Page 172 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

136 part I The energy–atmosphere System
F cus Study 5.1 Climate Change Heat waves
Heat waves are most deadly in midlatitude regions, where extremes of temperature and humidity become concentrated over stretches of days or weeks during the warmer months. Heat waves are often most severe in urban areas, where urban heat island effects worsen weather conditions, and indoor air-conditioning systems may be unaffordable for the poor.
The oppressive heat in an urban environment during such an event
can result in many deaths; those
most susceptible to heat-related illness are the young, the elderly,
and those with pre-existing medical conditions. The deadly effects of high temperatures, especially in cities, result from extreme daily temperature maximums combined with lack of nighttime cooling.
The Chicago heat wave of July
1995, which caused over 700 deaths
in the city core, is an example. The combination of high temperatures with the persistence of a stable, unmoving
air mass and moist air from the gulf of Mexico produced stifling conditions, particularly affecting the sick and elderly. The record temperatures logged at Midway airport (41°C) were exceeded by heat-index temperatures of 54°C in some apartments without air conditioning.
For nearly a week the heat-index values
for those dwellings signaled “extreme danger.”
Heat waves are a major cause of weather-related deaths. a heat wave paralyzed much of europe during the summer of 2003 when temperatures topped 40°C in June, July, and august. an estimated 40000 people died in
six western european countries, with the highest number in France.
Heat waves are often associated
with increased wildfires, as in russia during the summer of 2010 (Figure 5.1.1). The russian heat wave brought persistent high temperatures throughout eastern europe that were the most destructive in 130 years, causing an estimated 55000 heat-related deaths, massive crop losses, over 1 million hectares of land burned by wildfires,
▲Figure 5.1.1 Heat wave in Russia, summer 2010. american tourists in Moscow wear face masks to filter smoke from nearby forest fires as temperatures top 38°C (100°F). [Pavel golovkin/aP images.]
public, private, and academic sectors, is one of hundreds of professional organizations and national academies of sciences that are now on record as supporting action to slow rates of climate change. In the news on almost a daily basis, climate change has become one of the most complicated yet vital issues facing world leaders and human society in this century.
Heat Stress and the Heat Index
One of the challenges humans are facing in adapting to the effects of climate change is an increase in the fre- quency of heat waves, putting more people at risk from the effects of prolonged high temperatures during the summer season. By definition, a heat wave is a prolonged period of abnormally high temperatures, usually, but not always, in association with humid weather. Focus Study 5.1 discusses recent heat waves, such as Australia’s record-breaking summer of 2013.
Through several complex mechanisms, the human body maintains an average internal temperature ranging
within a degree of 36.8°C, slightly lower in the morning or in cold weather and slightly higher at emotional times or during exercise and work.* When exposed to extreme heat and humidity, the human body reacts in various ways (perspiration is one such response) to maintain this core temperature and to protect the brain at all cost.
Humidity is the presence of water vapour in the air and is commonly expressed as relative humidity (see full discussion in Chapter 7): the higher the amount of water vapour, the higher the relative humidity. Under humid conditions, the air cannot absorb as much moisture, so perspiration is not as effective a cooling mechanism as in dry environments.
When low humidity and strong winds accom- pany high temperatures, evaporative cooling rates are
*The traditional value for “normal” body temperature, 37°C, was set in 1868 using old methods of measurement. According to Dr. Philip Mackowiak of the University of Maryland School of Medicine, a more accurate modern assessment places normal at 36.8°C, with a range
of 2.7 C° for the human population (Journal of the American Medical Association, September 23, 1992).