, land degradation, and coastal development could have an impact on the availability of fresh water and on the health of the fisheries and agriculture industries.

3. Discussion of climate and socioeconomic models used

   In order to ensure some uniformity across the various sectors and regions, the National Assessment Synthesis Team has asked that the regions and sectors involved in the National Assessment follow a fairly standardized procedure with respect to both climate and socioeconomic and ecological scenarios forecasting future conditions.

   Climate: There is a range of options for climate scenarios: historical data, possible qualitative changes, "what if" scenarios (hypothetical, but quantitative, scenarios of possible futures), and general circulation models (GCM) of ocean/atmosphere patterns, including the "Canadian Global Coupled Model" (CGCM1), developed by the Canadian Centre for Climate Modelling and Analysis. Each approach has advantages and disadvantages, and the NAST believes that the use of all three will provide "a comprehensive understanding of sensitivities, potential impacts, and system boundaries." No decisions have been made yet as to how to use the models in the context of possible health effects of climate change.

   Socioeconomic and ecological: In our assessment, we will need to identify a few key socioeconomic and ecological variables that are likely to have the largest influence on the impact of climate change on health. A range of possible values for those variables will need to be identified. The NAST has collected population and economic projections for the year 2030 that have been developed by the National Planners Association. Only limited projections are available from the NAST for the year 2100, and they are obviously very uncertain. The health sector team has not yet identified the key future socioeconomic or ecological determinants to future impacts of climate change that might be used in modeling possible future health effects of climate change.

4. Complexities of analysis

   In the analysis, there are important relationships between variables that must be acknowledged and addressed:

   1. The sum of the effects of climate change may be greater than simply an accumulation of smaller effects. In other words, the change in risk of a disease or health effect may be influenced by changes across other sectors, e.g., water resources, agriculture, or coastal ecology. Such cross-sectoral changes may have adverse or ameliorating effects, and understanding the health effects of climate change will require integrating these broad impacts into our analysis.
   2. There are likely to be various synergies and surprises and possible feedback mechanisms that cannot be anticipated, and so can't be planned for. For example, the recent forest fires in Mexico, spurred by extreme drought, represented an unforeseen consequence of extreme climate conditions that affected respiratory health in the southern midwest.
   3. The impacts of climate change to various systems will occur simultaneously. The systemic nature of climate change poses unique challenges to resource managers. For example, water is directly affected by climate change and variability, and is also indirectly affected-for example, as agriculture is affected by climate change, the demand for irrigation water might increase, adding stress to the water system.
   4. International effects must be recognized, despite the focus of the analysis on the United States. The Intergovernmental Panel on Climate Change (IPCC) has said that the impacts of climate change will likely be most felt by people in developing countries, where population and environmental degradation have already put a great deal of stress on people's health, living conditions, and access to necessary resources, as well as on the region's ability to withstand extreme climate events. One possible result of climate change is increased risk that Americans will be exposed to infectious diseases when traveling overseas. Another possible outcome is an increase of migration into the United States of environmental refugees whose health may be poor.

5. Brief Summary of Physical Consequences of Climate Change and Their Potential Health Impacts in the United States

   This section will be an introductory summary of the analyses that are set out in the remainder of the report.

   The assessment cannot address every possible health effect; indeed, there may be many health effects that have not yet been anticipated. Four areas of effects we do not plan to address at this point are:

   1. The possibility that an increase in UV radiation exposure could lead to a rise in cancer rates, especially skin cancer rates.
   2. The relationship between risk to human health and economic losses (for example, the possibility that a fear of infectious disease might cause a reduction in tourism in some regions).
   3. Mental health problems resulting from stress caused by disaster.
   4. The effects of climate change on food growth and storage in the United States (for example, the possibility of increased grain molds due to wet seasons).

   These and other excluded topics will be specified in this introduction section. In addition, we will probably not be able to address in any detail, the "human welfare" aspects of climate change and responses to climate change-for example, having to keep children indoors more to avoid high temperatures and air pollution.

   As described more fully in the following sections, the assessment will focus on five key public health impact areas: (1) heat; (2) air pollution; (3) water and food-borne illness; (4) vector-borne disease; and (5) extreme events.

Heat-Related Morbidity and Mortality

It has been suggested that more frequent or severe heat waves could cause an increase in morbidity and mortality among the elderly, infants, and people with cardiovascular and respiratory disorders. Studies of certain U.S. cities have shown that the number of summertime heat-related deaths could increase over the next several decades under some climate scenarios.

The health sector assessment will look at what is known about the relationship between heat and morbidity and mortality in the United States. It will address questions such as whether there is any critical threshold temperature and whether the duration of the heat event is significant to the association between mortality and temperature.

The assessment will also look at how Americans are currently protected from the risk of heat-related mortality. What kind of housing do people live in? How widespread is air-conditioning in this country? What sorts of community response plans exist in various cities for dealing with serious and prolonged heat waves?

We will also identify any groups of people that are particularly vulnerable to heat, such as the urban elderly, children/infants, illegal immigrants living or traveling along the southern border, and people with cardiorespiratory or other illnesses.

Finally, the assessment will attempt to project future heat-related morbidity and mortality using the climate and socioeconomic models developed by the NAST, identifying the uncertainties in the analysis. Possible adaptive measures will be identified and discussed.

It has been suggested that any increase in heat-related mortality could possibly be offset by a decrease in cold-related deaths during milder winters. The possible reduction in cold-related mortality will be addressed to the extent there are data on the question.

Air Pollution-Related Respiratory Effects

In order to evaluate the potential for harmful health effects from air pollution in the future, the assessment will, to some extend, look at trends in air quality: What pollutants are currently regulated? What is the quality of air in U.S. urban and other areas? What are the primary sources of the air pollutant emissions? Special emphasis will likely be placed on pollutants, such as ozone, that are affected by temperature and thus likely to be affected by climate change. We may look at transboundary pollution as it relates to climate change.

The assessment will summarize what is known about the association between air pollution and adverse health effects, looking at toxicological studies, human clinical studies, and epidemiological/ecological studies. Vulnerable populations will be identified. The role of climate in the formation of secondary air pollution (e.g., ozone and fine particulates) will be explored; the assessment will also look at the relationship between weather/climate and natural emissions of air pollutants and natural allergens.

As with other sections, the assessment will look at current activities to reduce health risks from exposure to air pollution-legal and regulatory activities, air pollution alerts, and monitoring and research.

Finally, the assessment will attempt to project future air pollution-related morbidity and mortality using the climate and socioeconomic models developed by the NAST, identifying the uncertainties in the analysis. Possible adaptive measures will be identified and discussed.

Water- and Food-Borne Disease

Concerns have been raised that climate change could increase the risk of water-borne disease. As EPA has stated*:

Poor sanitation, poor erosion control management, coastal sewage release, and contamination of drinking water from agricultural fertilizers and waste may all increase the likelihood of water-borne disease. Any changes that affect the sea-water temperatures at the surface, nutrient levels, winds, currents, and precipitation patterns-also can change the marine ecosystem, leading to possible increases in diseases transmitted from fish and shellfish. Higher surface temperatures, for example, stimulate the growth of certain species of algae, in particular, toxic "red tides." When these algae are consumed by fish and shellfish, they pose a threat of food poisoning to humans.

Marine phytoplankton and zooplankton can shelter a dormant form of cholera when pH, temperature, salinity, and nutrient levels are insufficient to sustain the infectious form. When waters warm or when nutrient levels increase, cholera can become infectious again.

In addition, saltwater intrusion caused by changes in sea level is threatening drinking water supplies in many communities along the East Coast. Florida has already resorted to building a large number of desalinization plants.

The assessment will evaluate the current trends in morbidity and mortality associated with drinking water in the United States, as well as the ways in which we currently protect ourselves from this risk (for example, by chlorination). It will explore the relationship between storm events and contamination of surface water, which could lead to the possible contamination of drinking water and of foods, such as fruit crops, irrigated with contaminated water. People could also be exposed to contaminated freshwater sources as a result of flooding or similar events.

The assessment will evaluate whether it is possible to make projections about future trends in water- and food-borne contamination, and in morbidity and mortality related to contaminated freshwater and marine water, under the given climate and socioeconomic scenarios.

Vector-Borne Diseases

Concerns have been raised that climate change could have an impact on the habitat of disease-carrying organisms such as mosquitoes and rats and on the pathogens they carry. Some diseases of concern include malaria, dengue fever, and encephalitis. If climate change does increase the chance of exposure within the United States, the question remains whether people are adequately protected from disease because of vector control programs, housing conditions (e.g., the use of window screens and air conditioners), and other factors. The assessment will look closely at what is known and not known about the relationship between climate and vector-borne diseases and trends in such diseases in the United States. It will also attempt to project future trends in both the range of disease vectors within the U.S. and in adaptation strategies, and the potential negative side effects of some of these adaptive responses, e.g., use of pesticides.

Extreme Events

Climate change could alter the frequency and severity of extreme weather events. The assessment will investigate such changes in the U.S., including flash floods, mudslides, and storm surges. Baseline impacts of tornadoes and hurricanes will be assessed, though climatologists remain uncertain as to whether these type events will increase or decrease. The assessment will also consider what adaptation strategies are available and appropriate.