Identifying the sea level signal: Surf's up



Of all the dire consequences of the greenhouse effect, global sea level rise is potentially the most destructive to human life and property. But the processes that increase the volume of the oceans are so poorly understood that theoreticians are taking their lead from scientists trying to actually measure current changes in sea level that might be caused by the greenhouse effect. As with surface temperature, precipitation, and other measures of climate change, identifying the greenhouse signal is a daunting problem.

Climate models that predict mean temperature increases around the world of up to several degrees C in the next 50–100 years in response to human-induced global warming have given rise to a scientific consensus that mountain glaciers and ice sheets will begin to melt and the water in oceans will slightly expand, raising sea level. Such increases would inundate some of the most densely populated and highly cultivated areas on the planet, displacing and endangering many millions of people at a devastating economic and social cost.