Multidecadal variability:




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Arctic maritime surface air temperature (SAT) and pressure exhibit large amplitude multidecadal signal. This brings into question our current model of thinking about polar amplification. Observational evidence for polar amplification relies heavily on trends that are modulated by MDV (see next figure).
Arctic SAT trends can show warming or cooling depending on number of years chosen for calculating the trend. This oscillatory behavior is highly dependant on the strength of MDV.

The correlation pattern of station SAT and the NAO is characterized by positive values in the near-Atlantic region (red) and negative values over Greenland and the Canada (blue). This spatial pattern may be found in various other atmospheric, ice, and oceanic parameters.

Arctic surface-air temperature (SAT) and sea level pressure (SLP) records display strong multidecadal variability (MDV) on time scales of 50-80 years. Associated with this variability, the arctic SAT record shows two maxima: in the 1930-40s and in recent decades, with two colder periods in between. In contrast to the global and hemispheric temperature, the maritime arctic temperature was higher in the late 1930s-early 1940s than in the 1990s. Incomplete sampling of large-amplitude multidecadal fluctuations results in oscillatory arctic SAT trends. For example, the arctic SAT trend since 1875 is 0.09°C/decade, with stronger spring- and winter-time warming; during the 20th century (when positive and negative phases of the MDV nearly offset each other) the arctic temperature increase is 0.05°C/decade, similar to the Northern Hemispheric trend (0.06°C/decade). Thus, the large-amplitude MDV impacting the maritime Arctic may confound the detection of the true underlying climate trend over the past century. MDV-modulated trends for short records are not indicative of the long-term behavior of the arctic climate system. The accelerated warming and a shift of the atmospheric pressure pattern from anticyclonic to cyclonic in recent decades can be attributed to a combination of greenhouse effects and a positive MDV phase. Elucidating the mechanisms behind this relationship will be critical to our understanding of the complex nature of MDV. Adapted from Polyakov et al., 2003a.