The Case of Global Warming and Extreme Weather

The Case. That statement could have been uttered by climate scientists. They know global warming is the cause of the more extreme weather events we are experiencing, but it is hard to prove it. Global warming has increased the energy and moisture in the atmosphere, and that combination makes conditions ripe for severe storms and floods. Certainly, hurricanes occur and intensify over low-pressure areas fed by moisture and warmer oceans. To be accurate, however, climate scientists could only say, “When weather events occur, global warming is likely to make them more extreme.” However, the case against global warming is growing stronger. A number of recent research papers have shown global warming is the cause of extreme weather events, and the business community, particularly insurers, are beginning to take notice.

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The Link. The vapor pressure of water is one of the most important factors in determining weather. Water will evaporate from the surface until the air above it reaches its saturated vapor pressure. The saturated vapor pressure depends only on the temperature, which makes temperature the determining factor controlling the amount of moisture that the air can hold. If a mass of air saturated with moisture moves to higher altitudes or encounters a cold front and is cooled, the air becomes supersaturated, which leads to precipitation. Over the last century, the Earth’s average temperature has increased by about 0.8°C, which translates into an increase in the saturated vapor pressure of water of about 7%. When precipitation occurs, on the average, 7% more moisture is available. It is a reasonable conclusion that when it rains, it will rain more and when it snows, it will snow more. So strangely enough, global warming could actually lead to greater snowfall. However, it has been very difficult to prove, and certainly even more difficult to convince skeptics that that might be the case.

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Floods. Two recent research papers have established a link between global warming, increased rainfall, and flooding. A recent paper in Nature reported that the observed increase in rainfall in the Northern Hemisphere in the past 50 years and climate change are linked. The researchers analyzed the rainfall data in areas prone to flood and found that the rainfall has increased due to the warmer temperatures of the Earth. Their results “were based on a comparison of observed and multi-model simulated changes in extreme precipitation over the latter half of the twentieth century analyzed with an optimal fingerprinting technique.” They also found that the models seem to underestimate the observed increase in heavy precipitation with warming temperatures. Extreme precipitation in the future may be even more severe than now predicted.

The second paper, also published in Nature, has linked the increasing floods in England and Wales and global warming. The researchers generated several thousand climate model simulations of the autumn 2000 weather by using actual conditions and also by assuming conditions as they would have been had no greenhouse gas emissions or global warming occurred. They concluded that “the precise magnitude of the anthropogenic contribution remains uncertain, but in nine out of ten cases our model results indicate that twentieth-century anthropogenic greenhouse gas emissions increased the risk of floods occurring in England and Wales in autumn 2000 by more than 20%, and in two out of three cases by more than 90%.


Rivers in the Sky. Normally, when an air mass saturated with water moves ashore and is forced upward, it cools and precipitation falls until the clouds are no longer over-saturated. However, that is not the case for “rivers in the sky, weather patterns that carry a stream of air saturated with water into coastal regions continually for days. These “rivers in the sky”, cause flooding rains in coastal and inland mountains causing untold costs in property damage and human lives. One such river produced more than 40 inches of rainfall in the mountains of southern California in only four days in early January 2005. It caused widespread flooding and massive mudslides such as the one in La Conchita, California, which took 10 lives. The researchers say these “rivers in the sky” will become more common as global temperatures rise since warmer air means that the atmosphere can hold more water vapor. That is, unless global warming changes the weather patterns that produce them.

Droughts. The link between global warming and droughts has not been yet established by research. Areas that receive little moisture from the oceans would not benefit from the fact that the air can hold more water. Though higher temperatures mean that more water evaporates into the air, it also means that the air can hold more moisture before becoming saturated. Areas that normally experience droughts are much more likely to have less rainfall in the future. This past year has seen droughts in Russia, China, and South America that have limited the production of grain and increased the chances that some species may become extinct. The heat waves in Europe in 2003 and 2010, that caused widespread crop failure and wildfires, may have been the worst in 500 years. Certainly, more frequent and extensive droughts may occur in a warming world.

The Smart Money. The widespread damage caused by weather events related to global warming has caught the attention of the business community, particularly those who pay out insurance claims or invest large sums of money. Insurance companies ranked 2010 among worst years ever for climate disasters. Climate change is the culprit in many of the catastrophic natural disasters in 2010, according to insurance company Munich Re, one of the largest global insurance carriers. It added that trends are pointing to more frequent and riskier events in the future. Recently, a group of International investors, responsible for more than $15 trillion in assets, issued a global warming warning. They called for the world’s nations, particularly the United States, to move decisively to combat climate change or face the possibility of economic disruptions even worse than the global recession of the last two years. They also pointed out that “The economic opportunities are enormous for nations with the foresight to seize them while the risks of inaction are potentially catastrophic.”
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