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3. Heat and Severe Weather

Published onApr 10, 2020
3. Heat and Severe Weather

Things are not as simple as they seem.

—French public health official at the onset of the 2003 heat wave

Heat Waves and Illnesses

The 2003 European heat wave began quietly, with news stories that were often humorous. A Danish taxi driver wore a skirt to work. He did this because his employer would not let him wear shorts. An Italian candy maker suspended delivery of chocolate eggs so they would not melt. German garbage collectors began their workday an hour and a half earlier than usual to make removal of “fast-rotting rubbish” more tolerable.

Soon, reports of an unusual number of deaths began to trickle in. Five people older than eighty-nine years of age died in a single weekend at a retirement home near Paris. Fifty Parisians were reported to have died from heat-related illness in just one week. The true magnitude of the problem started to become apparent when Les Pompes Funèbres Générales, France’s largest group of undertakers, reported handling 50 percent more bodies than usual in a week. There were so many deaths that they had to rent refrigerated trucks to handle the unexpectedly large number of bodies. In what became a colossal understatement, a representative from the French health ministry was quoted as saying, “Things are not as simple as they seem.” The final death toll throughout Europe attributed to the 2003 heat wave is thought to be around seventy thousand.1

This was not an isolated event. In August 2010, the Weather Underground reported on the combination of wildfire-fueled air pollution and heat that affected the Moscow area. The temperatures in the region exceeded 30°C for twenty-seven days in a row.2 The Weather Underground quoted the head of Russia’s weather service as saying, “Our ancestors haven’t observed or registered a heat like that within 1,000 years.” The toll from that event was expected to be at least fifteen thousand. The extreme heat combined with air pollution levels that were two to three times “maximum safe levels,” and carbon monoxide levels soared to 6.5 times the so-called safe level.

Heat Illnesses

Kory Stringer seemed unlikely to be susceptible to a heat-related illness.3 This 335-pound, six-foot-four all-star offensive tackle for the Minnesota Vikings was twenty-seven years old when he took to the field for the last time on a hot summer day in 2001. On the day before he was stricken, he complained of exhaustion during practice. He was carted off the field, but vowed to return the next day. He did. On his final day, the temperature was around 90°F. The heat index, a measure of how hot it feels that is based on the humidity and actual temperature, was 110. The players were in full uniform. During the 2.5-hour practice, he vomited three times and left the field for an air-conditioned space. After complaining of dizziness, he was taken to a hospital, where his temperature was 110°F. He was unconscious until the time of death early the next morning.

Multiple heat-related medical conditions exist. These range in severity from heat rash to heat stroke, a life-threatening medical emergency and the cause of Kory Stringer’s death. Certain medications, such as those needed to treat high blood pressure, some mental conditions, heart disease, and the extremes of age, all increase the risk of developing a heat-related illness.

Heat rash, also known as prickly heat or miliaria, occurs when the pores of sweat glands become blocked. This traps perspiration under the skin and causes itching and a raised, punctate, red rash. Heat rash is usually self-limited and rarely requires medical attention. Washing with cool water and general cooling measures are usually sufficient treatment. This condition is most common in babies and young children, but adults may also be affected. Heat rash becomes less common with aging, when skin changes and the number of sweat glands is reduced.

Heat cramps are painful spasms of muscles that may occur during exercise in hot weather. The calf muscles are commonly affected, but any muscle group involved in exercise may be involved. Treatment consists of cooling, rest, stretching, and massage of the affected muscles. These measures generally suffice to relieve symptoms. Sport drinks or juice may help, as long as there are no medical contraindications to their use. Although rare, very severe, prolonged cramps may be associated with damage to muscles that releases a muscle protein (myoglobin) into the blood. High concentrations of myoglobin in the blood may tint the urine, making it the color of strong tea, and may impair kidney function.

Under normal conditions, the body has reflex-like mechanisms that are designed to keep the body temperature within narrow limits. In response to heat and/or exercise, the blood vessels in the skin dilate and sweat glands produce more perspiration. The evaporation of water has a cooling effect. When this cooling mechanism begins to fail, patients may develop heat exhaustion. Symptoms of this condition typically include a cool, moist skin associated with heavy sweating. Unless the lost fluid is replaced, patients will become dehydrated. This is likely to lead to additional symptoms, including dizziness or faintness, weakness, or excessive fatigue. At that stage, patients may have a weak, rapid pulse and low blood pressure, particularly when standing up after sitting or lying down. Cramps, headache, and nausea may also be present. It is imperative to move the affected individual to a cool location and for that individual to stop all activity and rest. Replacement of the lost fluid by administering cool water or a sport drink is important. Persistent or worsening symptoms require urgent medical attention to prevent heat stroke.

Heat stroke is the most severe of the heat-related illnesses. It is a medical emergency and suspected victims should be transported to an emergency room in an ambulance. Heat stroke occurs when the defenses against a rise in body temperature are overwhelmed. Heat stroke is diagnosed when the body temperature reaches 104°F (40°C) or higher. The skin may be either hot and dry or moist. Profuse sweating does not reliably exclude heat stroke. Patients are frequently nauseous and may vomit, contributing to the loss of body fluids. The skin is usually red, as blood vessels dilate maximally. Respirations and heart rate may be rapid. Headache and confusion may progress to loss of consciousness. Emergency treatment is mandatory and should consist of moving out of the direct sun and removing excess clothing while waiting for emergency first responders. If possible, ice packs and wet towels should be applied. Fluids should be given by mouth unless the affected person is unable to swallow due to an impairment of consciousness. Failure to act promptly can lead to coma, irreversible damage to the brain, or death.

The Epidemiology of Heat Illnesses

The US National Weather Service began to tabulate deaths due to severe weather in 1940 (, accessed April 22, 2014), at which time lightning was the leading cause of weather-related deaths. Lightning claimed 9,325 lives in the interval between 1940 and 2012. Like most other deaths due to weather, lightning deaths vary substantially from year to year. In order to smooth out the peaks and valleys between years, a ten-year moving average is a better descriptor. Moving averages are calculated for a year by averaging the data from the adjacent ten years. As years advance, the last year is dropped and the next year in the series is included. Using this method for reporting, the moving average for deaths due to lightning is smoothed out to thirty-five deaths per year. Heat fatalities were added to the database for the first time in 1986. Between then and 2012, 3,727 deaths were recorded, with a ten-year average of 117 per year, making heat the leading cause of weather-related mortality in the United States. The annual heat-death toll peaked at 1,021 in 1995, due in part to the Chicago heat wave.

Somewhat surprisingly, the Global Burden of Disease 2010 project does not list heat as a cause of death or a risk factor. However, the World Health Organization estimates that by 2004 global warming had become responsible for over 140,000 excess deaths each year.4 In the Working Group II’s contribution to the IPCC Fifth Assessment Report, heat is predicted to have a leading impact on health if global temperatures increase by 1.5C°. There will be further, dramatic increases if global mean temperatures rise by 4.0C°.5

Heat wave is a term that is used frequently, often without much or any precision—and there are good reasons for this. The effects of an increase in temperature are often complicated by other variables, such as the nature of the exposed population, the relative humidity, whether there is evening cooling or not, and others. The IPCC defines a heat wave in its glossary as “a period of abnormally and uncomfortably hot weather.”6 This definition poses many problems, including the definition of a period. How should one define abnormal or uncomfortable, and what is meant by hot? The World Meteorological Organization has a more precise definition: when the daily maximum temperature on five or more consecutive days exceeds the average by 5°C, compared to the period between 1961 and 1990. This strict definition makes it possible for climatologists and others to make precise measurements and draw statistically rigorous conclusions about trends. Although this definition is precise, it fails to include the effects of other variables that determine the impact of temperature on health.

The problems associated with defining a heat wave call to mind Justice Potter Stewart’s opinion with regard to obscenity in the landmark Supreme Court ruling in Jacobellis v. Ohio: “I know it when I see it.” Thus, it may well be that virtually any definition of heat wave will have shortcomings—but people who are living through one know it. The IPCC may have had a valid reason for publishing a definition that lacked precision.

Anatomy of a Heat Wave

Most heat waves come and go with little fanfare or documentation. The 1995 heat wave that affected Chicago, Illinois, is an exception.7 Like other heat waves, it was the result of a period of sustained high pressure in the upper atmosphere coupled with an unusually high level of moisture in the ground-level air. The official start of the heat wave occurred on July 12, when the temperature at both Chicago O’Hare and Midway airports reached 97°F, and it ended on July 16, when temperatures finally fell to 93°F at both sites—a temperature that was more typical for that time of the year.8 Although the National Weather Service issued warnings, the highs and lows for those days exceeded predictions. The forecasts were not well covered by the media, and therefore the public was generally unaware of the impending heat wave and the risks it faced. In the United States, it is unlikely that weather forecasters would fail to issue similar warnings today: weather is big business for local TV stations. However, in other parts of the world where weather forecasts are either poor or nonexistent, populations at risk would have little if any opportunity to prepare let alone take action to prevent heat-related problems.

The number of heat-related deaths varied somewhat among reports. The National Oceanographic and Atmospheric Administration’s report documented 495 heat-related deaths in Chicago between July 11 and July 27. In Milwaukee, Wisconsin, located about ninety miles (about 150 km) north of Chicago, there were eighty-five heat-related deaths during the same time interval.

The healthcare system in Chicago was stressed by the heat wave. During the peak week of the heat wave, hospital admissions were 11 percent higher than normal.9 Admissions of the elderly, those over sixty-five years of age, were up 35 percent. They usually required treatment for dehydration, heat stroke, and heat exhaustion, and these diagnoses accounted for most of the increase. Chronic medical conditions were additional risk factors for hospitalization. These included cardiovascular disease (up 23 percent), diabetes (up 30 percent), renal disease (up 52 percent), and nervous system disorders (up 20 percent).

Of course, people die every day—so how can we attribute a death to a given heat wave? One study did just this. Investigators reexamined the toll exacted by the Chicago heat wave by comparing deaths during the heat wave interval with fifty-day periods from prior years that were centered on the day of the temperature peak.10 They estimated that there were 692 excess deaths between June 21 and August 10. Deaths peaked on July 15, two days after the temperature peak, when 439 deaths occurred. The week of July 14 was the deadliest interval, when an average of 241 people died each day. There were 1,686 deaths that week: only 4.7 percent of these were reported to be due to heat alone, 28.1 percent included heat as a contributing factor, and 93.7 percent involved some form of underlying cardiovascular disease. Only a quarter of the deaths were considered somewhat premature. That is, these people would have died soon anyway, but the date of their demise came sooner than it might have. Technically, this is known as mortality displacement, or, more morbidly, as a harvesting effect. The relative risk for all-cause deaths on June 13, 1995, was 1.74; that is, Chicagoans were 1.74 times more likely to die during the heat wave than during a comparable year when temperatures were normal. African Americans were selectively at risk, but the mortality displacement in this population was lower.

A year after the disaster, a cohort of 339 friends or relatives of those who succumbed was interviewed. They were chosen if the person who died was older than twenty-four and if the death certificate specified heat or cardiovascular disease with or without heat as a contributing cause of death.11 An identical number of age- and neighborhood-matched individuals served as a control population. Those with known medical problems were at the highest risk. In this group of unhealthy individuals, those who had been visited by nurses—a marker for poor health—had the highest risk of death. This was followed, in order, by those confined to bed, those who were unable to care for themselves, and those who had mental problems, a heart condition, or a lung condition. Risks were lowered if individuals had been contacted by a city worker during the heat wave. Taken as a group, the greatest risk factors for dying were being bed-bound or living alone. Availability of air-conditioned places and access to transportation were protective factors.

There are important conclusions to be drawn from these retrospective analyses: it is possible to mitigate the effects of heat waves. Improvements in weather forecasting are critical. Heat waves are like any other natural disaster; preparation and timely action focused on those with the highest risk will save lives. For more, see the section of chapter 10 addressing adaptation to heat.

Chicagoans were not the only ones affected by heat. In an analysis of the data collected by the largest emergency room data system for the years 2009 and 2010, there were approximately 8,251 emergency room visits for heat stroke in the United States.12 This yields an annual incidence of 1.34 emergency room visits for this disorder for every 100,000 Americans. The highest incidences occurred among males (1.99 visits per 100,000) and those over eighty, who had about 4.45 visits per 100,000. Three and a half percent of those taken to emergency rooms for heat stroke died. As expected, heat stroke was the most common during the summer months of June, July, and August and more common in the South (1.61 visits per 100,000).

Although the National Weather Service’s data concerning weather-related deaths begins to identify heat as a critical health-related risk factor, the Chicago experience and now the broader US experience show that this statistic fails to capture the importance of heat-related illness in the United States. The problem is certain to be worse elsewhere where it is hot more often, the public health infrastructure is either nonexistent or poorly prepared to cope with heat waves, and adaptive measures, such as air conditioning, are minimal or nonexistent. These problems undoubtedly contributed to the more than 2,500 deaths reported in India in June 2015.13

Our Hotter Future

Under virtually every imaginable scenario, global and US surface temperatures will be hotter in the future than in the historical past. This was shown graphically in figure 2.6. This figure portrays likely temperatures for each of the four representative concentration pathways (RCPs) that are at the heart of the IPCC’s Fifth Assessment Report. As seen in the figure, there is not much difference in the projected temperatures by mid-century. However, with the high-emissions scenario, RCP8.5, surface temperatures increase sharply thereafter. This means that there will be more hot days and more instances of heat-related illness in this version of the future. In their analysis of these data, the authors of the American Climate Prospectus predict that Americans are likely to endure between two and three times as many days with temperatures in excess of 95°F compared to the years between 1980 and 2001 under RCP8.5.14 This is the IPCC scenario that predicts a business-as-usual future, with little in the way of effective measures to limit greenhouse gas emissions. This scenario predicts that many Americans will experience between 46 and 96 days per year when temperatures exceed the 95°F threshold. The authors of American Climate Prospectus combined their results with predictions from the Third National Climate Assessment and predicted that residents of the Southeast are likely to experience between 56 and 123 days, or almost one-third of the year, when temperatures exceed 95°F. Between 1981 and 2010, that number was nine. This huge additional heat burden is virtually certain to lead to additional morbidity from heat and other aspects of daily life that are dependent on temperature and on agricultural productivity.

The temperature of 95°F is not chosen arbitrarily for scrutiny. When the relative humidity is 100 percent, this is the maximum temperature at which a normal, resting, well-ventilated individual can maintain a normal body temperature by the evaporation of sweat. At higher temperatures, the humidity must be lowered or the individual must move to a cooler spot. Failure to act increases the risk for heat exhaustion or heat stroke, particularly if one engages in even relatively mild exercise. Threats posed by the combination of high temperatures and humidity are less likely to result in an increase in heat-related illnesses in the already-hot southern portion of the United States because of the ready access to air conditioning.15

Two contemporary studies differ in their predictions of who will be the most susceptible to rising temperatures. One group predicts that temperatures above 80°F will have the highest impact on those between the ages of one and forty-four years of age.16 This appears to be true in spite of an 80 percent reduction in mortality associated with heat after 1960 compared to heat-related mortality before that date. The protective effect after 1960 was due to air conditioning, in spite of the effects of heat on individuals with cardiovascular or respiratory diseases. Another group, using different methods, found that children less than a year old are the most susceptible to heat.17 Both groups agree that mortality rates are lowest when average daily temperatures are between 50°F and 59°F. Below that range, mortality due to respiratory diseases rises in association with colder temperatures. Above 90°F, mortality rises at a rate of 0.08 percent per degree. In an analysis of the relationship between heat and hospitalization rates in California, study authors found a much higher rate.18 They examined temperature and data for over two hundred thousand deaths, and found that a 10°F increase in the temperature was associated with a 213 percent increase in mortality.

The authors of the American Climate Prospectus conclude that heat-related mortality rates are not likely to change prior to the middle of this century, in accord with the various RCP scenarios that predict temperature changes in the future. This situation changes dramatically by the end of the century. The highest emissions scenario leads them to conclude that there will be between 3.7 and 21 deaths per one hundred thousand people. In a somewhat less likely conclusion, they predict that there will be a one in twenty chance that death rates will be higher than thirty-six per one hundred thousand. Table 3.1 presents a more complete picture of their results for different age groups for the RCP2.6 and RCP8.5 scenarios.

Table 3.1 Future climate change impacts on US mortality rates in the 2080 to 2099 time interval for the RCP2.6 and RCP8.5 scenarios

Age group



Less than one year of age

-1.1 to 2.5

3.2 to 17

1–44 years of age

0.2 to 1.5

3.1 to 7.6

45–64 years of age

-1.3 to 2

2.8 to 14

Older than 65 years of age

-25 to 17

-21 to 90

Note: The likely change range, in deaths per one hundred thousand, represents the 17–83 percent confidence limits. Extracted from T. Houser, R. Kopp, S. M. Hsiang, et al., American Climate Prospectus: Economic Risks in the United States (New York: Rhodium Group, LLC, 2014).

A more global approach to evaluating heat-related mortality has been taken by a group of Japanese investigators.19 Using complex modeling techniques, they identified an optimum temperature at which the fewest deaths occurred in the Tokyo region, where year-round temperatures average about 28°C. From this baseline, they used temperature and other variables such as population size and degrees of adaptation to estimate the number of expected excess deaths due to heat in various World Health Organization regions in 2030 and 2050. In the North American high-income segment, they projected a population size of 401 million in 2030, with a baseline mortality of about 2,400 deaths. Assuming 0, 50, and 100 percent adaptation, they estimated that there would be around 7,400, 4,700, or 2,700 excess deaths, respectively, due to heat. By 2050, the population projection was expected to be around 447 million, with around 15,400, 7,900, or 3,200 excess heat-related deaths, respectively, depending on the level of adaptation. These results buttress the assertions made by the IPCC in terms of the value of adaptive measures designed to reduce the health effects of heat.20 Table 3.2 shows additional data.

Table 3.2 Excess deaths due to heat for various World Health Organization regions

Heat and Healthcare Delivery

It is impossible to conclude that climate change is the cause of any given heat wave. However, it is possible to estimate the probability of recurrent episodes of hot weather. One group of climate scientists has done just that. They concluded that human activity has more than doubled the probability of experiencing an even worse heat wave than the one that gripped Europe in 2003.21 Another group reached a similar conclusion.22 Working from a baseline taken between 1999 and 2008, this group concluded that the probability was greater than 95 percent that a 2003-like heat wave had “more than doubled under the influence of human activity in spring and autumn, while for summer it is extremely likely that the probability has at least quadrupled.”23 These and other findings have profound implications for those charged with planning for the future and how to mitigate the effects of climate change.

Not everyone is equally at risk for the development of a severe illness or death during heat waves. The Chicago experience showed that living conditions were important in determining the risk of death.24 Markers for social vulnerability and poverty, such as absence of air conditioning, confinement to bed, and the need for Meals on Wheels, were markers for increased risk. Listening to the radio and reading newspapers were found to be associated with an increased knowledge of the health risks associated with the heat wave.

Fewer people die during mild winters. This defers death for some, placing those who might have died during the winter at greater risk for hospitalization and death during an ensuing hot summer.25 Although confinement to a healthcare facility might be expected to reduce risk, this is not always the case. A comprehensive evaluation of the effects of the 2003 heat wave on hospitals in the United Kingdom revealed a number of ways hospitalized patients were vulnerable.26 Problems with the power grid, including failure of freezers and information technology equipment, are risk factors for those in the hospital. The study found that the use of portable air-conditioning equipment taxed already strained power supplies and led to power failures. Some laboratory equipment was not adequately heat resistant and failed due to the heat. Finally, the heat itself had unspecified adverse effects on the hospital staff and patients.

It is almost a “no-brainer” to conclude that warming due to climate change will lead to more severe effects on health. In one quantitative approach to predicting the effects of heat on health, two investigators from the London School of Tropical Medicine and Hygiene evaluated data from over one hundred US communities between the years 1887 and 2000 in order to determine whether prolonged spells of hot weather carried an extra risk for death beyond that associated with the usual risk for each day. The investigators concluded that there was a daily risk from high temperatures. They referred to this as the main effect. A so-called added effect of sustained high temperatures appeared after four days of hot temperatures. Although the added effect was important, it was outweighed by the main effect.27

Mitigation of Heat Effects

One of our challenges will be to develop and use effective measures designed to adapt our social systems and the built environment to higher temperatures. Adaptation works. Largely because of the spread of air conditioning, investigators have found that the mortality on hot days fell by around 80 percent in the years from 1960 to 2004 compared to the years between 1900 and 1959.28 Before 1960, these authors presumed that there were around 3,600 deaths annually compared to six hundred premature deaths after 1960. This information has serious implications for the future in both the United States and the rest of the world as surface temperatures climb, regardless of emissions. A separate study estimates that residential electricity bills will increase by 15–30 percent to pay for the increase in air conditioning.

Risks associated with heat waves are like other risks; they are a function of the hazard, the vulnerability to the hazard, and the level of preparedness. The published experiences of others tell us what we need to do. Cities need to be designed and reengineered to resist the effects of heat and the buildup of trapped heat caused by the combined effects of hot weather, building design, and energy use, the so-called heat islands. Effective measures include planting trees and other vegetation, sometimes on the roofs of new or existing buildings. These measures reduce the need for air conditioning, trap and use storm water, and enhance the aesthetic value of property. Reflective, cool roofs produce similar benefits by reducing the need for air conditioning. Cooperation between city governmental agencies and nonprofit institutions, such as Visiting Nurse Association, Meals on Wheels, and others, can provide a mechanism to monitor the health of the individuals at the greatest risk: the sick and those who live alone who may be home- and bed-bound. The Chicago experience, like that of other municipalities, points out the need for cooling shelters for those without air conditioning. Hospitals and other healthcare institutions need disaster plans that include heat emergencies. Planning for heat emergencies will save lives. Additional mitigating factors are discussed in chapter 10.

Extreme Weather Events

Aside from heat, most extreme weather events do not have specific health problems identified with them. Nevertheless, cyclones and hurricanes, floods due to intense precipitation or storm surges, tornadoes, and other weather events take a toll on lives. Climate change is likely to have effects on these extreme weather events.

Warming of the climate drives extreme weather events. As the earth’s surface, atmosphere, and oceans warm, fundamental physical principles dictate that more water will evaporate from bodies of water and the soil. This increase in the water content of the atmosphere leads to storms and increases in precipitation, deaths and injuries, and property damage. According to the National Climatic Data Center, there have been 151 weather or climate disasters since 1980 for which costs were at least $1 billion (adjusted to 2013 dollars). The total estimated cost is over $1 trillion. Seven of these events took place in 2013.

Extreme Precipitation

Heavy rains and flooding are big news. The following samples are culled from reports from May 16, 2014, a date chosen for no particular reason: “Record rain floods Triangle roads ... knock out power [as] a record 3.38 inches of rain,” Raleigh (NC) Newsobserver; “Isolated storms, heavy rain pose flood risks Friday,” Baltimore Sun; “Heavy rains flood streets, creeks, and cancel flights in North Texas,” Dallas Morning News; “Serbia and Bosnia-Herzegovina have been hit by some of the worst flooding in each country’s history,” and “A plodding system that has left flooding in multiple Midwestern and Southern states continued to creep up the East Coast, bringing a serious flash flood threat and major flooding to areas of the Mid-Atlantic,” according to the Weather Channel.

Rain is common in the Pacific Northwest, but the record book went out the window in the spring of 2014. Rainfall was 200 percent above normal for the forty-five days prior to March 22, 2014, when a landslide obliterated a small community four miles east of Oso, Washington.29 Soil saturation had created an unstable condition that caused the collapse of a hill. The landslide that resulted engulfed an area of approximately one square mile. At least forty-one people died.

Although any one of these single events may be completely unrelated to climate change, as a group they are consistent with the pattern of increased rainfall observed over the past several decades while global surface temperatures have been increasing and with predictions for the future.

A detailed sixty-two-year study of the rainfall over the central portion of the United States—a region that includes Texas, Louisiana, and parts of Mississippi north through the Mississippi River valley to Minnesota, Wisconsin, Michigan, and Ohio—was published in 2012.30 The investigators included just those sites that had rainfall-measuring devices that met strict, predefined criteria for accuracy. They found a significant redistribution of rainfall when they compared the 1948–1978 era to a thirty-one-year period that ended in 2009. There was an increase in the frequency of days with “very heavy” rainfall exceeding three inches (76.2 mm) and “extreme precipitation events,” defined as daily rainfall exceeding six inches (154.9 mm). In this region, there were sites with up to a 40 percent increase in the frequency of daily and multiple-day occurrences of these extreme precipitation periods. Tropical storms did not contribute to these results. The intensity of precipitation—that is, hourly totals—remained constant during the sixty-two years of the study period.

This regional trend is illustrative of the changes in rainfall patterns throughout the United States. Although the total amount of rainfall in the United States has increased by about 7 percent during the past one hundred years, the amount of rain falling during the heaviest downpours (the highest 1 percent) has increased by as much as 71 percent in the Northeastern part of the nation.31 Table 3.3 shows regional change data.

Table 3.3 Observed changes in heavy rainfall patterns in the United States, 1958–2012


Percent change in heaviest 1 percent

Northeast (ME, VT, NH, MA, NY, PA, NJ, DE, MD, WV)


South (VA, KY, TN, NC, SC, GA, AL, MS, FL, LA, AR)


Midwest (OH, MI, IN, IL, WI, MO, IA, MN)


Great Plains (MT, ND, SD, WY, NB, KS, OK, TX)


Pacific Northwest (WA, OR, ID)


Southwest (CA. NV, UT, AZ, NM, CO)






Puerto Rico


Hurricanes and Cyclones

Few natural events unleash more power than tropical hurricanes and cyclones. The web provides many values for the amount of energy they release. One of the most reliable calculations has been made by the NOAA Hurricane Research Laboratory.32 The laboratory estimates that a mature hurricane releases about 1.5 × 1012 watts per day, an amount roughly equal to about half of the electricity-generating capacity of the entire world! No wonder these storms often cause tremendous amounts of damage.

Because these storms have such a high potential for causing huge amounts of damage from their wind, rain, and storm surges, climatologists have struggled to predict the effects of climate change on their frequency, intensity, and the paths they are likely to follow. The absence of a longstanding accurate historical record is a significant problem. Aircraft were first used to monitor severe tropical storms in the 1940s. Although planes are still used, the data collected during these flights have been augmented by satellites first launched in the 1960s. The best data are from the North Atlantic, as monitoring is most intense over this region. These data have shown that there are periodic oscillations in hurricane activity in this region, known as the Atlantic multidecadal oscillation. These oscillations are thought to be due to normal factors, which form a starting point for modeling studies designed to predict future activity.

Tropical climates control the activity of hurricanes.33 Therefore, changes in tropical climates, whether they are due to human or natural activity, can be expected to have important effects on hurricane activity. Volcanic eruptions act to cool the tropics as a result of the injection of dust (particulates) and sulfur dioxide into the stratosphere. Greenhouse gas emissions have the opposite effect. As the result of the Clean Air Act, particulate emissions by US sources have declined significantly, thereby diminishing their cooling effect. This is particularly true for the sulfate-containing particles that originate primarily from burning coal.34 Dust from the Sahara Desert, due to the combination of natural and human activity, also has an effect on the temperature of the tropical North Atlantic. The sum of all of these agents acting in opposite directions helps determine the temperature of the sea surface and hence the probability and strength of hurricanes.

When these factors are incorporated into climate models, it seems likely that the number (or frequency) of tropical cyclones, including hurricanes, will not change much in the future. That is the good news. The bad news is that the models predict that of the storms that do form, more of them will be in the category 4 and 5 range, as defined by the Saffir-Simpson scale.35 According to this scale, category 4 storms have winds between 130 and 156 mph (209–251 km/h), and category 5 storms have winds greater than or equal to 157 mph (252 km/h).

Wikipedia is a rich source of varied information about Hurricane Sandy, also referred to as Superstorm Sandy. Sandy was only a category 3 storm at its peak when it made landfall in Cuba. Its winds diminished to category 2 (96–110 mph, or 154–177 km/h) when it reached the North Atlantic. However, it was huge, with winds reaching over a diameter of 1,100 miles. Because of its size, the configuration of the New York Harbor region, and the fact that the storm surge coincided with the high tide in New York, it caused about 286 deaths in the United States and $68 billion in property damage. Healthcare institutions were poorly prepared, and many were damaged severely. Bellevue, New York University’s Langone Medical Center, and Coney Island Hospital had to be evacuated after multiple critical aspects of their infrastructure failed.

Katrina was a category 3 hurricane when it made landfall in Louisiana.36 She was one of the costliest storms ever, causing over $110 billion in damages and claiming over 1,800 lives. For a chilling account of the effects of Hurricane Katrina on Memorial Hospital in New Orleans, read the Pulitzer Prize–winning Five Days at Memorial: Life and Death in a Storm-Ravaged Hospital, by Dr. Sheri Fink.37

Severe Thunderstorms and Tornadoes

Few weather events are more dramatic than tornadoes. Although forecasting has improved substantially, they often strike suddenly with little warning. Severe property damage and loss of life are not rare when tornadoes strike population centers.

Severe thunderstorms may be accompanied by strong winds, hail, torrential rain, and, on occasion, tornadoes. Severe thunderstorms that rotate are known as supercells and are the most likely to spawn tornadoes. Thunderstorms are caused by warm air that rises rapidly in association with large differences in surface winds and winds at about 6 km above the earth. The technical term for the tendency for air to rise is related to the amount of energy available when a segment of the atmosphere is lifted a defined distance in the atmosphere: convective available potential energy (CAPE). Warm water in the Gulf of Mexico, typical wind patterns, and the presence of the Rocky Mountains interact to make the Great Plains and the Eastern part of the United States particularly susceptible to the development of these events.

Although the ability to make short-term predictions and issue warnings about severe thunderstorms has improved dramatically, very long-term predictions that extend to the end of the century are much more tenuous. One problem centers on the absence of high-quality data from the past. Changing definitions and the absence of data-recording sites have made it difficult to characterize the frequency of these storms in the recent past.

Several recent reports illustrate the difficulty in predicting the effects of climate change on thunderstorm activity. One such analysis concludes that CAPE will increase as the climate warms, a change that would be likely to increase storm frequency.38 However, the author of this analysis, H. E. Brooks, concludes that this effect will be countered to a degree by changes in wind shear that are likely to occur simultaneously. Brooks concludes that the accuracy of long-range predictions is likely to be problematic. A group from Stanford and Purdue examined the lack of synchrony between CAPE and wind shear and determined that the warming climate will lead to more days when the relationship between these variables will favor the formation of severe thunderstorms.39 They conclude that severe thunderstorms will indeed become more common unless greenhouse gas effects are lessened.

The Trajectory toward the Future

The earth’s temperature increases as climate change becomes more pronounced, and this will have multiple effects. Heat waves will claim more lives, particularly in developing nations and among the socially disadvantaged, due to heat-related illnesses such as heat stroke and heat exhaustion. Heat will evaporate more water from lakes, rivers, and oceans, causing increases in precipitation in some areas and droughts in others. More intense hurricanes are likely. It is probable that there will be more tornadoes and severe thunderstorms. Humans will not do well in the heat, and neither will the earth’s ecosystems.

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