Tl. Delworth et Kw. Dixon, Implications of the recent trend in the Arctic/North Atlantic oscillation for the North Atlantic thermohaline circulation, J CLIMATE, 13(21), 2000, pp. 3721-3727
Most projections of greenhouse gas-induced climate change indicate a weaken
ing of the thermohaline circulation (THC) in the North Atlantic in response
to increased freshening and warming in the subpolar region. These changes
reduce high-latitude upper-ocean density and therefore weaken the THC. Usin
g ensembles of numerical experiments with a coupled ocean-atmosphere model,
it is found that this weakening could be delayed by several decades in res
ponse to a sustained upward trend in the Arctic/North Atlantic oscillation
during winter, such as has been observed over the last 30 years. The strong
er winds over the North Atlantic associated with this trend extract more he
at from the ocean, thereby cooling and increasing the density of the upper
ocean and thus opposing the previously described weakening of the THC. This
result is of particular importance if the positive trend in the Arctic/Nor
th Atlantic oscillation is a response to increasing greenhouse gases, as ha
s been recently suggested.