Impacts of Temperature Extremes

Christopher R. Adams
Cooperative Institute for Research in the Atmosphere
Foothills Research Campus
Colorado State University
Fort Collins, CO


Extremes of heat and cold have a broad and far-reaching set of impacts on the nation. These include significant loss of life and illness, economic costs in transportation, agriculture, production, energy and infrastructure. The 1976 - 1977 winter freeze and drought is estimated to have cost $36.6 billion in 1980 dollars. In 1980 the nation saw a devastating heat wave and drought that claimed at least 1700 lives and had estimated economic costs $15 - $19 billion in 1980 dollars. While these are atypical examples, in recent years on average there are about 1200 deaths due to extreme hot and cold weather.

While there are numerous case studies of particular events, little systematic knowledge exists on the impacts across various sectors of the nation. The most rigorously documented impacts are the health impacts, based to a large part on epidemiological studies conducted by the U.S. Centers for Disease Control and Prevention (CDC) and others in the public health arena.

Extreme Heat

On average over the last 30 years, excessive heat accounts for more reported deaths annually than hurricanes, floods, tornadoes, and lightning combined.

Much of the literature on extreme heat impacts combines heat and drought into one climatological event. This is especially true of the work assessing the economic impacts. It is often unclear if the effects are from a short duration heat wave or a longer term drought. In many cases the two hazards are inextricably linked. In the area of health impacts, the focus has been on the temperature as a causal agent of health impacts.

Health Impacts

The July 1995 Heat Wave killed 522 people in Chicago alone. Research by CDC found that on average 384 people were killed by excessive heat each year during the period 1979 - 1992 (NOAA, 1995). (This is significantly higher that the numbers reported in the National Weather Service's (NWS) Summary of Natural Hazards Deaths. This is due to the research methodology of local NWS offices relying on published accounts of events. They do not have access to the death certificates used by CDC.) Attributing excessive heat as a cause or contributing factor in mortality has varied considerable across jurisdictions. This has led to speculation that the actual, as opposed to reported, death toll is much higher. For example, one study suggests that the actual death toll of the 1980 heat wave may be 5,000, not the official number of 1700 (Kilbourne, 1997). Other studies indicate that diagnosis of heat-related deaths have been regularly underestimated by 22% to 100%. A recent National Oceanic and Atmospheric Administration(NOAA) sponsored Heat Wave Workshop focused on the health impacts of heat waves, better forecast techniques, and community preparedness. The health effects were viewed as preventable to a large extent with improved forecasts, warnings, community preparedness and appropriate community based response. Officials from CDC referred to heat waves as a known, preventable epidemic.

Those at greatest risk of death in heat waves are the urban-dwelling elderly without access to an air-conditioned environment for at least part of the day. Thus the issues of prevention and mitigation combine issues of the aging and of public health.

One area not well understood is the morbidity, or injury and illness, associated with heat waves and excessive heat. The research has focused on mortality, in part because mortality data was available. This is a critical area for research in understanding and preventing the deleterious effects of excessive heat. Scientists at the NOAA Heat Wave Workshop identified this as a high-priority research need.

Transportation Impacts

There are several impacts on transportation documented in case studies. Aircraft lose lift at high temperatures. Phoenix airport has been closed due to periods of extreme heat that made aircraft operations unsafe. Highways and roads are damaged by excessive heat. Asphalt roads soften. Concrete roads have been known to "explode" lifting 3 - 4 foot pieces of concrete. During the 1980 heat wave hundreds of miles of highways buckled (NOAA, 1980). Stress is placed on automobile cooling systems, diesel trucks and railroad locomotives. This leads to an increase in mechanical failures. Train rails develop sun kinks and distort. Refrigerated goods experience a significant greater rate of spoilage due to extreme heat.


Various sectors of the agriculture community are affected by extreme heat. Livestock, such as rabbits and poultry, are severely impacted by heat waves. Millions of birds have been lost during heat waves. Milk production and cattle reproduction also decreases during heat waves. Pigs are also adversely impacted by extreme heat. In terms of crop impacts in the summer of 1980, it is unclear that the impacts are of very high temperatures for a few days, versus the above average summer temperatures versus the drought. We do know that high temperatures at the wrong time inhibits a crop yields. Wheat, rice, maize, potato, and soybean crop yields can all be significantly reduced by extreme high temperatures at key development stages.


The electric transmission system is impacted when power lines sag in high temperatures. Last summer a major west coast power outage impacting 4 states was blamed in part on extreme high temperatures causing sagging transmission lines to short out. The combination of extreme heat and the added demand for electricity to run air conditioning causes transmission line temperatures to rise.

The demand for electric power during heat waves is well documented. In 1980, consumers paid $1.3 billion more for electric power during the summer than the previous year. The demand for electricity, 5.5% above normal, outstripped the supply, causing electric companies to have rolling black outs.

Water Resources

The demand for water increases during periods of hot weather. In extreme heat waves, water is used to cool bridges and other metal structures susceptible to heat failure. This causes a reduced water supply and pressure in many areas. This can significantly contribute to fire suppression problems for both urban and rural fire departments.

The rise in water temperature during heat waves contributes to the degradation of water quality and negatively impacts fish populations. It can also lead to the death of many other organism in the water ecosystem. High temperatures are also linked to rampant algae growth, causing fish kills in rivers and lakes.

Extreme Cold

The average number of deaths attributed to cold is 770 yearly, substantially higher than the number attributed to heat (Kilbourne, 1997).

Health Impacts

The health impacts of extreme cold are greater in terms of mortality in humans. It appears that the causal mechanism for cold-related mortality is not so much a single cold snap as it is a longer term chronic exposure. Thus the deadly nature of heat waves per se appears to be greater than that of short periods of extreme cold. Research indicates that those at risk are primarily either engaged in outdoor activity, or are the elderly who are chronically exposed to colder indoor temperatures. This mechanism of injury causes a different set of problems for community mitigation than the heat problem.


There are a variety of transportation impacts due to cold weather. Diesel engines are stressed and, often fuel gels in extreme cold weather impacting trucking and rail traffic. Rivers and lakes freeze, stopping barge and ship traffic. Subsequent ice jams threaten bridges and can close major highways. Cold temperatures take their toll on vehicle batteries. Shear cold temperatures stress metal bridge structures. Transportation losses for the winter of 1976 -77 came to $6.5 billion (in 1980 dollars) (NOAA, 1982).


Cold temperature impacts on agriculture are frequently discussed in terms of frost and freeze impacts early or late in growing seasons. Absolute temperature and duration of extreme cold can have devastating effects on trees and winter crops as well. Prolonged cold snaps can impact livestock not protected from the frigid temperatures. In the winter of 1983-84, a single cold snap around Christmas destroyed over $1 billion of the citrus crop in Florida. Louisiana lost 80% of its citrus crop. Tennessee estimated $15 million in agriculture losses. Texas experienced hundreds of millions of dollars in crop damage (NOAA, 1983).


Energy consumption rise significantly during extreme cold weather. In the winter of 1976-77 additional energy consumption cost $3.8 billion (1980 dollars). This includes increase costs of electricity, fuel oil, and coal.

Water Resources and Infrastructure

Extreme cold temperatures can cause significant ground freezing problems, especially if there is little snow cover. Buried water pipes can burst causing massive ice problems and loss of water pressure in metropolitan areas. This poses a variety of public health and public safety problems. On case of a broken water main in Denver, Colorado forced the entire evacuation in sub-zero temperatures of the medically fragile patients of the Veteran's Hospital. Other cases of broken water mains have shut down subway systems and financial centers.

Schools often close during extreme cold snaps to protect the safety of children who wait for school buses.


The total impacts of temperature extremes are not fully documented and known. Much of the documentation of temperature impacts combines other meteorological events and uses climatological scales of space and time. The nature of seasonal impacts is more cumulative and complex than the impacts of cold snaps and heat waves. Yet the impacts are measurable. Weather forecasting must take into account the hazards and impacts of temperature extremes to provide useful, understandable and timely information for the nation to reduce natural disasters.


Kilbourne, Edwin M., "Heat Waves and Hot Environments" in Noji, Eric K., editor, The Public Health Consequences of Disasters, New York, Oxford University Press, 1997: 245-269, 270-286.

NOAA 1980, Impact Assessment: U.S. Social and Economic Effects of the Great 1980 Heat Wave and Drought, U.S. Department of Commerce, National Oceanic and Atmospheric Administration, Environmental Data and Information Service, Center for Environmental Assesment Services, Washington, DC. September.

NOAA 1982, Impact Assessment: U.S. Social and Economic Effects of the Record 1976-77 Winter Freeze and Drought, U.S. Department of Commerce, National Oceanic and Atmospheric Administration, Environmental Data and Information Service, Center for Environmental Assessment Services, Washington, DC. January.

NOAA 1983, Storm Data, U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Climate Data Center, Ashville, NC, December.

NOAA 1995, The July 1995 Heat Wave Natural Disaster Survey Report, U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Weather Service, Silver Spring, MD, December.

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