CONCLUSIONS AND RECOMMENDATIONS

Physical climate science has developed some skill at estimating the changing likelihoods of the occurrence of certain kinds of climate events, such as heat waves and certain precipitation anomalies, at a decadal time-scale and at a global and, in some cases, a continental or subcontinental geographic scale. However, the ability to foresee specific climate events on a decadal time-scale at the level of medium-sized countries is still in its infancy. Predictive skill at such time horizons and levels of resolution depends on having a more extensive observational system than currently exists and on developing an improved understanding of interannual and decadal processes of climate variability that can be incorporated into predictive models. Estimating the risks of extreme climate events—and especially estimating the places they will occur—is particularly challenging because predictive skill is harder to acquire and to validate for infrequent events and because the frequency and character of such events may change as climate trends continue.

The current state of understanding does not suggest that the distributions of single climate event types in particular places will change sharply in the coming decade, but neither can it preclude such a possibility with high confidence. It is safe to say that extreme climate events will change in their frequencies, intensities, and probably also their locations in the coming decade. The most likely scenario is a continuation of the temperature and precipitation trends of recent decades, probably with a slow rate of change for now, but with the possibility of a faster one later. However, the effects of the ENSO cycle superimposed on longer-term climate trends will exacerbate some extremes and dampen others in complex ways. In addition, there remains the possibility of unprecedented extreme events or conjunctions of events that might occur as a result of abrupt climate change or other climatic phenomena (for example, a more rapid rise in sea level if the melting of ice sheets were to accelerate).

Conclusion 3.1: Given the available scientific knowledge of the climate system, it is prudent for security analysts to expect climate surprises in the coming decade, including unexpected and potentially disruptive single events as well as conjunctions of events occurring simultaneously or in sequence, and for them to become progressively more serious and more frequent thereafter, most likely at an accelerating rate. The climate surprises may affect particular regions or globally integrated systems, such as grain markets, that provide for human well-being.

Some events or conjunctions of events may arise from connections within the Earth system, such as aspects of the ENSO cycle and other



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