ABSTRACT
Another aspect of the global climate system that is even less well understood is that of long-term climate trends (of 20 to 50 years) that have in the past substantially altered the climate in some regions of the world. These trends could be the result of either global warming or interdecadal natural variability or both. Attribution of these trends to a specific cause is a complex issue because they may also be influenced by many natural or local human-driven processes. However, irrespective of their relation to global climate change, these trends do produce important social and economic impacts, adaptation strategies for which could also provide important insights into adapting to future climate change. Since such trends result in entirely new climatic conditions, adapting to them is much more complex than adapting to interannual climate variability. Sometimes it may be decades before there is public or even technical awareness of such trends and their associated costs or opportunities, while in other cases responses may be relatively fast.
