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a significant and sometimes dominating environmental force. Records from the geological past indicate that never before has the Earth experienced the current suite of simultaneous changes: we are sailing into planetary terra incognita.
Global environmental change challenges the political decision-making process by its uncertainty, its complexity and its magnitudes and rates of change.
Because of the uncertainties involved, decision-making will have to be based on risks that particular events will happen, or that possible scenarios will unfold. A lack of certainty does not justify inaction - the precautionary principle must be applied.
Because of its complexity, global environmental change is often gradual until critical thresholds are passed, and then far more rapid change ensues, as seen in the growth of the ozone hole. Some rapid changes - such as the potential melting of the Greenland ice sheet - would also be irreversible in any meaningful human timescale, while other changes may be unstoppable, and indeed may have already been set in motion.
Because of the magnitudes and rates of change, we are unsure of just how serious our interference with the dynamics of the Earth's system will prove to be, but we do know that there are significant risks of rapid and irreversible changes to which it would be very difficult to adapt.
The first step toward meeting the challenge presented by global change is to appreciate the complex nature of the Earth's system, the ways in which we are affecting the system, and the economic and societal consequences. Scientists and policy-makers must establish a dialogue to communicate current knowledge and to guide future research.
Real policy progress must address the need for large-scale change, technological advances and global cooperation. Incremental change will not prevent, or even significantly slow, climate change, water depletion, deforestation or biodiversity loss. Breakthroughs in technologies and natural resource management that will affect all economic sectors and the lifestyles of people are required.
Although action at local, regional and national levels is important, international frameworks are essential for addressing global change. We must develop new approaches that consider the diversity of national circumstances and interests, based on a shared political will for action. Never before has an effective multilateral system been more necessary.
The evidence of our impact on our own life-support system is growing rapidly. Will we accept the challenge to respond in a precautionary manner, or wait until a catastrophic, irreversible change is upon us?
Margot Wallström is the European Commissioner for the environment. Bert Bolin is the founding chair of the Intergovernmental Panel on Climate Change. Paul Crutzen was awarded the 1995 Nobel Prize in Chemistry. Will Steffen is executive director of the International Geosphere-Biosphere Program. This comment is based on "Global Change and the Earth System: A Planet Under Pressure," which looks at the findings of the International Geosphere-Biosphere Program.
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