It’s healthy to be skeptical about the various claims people make about climate change. When I posted the graph showing a steady decline of the length of the skating season one person rightly said that there might be other factors at play. For instance (he suggested) the NCC may be under pressure to save money after the end of Winterlude and this might have had an influence on a shortening skating season over the years.
So I took another look at the numbers.
Opening Dates Consistent with Climate Change Expectation
I figured that the NCC would be enthusiastic about getting the canal open so that perhaps looking only at opening dates would eliminate any NCC bias (if there were any).
What you see to the right here (click to enlarge) is a steadily later and later canal opening over the years; supportive of a weather dependent phenomenon. The longest the canal ever stayed open was in the 1971-72 season when it closed on March 25th, so I compared every year’s opening date in terms of how many days before March 25th it occurred. I then overlaid the 10 year rolling average to smooth out the curve. That’s what you see in red.
So this is a second perspective on the same data and it conforms to what we’d expect global warming to be doing to our skating in Ottawa.
Closing Dates Aren’t
I know that the NCC has claimed in the past that they don’t close the canal to skating based on cost-control measures.* If my skeptical friend was right, the influence of NCC penny-pinching combined with climate change melting should mean that the canal would close earlier and earlier every year. But that’s not what I found.
This next graph shows the same curve as the one above, but added to it is the closure information. Again, I compared each year’s closure date to the record-setting March 25th and found not the anticipated earlier-and-earlier trend, but instead that canal skating has been drawn out later into the end of winter on average over time. That’s the purple averaging line near the bottom. If the skating season was getting shorter at the February/March end we would expect that purple line to trend upward, not down.
The light blue line in the middle represents closing dates minus opening dates, then averaged over 10 years. This, derived a different way, is (reassuringly) the same curve I arrived at in my first post.
What does this mean?
- for sure it means that on average the loss in length of skating season is due to later openings, not earlier closings
- it seems to mean on average that ice is forming slower but not melting sooner
- it seems also to mean that the NCC aren’t penny-pinching on closing the canal early
So now I’m trying to figure out what factors might influence the canal to remain open later on average over the decades. The 2005 NCC report on the implications of climate change lists a number of techniques that the NCC have used to counter the impact of global warming, but I didn’t note any that would extend the skating season. I’ll keep thinking about this.
I also plan to take closer looks at temperature records locally, but until I have time for that I won’t know if part of the answer lies with weather.
What About Mid-Season Thaws?
I’ve been wanting to track the total days of skating per season over the decades. Not only should climate change be shortening the skating season end-to-end, but one might expect that the days when the canal is closed due to a “January thaw” would increase on average over time as well.
I’ve been frustrated in this. The NCC was unable to give me data on mid-season closures prior to 1995. I used the Ottawa Public Library’s tools to do keyword searches on the Ottawa Citizen back issues and learned a little more but the record there only begins in 1985. Plus the Citizen didn’t always mark the start of canal closure or re-opening. Google News has older newspaper images but their inclusion of copies of the Ottawa Citizen in the 1970 to 1985 range is spotty and I could draw almost nothing there (except that organized skating on the canal was talked about at least in concept as early as 1949 – it actually began in 1971).
Unless I find a better source of data, to nail this info down will likely take a few days manually turning pages in Library & Archives Canada, the NCC Library and the Ottawa Room at the Ottawa Public Library. So it will have to wait.
* One notable exception to NCC claims not to close the canal due to budget constraints: In 1993 the NCC cried poor and began collecting donations on the canal, claiming that first season to have brought in $30k and to have used it to extend the skating season from a scheduled Feb 15 close to Feb 28 when weather intervened. I didn’t find any other references to “scheduled” closures.