In many models an SPG collapse precedes an AMOC collapse, where after SPG convection ceases, that in the Nordic seas increases at first (warming), but after some decades it also stops there and starts cooling. There is large uncertainty, but an SPG collapse does increase the risk of an AMOC collapse

*increases -> decreases

The impacts of subpolar gyre tipping may not be as severe as those of a full AMOC collapse, but the fast timescale and possibility of it happening in the near future are worrying. The risk is real, with the most realistic models all showing a collapse, and the impacts on Europe will be substantial.

Those physically realistic models predict subpolar gyre tipping around 2040-2050. This would lead to a local cooling of 1-2 degrees in 10 to 20 years. The Nordic seas would warm, the jet stream shift northward and in summer high pressure over Scandinavia could lead to more (intense) heat waves.

We tested whether this mechanism is represented in climate models. The process of convection is captured by most models, but the feedbacks with the gyre strength are only found in a handful of models. The models that do capture these gyre feedbacks well, are also the models which show abrupt shifts.

Mechanism: Strengthening of the gyre circulation directly leads to divergence and lower salinity, but on longer timescales it increases salinity due to transport by eddies. An increase in salinity causes convection, changing the density in the water column. This density change strengthens the gyre.

The mechanism of bistability in the subpolar gyre is a feedback between the gyre strength and the density in its centre. If the surface density increases, convection won't take place, weakening the gyre. A weaker gyre transports less salty waters to the centre, weakening convection even further.

In some climate models abrupt cooling in the subpolar gyre region is found, corresponding to a collapse of convection. Such tipping of the subpolar gyre might already occur around 2040 and could impact the stability of the AMOC.

For an analysis of abrupt shifts see: doi.org/10.1111/nyas...

The subpolar gyre is a wind-driven ocean circulation through the Irminger and Labrador seas. Warm and salty water from the Gulf Stream enters the gyre, where it cools down. This increases the density of the salty waters and leads to convection; the mixing of surface waters with those at depth.

🔥✊Urgent en ingrijpend, maar noem het liever niet radicaal. Met huidige klimaatbeleid stevenen we af op 2,7C opwarming in 2100, want een ongekende ontwrichting van de samenleving zou betekenen. Dat niet serieus nemen, dát is radicaal!

Lees het artikel hier ⤵️
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“We are the most intellectual species to walk the planet, but we’re not intelligent. If you’re intelligent you don’t destroy your only home.”

Dr. Jane Goodall