Sea Ice Extent Calculator

Nothing in the calculation — it's collected purely as context for the user, as its helpText notes. The projected extent depends entirely on the temperature and warming inputs (current anomaly, additional warming, Arctic amplification, and ice sensitivity), not on how many years you expect that warming to take, since the model has no time-dependent decay or trend rate built in.

The Arctic warms roughly 2-4 times faster than the global average due to feedbacks like reduced ice/snow albedo, so the calculator first multiplies your combined current-plus-additional global warming by the Arctic amplification factor to get the actual regional warming that drives ice loss. That Arctic-specific warming figure is then multiplied by the ice sensitivity (million km² lost per °C of Arctic warming) to get projected ice loss.

It solves the same loss equation in reverse: starting from the baseline extent (6.9 million km²) minus the 1 million km² ice-free threshold, divided by the product of your ice sensitivity and Arctic amplification inputs. That gives the amount of global warming above pre-industrial levels required to cross the ice-free threshold under your other assumptions, independent of the current/additional warming values you entered elsewhere.

It's a downstream estimate, not a feedback loop the model actually runs — it takes the ice already lost from your current extent (not from the historical baseline) and multiplies it by a fixed 0.5 W/m² per million km² factor representing extra solar energy absorbed once reflective ice is replaced by darker ocean. The projected extent itself doesn't get revised based on this forcing, so the calculator doesn't capture the real-world reinforcing loop where that absorbed heat would accelerate further ice loss.