Weather Extremes

Introduction

Extreme weather refers to weather that is unusually violent in nature or that is abnormal in its frequency of occurrence or length. Tornadoes and hurricanes are well-known forms of weather whose force and destructive power is extreme.

Hurricanes may also be an example of weather that is extreme from the point of view of frequency. Although still debatable, evidence has been published by agencies including the World Meteorological Organization (WMO) and the U.S. Environmental Protection Agency (EPA) that supports the view that hurricanes spawned in the equatorial region between North and South America are becoming more frequent in both their occurrence and ferocity as a result of global warming—the warming of Earth’s atmosphere that has been present for the past 150 years, which has been accelerating since the mid-twenty-first century.

Extreme weather also includes droughts, flooding, high winds, blizzards, and colder than normal winter time temperatures. In various regions of the globe, all these types of extreme weather are occurring more often. Whether this is directly due to the atmospheric changes occurring because of global warming is debatable, but scientific evidence to support this view is accumulating.

Historical Background and Scientific Foundations

Determining whether extreme weather events such as hurricanes are increasing in frequency and intensity requires knowledge of the past trends. Since records of hurricanes, cyclones, and typhoons have been in existence for centuries beginning with mariners, and satellite monitoring has been used since the 1970s, there is a great deal of data on these extreme weather events. As well, other atmospheric parameters such as temperatures have been recorded for a long time.

What is also necessary is to model future weather trends based on the incorporation of the atmospheric changes that are taking place due to global warming and the influence of the warming ocean. Several models have been developed; these are collectively termed Atmosphere-Ocean Global Climate Models. These models tend to accurately portray the present climate, which increases confidence that their predictions of future weather will be reasonably accurate, as long as all factors influencing weather have been accounted for.

Models developed by agencies including the U.S. National Oceanic and Atmospheric Administration (NOAA) and the Canadian Center for Climate Modeling and Analysis support the notion that the frequency and severity of hurricanes could increase as the atmosphere and tropical ocean continues to warm. The basis is the warmer air overlying the increasingly warming tropical ocean. The more intense rising of the air into the atmosphere and subsequent return of colder air from aloft, combined with wind, begins the spiral pattern of the storm, whose ferocity is fueled by the continued supply of warmer air from the ocean’s surface.

Ocean measurements conducted by Woods Hole Oceanographic Institution and other agencies since the 1950s have demonstrated the warming of the tropical ocean at the surface and to depths of over 1,000 ft (304 m). Indeed, measurements of ocean and atmospheric warming indicate that the amount of heat absorbed by the ocean exceeds that absorbed by the atmosphere by about 20 times. Because warm air can hold more water vapor than colder air, a result has been the increased content of warm water vapor over the tropical ocean. These conditions are prime for the establishment of extreme weather.

A paper published in the journal Science in 2005 that examined satellite data from the 1970s onward con-

WORDS TO KNOW

ATMOSPHERE: The air surrounding Earth, described as a series of layers of different characteristics. The atmosphere, composed mainly of nitrogen and oxygen with traces of carbon dioxide, water vapor, and other gases, acts as a buffer between Earth and the sun.

GAIA HYPOTHESIS: The hypothesis that Earth’s atmosphere, biosphere, and its living organisms behave as a single system striving to maintain a stability that is conductive to the existence of life.

GLOBAL WARMING: Warming of Earth’s atmosphere that results from an increase in the concentration of gases that store heat, such as carbon dioxide (CO₂).

cluded that the number of category 4 and 5 hurricanes, the most severe and destructive forms, had increased. At the same time, the number of less intense hurricanes decreased. The increase matches with data showing a warming tropical ocean and atmosphere. Surface-based studies that charted surface wind and temperature have confirmed the satellite observations, and have indicated that an annual increased ocean surface temperature of about 0.45°F (0.25°C) boosts the likelihood of severe weather by 60%.

Climate models also support the link between climate change and other aspects of extreme weather. For example, a downpour can be considered as extreme weather, as it is rainfall that exceeds the normal pattern of rainfall over time. Short but very heavy rain can overwhelm the capability of drainage systems such as sewers in urban settings. The result can be flooding. Similarly, the runoff of excessive amounts of water into a watercourse during and shortly after a heavy rain can exceed the capacity of the watercourse to contain the water, creating a flood. Monitoring in the United States and Canada through the last century has shown that short duration heavy rains have increased in frequency; one-day rainfalls of more that 2 inches (50 mm) have increased in the United States by 20% since the beginning of the twenty-first century, for example. Predictions from Canadian climate models are that such storms that currently tend to occur about once every 20 years will occur once every 10 years by the end of this century.

Flooding in tropical regions brings the added possibility of the development of diseases of microbial origin such as cholera, since the bacteria are able to grow and multiply in the warm water, and infect people whose resistance to infection has been lowered by injury.

Another related type of extreme weather in northern climates is excessive snowfall. As for extreme rainstorms, the frequency of blizzards, which can bring cities to a standstill and which are hazardous for road and air transportation, have increased since the mid-1970s.

Another type of extreme weather is known as a heat wave, where the temperature becomes much hotter than normal for the time of year and lasts longer than normal. Many regions of the world including Africa, the United Kingdom, Europe, and North America have experienced more frequent heat waves since the mid-twentieth century. In regions that have shortages of water, heat waves are very serious and can be lethal.

Impacts and Issues

The possibility of more frequent and severe weather could put coastal human populations in affected regions more at risk of personal harm and property damage. Secondarily, the economies of the affected countries would suffer, as damage claims soared and government-funded and maintained relief efforts were put into action more often. As of 2008, for example, the costs to the U.S. government associated with 2005’s Hurricane Katrina are estimated at over $80 billion.

Climate scientists generally agree that one important influencing factor in extreme weather is the regular oscillating weather patterns known as El Niño and La Niña. These oscillations can trigger extreme weather events that include cyclones, droughts, and increased precipitation in different regions of the Pacific. As well, the influence of a La Niña can extend to the Caribbean, and may influence development of tropical storms.

The influences of El Niño and La Niña may increase still further if the frequency of the weather oscillations is affected by global warming. Some climate scientists assume that this is occurring, but this view is not universal.

Analysis of the ocean conditions at the time of Hurricane Katrina indicates that the temperature of the Gulf of Mexico was crucial in fueling the increased intensity of the storm as it crossed the open water of the gulf en route to the Gulf Coast region of the United States. Normally, as a tropical storm builds, deeper ocean water is stirred up to the surface. Because this water tends to be colder, it acts to diminish the storm. However, because the gulf water temperature has increased in the past 50 years, the deeper waters did not diminish Hurricane Katrina, but instead made the storm even more powerful. The results for the Gulf Coast were devastating.

Elsewhere in the world, extreme weather such as droughts and monsoon flooding are already affecting people especially in undeveloped regions, where an already tenuous existence is becoming even more difficult.

See Also Dust Storms; Floods; Global Warming; Landslides; Tsunami Impacts; Volcanoes

BIBLIOGRAPHY

Books

Banta, John. Extreme Weather Hits Home: Protecting Your Buildings from Climate Change. Gabriola Island, British Columbia, Canada: New Society Publishers, 2007.

Burt, Christopher. Extreme Weather. New York: W.W. Norton, 2007.

Mogil, Michael. Extreme Weather: Understanding the Science of Hurricanes, Tornadoes, Floods, Heat Waves, Snow Storms, Global Warming and Other Atmospheric Disturbances. New York: Black Dog & Leventhal Publishers, 2007.

Periodicals

Emanuel, K. “Increasing Destructiveness of Tropical Cyclones over the Past 30 Years.” Nature 436 (2005): 686–688.

Webster, P. J., et al. “Changes in Tropical Cyclone Number, Duration, and Intensity in a Warming Environment.” Science 309 (2005): 1844–1846.

IN CONTEXT: EXTREME WEATHER

Increased extreme weather is a predicted consequence of global climate change. In August 2007, scientists at the World Meteorological Organization (WMO), an agency of the United Nations, announced that during the first half of 2007, Earth showed significant increases above long-term global averages in both high temperatures and frequency of extreme weather events (including heavy rainfalls, cyclones, and wind storms). Prior to the release of the findings, the global average land temperatures for January and April of 2007 were the warmest recorded for those two months since records began in 1880.

Web Sites

NASA: Goddard Institute for Space Studies. “NASA Study Predicts More Severe Storms with Global Warming.” August 30, 2007. http://www.giss.nasa.gov/research/news/20070830/ (accessed April 20, 2008).

Brian D. Hoyle