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Severe impact of the 2003 European heat wave on ecosystems

Potsdam,
22 Sept. 2005

The 2003 European heat wave and drought had a massively negative impact on growth in European ecosystems. Agricultural crops and forests were much less productive than normal, and all ecosystems absorbed less of the greenhouse gas carbon dioxide from the atmosphere. These findings are the first continent-wide assessments of ecosystems during the heat wave. They are based on measurements, satellite observations and computer models, collated by European researchers in the CarboEurope-IP project, with participation of the Potsdam Institute for Climate Impact Research (PIK). The study appears in this week's Nature magazine.

The European heat wave during the summer of 2003 produced the warmest August on record, unleashed massive forest fires, and claimed an estimated 35,000 lives. Now, researchers in the European Union funded CarboEurope-IP consortium have identified another baleful consequence of the extreme weather pattern in 2003, as published this week (9/22/2005) in Nature: Vegetation growth across Europe was reduced during the dry and hot summer in an unprecedented way, by about 30 %. This meant not only that crop yields and forest growth were lower than normal, but also that ecosystems absorbed less carbon dioxide from atmosphere or even released it. The low rainfall and extreme temperatures in Western Europe (which partly exceeded 40 °C) combined to hinder plant growth in a way that was unprecedented in Europe over the past century.

These results contrast current perceptions that climate warming might generally enhance plant growth and prolong the growing season in temperate climates, processes which were assumed to increase the amount of carbon stored in the biosphere. Instead, it is shown that rising concentrations of greenhouse gases and the induced warming may provoke other changes (e. g. by enhancing summer drought). Under these conditions, no 'fertilization effect' of CO2 on vegetation productivity can be found anymore.

In order to make this assessment, researchers combined direct observations of carbon dioxide uptake or release from ecosystems with satellite images and crop yield records, using computer simulations covering all European ecosystems. In Germany, the Max Planck Institute for Biogeochemistry (Jena) and the Potsdam Institute for Climate Impact Research played leading roles in the analysis.

The additional effects of the massive fires have not been included in the calculations, and it is still too early to estimate the long-term damage of such a climatic extreme on vegetation. Future climate simulations predict that such extreme weather events will become more frequent during the present century. Therefore, these results raise important questions about the ability of ecosystems to resist against climatic change.

Original article:
Ph. Ciais, M. Reichstein, N. Viovy, A. Granier, J. Ogeé, V. Allard, M. Aubinet, N. Buchmann, Chr. Bernhofer, A. Carrara, F. Chevallier, N. De Noblet, A. Friend, P. Friedlingstein, T. Grünwald, B. Heinesch, P. Keronen, A. Knohl, G. Krinner, D. Loustau, G. Manca, G. Matteucci, F. Miglietta, J. M. Ourcival, D. Papale, K. Pilegaard, S. Rambal, G. Seufert, J. F. Soussana, M. J. Sanz, E. D. Schulze, T. Vesala & R. Valentini (2005): Europe-wide reduction in primary productivity caused by the heat and drought in 2003. Nature, doi: 10.1038/nature03972.

Contact at PIK:
Dr. Markus Reichstein, email Markus.Reichstein@pik-potsdam.de,
phone +49/(0)331/288-2550

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