I have a heat budget question. This may be all complete rubbish but comes out of thinking about the after-effects of the GAC with many gaps in the ice freezing over, and therefore increasing the area graph.

When ice melts, heat is absorbed to make the transition from solid to liquid (latent heat). Conversely, when ice is made, heat must be released. That's a strange way of looking at it, but the enthalpy of the system is constant.

So, assuming that the heat is released into the air as it seems to me that the air drives ice formation, what is the impact on air temperature? Some very rough calculations:

The heat of fusion for water is 334 joules per gram. There are 10^6 g in 1 m^3 of water so the heat of fusion for 1 m^3 of water is 334 x 10^6 joules or 0.334 x 10^6 kj.

Assume an open sea area of 10km x 10km in which of 0.25m thick forms. The volume of ice is 0.25 x 10^8 m^3. Therefore the total heat of fusion is 0.0835 x 10^14 kj, or 8.35 x 10^12 kj.

Assuming cold temps and taking some approximations, the density of air is 1.39 kg / m^3. The specific heat of air is defined in kj/kg K and is close enough to 1. That means that 1 kj will raise the temperature of 1 kg of air by 1 degrees K.

If we take a volume of air 100km x 100km x 100m thick (assuming it is blowing over the ice) then that is 10^12 m^3. The weight is 1.39 x 10^12 kg. Dividing the kj released from freezing the ice by that weight gives around 6 degrees K temperature rise.

Therefore it seems to me that the freezing of the open areas opened up by the GAC will have had some not insignificant effect on the air temperatures. This will reduce the FDDs by some factor.

I guess the effect on air temperature could be determined by correlating rises with polynyas refreezing. Probably going to be difficult to pick out the values.

So there appears to be a triple impact of the GAC:

- air temperature increased due to new ice formation, decreasing FDDs for other ice

- ice export to warmer ocean areas

- thin ice formed is less rigid and more prone to eventual melting, breakup and warming via insolation in the summer