2005: Forests are burning across Spain and Portugal and harvests are being wiped out by drought. Some claim that this is the worst drought to hit the Iberian peninsula in 60 years. Switzerland, on the other hand, experiences so much rain fell at the end of August that alpine valleys are cut off from the outside world and mudslides occur along the slopes.

As a sweeping glance at reports in the mass media shows, the victims of the latest climatic capers in Europe are the Mediterranean and the Alps. The results of ATEAM (Advanced Terrestrial Ecosystem Analysis and Modelling), a broad-based European project, now published in Science (1) suggests that these regions might continue to be most affected by climate change. Using various models and together with other European researchers, Professor Harald Bugmann and Dr. Bärbel Zierl from the ETH Chair of Forest Ecology demonstrate that global change will raise problems for land, forest and water management, as well as for tourism in many regions of Europe. The scientists pinpoint the reasons for this in climate change and a changing land use. For human beings, this will mean fewer reliable services from Mother Nature with regard to nutrition, water and recreation.

Water shortage in the Mediterranean

Researchers have calculated that climate change will aggravate the already precarious water situation in Mediterranean regions. By 2080 a further 14 to 38 per cent of the population in these areas might be affected. The increasing water consumption for irrigation and tourism will become a burden to them. Furthermore, the researchers expect that in Mediterranean regions in particular–but also in the central alpine valleys–the danger of forest fires will grow and dry periods will become more frequent and last longer they do today.

Sufficient snow only above 1,700 metres

Higher temperatures mean that the snow line in the alps will rise. In their model Bugmann and Zierl proceed from the assumption that by the end of the century the altitude, above which one can be sure to find a snow cover sufficient for wintersport, will rise first to 1500 metres above sea level, in a worst-case-scenario even to 1700 metres. "A rise in the snow line of 300 to 400 metres will mean that and additional 20 to 25 per cent of the skiing regions will run into economic problems," says Bugmann. Already today, regions below 1300 metres that cater to ski tourism–which means one in seven of Switzerland's skiing resorts–are no longer profitable.

Moreover, scarcity of snow will not only cause a problem for skiing regions. Climate change, so the researchers deduce, will interfere with one of the alpine region's more vulnerable processes, namely their role as a temporary water reservoir in the form of ice and snow. One consequence would be a great change in the drainage regime. The snow will melt earlier and the danger of floods in May and June will be brought forward by up to two months. High water in winter will become more frequent because precipitation will fall more often as rain instead of snow.

Summer drainage, however, would probably fall, and in dry parts of pre-alpine regions rivers could even dry up. This would lead to shortages, for example, in irrigation for agriculture. "Half of the water drainage during summer in the Netherlands today comes from the Alps," is how the ETH professor makes the importance of the Alps as a water catcher and water reservoir clear.

First a sink, in 50 years time a producer of CO2: Mountain regions react very sensitively to climate change. (Picture: H. Bugmann / ETH Chair for Forest Ecology). large

First a sink, then a source

The study also confirms that the European ecosystem currently sequestrates great quantities of CO2. This also applies to mountain ecosystems, as Bugmann and Zierl demonstrate. Mountain forests will continue to function as CO2 sinks over the coming decades, because the warmer climate favours the growth of forest, especially at the upper timber line. This means that more carbon-dioxide is sequestrated than emitted. Besides this the land use will change too. The cultivation of increasingly "unprofitable" agricultural areas will be abandoned. Forests will spread, and sequestrate even more CO2.

"But trees don't just continue to grow for ever," warns Bugmann. Computer simulations show that a C02 saturation will be reached in the second half of the 21st century. In clear text this means that in a few decades forest and soil will release more CO2 than they absorb today and will mutate from sinks to sources of carbon dioxide.

Such carbon calculations, however, are subject to considerable uncertainties. It is far more difficult to make precise quantitative assertions about the carbon cycle than the water balance, says Bugmann. Nevertheless, he is convinced that biogeochemical models could be improved by the inclusion of data from new studies on the carbon cycle of ecosystems, for instance the one investigating the effects of the 2003 heatwave on the carbon balance of forest and grassland habitats(2). This study had shown that under the influence of drought and heat, Europe's forests and grassland had released a lot of carbon into the atmosphere.

In their work carried out within the framework of the ATEAM project, Harald Bugmann and Bärbel Zierl concentrated on the ecosystem services of the mountains. "Mountain regions are important because they have a considerable influence on people's well-being," stresses Bugmann. Mountains cover a quarter of the total land surface of our planet, provide living space to 600 million people and contain a high level of biodiversity. Moreover, they provide extensive regions with water, absorb carbon and are important for the tourist industry. The five case studies from Switzerland and Germany that the ETH researchers chose for their investigation represent roughly half of the Alpine area.

Taking economic interests into account

An innovation in the ATEAM project was the inclusion of stakeholders from industry and politics and their interests and points of view were allowed to flow into the design of the research project. The study is based on new scenarios of climate change, which are based on results from the IPCC (Intergovernmental Panel on Climate Change). These results were adapted for individual areas in Europe and then combined with related consistent regional scenarios on land use. In this way it became possible for the first time to investigate the effects of these two drivers of global change on the terrestrial ecosystems.