The Earth System is complex and composed of interacting components. Non-linear interactions within and among these components, supplemented by the inherent difficulties in anticipating human behaviour, impose limits on the predictability of the Earth System.

As human pressures within the Earth System increase, several critical thresholds are approaching or have been exceeded, beyond which abrupt and non-linear changes to the life-support functions of the planet could occur. This has significant implications for human well-being now and in the future. For example: climate variability and extreme weather influence food security; crossing of thresholds leads to significant health impacts, as shown by the increase in malaria in response to rising temperatures; increased frequency and severity of climatic events affect both natural assets and human security; and accelerating changes such as of temperature and sea level rise affect the social cohesion of indigenous communities: in Alaska, for example, permafrost thawing and increased flooding are forcing villages to relocate.

Traditional expert-driven, top-down approaches to problem solving are not flexible enough to address complex, non-linear changes in the Earth System effectively. After more than 20 years of tackling problems of unsustainable development as more or less isolated issues, an integrated Earth Systems approach is needed for informed and effective decision-making.

There is an urgent need to address the underlying drivers of the human pressures on the Earth System. At the same time, it is necessary to adopt approaches that can deal better with the complexities and inherent uncertainties of the Earth System. This must include three elements: basic research to understand interactions and feedbacks; sustained long-term monitoring and observation to underpin basic research; and regular evaluation of progress to allow the adjustment of responses when observations indicate that this is necessary.

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