invited Talk, 3rd British-German Frontiers of Science Symposium, Royal Academy of Sciences and Alexander von Humboldt Foundation, North Buckinghamshire (UK): 2011-05-12 - 2011-05-15
Recent climate change alters both mean conditions and extremes of climatic variables. Ecosystems are expected to react stronger to changes in extreme events such as drought than to changes in mean conditions such as slight warming. Research on extreme events, however, faces several challenges: (1) different definitions of “extreme” are used and comparability between studies is thereby limited. (2) Contrasting time scales are involved as the climatic extreme often has a short duration (hours to days) while responses in the ecosystems may only become obvious within years or decades. (3) Interactions between climatic variables are relevant for the response of ecosystems. Joint extremes (drought accompanied by heat waves) or the interaction between trends and extreme events (general warming accompanied by single frost events) clearly matter. (4) The variability of climatic conditions itself is a strong driver of ecosystem functioning that can affect organisms independent from absolute minimum or maximum values. (5) Organisms adapt to regularly repeating extremes, e.g. trees shed their leaves before winter to avoid frost damage. Winter as a regularly occurring event might become irrelevant in temperate ecosystems with climate change. The loss of winter, however, is also highly relevant for the functioning of ecosystems. (6) Finally, the response of ecosystems depends strongly on positive and negative interactions between the involved organisms. All these points pose challenges for the understanding of the effects of extreme events on ecosystems. The last point, however, will be discussed as a key for adaptation of ecosystems to adverse effects in their functioning. Diversity, within and between species as well as on the landscape level could be used as an insurance against negative effects of climate change through ecosystem functions to human well-being.