Climate studies have previously concentrated on issues such as the global mean temperature. Although often not emphasized, scientists have also been investigating climate variability, particularly in observations (IPCC, 2007 Section 3.8). A study published 14 November 2011 has now confirmed that the climate variability itself has been increasing. For example, both droughts and floods have been occurring more often.
Human Perception of Climate Change
The perception of climate change by each individual person can be unrepresentative of the global situation. Although there has been global warming, not all observing stations have recorded increases in temperature within the last 20 years.
One might also expect that increases in global temperature would give rise to warmer summers and milder winters. This has not always coincided with experience, as the cold 2009-2010 winter showed for many people in the USA and Europe. Regarding weather variability, it is even more difficult to be certain about any change, based on experience alone.
Information about extreme events such as floods or hurricanes are broadcast rapidly around the world and with modern communications, people have become much more informed about these events. This alone tends to color one's judgement, suggesting that there might be a trend in extremes when no such trend might be occurring. In addition, with population growth, many societies have encroached upon regions where the climate may be less hospitable, and this may have increased the tendency towards "human impact news stories" relating to climate effects.
Extreme climate variations can have devastating effects. But, to see whether such occurrences have been increasing, a detailed statistical analysis is needed to extract clear signals from the observational record.
Changes in Climate Variability
In the 2007 IPCC report, clear evidence was shown for the increase in heavy precipitation with an increase in flooding. Likewise category 4 and 5 storms have increased globally since 1970. Further evidence for the increase in severe storm frequency has been published after the IPCC report (Elsner et al., 2008), which indicated that a 30% increase in severe storms can be expected for each 1C (2F) rise in temperature. If this were projected into the future, we might expect to see a doubling of severe storm frequency before the end of the century.
An increase in the variability of precipitation has now been further confirmed in a paper published in the Journal of Climate (Medvigy and Beaulieu, 2011). The suggestion is that for those locations in which precipitation was gradual, the weather now tends to oscillate more towards heavy downpours or dry conditions.
The study found that between 1984 and 2007, climate variability had increased for 35% of the world. Asia and Equatorial Africa were found to reveal the largest increase in variability. However, the tropics can be thought of as the engine of the atmosphere, and changes there reach midlatitudes in due course.
Implications for the Biosphere
The increases in extreme drought and flooding have put increasing social and financial pressures on many countries. There is also a danger that diseases and pests might spread. For example, Increased flooding increases the chances of mosquito infested water.
Also, plants generally grow better when supplied with a consistent pattern of sun and rain (Medvigy, 2010). If climate variability were to increase further, then the ability of plants to grow healthily could be compromised. This could result in less atmospheric CO2 processed by plants and higher concentrations in the atmosphere than currently expected. Such an outcome could have a major effect on the food supply of people and animals.
References
Elsner, J. B. et al., (2008), The increasing intensity of the strongest tropical cyclones, Nature, 455, 92-95.
Erratic, Extreme Day-To-Day Weather Puts Climate Change in New Light, Science Daily, published on line, Nov 15, 2011
IPCC (2007), Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, 2007, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
Kelly, M., Erratic, extreme day-to-day weather puts climate change in new light, News at Princeton, published on line November 15, 2011.
Medvigy et al. (2010), Responses of terrestrial ecosystems and carbon budgets to current and future environmental variability, PNAS,107, 8275-8280.
Medvigy, D. and C. Beaulieu (2011), Trends in daily solar radiation and precipitation coefficients of variation since 1984, Journal of Climate, DOI: 10.1175/2011JCLI4115.1
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