Hat tip to reader Fred Thu of France for this post:

Arctic Research Consortium of the United States (ARCUS)

Study of Environmental Arctic Change

September Sea Ice Outlook: June Report

Report Released: 24 June 2009

Status

On 15 May 2009, a request was sent to the contributors of the 2008 Sea Ice Outlook and the broader arctic sea ice community to provide an estimate of mean September 2009 sea ice extent based on May 2009 data. We are pleased to welcome three new groups making contributions. Responses were received by the first week in June. Additional information about the Outlook can be found on the background page.

Approach and Disclaimer

The Sea Ice Outlook provides a forum for researchers to evaluate their understanding of the state of arctic sea ice and for the community to jointly assess a range of factors that contribute to arctic summer sea ice minima. The Sea Ice Outlook is not a formal consensus forecast or prediction for arctic sea ice extent, nor is it intended as a replacement for existing efforts or centers with operational responsibility.

Results

With 15 responses, half represent a mean September Outlook extent estimate of 4.9–5.0 million square kilometers. The remaining estimates had a range of 4.2–4.7 million square kilometers (Figure 1). As in 2008, the individual responses were based on a range of methods: statistical, numerical models, comparison with previous observations and rates of ice loss, or composites of several approaches; details can be found in the individual outlooks available at the end of this report. The range of estimates for September 2009 sea ice extent is rather narrow, at least compared to the contributions from the 2008 Outlook. Further, the values of uncertainty estimates, from those groups which provide them, are close to 0.5 million square kilometers. Thus, many 2009 Outlook estimates overlap with a consensus value near persistence with the 2008 September mean sea ice extent.

{Click the image for expanded view}

Figure 1. Distribution of individual outlook values for September 2009 sea ice extent.

Review of Lessons from 2008

There was a general agreement between Outlook projections and observations in the 2008 effort. The median projected September ice extent from the 2008 May Outlook was 4.2 million square kilometers; the observed 2008 value was 4.7 million square kilometers. These numbers compare to a 1979–2007 climatological mean extent of 6.7 million square kilometers. Moreover, the 2008 Sea Ice Outlook provided a successful forum for community synthesis, an important first step toward better understanding arctic sea ice loss. There was enthusiasm for the project from the larger arctic and climate communities.

A considerable amount of insight was gained from comparing 2007 and 2008 sea ice conditions and the oceanic and meteorological forcing over these summers. A year ago it was uncertain as to whether most first-year sea ice would continue to melt out every year as in 2005 and 2007 (work by Ron Kwok presented at the Outlook Workshop in March 2009). It seems, however, that in years like 2008 with more normal meteorological summer conditions compared to 2007, it is rather difficult for all the first-year sea ice to melt out near the North Pole (see comments by Stroeve et al., number 3 below). Don Perovich reports that based on ice mass-balance buoys, there was increased bottom melt in regions of low ice concentration such as the Beaufort Sea in both 2007 and 2008. These distributed buoys will be of interest as we move into the 2009 melt season. Initial conditions in May, and especially the 40% loss of multi-year sea ice in the last four years, suggest that that it will be difficult for the sea ice to return to extents of the 1980s and 1990s. Thus, the 2008 Outlooks were correct in estimating sea ice extent well below that of climatology, but some overestimated the amount of first-year sea ice melt back (see comments by the Canadian Ice Service, number 13 below). Model results also suggest that the summer meteorology needs to be supportive as in 2007 to sustain a substantial additional September sea ice loss.

Late Spring 2009 Conditions

With regards to initial conditions for May 2009, Figure 2 from Nghiem et al. shows the map of sea ice classes derived from QuikSCAT. Their full abstract is added as Appendix 1. Although fall 2008 had almost 50% more multiyear sea ice than fall 2007, on 1 May 2009, the perennial ice extent had been reduced to 2.1 million square kilometers, which is virtually equivalent to the 2.2 million square kilometers of perennial ice extent on 1 May 2008. The sea ice on the Eurasian side of the North Pole is primarily second-year sea ice remaining from summer 2008; indications are that part of this sea ice exited Fram Strait under the influence of a more positive Arctic Oscillation climate pattern in winter and spring 2009. Figure 2 also suggests regions of earlier than normal melt. Christian Haas and Stefan Hendricks, based on aircraft supported measurements, show continued thick sea ice north of Canada and Greenland. Their results are further presented as Appendix 2. A third set of information is from the Catlin Arctic Survey near 130° W as far north as 85.5° N. Preliminary results suggest that the spatial extent of the thicker multi-year ice is reduced compared with expectations from backscatter data and that the distribution of sea ice types has shifted, favoring both old and young sea ice. More information is available at http://www.catlinarcticsurvey.com/science.

Figure 2. Arctic sea ice distribution for perennial ice (white), mixed ice (aqua), seasonal ice (teal), ice with a current melting surface (red), and ice with a melted surface within the previous ten days (magenta). The extent of perennial ice was about the same on 1 May 2009 and 1 May 2008, although there is more second year ice in 2009, due to more ice surviving the summer of 2008. The springtime perennial ice extent was the lowest in 2008, as observed by QuikSCAT data in the decade of the 2000s and by the buoy-based estimates in the last half-century. The rapid reduction rate and the temporal characteristics of this winter and spring are similar to 2007 when the drastic decrease of perennial ice preconditioned the record low of the total ice extent in summer 2007. Credit: Nghiem et al.

Figure 3. The graph above shows daily sea ice extent as of 2 June 2009. The solid blue line indicates 2009; the dashed green line shows 2007; and the solid gray line indicates average extent from 1979 to 2000. The gray area around the 1979–2000 average line shows the standard deviation range of the data. Credit: National Snow and Ice Data Center (NSIDC).

The National Snow and Ice Center (NSIDC) (http://nsidc.org/arcticseaicenews/) noted that although the 2009 melt season started slowly, the pace of sea ice loss quickened through May (Figure 3).

Thus, we can summarize that there is nothing in the arctic sea ice conditions at the end of May that would preclude a major sea ice loss year by September. From the lessons learned by contrasting the meteorology of 2008 with 2007 and from the ensemble runs of the two projects that ran numerical sea ice models with multiple historical years of meteorological forcing, there are many ways (cold followed by warm or warm followed by cold, for example) to arrive at a near average summer forcing with respect to the September sea ice extent. However, there are only a few ways of sustaining three months of forcing favoring ice retreat such as in 2007.

Our Russian colleague (Oleg Pokrovsky, number 4 below) suggests that the greater area of the North Pacific may be turning warm again after a string of cold years. The response is complex. Cold years in the greater Pacific support winds, which in fact were favorable for Pacific arctic sea, ice loss. The sea ice extent in winter and spring 2009 in the Pacific arctic sector has been locally above normal. Both of these factors—local cold temperatures and warmer temperatures farther away—would delay an early sea ice melt. The North Pole Environmental Observatory web camera shows no indication of surface melt well into the third week in June. The NSIDC site notes the warm May throughout the Arctic.

These considerations seem to be reflected in the narrow range of contributions to the 2009 Sea Ice Outlook: reduced sea ice initial conditions at the end of May compared to climatology combined with mean summer meteorological forcing—given the predictive uncertainty in those quantities—suggest persistence or a slight increase in extent in 2009 compared to 2008. However, given the May sea ice state, it is not unreasonable to give a small but important probability of a major sea ice loss event in summer 2009, as noted by the Kauker (number 2 below) and National Ice Center (NIC, number 5 below) groups who provide probability distribution estimates.