On this day in history,...

...in 1987, Wallace S. Broecker published his seminal paper “Unpleasant Surprises in the Greenhouse?” in Nature, introducing the now-iconic metaphor of the ocean’s “conveyor belt.” This conceptual breakthrough brought widespread attention to the Meridional Overturning Circulation (MOC) as a key regulator of Earth’s climate system and a potential trigger for abrupt climate shifts.

Broecker’s work synthesized decades of oceanographic research and paleoclimate evidence to argue that disruptions in the Atlantic component of the MOC could lead to rapid changes in temperature and precipitation patterns across the globe. The “conveyor belt” imagery he introduced helped crystallize the idea that the global ocean circulation is not merely a passive background process, but a dynamic and sensitive component of the climate system.

The foundation for this insight was laid nearly three decades earlier by oceanographer Henry Stommel, who in 1958 developed a theoretical model of thermohaline-driven circulation. Stommel's model showed how small differences in temperature and salinity could drive a large-scale overturning circulation, particularly in the Atlantic. While he did not use the modern terminology, Stommel was the first to articulate the physical basis of what would later be called the MOC.

Broecker’s 1987 paper transformed this theoretical understanding into a climate warning, emphasizing the ocean’s potential for dramatic and nonlinear responses to freshwater inputs and warming — an idea that remains central to contemporary climate research.

Sources

•    Broecker, W. S. (1987). Unpleasant Surprises in the Greenhouse? Nature, 328, 123–126. https://doi.org/10.1038/328123a0
•    Stommel, H. (1958). The Gulf Stream: A Physical and Dynamical Description. University of California Press, 202 pp.
•    Rahmstorf, S. (2002). Ocean circulation and climate during the past 120,000 years. Nature, 419, 207–214. https://doi.org/10.1038/nature01090