A Historical Perspective on Arctic Warming: Part One
There are two elements to the contrarian views on the ECWP in the Arctic. First, they argue that during the ECWP the Arctic was warmer than present. Secondly they have used the ECWP as a means of casting doubt on the main drivers of global warming. These contrarians argue that internal caused the ECWP and that this may have contributed to recent Arctic warming, thereby suggesting that to es may be lower than current estimates. Some of these discussion points have also somehow found themselves in the IPCC AR5's Chapter 10 where the following claim is made.
"Arctic temperature anomalies in the 1930s were apparently as large as those in the 1990s and 2000s. There is still considerable discussion of the ultimate causes of the warm temperature anomalies that occurred in the Arctic in the 1920s and 1930s."
The challenge with describing Arctic surface air temperature changes is that the observational network is sparse, something we noted and corrected for in Cowtan and Way (in press). Using a single observational network therefore has the potential to mislead - particularly on short timescales. However, comparison of all available long records for the Arctic (here defined as s North of 60° N) shows relatively strong agreement amongst the various products (Figure 1).
To compare the relative distributions of monthly anomalies we take the warmest 120-month period (10-year) during the ECWP and compare it to the warmest 120-month period during the recent warm period (Figure 3). Comparison of these two periods reveals a clear shift in the average air temperatures and also an increase in the probabilities of warm months over the past decade. Recently, it has also become increasinly rare for even a single month to have a below-normal average temperature, in contrast with the ECWP where this was common.