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How are
people changing
the climate?
Read more |
1. Man-made climate change?
Abrupt changes
Earth’s history has many examples of abrupt climate changes. During the last Ice Age, which ended around 10,000 years ago, sudden climate changes occurred about every 1000 years. |
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Scientists have drilled deep into the inland-ice on Greenland, and analyzed layers of ice that have lain there for tens of thousands of years. The analyses show that several times the average temperature on Greenland changed by 8–16 °C over a short period of time – as little as a decade or two! The climate has been far more stable after the Ice Age ended, but with moderate climate variations such as the Little Ice Age in Europe (about 1400–1850). |
Sources of abrupt changes |
A gradual warming of the Earth – for example, due to stronger solar radiation or increased greenhouse effect – can lead to abrupt changes in the climate system when a threshold is reached. For example, the abrupt climate changes during the last ice age probably occurred when the large inflows of freshwater from melting glaciers stopped flowing into the oceans, starting the large currents in the Atlantic Ocean that transport heat to Northern Europe. Scientists think it unlikely that we will experience such dramatic changes in the ocean currents as there were during the ice age. But they cannot rule out the possibility that the strength of the ocean currents can change quickly and lead to rapid climate changes in Europe.
Another possible source of abrupt climate change is the enormous amounts of the greenhouse gas methane (CH4) trapped in the frozen ground in the Arctic. If global warming causes the permafrost to thaw and the methane to be released, this can lead to very rapid warming.
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ABRUPT: Reconstructed summer temperature in the Scandes Mountains, Sweden over the last 10 000 years. The curve shows a quite abrupt cooling episode that took place approximately 8 200 years ago. This event is also seen in temperature reconstructions from other locations in Europe and in ice cores from Greenland. It was probably caused by shifts in ocean currents, caused by huge amounts of freshwater which were released to the oceans when the melting ice caps still left over North America after the Ice Age suddenly released huge amounts of freshwater that had been trapped in lakes behind the ice. The temperature reconstruction was possible because scientists know what temperatures pine trees need to grow in the Scandes mountains. From plant remains, the scientist determined the maximum height above sea level where pine trees could grow at various times. A high limit for pine trees means a relatively warm climate. Source: Dahl and Nesje, The Holocene 6(4) 381-398 (click to enlarge, 21 kB)
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Modelling abrupt changes
Climate models are best used to estimate gradual changes resulting from higher concentrations of greenhouse gases, and are often unable to predict abrupt changes. Calculating the likelihood of and consequences of abrupt climate changes is very uncertain – partly because we do not know exactly where the “thresholds” lie, or what causes the abrupt changes. Thus we know little about when, where and how abrupt climate changes resulting from a warmer atmosphere will occur.
Consequences of abrupt changes
Sudden and unexpected climate changes often have serious consequences. Abrupt changes do not allow us the time or opportunity to prepare. And for animal and plant life, abrupt changes are particularly serious, especially for species that have long lifetimes, are not very mobile, are specially adapted to one habitat, or in any other way have few possibilities to adapt. Sudden climate changes can give such species little time to find new habitats, and they might therefore face extinction. |
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Author: Camilla Schreiner - CICERO (Center for International Climate and Environmental Research - Oslo) - Norway. Scientific reviewers: Andreas Tjernshaugen - CICERO (Center for International Climate and Environmental Research - Oslo) - Norway - 2004-01-20 and Knut Alfsen - Statistics Norway - Norway - 2003-09-12. Educational reviewer: Nina Arnesen - Marienlyst school in Oslo - Norway - 2004-03-10. Last update: 2004-03-27. |
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