The fate of a critical ocean current may depend more on how fast our planet heats up than the temperature level we ultimately end up with. Earth could warm by more than 5°C above pre-industrial levels but still enjoy a functional Atlantic Meridional Overturning Circulation (AMOC), so long as this warming happens very slowly. But very fast warming, similar to the current rate, could push the AMOC towards collapse at just 2°C above pre-industrial levels.
Mysterious ‘cold blob’ in the Atlantic suggests the AMOC is weakening René van Westen at the University of Utrecht in the Netherlands and his colleagues used a state-of-the-art climate model to simulate the stability of the AMOC under three different rates of warming. The first scenario modelled a very slow increase of carbon dioxide concentrations of 0.5 parts per million each year; the second a rate five times faster; and the final scenario a rate 10 times faster, which is comparable to today’s rate. The team found that, under very slow rates, the AMOC remained stable beyond 5°C of warming.
But under current rates, the AMOC collapses at about 2°C of warming. Unless the world dramatically reduces its emissions, this could happen around 2060, says van Westen. The loss of Antarctica’s doomsday glacier would transform our planet.
Now scientists are revealing the secrets of this remotest of places, and asking the question: is its demise inevitable? The AMOC carries warm, salty water from the Gulf of Mexico towards the north Atlantic Ocean, where it cools and sinks, flowing back south along the ocean floor. Without the AMOC, much of Europe would suffer a 10 to 30°C drop in wintertime temperatures, while rainfall patterns around the world would shift dramatically, with catastrophic consequences.
To drive the flow of the current, surface water around Greenland must sink into the deep ocean. This depends on the surface water cooling and becoming dense enough to descend into the deep ocean. Keeping the warming at a slow pace allows both the surface water and the deep water of the ocean to change at roughly the same pace, says van Westen.
For decades, the oceans have absorbed much of the excess heat caused by greenhouse gases. The latest observations suggest they are reaching their limits, so how worried should we be? But translating results from a climate model to the real world is tricky.
Extract — continue reading at the source.
