A Capricious Beast Ever since the days when he had trudged around fossil lake basins in Nevada for his doctoral thesis, Wally Broecker had been interested in sudden climate shifts. The reported sudden jumps of CO2 in Greenland ice cores stimulated him to put this interest into conjunction with his oceanographic interests. The result was a surprising and important calculation. The key was what Broecker later described as a "great conveyor belt'"of seawater carrying heat northward. . . . The energy carried to the neighborhood of Iceland was "staggering," Broecker realized, nearly a third as much as the Sun sheds upon the entire North Atlantic. If something were to shut down the conveyor, climate would change across much of the Northern Hemisphere... There was reason to believe a shutdown could happen swiftly. In many regions the consequences for climate would be spectacular. Broecker was foremost in taking this disagreeable news to the public. In 1987 he wrote that we had been treating the greenhouse effect as a 'cocktail hour curiosity, ' but now 'we must view it as a threat to human beings and wildlife.' The climate system was a capricious beast, he said, and we were poking it with a sharp stick.