Executive summary

The Third Assessment Report of the Intergovernmental Panel on Climate Change represented a consensus among the world’s leading climate scientists that rapid climate changes were occurring on a global scale.

In particular, the marked warming that had occurred over the past half century was, they concluded, substantially caused by the build-up of greenhouse gases in the troposphere as a result of anthropogenic activities. Globally, 1998 was the warmest year of the warmest decade of the warmest century of at least the last millennium.

Such fluctuations, the IPCC suggested, were already capable of being associated with changes in a diverse set of physical and biological indicators in many parts of the world. Indicators of climate change are primarily used to simplify a complex reality and to communicate, more succinctly, critical information regarding climatic trends.

They also provide an essential early warning system by making available information that may point to an environmental problem which is capable of being ameliorated before it becomes critical.

In establishing indicators, a distinction can be made between primary indicators, based on analysis of directly observed meteorological data, and secondary indicators, based on the responses of the living world to climate changes which provoke a response in living organisms.

Full executive summary in report.