In the past year or so natural disasters of biblical proportions have been visited on the world. Maria Ahmed asks whether these are random events, or has mankind had a hand in them?

Natural disasters have caused massive death and destruction over the past year or so. In December 2004, the Indian Ocean tsunami killed 275,000 people – the seventh-deadliest disaster in recorded history. Then, in August, Hurricane Katrina ripped through the levees protecting New Orleans from Lake Pontchartrain: almost 1,400 people died in the flood; 4,000 remain unaccounted for. The death toll from October’s Kashmir earthquake is close to 80,000, and the number looks set to rise.
The last act of God to wipe out more than 100,000 people was 30 years ago: the 1976 earthquake in Tangshan, China, with an official death toll of 242,000. The scale of lives and livelihoods destroyed over the past year or so has focused attention on several questions. Are natural disasters becoming more frequent? Are they more severe, both in physical intensity and human devastation? If so, why? No one can stop the Eurasian and Indian plates from moving, but how else might humans be agents, as well as victims, of natural disasters in the 21st century?

Random or trend?

The scientific jury is still out on the possibility that weather-related disasters are now greater in number or intensity. At a meeting of the United Nations Climate Change Conference in Montreal in December, Thomas Loster, head of the Munich Re Foundation, said that weather-related natural disasters cost more than $200 billion in 2005 (of which around $70 billion were insured), making it the costliest year on record. According to him, this indicates that climate change is already fully under way.

The Inter-Governmental Panel on Climate Change has agreed that global warming is happening, and that it is “attributable to human activities”. But while it predicts rises in the sea level and changes in rainfall patterns, the panel is uncertain about extreme weather events. Climatologists find it difficult to attribute any one year’s hurricanes, floods or droughts to a single cause such as global warming. Kerry Emmanuel, professor of meteorology at the Massachusetts Institute of Technology, published a 30-year study in Nature in 2005 showing that hurricanes’ destructiveness is correlated with higher sea surface temperatures. But he could not determine whether climate change or natural variation had caused the higher temperatures.

No one doubts, however, that when a disaster strikes, more lives are put at risk than in earlier decades because of rising populations. Since 1950 the world population has more than doubled to 6 billion, and could rise by a further 50% by 2050. Pakistan’s population has quadrupled since 1950, to 158 million, with the increase particularly pronounced in the north, the area most prone to deadly earthquakes. Indonesia’s population tripled to 223 million in the same period. From Yueyang to Memphis, people are living below sea level and along seismic fault lines in unprecedented concentrations. The UN’s latest Reducing Disaster Risk report says that each year 130 million people are exposed to earthquakes, 119 million to tropical cyclones and nearly 200 million to catastrophic flooding.

Particularly at risk, says Jan Egeland, director of UN Disaster Relief, are the world’s “mega-cities” – densely populated cities with 10 million or more inhabitants. The biggest is Greater Tokyo with a population of 35.5 million, where seismologists predict that a serious earthquake is long overdue. Mexico City, New York-Newark, Bombay and São Paulo are the next biggest. As growing populations struggle to find a place to live, the often unregulated build-up of tunnels, car parks, shopping precincts and, sometimes, slums, leaves them highly vulnerable to earthquakes and floods. Shortly after the Indian Ocean tsunami, Egeland warned that if a disaster occurred in one of these mega-cities, the casualty rate could be a hundred times that of the Indian Ocean tsunami.

The power of nature and money

Population growth was not a big factor in the New Orleans tragedy. Between 1950 and 2005 the city’s population increased by just 80,000 to 480,000, because of an exodus of whites during the 1960s and 1970s. Rather, the tragedy that unfolded demonstrated the devastating impact of government failure. Despite centuries of knowledge of the city’s vulnerability, and specific and recent warnings from the US Army Corps of Engineers, the lacklustre Federal Emergency Management Agency failed to make the most rudimentary of preparations. Warning systems, evacuation planning, relief efforts and inter-agency coordination all lagged behind what was expected of the world’s richest country.

Other countries are simply too poor to take the necessary precautions. Over the summer of 2005 there were earthquakes off the coast of northern California strong enough to be felt on land, and in eastern Honchu. Both were of similar magnitude to the Kashmir earthquake, though not directly under large centres of population. In Honchu, 39 people were injured and one building collapsed, while in California there was a small tsunami but no damage. Buildings in earthquake-prone San Francisco and Japan have been designed to be flexible so that they sway as the ground shakes, and supports are built into old buildings. So far, this has been a non-starter for a country as poor as Pakistan, although construction companies have now drawn up designs for low-cost earthquake-proof houses.

The UN Reducing Disaster Risk report says that although just 11% of the people exposed to natural hazards live in poor countries, they account for more than half of recorded deaths. Last year might have been the most financially damaging on record for natural disasters, but Munich Re’s $200 billion estimate could be an underestimate of the true cost. Half of these losses occurred in America alone and, as the report points out, assessments of financial damage are skewed towards losses in wealthy countries, and do not capture the full impact of disasters on the poor: “The real killer is poverty, not the forces of nature,” it says.

Disasters glossary of terms

A drought is a prolonged period of dry weather when the water supply falls below human demand.

Earthquakes occur because of the movement of the 12 tectonic plates that make up the earth’s crust. Heat from the earth’s core forces hot liquid up, through the semi-molten mantle, towards the crust. The plates float on these “convection currents”, straining the fault lines, and when the rock separating the plates gives way, seismic movement occurs.

Floods are caused by excess rainfall, usually during storms, that forces a river to swell in its lower reaches until there is too much water for the ground to absorb. Melting snow or glaciers upstream will increase the pressure on rivers. Sea floods are caused by heavy “storm surge” rain as a hurricane moves from sea to land, heavy rains, such as the Bangladesh monsoons, or tsunamis and tidal waves.

A hurricane forms over the oceans, when evaporated water forms stormclouds. Acceleration, caused by the earth’s rotation, makes the storm spin. A hurricane is declared when the wind speed exceeds 74mph. A “hurricane” in the north Atlantic and the north-east Pacific is called a “typhoon” in the north-west Pacific, and a “cyclone” in the south Pacific and Indian Ocean.

Exactly how thunder storms cause tornadoes is not fully understood. Scientists believe that cool air moves over a layer of warm air, forcing the warm air to rise rapidly. The spinning, funnel-shaped column of air can blow at up to 300mph. Tornadoes can occur singly, or in large outbreaks along “squall lines.”

A tsunami is a chain of fast-moving waves caused by a powerful disturbance on the ocean floor, such as an earthquake or volcanic eruption. The impact generates a wave that travels across the ocean at speeds of around 500mph. Tsunami waves lose little energy, and gain suddenly in height – up to 30 metres – when they reach shallow water near the coast. There can be more than 100km in distance, and an interval of an hour, between waves in the chain.

Like earthquakes, volcanoes form at the boundaries between plates in the earth’s crust. When two plates collide, one is forced below the other into the mantle. Water from the crust lowers the melting point of rock in the semi-molten mantle, and it forms liquid “magma”. Magma is lighter than solid rock, and forces its way up towards the earth’s crust, to accumulate just below the surface in a magma chamber. A volcanic eruption is magma bursting onto the earth’s surface when the pressure in the chamber becomes too great.