What was done
The authors used a combination of long-term satellite tracking data, climate data and remotely sensed sea ice concentrations to detect localized habitat trends of the narwhal (Monodon monoceros) in Baffin Bay between Greenland and Canada - which is home to the largest numbers of the world's narwhals - to study the species' vulnerability to ongoing and projected climate change.

What was learned
The authors report that "since 1970, the climate in West Greenland has cooled [our italics], reflected in both oceanographic and biological conditions (Hanna and Cappelen, 2003)," with the result that "Baffin Bay and Davis Strait display strong significant increasing [our italics] trends in ice concentrations and extent, as high as 7.5% per decade between 1979 and 1996, with comparable increases detected back to 1953 (Parkinson et al., 1999; Deser et al., 2000; Parkinson, 2000a,b; Parkinson and Cavalieri, 2002; Stern and Heide-Jorgensen, 2003)."

What it means
Laidre and Heide-Jorgensen report that "cetacean occurrence is generally negatively correlated with dense or complete ice cover due to the need to breathe at the surface," and that "lacking the ability to break holes in the ice," narwhals are vulnerable to reductions in open water availability, as has been demonstrated by ice entrapment events "where hundreds of narwhals died during rapid sea ice formation caused by sudden cold periods (Siegastad and Heide-Jorgensen, 1994; Heide-Jorgensen et al., 2002)," which events are becoming ever more likely as temperatures continue to decline and sea ice cover and variability increase, which latter two trends were found by them to be "highly significant at or above the 95% confidence level."  Hence, they conclude that "with the evidence of changes in sea ice conditions that could impact foraging, prey availability, and of utmost importance, access to the surface to breathe, it is unclear how narwhal sub-populations will fare in light of changes in the high Arctic."

All we would add is that narwhal prospects in this particular part of the world (the Arctic, where CO2-induced warming is supposed to be significantly greater than that experienced nearly everywhere else on the planet) are definitely not good, in light of past and current temperature and sea ice trends.

References
Deser, C., Walsh, J.E. and Timlin, M.S.  2000.  Arctic sea ice variability in the context of recent atmospheric circulation trends.  Journal of Climatology 13: 617-633.

Hanna, E. and Cappelen, J.  2003.  Recent cooling in coastal southern Greenland and relation with the North Atlantic Oscillation.  Geophysical Research Letters 30: 32-1-32-3.

Heide-Jorgensen, M.P., Richard, P., Ramsay, M. and Akeeagok, S.  2002.  In: Three recent Ice Entrapments of Arctic Cetaceans in West Greenland and the Eastern Canadian High Arctic.  Volume 4, NAMMCO Scientific Publications, pp. 143-148.

Parkinson, C.L.  2000a.  Variability of Arctic sea ice: the view from space, and 18-year record.  Arctic 53: 341-358.

Parkinson, C.L.  2000b.  Recent trend reversals in Arctic Sea ice extents: possible connections to the North Atlantic oscillation.  Polar Geography 24: 1-12.

Parkinson, C.L. and Cavalieri, D.J.  2002.  A 21-year record of Arctic sea-ice extents and their regional, seasonal and monthly variability and trends.  Annals of Glaciology 34: 441-446.

Parkinson, C., Cavalieri, D., Gloersen, D., Zwally, J. and Comiso, J.  1999.  Arctic sea ice extents, areas, and trends, 1978-1996.  Journal of Geophysical Research 104: 20,837-20,856.

Siegstad, H. and Heide-Jorgensen, M.P.  1994.  Ice entrapments of narwhals (Monodon monoceros) and white whales (Delphinapterus leucas) in Greenland.  Meddeleser om Gronland Bioscience 39: 151-160.

Stern, H.L. and Heide-Jorgensen, M.P.  2003.  Trends and variability of sea ice in Baffin Bay and Davis Strait, 1953-2001.  Polar Research 22: 11-18.