I’ve been investigating the NOAA OLR (Outgoing Long-wave Radiation) data to try to find where things have changed by more than the global average. I’ve found a ‘step change’ in the high latitudes which occurred between 2002 and 2006.
Curiously, this increase appears to be mainly in winter rather than summer:
This seems to fly in the face of received wisdom on increased summertime melt exposing the relatively warm ocean to the cold September air, which only gets a few hours daylight, reducing the diurnal TOA insolation of 100W/m^2 or so. Note this will be changed by cloud cover.
So what is the cause of this? Reduced winter ice cover in the polar region? Warmer north Atlantic ocean surface? Less wintertime cloud cover? increased co2? The Arctic ocean SST anomaly rose over that period, but is this enough to cause the OLR anomaly? Why doesn’t the previous rise from 1995 do the same?
It’s a bit of a mystery to me at the moment, but someone may have a ready answer. I just wish I’d spotted this before our visit to Cambridge.