Taking a closer look, however, reveals the reason for the apparently poor correlation: The large seasonal cycle in sea ice extent data. The cycle obscures the overall trend in sea ice data—and the correlation of that trend with the trend in Arctic tropospheric temperature. Once that cycle is removed via a 12-month moving average, the trend in sea ice extent and the negative correlation between extent and temperature is clearly revealed.
The direct comparison shows that the decline in Arctic sea ice extent has accelerated as Arctic tropospheric temperature increased.
|Extent = 11.6846713 + -0.9177708x + -0.2355697x2, where x = temperature|
The R2 value for that correlation is quite high, R2 = 0.7865 and p-value = <0.00000000000000022. Now does that correlation prove that higher Arctic tropospheric temperatures caused the sea ice decline? No. Correlation by itself does not imply causation. It could be warmer ocean currents and/or changes in wind patterns. However, that argument doesn't address what caused the ocean currents to warm and the wind patterns to change—and the answer is increasing air temperatures cause the oceans to warm and change wind patterns. No matter what, the physical cause of the ice melt ultimately goes back to warmer air temperatures. When you have a correlation backed by a physical mechanism, that DOES imply causation.