Recent Changes in the Variability and Seasonality of Temperature in the Northern Hemisphere

Recent studies have found a decrease in temperature variance in the mid and high latitudes of the Northern Hemisphere. To explore the processes contributing to the change, this study investigates potential linkages between recent changes in temperature variability and seasonality in the Northern Hemisphere. The mean and variance of daily temperature anomalies are calculated for each year over a 35-year period and compared to a base period. For temperature in the Northern Hemisphere, a noticeable warming trend amplified in the high latitudes was observed, coincident with a significant decrease in variability in the mid and high latitudes, consistent with previous studies. Decreasing trends in the amplitude and increasingly delaying trends in the phase of the seasonal cycle of temperature are spatially correlated with sea ice loss and consistent with an increasing local heat capacity. To determine whether the changes in the seasonality of temperature may have contributed to the changes in temperature variance because of the use of a fixed base period, the amplitude and phase trends were individually artificially removed from the temperature record. The modified temperature record shows only moderate changes in variance, suggesting that changes in seasonality associated with sea ice loss may be linked to variance changes.