Trends and variability in summer sea ice cover in the Canadian Arctic based on the Canadian Ice Service Digital Archive, 1960-2008 and 1968-2008

The Canadian Ice Service Digital Archive (CISDA) is a compilation of weekly ice charts covering Canadian waters from the early 1960s to present. The main sources of uncertainty in the database are reviewed and the data are validated for use in climate studies before trends and variability in summer averaged sea ice cover are investigated. These data revealed that between 1968 and 2008, summer sea ice cover has decreased by 11.3% ± 2.6% decade−1 in Hudson Bay, 2.9% ± 1.2% decade−1 in the Canadian Arctic Archipelago (CAA), 8.9% ± 3.1% decade−1 in Baffin Bay, and 5.2% ± 2.4% decade−1 in the Beaufort Sea with no significant reductions in multiyear ice. Reductions in sea ice cover are linked to increases in early summer surface air temperature (SAT); significant increases in SAT were observed in every season and they are consistently greater than the pan‐Arctic change by up to ∼0.2°C decade−1. Within the CAA and Baffin Bay, the El Niño‐Southern Oscillation index correlates well with multiyear ice coverage (positive) and first‐year ice coverage (negative) suggesting that El Niño episodes precede summers with more multiyear ice and less first‐year ice. Extending the trend calculations back to 1960 along the major shipping routes revealed significant decreases in summer sea ice coverage ranging between 11% and 15% decade−1 along the route through Hudson Bay and 6% and 10% decade−1 along the southern route of the Northwest Passage, the latter is linked to increases in SAT. Between 1960 and 2008, no significant trends were found along the northern western Parry Channel route of the Northwest Passage.