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How are
people changing
the climate?
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1. Man-made climate change?
Abrupt changes
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The geological history of the Earth shows that there have been many abrupt changes in climate in the past. During the last Ice Age, sudden climate changes occurred about every thousand years.
Scientists have drilled deep into the ice on Greenland and have analyzed layers of ice that have been there for tens of thousands of years. The analyses show that the average temperature on Greenland changed several times by 8 to16 oC over a short period of time – as little as a decade or two! The climate has been far more stable since the Ice Age ended and there have only been moderate climate variations since. These include the Little Ice Age in Europe between 1400 and 1850 when temperatures where much lower than average.
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Sources of abrupt changes |
A gradual warming of the Earth – for example, due to stronger solar radiation or an 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 changing ocean circulation patterns. Scientists think it unlikely that we will see dramatic changes in ocean currents in the future but they cannot rule out the possibility that the strength of the ocean currents will 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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1. Abrupt changes: 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 the 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 water 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 able to estimate gradual changes in climate resulting from higher concentrations of greenhouse gases and are often unable to predict abrupt changes. Calculating the likelihood 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. As a result 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. For animal and plant life, abrupt changes are particularly serious, especially for species that, for example, have long lifetimes, are not very mobile or are specially adapted to one habitat. Sudden climate changes can give such species little time to find new homes and they might, therefore, face extinction. |
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About this page:
Author: Camilla Schreiner - CICERO (Centre for International Climate and Environmental Research - Oslo) - Norway. Scientific reviewers: Andreas Tjernshaugen - CICERO, Norway - 2004-01-20 and Dr. Knut Alfsen - Statistics Norway, Norway - 2003-09-12. Educational reviewer: Nina Arnesen - Marienlyst School, Oslo, Norway - 2004-03-10. Last update: 2004-03-27.
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