The shape marked out by the smoothed curve in Figure b is significant because the warmth of the last few decades appears to be unprecedented in this 1000-year period (and longer); i.e. it rises above the range of natural variability, and exceeds even the uncertainty in the proxy data record (at the 95% confidence level).

It is one thing to detect a global warming trend but quite another to establish with a given level of confidence that it has been caused by human activity – specifically, the increase in greenhouse gas concentrations and associated radiative forcing since pre-industrial times. Establishing ‘cause-and-effect’ relationships in the behaviour of complex natural systems is always difficult, and often controversial.

However, the overwhelming scientific consensus is that the human impact on the atmospheric burden of greenhouse gases has made a significant contribution to recent climate warming – and hence, by implication, to the observed changes in other climate variables, and in physical and biological systems. But what of the future?

At a time when climate change is already beginning to create sever problems for many communities, what might lie ahead in a future that could see a dramatic rise in atmospheric pollution as a result of population increase?

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