Arctic sea ice depletion since 1979 has caused little or no warming of Arctic temperatures outside the low troposphere

Several new and independent studies do not support nor confirm a hypothesis for either an appreciable or a detectable impact of Arctic sea ice loss on mid-latitude weather during Fall. Supporting material is given below, which are also relevant in order to clarify what can, and cannot be said, concerning Arctic sea ice-Sandy linkages.

First, the FV2012 empirical study made the assumption that observed trends in Arctic temperatures throughout the deep tropospheric column during recent decades were solely caused by Arctic sea ice loss. This was key to their conjecture for the existence of strong evidence that Arctic sea ice affected mid-latitude weather patterns. Subsequent studies by Screen et al. (2012a,b) have tested such an assumption, and find contrary indications. Their work has found significant differences between the trends in recent decades and those related to an Arctic sea ice impact. Most notably, the new findings of Screen et al. reveal that reduction in Arctic sea ice does not induce a deep troposphere warming, consistent with results from other previous studies also reviewed in Bader et al. (2011). This new finding undermines the notion that a deep tropospheric Arctic amplification is a consequence of sea ice loss, a feature invoked under the FV2012 hypothesis to argue for an sea ice induced reduction in mid-latitude westerlies via weakened pole-to-equator temperature gradients.

Second, in a separate study, Screen et al. (2012) conducted one of the more realistic climate simulations to address the possible effects of sea ice loss on climate to date. This used realistic time-evolving sea ice from 1979-2009, specified as a forcing for 2 different climate models. These possessed high vertical resolution to better represent the Arctic boundary layer, and also high horizontal resolution to better model storms and the jetstream. In addition, the period was simulated 13 times so as to better identify the intrinsic variability of 30-yr trends, and thereby more clearly extract the sea ice-induce signal. Their results reveal an appreciable un-forced intrinsic variability in trends of Arctic and mid-latitude climate during this 31-year period. Indicated hereby is the difficulty and the peril of attributing the observed trend patterns during this period to Arctic sea ice loss alone, as in FV2012. The multi-model ensemble average also identified a weak sensitivity toward a trend in the negative phase of the early winter NAO, consistent with the preponderance of evidence reviewed in Bader et al. (2011) The authors state, however, that such a signal is “easily exceeded by intrinsic atmospheric variability. One implication of this result is that such a circulation response to Arctic sea ice loss may be difficult or impossible to detect in observations”. Another recent study, but focused on the 2007 extreme sea ice year (Orsolini et al. 2012), used an advanced weather forecast system. They also found little evidence for an appreciable mid-latitude climate response to sea ice loss in October or November, though an weak NAO-like signal occurred in model runs for December, yet whose phase was opposite in sign to that in Screen et al. (2012).

Figure 10 from Screen et al. (2012) showing vertical cross sections of simulated 31-yr trends during November-December for 1979-2009 of heights (shading), and zonal winds (contours, 1 m/s). Each plot is a individual run ; the super-ensemble mean is shown in lower right. Shaded ensemble mean height departures are about 10m

Figure 10 from Screen et al. (2012) showing vertical cross sections of simulated 31-yr trends during November-December for 1979-2009 of heights (shading), and zonal winds (contours, 1 m/s). Each plot is a individual run ; the super-ensemble mean is shown in lower right. Shaded ensemble mean height departures are about 10m

In sum, whereas there is compelling evidence that Arctic sea ice decline has been a major cause of Arctic amplification in near-surface warming trends over the last 3 decades, strong evidence indicates that Arctic sea ice decline has had little or no impact on temperature trends outside the low troposphere. The possible signal of remote impacts on weather and climate due to the loss in Arctic sea ice is thus currently hard to confirm and remains uncertain.

Screen, J. A., C. Deser, and I. Simmonds, 2012a: Local and remote controls on observed Arctic warming, Geophys. Res. Lett., 39, L10709, doi:10.1029/2012GL051598.

Kumar, A., J. Perlwitz, J. Eischeid, X. Quan, T. Xu, T. Zhang, M. Hoerling, B. Jha, and W. Wang , 2010: Contribution of sea ice loss to Arctic amplification, Geophys. Res. Lett., 37, L21701, doi:10.1029/2010GL045022.

Screen, J., C. Deser, I. Simmonds, and R. Tomas, 2012: The atmospheric response to three decades of observed Arctic sea ice loss. J. Climate. doi:10.1175/JCLI-D-12-00063.1, in press.

Orsolini, Y., R. Senan, R. Benestad, and A. Melsom (2012), Autumn atmospheric response to the 2007 low Arctic sea ice extent in coupled ocean–atmosphere hindcasts, Clim. Dyn., 38, 2437-2448. doi:10.1007/s00382-011-1169-z