In the opinion of a number of scientists, human-induced changes in earth’s atmosphere and oceans have made our planet a dangerous place by contributing to more frequent and more severe natural disasters. And the future looks uncertain. “We’re in the middle of a large uncontrolled experiment on the only planet we have,” said an editorial on climate change in Science magazine.
So that we can better grasp how human activity might be affecting the frequency and severity of natural disasters, we need to understand a little about the underlying natural phenomena. For example, what causes severe storms, such as hurricanes, to form?
Planetary Heat Exchangers
Earth’s climate system has been likened to a machine that converts and distributes solar energy. Because the Tropics get most of the sun’s heat, the resulting temperature imbalance sets the atmosphere in motion.Earth’s daily rotation causes this mass of moving, moist air to form eddies, some becoming depressions, or areas of low atmospheric pressure. Depressions, in turn, may develop into storms.
If you observe the general path of tropical storms, you will notice that they tend to move away from the equator
In terms of lives lost, the worst natural disaster in U.S. history resulted from a hurricane that slammed into the island city of Galveston, Texas, on September 8, 1900. Storm waves claimed between 6,000 and 8,000 lives in the city, plus up to 4,000 in nearby areas, and demolished some 3,600 houses. In fact, not one man-made structure in Galveston remained unscathed.
Changes in the weather, however, may be just one symptom of global warming. Another potentially harmful consequence may already be in evidence.
Rising Sea Levels and Deforestation
According to an editorial in the journal Science, “sea levels have risen 10 to 20 centimeters [four to eight inches] in the past century, and more is in store for us.” How might this be related to global warming? Researchers point to two possible mechanisms. One is the prospect of the melting of land-based polar ice and glaciers, which would add to the volume of the oceans. The other factor is thermal expansion
The tiny Pacific islands of Tuvalu may already be experiencing the effects of rising sea levels. Smithsonian magazine notes that data collected on the atoll of Funafuti shows that the sea level there has risen “an average of 0.22 inches [5.6 mm] annually over the past decade.”
In many parts of the world, population growth means more urban sprawl, more shantytowns, and more environmental degradation. These developments may tend to magnify the severity of natural disasters. Consider some examples.
Haiti is an island nation with a high population and a history of deforestation. A recent news report suggested that as bad as Haiti’s economic, political, and social problems may be, nothing threatens the country’s existence more than deforestation. This threat became tragically evident in 2004, when torrential rains caused mud slides that claimed thousands of lives.
Time Asia points to “global warming, dams, deforestation and slash-and-burn farming” as exacerbating factors in the natural disasters that have plagued South Asia. At the other extreme, deforestation can worsen drought by causing soil to dry out more quickly. In recent years, droughts in Indonesia and Brazil have paved the way for record-breaking fires in forests that are normally too wet to burn. Extreme weather, however, is by no means the only cause of natural disasters. Many lands are subject to disasters that are generated deep inside the earth.
When the Ground Convulses
Earth’s outer crust is made up of plates of various sizes that move in relation to one another. Indeed, there is so much movement in the crust that several million earthquakes may occur each year. Of course, many of these go undetected.
It is said that about 90 percent of all earthquakes occur along faults at the perimeter of plates. Although rare, sometimes very destructive quakes also occur within the plates. According to estimates, the deadliest quake in recorded history was one that struck three provinces in China in the year 1556. It may have claimed as many as 830,000 lives!
Quakes can also have lethal aftereffects. For example, on November 1, 1755, a quake flattened the city of Lisbon, Portugal, which had a population of 275,000. But that was not the end of the horror. The quake caused fires and also tsunamis estimated to be up to 50 feet [15 m] high, which raced in from the nearby Atlantic Ocean. All told, the city’s death toll exceeded 60,000.
Again, however, the scale of such disasters hinges to some extent on the human element. One factor is population density in high-risk areas. “Nearly half the world’s big cities now lie in areas of seismic risk,” says author Andrew Robinson. Another factor is buildings
“At least 20 volcanoes will probably be erupting as you read these words,” states a report by the Smithsonian Institute in the United States. Broadly speaking, the theory of plate tectonics says that earthquakes and volcanoes will occur in similar regions
Subduction volcanism is the biggest threat to people in terms of both the number of eruptions observed and their occurrence near populated areas. The Pacific Rim, dubbed the Ring of Fire, is peppered with hundreds of such volcanoes. A small number are also found at hot spots away from plate boundaries. The Hawaiian Islands, the Azores, the Galápagos Islands, and the Society Islands all appear to be the product of hot-spot volcanism.
Actually, volcanoes have played a long and constructive role in earth’s history. According to a university Web site, as much as “90% of all the continents and ocean basins are the product of volcanism.” But what causes some eruptions to be extremely violent?
Eruptions begin with an upwelling of magma from earth’s hot interior. Some volcanoes simply ooze lava, which seldom moves fast enough to catch people by surprise. But others explode with more energy than a nuclear bomb! The underlying factors include the composition and viscosity of the molten material that feeds the volcano and the amount of gases and superheated water dissolved in that material. As the magma nears the surface, captured water and gas rapidly expand. With the right magma composition, the effect is much like soda that blasts from an opened beverage can.
Fortunately, volcanoes often give advance warning of an eruption. Such was the case with Mount Pelée on the Caribbean island of Martinique in 1902. Mount Pelée erupted, venting a searing mass of pyroclasts
Will Natural Disasters Increase?
The International Federation of Red Cross and Red Crescent Societies states that during the past decade, geophysical and weather-related disasters have increased by over 60 percent. “This reflects longer-term trends,” says the report, which was published before the catastrophic December 26 tsunamis in the Indian Ocean. To be sure, if populations in high-risk areas continue to climb and forests continue to decline, there is little cause for optimism.
Additionally, many industrialized countries continue to pump ever more greenhouse gases into the atmosphere. According to an editorial in the journal Science, procrastinating on emissions reduction “is like refusing medication for a developing infection: It guarantees that greater costs will have to be paid later.” Pointing to those costs, a Canadian report on disaster mitigation stated: “Climate change can be argued to be the most pervasive and far-reaching environmental issue ever dealt with by the international community.”
At present, however, the international community cannot even agree on whether human activities contribute to global warming, let alone how to manage it.