#99 – Gavin’s in-line question:

[Response: What data are you looking at here? I know of no such sea ice data set that would demonstrate this. – gavin]

You are making my point.

We don’t have very high quality data for the Arctic much before 1978.

We have lower quality data which make this point.

Jones et al. data set shows the temperature in the Arctic higher in the 1930s than currently.

The Arctic Climate Impact Assessment, p. 52, talks about the temperature in the Arctic over the last millennium and seems to support several rises and falling trends in the Arctic over that time period.

Roald Amundsen completed the first sailing of the Northwest passage in 1903–1906 – so I assume it was pretty warm in the arctic then (I admit this one is implied).

The point is that the temperature has been higher in the Arctic in the past – more than once even – so what is different about today than those other times?

[Response: Thank you. You clearly demonstrate that you have no data that shows that sea ice was equally low in the 1930s. The little data there is (from ship reports mainly) indicate that this was not actually the case. If you wanted to use an example where the prevailing data did suggest less ice then than now, you’d have to go back to the Early Holocene (say 8 to 6,000 years ago). There are beach deposits and large faunal remains in what are now frozen inlets across the Archipelago and northern Greenland. However, why that happened then is easier to understand – the orbit of the Earth at that time meant that summertime solar irradiance in the Northern Hemisphere was greater than it is now, and summer temperatures were higher as a result. This is not therefore the cause of today’s changes, but the example does serve to indicate that sea ice is indeed sensitive to the radiative balance. It is thus not surprising that sea ice is retreating when we have our own radiative perturbation underway. – gavin]