Climate Change Information Sheet 16
Climate disasters and extreme events
- The climate varies naturally on all timescales. Variations can be caused by external forces such as volcanic eruptions or changes in the sun's energy output. They can also result from the internal interactions of the climate system's various components - the atmosphere, oceans, biosphere, ice cover, and land surface. These internal interactions can cause fairly regular fluctuations, such as the El Nino/Southern Oscillation (ENSO) phenomenon, or apparently random changes in climate.
- Natural variability often leads to climate extremes and disasters. On timescales of days, months, and years, weather and climate variability can produce heat waves, frosts, floods, droughts, severe storms, and other extremes. A climate extreme is a significant departure from the normal state of the climate system, irrespective of its actual impact on life or the earth's ecology. When a climate extreme has a major adverse impact on human welfare, it is called a climatic disaster. In some parts of the world climatic disasters occur so frequently that they may be considered part of the norm. It is possible that greenhouse gasinduced climate change will alter the frequency, magnitude, and character of both climate extremes and climatic disasters.
- Every region of the world experiences recordbreaking climate extremes from time to time. In 1995, for example, summer heatwaves affected both the US Midwest and the Indian subcontinent. More than 700 people died from heat stress in the US; 500 died in northern India when June temperatures soared to 50 degrees Celsius. Earlier that year, river flooding in the Netherlands caused the evacuation of over 200,000 people and almost half a million livestock. It was the worst flooding since the Dutch sea dikes failed in 1953. In the first decades of this century, a trend towards increased drought in the North American Midwest culminated in the "Dust Bowl" decade of the 1930s, after which conditions eased. More recently, annual rainfall over the Sahel zone of northern Africa during nine of the years since 1970 has dropped more than 20% below the average prevailing during this century's first seven decades; those previous 70 years saw only one extreme of this magnitude.
- Do today's frequent reports of recordbreaking events mean that climate extremes are becoming more common? According to the Intergovernmental Panel on Climate Change, "there are inadequate data to determine whether consistent changes in climate variability or weather extremes have occurred over the 20th century". There have been some regional trends but "some of these changes have been toward greater variability; some have been toward lower variability". It may simply be that people are much more aware of extreme events because the communications revolution has made news and information so much more widely available than ever before.
- Increased human vulnerability is transforming extreme events into more climatic disasters. People in many parts of the world are being forced to live in more exposed and marginal areas. Elsewhere, highvalue property is being developed in highrisk zones. This has been reflected in the severe pounding that the insurance industry has received from a series of "billion dollar" storms since 1987.
- In the future, global climate change may significantly affect the frequency, magnitude, and location of extreme events. Any shift in mean climate will almost inevitably affect the frequency of extreme events (see figure). In general, more heatwaves and fewer frosts could be expected, and more intense rainfalls may lead to increased flooding in some regions. However, extreme events last for a relatively short time and are usually a local experience, making it difficult for scientists to predict how these events might respond to climate change. For example, a warming of the tropical oceans would by itself be expected to increase the frequency, and perhaps the severity, of tropical cyclones. But other factors, such as changing winds or storm tracks, might offset this effect at the local level. In any case, growing human vulnerability to climate extremes, combined with the uncertainties of climate change, clearly offers cause for concern.
- While extreme events are inherently abrupt and random, the risks they pose can be reduced. Improved preparedness planning is urgently needed in many parts of the world, with or without climate change. Better information, stronger institutions, and new technologies can minimize human and material losses. For example, new buildings can be designed and located in ways that minimize damage from floods and tropical cyclones, while sophisticated irrigation techniques can protect farmers and their crops from droughts.
- Scientists cannot state that today's extreme events result from climate change. They simply do not understand the climate system and the effects of greenhouse gas emissions well enough to conclude that particular events are linked to the general problem. (It is possible that in future decades they may look back and realise with the benefit of hindsight that certain events indeed were linked.) Nevertheless, monitoring and studying extreme events, and learning how to predict and cope with them, must be a priority. Of all the effects of climate variability in the decades to come, extreme events are likely to be of greatest consequence for human well-being.
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