Empirical Case Studies: Potentials of Global Risks: Climate Risks. Gerhard Lammel, Marx Planck Institute for Meteorology, Bundesstrasse 55, 20146 Hamburg, Germany
Risks are caused by the extremes of the natural climate variability (undisturbed climate) or by the impacts of the climate change currently on the move (anthropogenically disturbed climate as a result of enhanced greenhouse gas concentrations). The predictability of extremes such as droughts, hurricanes, and floodings did improve, however, as climate variability is incompletely understood and by principal reasons, it remains limited. Moreover, the attribution of local and regional phenomena to natural or anthropogenic causes is in most cases not achievable.
Climate change introduces new risks because regional weather patterns change and extremes so far unknown to regions will arise. The rate of the increase of the global near surface temperature is the highest since 10000 years b.p. Adaptation of ecosystems and mankind is expected to be particularly arduous or impossible in coastal zones in general and in inadequately managed agricultural areas, besides others. Some pests and diseases will spread as a consequence of warmer regional climates. Even sudden re-organisations of the global climate system are at risk to be triggered by the man-made gradual warming: From our understanding of the coupled atmosphere-ocean system (which can be tested in model experiments) we have to accept, that a shutdown of the thermohaline circulation in the northern Atlantic ocean is a realistic scenario: A new ice age for large parts of Eurasia would result.
As considerably delayed by buffering processes involving the ocean, most risks of global warming can be characterized as "Cassandra". In some cases, the probability of occurrence is unknown ("Pythia"). Others related to inadequate adaptation to the natural climate variability are attributed to the "Sword of Damocles" type of risks.
The international community agreed upon a common effort to cope the risk of a global climate warmer than acceptable to mankind and the ecosystems and on a first, though still insufficient measure (Article 2 of and Kyoto protocol to the UN Framework Convention on Climate Change).
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