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could add to the amount of fresh water entering the North Atlantic in several ways. As
higher temperatures increase evaporation rates in the tropics, the additional water vapor is
transported to higher latitudes by prevailing wind currents, eventually to fall as rain or
snow when the air is sufficiently cooled. Melting glaciers, ice sheets, and sea ice caused
by global warming may also add significant amounts of fresh water to the North Atlantic.
The rupture of an ice dam holding back large quantities of melted water in Greenland or
elsewhere in the Arctic could suddenly release large quantities of fresh water into the North
Atlantic causing a rather abrupt interruption of the sinking action. Such an event in the
Hudson Bay area is believed to have been the cause of the 8,200 cooling event.
Could human-induced global warming disrupt the North Atlantic sinking action in
the coming decades and thus trigger a significant cooling in the region? The NAS report
concludes that human activities could trigger abrupt climate change by altering the THC.
A shutting down of the THC would probably not induce a new glacial period, but it could
cause massive changes in the oceans, such as impactin circulation regimes, upwelling and
sinking areas, seasonal sea ice, ecological systems, and sea levels. Atmospheric impacts
might include changes in land-sea temperature contrasts, storm paths, the hydrological
cycle, and extreme weather events (NAS, 2002, 108-9). The current state of the science of
abrupt climate change does not offer much of a basis for assessing the probability of an
interruption of the THC within the next hundred years. It is likewise difficult to anticipate
how such a development would interact with other trends. If a disruption of the THC does
not occur for several decades, the resultant cooling may do little more than offset human-
induced global warming. A significant cooling would also slow down the melting of snow
Convention