We’ve already discussed Arctic sea ice volume in this series. But today we’re going to focus on the Canadian Arctic because the records go back to the early 1970s. You might have seen graphs of disappearing Arctic sea ice, all of which seem to begin around 1980 when satellite coverage begins. But there are strong hints that the data from the 1970s shows much lower ice coverage. For instance, Tony Heller has pointed out that the first IPCC report in 1990 showed very low Arctic sea ice in the 1970s but then subsequent IPCC reports (drum roll please) adjusted the record so the 1970s ice coverage became high relative to later decades. Oh, there’s a big surprise. Unfortunately they forgot to tell the Canadian Ice Service, whose data are online in case you want to #lookitup. And, to save you the effort at least initially, we did so ourselves and here is what it shows:

This graph shows the Total Accumulated Ice Coverage (in percent terms) from Sept 3 to May 14 for each year from 1971 to 2024. And note that blue is actual and grey is “interpolated” so there’s more than a little uncertainty here in what’s generating the supposed downward trend.

The 2025 record at the end is not comparable since the ice season hasn’t ended. As you can see the percentage ice coverage in the Canadian Arctic in the early 1970s was low compared to the entire interval afterwards. Which matches the raw satellite record for the entire Arctic.

It’s one of those inconvenient truths that are out there if you know where to #Lookitup.