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9.18.2005

The science of climate change

This is an article from the official Canadian Meteorological Service, so this is government approved data!!

Is Extreme Weather Becoming More Common?

Is the world’s weather becoming more extreme? So far, during the 1990s alone, the world has witnessed at least half a dozen floods of epic proportions in Canada and the United States, central Europe, and southern China as well as intense droughts in northern China, northern Vietnam, North Korea, and southern Europe. In 1993, the northeast coast of the United States received its biggest snowstorm in more than a century. At the end of 1996, it was the turn of Victoria, which was paralyzed by the biggest snowfall in its recorded weather history. Then, in January 1998, Canada’s worst-ever ice storm left the Montreal area and eastern Ontario without power for weeks. Western Europe, usually noted for the moderation of its climate, was pounded by four major storms in the winter of 1990. In 1987, southern England was hit by its worst storm since 1705. In 1995, heat waves killed more than 500 people in northern and central India and more than 550 in Chicago, numbers that pale in comparison, however, to the estimated 5,000­10,000 heat-related deaths that occurred in the central and eastern U.S. in the summer of 1980.

The sheer number of such events within the past two decades raises some serious questions about the current and future state of the global climate.
Are these events part of a long-term trend towards more extreme weather, or are they just a temporary aberration? Are they the result of purely natural forces? Or could they be linked in some way to climate change caused by the buildup of greenhouse gases in the atmosphere? The answers to these questions are vitally important. Hurricanes, floods, droughts, and other extreme weather events have the potential to cause death and destruction on a catastrophic scale. If they become more common, the costs to society will increase enormously. If these extremes are an inevitable consequence of greenhouse warming, then our current estimates of the impacts of climate change, serious as they are, will have been far too optimistic, and the need to make decisive cuts in greenhouse gas emissions will become even more pressing, as will the need to undertake increasingly expensive adaptive measures.

Is Extreme Weather Becoming More Common?

The number of extraordinarily severe floods, storms, and other weather calamities that have occurred within the past 15 to 20 years would seem to suggest that such events are becoming more common. Figures compiled by the world insurance industry, for example, show a dramatic increase in losses from weather-related disasters in recent decades. For all of the 1960s insured losses from windstorms amounted to $2.0 billion (in 1990 U.S. dollars) worldwide. By the 1980s that figure had crept up to $3.4 billion for the decade. In just the first three years of the 1990s, however, it leapt to $20.2 billion. Before 1987 a billion-dollar insurance loss from climate events was rare, but between January 1988 and January 1997 there were 23 such events in the United States alone. Canada has not yet had a billion dollar insurance loss from a weather disaster, although total costs (including insured and non-insured losses) for a few events, such as the 1996 Saguenay flood and the 1998 eastern ice storm, have exceeded this amount.

These figures certainly suggest a major rise in the number of destructive weather events, but cost alone is not necessarily an accurate indicator of climate trends. As well as being influenced by the number and severity of such events, costs also reflect the size and wealth of the population affected by them, and these numbers have been increasing as well. Two American researchers, Roger Pielke, Jr. and Christopher Landsea, for example, have suggested that increased damage costs from hurricanes in the U.S. can be attributed to three factors: inflation, population growth in vulnerable coastal areas, and the increasing prosperity of the people affected. When these factors are taken into account, they argue, the economic impact of hurricanes in the U.S. has actually declined in recent decades.

Apply the same kind of analysis to world losses from natural disasters as a whole, however, and the results are quite different. Data from Munich Re, one of the world’s largest re-insurance firms, show that direct economic losses (in 1992 U.S. dollars) from natural disasters worldwide increased by a factor of 43 between the last half of the 1960s and the first half of the 1990s. Global wealth (as measured by GDP), on the other hand, increased by a factor of 2.5 and population by 25%. That means that, with inflation already adjusted for by the use of constant dollars, economic growth and population increase account for less than a fourfold rise in these losses. Other population factors, such as migration to vulnerable areas, might well account for further losses, but it is unlikely that they could explain all of the remaining increase. Since by far the largest part of the increase in these losses was due to weather-related events, an increase in severe weather is a possibility that has to be looked at seriously.



Nevertheless, work completed in the last few years has shown the emergence of some significant regional trends, although no consistent pattern of change in weather extremes is yet apparent globally. The most reliable trends are those for temperature and precipitation (not surprisingly, since these are the most widely measured climate variables). Many parts of the world have shown a decrease in the occurrence of low temperature extremes, as would be expected in a warming climate. Surprisingly, though, there has not yet been a noticeable increase in high temperature extremes. The reason appears to be related to the tendency regions for winter temperatures to have increased more than summer temperatures and for overnight lows to have warmed more than daytime highs.

Temperature, therefore, has actually shown a lessening of extremes, at least so far, but a tendency towards more extreme precipitation is apparent across much of the land area of the Northern Hemisphere. Heavy rainfalls have increased in Japan, the United States, the former Soviet Union, China, and countries around the North Atlantic rim. Canadian records also reveal a trend towards heavier precipitation since 1940, although the increase has been mainly confined to the North.

Drought, on the other hand, has become more common since the 1970s in parts of Africa as well as along the coasts of Chile and Peru and in northeastern Australia. The North American prairies also saw an increase in drought during the 1980s, although these years were not as dry as either the 1930s or the 1950s.