The largest source of Antarctic Bottom Water in the thermohaline circulation, prior to 1976, was a polynya (area of open water) that formed in ice of the Weddell Sea each winter, from current deflected off an undersea ridge. Anthropogenic warming caused a freshwater lid that shut down the Weddell Sea polynya. As a result, the subtropics are warmer, with more high pressure areas and stronger trade winds. This impacts the northern hemisphere by increasing the flow of warm water from the Atlantic into the Arctic.
The Weddell Sea polynya, an area of open water the size of New Zealand, was the most productive source of cold Antarctic bottom water in the 1970s. Relatively warm salty water is pushed upwards by ocean currents moving over a ridge in the Weddell sea. Before 1980 this salty water reached the surface releasing large amounts of heat, then cooled and sank to the bottom of the ocean. The heat kept the huge hole in the ice pack called a polynya open, and a massive oceanic convection cell formed in the Antarctic winter.
The failure of the huge convection cell in the Weddell sea has reduced the transport of heat, salt and ocean water towards Antarctica. Heat has built up in the tropical and subtropical oceans. The strong thermal gradient between cold Antarctica and the warming waters in the southern hemisphere's temperate zone and subtropics has intensified the winds around Antarctica as the jet stream was pushed closer to Antarctica by the expanding subtropical belt. Moreover, the heating of the tropical oceans has increased tropical convection. These processes have combined to intensify the water cycle, strengthen the subtropical high pressure areas, and increase the strength of the trade winds.
The strengthened winds have spun up the strong current that rings Antarctica called the Antarctic Circumpolar Current. This ring of fast moving water tends to block the transport of warm subtropical water towards Antarctica. However, the geography of the northern hemisphere has the opposite effect on the poleward transport of warm subtropical water. The Atlantic ocean is aligned to funnel warm subtropical water into the Arctic ocean as the subtropical highs strengthen and the trade winds speed up. Thus, the collapse of the Weddell Sea polynya has lead to increased transport of oceanic and atmospheric heat towards the Arctic. The rapid warming of the Arctic and the extraordinarily rapid decline of Arctic sea ice, which was not predicted by climate models, is a likely consequence of the collapse of the Weddell Sea polynya, which had been the most productive source of Antarctic Bottom Water (ABW).
The IPCC's models have not considered the effects the collapsing production of Antarctic Bottom Water and political policy has not kept up with the IPCC. We are moving rapidly into uncharted waters as the Arctic melts. Global political policies are not keeping up with the rate of change and our models have, to date, underestimated the rate of change. We are witnessing a total failure of global leadership to deal with changes we caused that are spiraling out of control. [emphasis mine]
This article shows how new scientific discoveries are unfolding so rapidly they can't be quickly integrated into a whole picture of our destabilizing ecosphere, even at 400 ppm of CO2. Climate Change isn't just accelerating. The rate Climate Change acceleration is exceeding our capacity to comprehend what's happening to us now in real time, let alone our ability to see what's ahead at 600 ppm.
Thanks for including the link to the Smithsonian Magazine article, with more explanation of Antarctic bottom water, thermohaline circulation in general, and its importance to our climate.