Let’s take a look at two signs of a warming world: the shrinking arctic sea ice and the lengthening frost-free period on the Prairies.
I find it interesting that if arctic sea ice levels are not breaking records, it no longer seems to make it into the headlines.
This year’s arctic sea ice minimum was reached on Sept. 12 and was around 4.38 million square kilometres. This was the sixth lowest reading in the 46-year satellite record. To put that into perspective, every year since 2014 has been one of the 10 lowest years, much like global temperatures.
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In the 1980s, arctic sea ice minimums averaged between 6.5 and 7.5 million square km. Around 2000, they were in the 5.5 to six million square km range. Compare those numbers to the 2020s, which have been averaging in the four to five million range, and you can see how significant the drop in summer ice coverage has been.
As of Oct. 1, the Northwest Passage deep water route had an all-time record low ice level, breaking the previous record set in 2011.
Also of interest is the age of the ice. In the 1980s, there were about four million square km of multi-year ice and about two million square km of ice older than four years. Today, there are about 1.5 million square km of multi-year ice and only about 120,000 square km of ice older than four.
As the National Snow and Ice Data center put it, ”the Arctic Ocean has lost 95 per cent of its oldest and thickest ice.” This is important because young thin ice melts more easily than thick old ice.
Now to our look at frost — fall frosts, spring frosts, and the length of the frost-free season. In the 1980s, my climate thesis in university was titled: Changes in the Length of the Frost-Free Season Across Southern Manitoba. I still have an interest in this topic.
In the past, the best way to discuss this topic was to explain the extensive data. These days, I think the best way is to use a couple of tables.
For this study, I used the same main reporting centres in each province that I use for monthly looks at weather. The first table shows the average date of the last spring frost (LSF), the first fall frost (FFF), and average length of the frost free season (FFS). The tables are in order from earliest to latest spring and fall frosts and then by the length of time for the frost free season.
The second table shows this year’s values.
A couple things stand out. First,all locations had a longer than average frost-free season, and in some cases much longer. Second, there is one location that really jumps out, and that is Calgary, which on average has a frost-free season of 119 days. This year Calgary saw the frost-free season stretch to 153 days, a full month longer than average (34 days).
Edmonton, at 28 days longer than average, had the next biggest difference between the average frost-free season and this year. The two other stations with very long frost-free seasons were Winnipeg and Brandon, both at 143 days compared to the average of 122 days, or 21 days longer.
Looking back at my thesis data, I am only able to compare frost data with the three Manitoba stations. In my thesis I looked at decadal trends in length of the frost-free season, with data sets ranging from the 1870s for Winnipeg, 1890s for Brandon and 1900s for Dauphin.
Winnipeg’s frost-free season in the 1880s was about 105 days, but by the 1920s and ‘30s it had risen to 117 days. Then it fell back to around 112 days in the 1940s. Since then, there has been a mostly slow and steady rise in average length of the frost-free season to the current value of 122 days.
Brandon has seen a much greater increase in the frost-free season. In the 1890s, the average was 91 days. With a few ups and downs over the next 130 years, the overall trend has been a steady increase to the current value of 122 days.
Dauphin’s data is quite interesting. In the 1900s, the frost-free season was 105 days. It then jumped to 125 days during the 1930s before dropping back to around 100 days by the 1950s. Since then, much like Winnipeg and Brandon, there has been a relatively steady increase to the current value of 119 days.
I wish I had the data and time to dig into Saskatchewan and Alberta’s frost-free season trends. I would not be surprised if the overall trends in these two provinces mirrors what is happening in Manitoba.
