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function of temperature and salinity[1]. The heating and cooling of water as it is carried along by the thermohaline forms a kind of conveyor belt that keeps the oceans well mixed through much the same mechanism responsible for the mesmerizing motion of the liquid in a lava lamp. However, the fact that the thermohaline’s motion is primarily driven by differences in salinity and temperature means that it is extremely vulnerable to disruption by changes in those two factors. As CO2 concentration in the atmosphere increases and ocean temperatures increase accordingly, melting glaciers and other freshwater ice stored along routes that are accessible to the ocean can result in significant influxes of fresh (and cold) water. This alters both temperature and salinity of the oceans, disrupting the thermohaline and inhibiting the ocean’s ability to act as a carbon sink. Teller et. al. (2002) argue that a similar large-scale influx of cold freshwater (in the form of the destruction of an enormous ice dam at Lake Agassiz) was partially responsible for the massive global temperature instability seen 15,000 years ago during the last major deglaciation[2].

(3) Perhaps most simply, increased acidification of the oceans (i.e. increased carbonic acid concentration as a result of CO2 reacting with ocean water) means slower rates of new CO2 absorption, reducing the rate at which excess anthropogenic CO2 can be scrubbed from the atmosphere.

Examples like these abound in climatology literature. As we suggested above, though, perhaps the most important question with regard to climate feedbacks is whether the net

  1. Vallis and Farnetti (2009)
  2. In this case, the temporary shutdown of the thermohaline was actually responsible for a brief decrease in average global temperature--a momentary reversal of the nascent warming trend as the climate entered an interglacial period. This was due to differences in atmospheric and oceanic carbon content, and were a similar event to occur today it would likely have the opposite effect.