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The sun or mankind - Which is the strongest in climate change?

Potsdam, 27 March 2003


Climate researchers have been debating for some time whether the influence of changing solar activity or that of mankind exerts the greatest influence on climate change. The latest study from the Potsdam Institute for Climate Impact Research (PIK) shows that until the mid-19th century, climate changes are mainly traceable to changed sun activity and volcanic eruptions. Since that time, however, mankind has played the decisive role in climate change.

According to the new study by the Potsdam scientists, changes in solar activity and volcanic eruptions were the predominant force in climate variability over the last millennium. Especially cold periods during the "Little Ice Age" (15th to 19th century) occurred in conjunction with phases with particularly few sunspots. One of these cold phases, the so-called Maunder minimum, lasted from around 1645 to 1715. An especially strong cooling was also caused by the eruption of the Tambora volcano in Indonesia in 1815, which was followed by a year without a summer.

Since the start of industrialisation around 1850, increasing concentrations of greenhouse gases in the atmosphere have led to increasing warming. This warming is offset by the effect of deforestation, since the Earth's surface is lighter following deforestation and reflects more sunlight.
The new study contains the surprising result that the Little Ice Age was prolonged in the 19th century by the effect of deforestation, although natural factors such as changes in solar activity and a reduction in volcanic activity would otherwise have led to warming earlier.

The concentration of greenhouse gases has increased at an accelerating rate in the 20th century, while the intensity of deforestation in the mid-northern latitudes has decreased. Over recent decades the influence of mankind through the emission of greenhouse gases has been the strongest factor and this is likely to remain the case in the future.

The current work is based on computer simulations using the CLIMBER Earth system model, which was developed at PIK. This extended climate model describes the interactions between atmosphere, ocean and vegetation. Values for the driving forces influencing climate, such as solar activity, volcanic eruptions, atmospheric carbon dioxide concentrations and human land use are fed into the model, which then calculates the response of the climate system to these forcings. Eva Bauer, PIK scientist and lead author of the study, summarizes, "The results are convincing. These simulations agree more closely than earlier ones with climatic data sets of tree-ring and ice-core data for the last thousand years".

The study was published on 19th March in the journal Geophysical Research Letters.

The Potsdam Institute for Climate Impact Research (PIK) was founded in 1992 and employs 121 scientists. Its research on climate change, climate impacts and sustainable development is of international renown. PIK is a member of the Leibniz Association.

Contact:
Dr. Eva Bauer, eva.bauer@pik-potsdam.de, Tel. +49-0331-288-2588

Press office:
Anja Wirsing, anja.wirsing@pik-potsdam.de, Tel. +49-331-288-2507

Original article:
Bauer, E., Claussen, M., Brovkin, V. and Hünerbein, A. 2002: Assessing climate forcings of the Earth system for the past millennium, Geophys. Res. Lett., 30 (6), 1276, doi:10.1029/2002GL016639

Graphic material can be viewed on the internet:
www.pik-potsdam.de/news-1/press-releases/archive/2003/klimaschwankungen (German version only)
The reproduction of this text is permitted free of charge.

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