The evolution of the temperatures averaged over the area north of 60°N (Fig.  3 a, b) shows a long-term cooling trend in both winter and summer, with a total cooling of about 2°C.

The temperature evolution in July follows closely the summer insolation curve (Fig.  3 b), whereas the January temperatures remain at about the same level until 6 kyr BP, after which an enhanced cooling phase is noted that lasts until 1 kyr BP (Fig.  3 a).

This also explains the long-term cooling trend in winter temperatures (Fig.  3 a), which shows no sign of a direct response to the increase in insolation (+12 W/m ² ) in contrast to the mid-latitudes where a winter increase in temperature is noticed over the continents..