The sun produces heat from nuclear reactions deep inside it. All life on Earth depends on this heat.
Credit: NASA/SDO

This summer, the entire globe experienced a heat wave. Western states in America experienced a record-breaking heat wave in late August and early September of 2022.

A heat wave is a period over which the temperature rises well above normal for a particular region. Heat waves may be less dramatic than such natural disasters as hurricanes, earthquakes, or tornadoes, and heat waves tend to cause less damage to property. However, heat waves rank among the deadliest extreme weather.

The varying nature of local climate makes it difficult to establish a simple definition of a heat wave. The temperatures of a heat wave must be hot relative to the average temperatures at a place during a particular time of year. For example, a temperature of 90 °F (32 °C) during the summer is not out of the ordinary for the northern African country of Sudan. However, it would be an exceptionally high temperature for the northern U.S. state of Alaska. Meteorologists agree that high temperatures must persist for more than one full day to be considered a heat wave.

This chart can be used to determine the heat index (HI), a number that describes how people are affected by the combination of temperature and relative humidity. As the temperature and relative humidity rise, the heat index increases. The higher the index, the greater the likelihood that people will develop heat-related illnesses. The risk of illness is low when the index is below 80 °F.
Credit: World Book chart by Linda Kinnaman

Heat waves are sometimes accompanied by high relative humidity. Relative humidity is the amount of water vapor in the air compared with the amount the air can hold at saturation. High relative humidity interferes with the human body’s ability to cool itself through the evaporation of sweat. Thus, high humidity can make a heat wave more uncomfortable and dangerous. Some weather agencies make use of a measure called the heat index, which factors in relative humidity to give a measure of how hot the air feels.

Heat waves are generally created by areas of high air pressure. Meteorologists call these areas highs or anticyclones. Warm highs bring high temperatures and air that contains little moisture. These highs are large weather systems that may affect a region for an extended time. In the summer, a warm high sometimes stalls over North America, for example, causing a heat wave.

The high temperatures of a heat wave can cause dehydration and hyperthermia in people and in animals. Dehydration is a condition in which the body loses too much water. In severe cases, dehydration can lead to a fast heartbeat, low blood pressure, shock, and death. Hyperthermia is a condition that occurs when the body becomes overheated. Forms of hyperthermia include heat exhaustion, heat cramps, and heatstroke (also called sunstroke). Heatstroke is a serious condition that can cause permanent neurological damage and death.

Elderly people, infants, and people with long-term illnesses may suffer heatstroke more readily than others during a heat wave. Hyperthermia can be particularly dangerous for people with long-term medical conditions. Such conditions as asthma, diabetes, heart failure, and high blood pressure place the body’s organs under stress. The added stress from hyperthermia can induce heart attack, breathing failure, and other fatal medical events among such people.

The complexity of diagnosing heat-related deaths has made it difficult for experts to track the toll of heat waves. The World Health Organization estimated that heat waves killed more than 166,000 people between 1998 and 2017. Another study found that approximately 500,000 heat-related deaths occurred worldwide between 2000 and 2019. Despite the uncertainties, experts agree that heat waves are deadly. In 2003, for example, Europe suffered a catastrophic heat wave in which some 70,000 people died.

Heat waves can also put stress on electric power and water services. People’s use of air conditioning strains the electrical grid. Power plants may need more water for cooling. People may also use more water to try to keep cool. When demand for electricity exceeds generating capacity, officials may have to reduce voltage to prevent a blackout. Such a reduction, called a brownout, may damage electrical equipment or cause the equipment to operate less efficiently. High temperatures also buckle pavement and warp railroad tracks.

Drought kills crops. Two farmers examine a Kansas corn field that has been affected by a drought in 2012. Climate scientists suspect such droughts might become more common in some areas due to the effects of global warming.
Credit: © Mashid Mohadjerin, The New York Times/Redux Pictures

Heat waves are dangerous to plants and animals as well. Excessive temperatures can kill animals that cannot find ways to keep cool. Prolonged heat can wither plants. Droughts usually accompany heat waves, compounding the danger to living things. Heat waves and droughts dry out the ground and plants, increasing the likelihood and severity of wildfires.

A Russian firefighter sprays water on a wildfire in the Ryazan region, southeast of Moscow. In 2010, a devastating wave of wildfires wept across Russia following a record-setting heat wave.
Credit: AP Photo

Data suggest that heat waves are increasing in duration, frequency, and intensity. The time of year in which heat waves occur is also expanding. Most climatologists think that climate change brought about by human-caused global warming is driving these changes.

People must exercise caution during heat waves to avoid health problems. Experts advise wearing light-colored, loose-fitting clothing when outdoors and avoiding going out during the hottest part of the day. People should drink fluids regularly but avoid beverages with alcohol or caffeine, which can contribute to dehydration.

People who are homeless or who live in homes without air conditioning are particularly vulnerable to heat waves. During a heat wave, local governments may open air-conditioned cooling centers where people can stay to cool down.

People can help to protect their community during a heat wave. They can air condition their homes only to what temperature is necessary, conserving power. People might be asked to limit water use at certain times to prevent drops in their community’s water pressure. They may be asked to conserve water if the heat wave is accompanied by a drought. Because heat waves increase the risk of wildfires, people may be prohibited from starting fires outdoors.

Brontosaurus.
Credit: © Emiliano Troco

Sauropods were the most spectacular of the dinosaurs. Their long necks supported small heads that took in needles and leaves. Despite such a nutrient-poor diet, they reached sizes and lengths unparalleled in any other terrestrial (land-dwelling) animals. How—and why—did they get so large? A recent study may have discovered a lead to unraveling the physiology of these amazing animals. 

Over tens of millions of years, the arrangement of the continents has shifted through the action of plate tectonics. Geologists can trace how a location has moved over the face of Earth to determine its paleolatitude. The paleolatitude is the position of a point on the Earth’s surface in relation to the equator at a time in the distant past. Both latitude and paleolatitude are measured on a scale of 0° (the equator) to 90° (the poles). Higher latitudes experience cooler temperatures and less sunlight in winter. 

Dinosaurs reigned during the Mesozoic Era—a time of warmer climates. Despite the planet being largely ice-free, regions near the poles still faced cold winters and weeks or months without sunlight. Nevertheless, dinosaurs have been found at high paleolatitudes, including in Antarctica and Alaska. At least some of these dinosaurs remained there through the winter. 

Sauropod fossils, however, are conspicuously absent from these polar locations. No sauropod fossil has been discovered from a paleolatitude higher than about 65°. Instead, these chilly climates were strictly occupied by meat-eating theropods and some plant-eating dinosaurs called ornithischians. 

Some paleontologists (scientists who study prehistoric life) suspected the absence of fossils suggest that sauropods preferred warmer climates. But others thought that sauropods might not have fossilized well near the poles for some reason, or that the fossils are still waiting to be discovered. 

A team led by Alfio Alessandro Chiarenza of the University of Vigo in Spain analyzed the paleolatitude of all the places where sauropod fossils have been found. The team published their findings last month in the scientific journal Current Biology. They determined that the absence of sauropods at high paleolatitudes was not due to incomplete sampling. Chiarenza’s team used models of the Mesozoic climate and found that sauropods preferred savanna-type habitats. Sauropod ranges were tightly constrained by the lowest predicted temperature. 

Why didn’t (or couldn’t) sauropods brave the cold? They might have cooled down too quickly, despite their massive sizes. Many theropods—and possibly some ornithischians—had downy or hairlike feathers that could be used to keep them warm. Sauropods lacked any such insulation. Furthermore, a sauropod’s long necks and tails might have lost heat quickly when exposed to bitter-cold winds. 

Sauropods buried their eggs in the earth to keep them at a stable temperature. But this method probably would not have kept the eggs warm enough in cold climates. In contrast, theropods sat on their eggs and ornithischians covered their eggs in rotting plants. Both of these approaches could keep the eggs warm even in cold climates. 

Chiarenza’s team proposes that sauropods did not possess as high of a metabolism as theropods and ornithischians. Historically, scientists have classified animals as endothermic (“warm-blooded”) or ectothermic (“cold-blooded”). Endothermic animals tend to produce more of their own body heat, while ectothermic animals tend to rely more on their environment for heat. This is a false division, since every animal is somewhat reliant on its environment for heat. But animals classified as endothermic can usually survive in cooler temperatures. Reptiles, the classic endotherms, are concentrated near the equator. 

In many ways, this makes a lot of sense. A lower metabolism would have enabled sauropods to survive on less food. Their huge size would cause them to lose less heat to their environment, much like a well-insulated building. Growing evidence suggests that the ancestor of dinosaurs and crocodilians (a group of reptiles) had a high metabolism, but crocodilians “slowed down” when dinosaurs took over most environmental niches. A similar changed might have occurred in sauropods as well, enabling them to attain colossal sizes. Sometimes slow and steady wins the race. 

In this photograph from July 2021, One World Trade Center (left) and other New York City buildings are shrouded by smoke and haze from wildfires in western North America.
Credit: © Bjoern Kils, New York Media Boat/Reuters/Alamy Images

Have you looked at the sun or moon low in the sky in the past few weeks? You may have noticed them take on hues of orange and red. A hazy film may have blurred out the horizon. These visual effects were caused by smoke and haze from fires in western North America, in what is shaping up to be another record wildfire season. So far this year, wildfires have scorched nearly 3 million acres (1.2 million hectares) in the United States alone.

The Dixie Fire is the largest in California, burning almost 250,000 acres (100,000 hectares). It began near where the deadly Camp Fire burned in 2018, killing more than 80 people. Both fires were sparked by equipment from the utility company Pacific Gas and Electric Co. (PG&E). This month, PG&E announced its intent to bury 10,000 miles (16,000 kilometers) of power lines in areas of the state most at risk for wildfires. The project—which PG&E had long resisted—is estimated to cost at least $15 billion.

California usually dominates the wildfire season. The largest fire of the season, however, belongs to Oregon. The Bootleg Fire started on July 6 and has burned more than 400,000 acres (160,000 hectares). The fire persevered through rain and continues to defy efforts to contain it.

The Bootleg Fire threatened Mitchell Monument, dedicated to the only civilians killed on U.S. soil during World War II (1939-1945). Toward the end of the war, Japan released more than 9,000 bomb-carrying balloons, intended to land on the West Coast of the United States. The bombs caused mostly minor damage. But one bomb killed five members of a picnicking family near Bly, Oregon. Firefighters battling the Bootleg blaze worked to save the forest around the monument, including trees damaged by the bomb blast.

Nearby Idaho and Montana also have dozens of fires. The Canadian province of British Columbia declared a state of emergency due to the hundreds of wildfires raging there. The government of Mexico sent firefighters to the province to assist. Outside North America, fires burned in Greece, Turkey, Russia, and Italy.

Smoke from the North American fires drifted east on the prevailing winds, reducing air quality across the continent. Air quality was affected as far away as New York City. The smoke threatened people with such medical conditions as asthma, chronic obstructive pulmonary disease (COPD), and heart disease.

Climatologists and other experts blame the severe fire outbreaks on the intense drought gripping the western half of the continent. In June, a sizzling heat wave killed hundreds of people in Oregon, Washington, and British Columbia. Experts strongly suspect the drought and heat were intensified by climate change.

October 11, 2017

On Monday, October 9, multiple wildfires swept across northern California, destroying some 2,000 homes and other buildings, killing 21 people and displacing tens of thousands of others. California Governor Jerry Brown declared states of emergency in Butte, Lake, Mendocino, Napa, Nevada, Sonoma, and Yuba counties, where the destruction is worst. Dozens of people remain missing as the fires continue to burn.

Firefighters hose the flames of a burning home in the Napa wine region of California late on Oct. 9, 2017. Credit: © Josh Edelson, AFP/Getty Images

Unusually hot and dry weather this summer has created ideal conditions for wildfires across northern California. At least 15 separate blazes broke out over the weekend, and strong winds whipped the flames across some 114 square miles (295 square kilometers). Napa and Sonoma counties, the heart of California’s wine country, were hardest hit. The status of the grape harvest remains unclear, but damage from fire and smoke is almost certainly widespread. Fires devastated parts of the city of Santa Rosa, where entire neighborhoods have been left in ashes and cinders.

Skies from San Francisco to Sacramento to Eureka remain choked with smoke and haze, and an orange glow illuminates the night. Numerous roads, schools, and business are closed, and several hospitals in the fire zone have been evacuated. Thousands of firefighters and numerous firefighting aircraft—including the massive Global SuperTanker (a converted Boeing 747 airliner)—are battling the blazes. Amy Head, the fire captain spokesperson for Cal Fire, the state agency responsible for fire protection, said the fires were probably linked to a warming climate. “It has been hotter, it has been drier, our fire seasons have been longer, fires are burning more intensely, which is a direct correlation to the climate changing,” she said.

Another state of emergency was declared on Monday in southern California’s Orange County, where a wildfire destroyed several homes in the affluent Anaheim Hills neighborhood and forced the evacuation of hundreds of residents.