Sunday, December 13, 2009

Winter Interest: Bye-bye Zone 3b?

The Home Bug Garden broke a record this morning: -40 C (aka -40 F) from at least 6:30 am until after 9 am. The previous record low, a smeary -39 C on our red alcohol thermometer, is burned into my memory, but alas, not recorded in my notes. My Garden Journal started on Canada Day (1 July) 2004, just in time for the 2 July flood. But regular recording of daily high and low winter temperatures didn’t start until 2006 – obsession with the weather takes a while to develop in a transplanted Queenslander used to constant warm, sunny days. So, this morning was the coldest in the HBG, but that’s a long shot from Edmonton’s coldest on record: -48.3 on 28 December 1938 (when Edmonton was a much smaller city) and matched at the International Airport on 26 January 1972 (just a few years after the airport opened).

When I checked the Environment Canada Weatheroffice website this morning, my clean, sharp -40 was perfectly bracketed by the -35 C at the City Centre Airport and the -45 C at the International Airport. Ten degrees Celsius seems like a startling difference for two airports so close together. The City Centre is a bit further north (53 34.2 vs 53 19.2 N), but ~50 m lower in elevation (671 vs 723 m). All else being equal, a site 50 m lower would be expected to average about 0.34 degrees warmer. The annual mean daily temperature of the City Centre (3.9 +/- 1.1), however, averages a full degree and a half Celsius higher than the International Airport (2.4 +/- 1.2).

This does seem strange for two weather stations only 30 km apart, and given the recent Climategate leak, perhaps a little paranoia is in order. The City Centre has been consistently claiming higher highs and higher lows than I can find on my thermometer (at almost the same elevation, 669 m, and only 15 km south). Could they be fudging the data to make things look warmer? I doubt it – as far as I can make out from the CRUtape Letters, all the value adding to the temperature data happens later, once the ‘scientists’ discover that the data does not agree with their models, and therefore, must be wrong.

Moreover, a simpler and well supported alternative answer is available – the Urban Heat Island Effect (UHI) - all the buildings and tarmac that absorb heat during the day and radiate it out at night and all the energy burned to keep the city going add up to a warmer local climate. So while the City Centre is usually warmer at night than my backyard, the backyard is often warmer than the International Airport. For morning lows, I’m often halfway in between – not surprising since the HBG is situated halfway in between the two airports and is in an area that is maybe half as urbanized as the City Centre. Daytime highs are more variable, but are more like the Airport than like downtown. UHI seems like a good explanation for these differences – and I would imagine that the International Airport is warmer than the rural areas around it.

My friend at Gardening Zone 3b near the City Centre seems to have an unfair share of UHI, but he displays the results beautifully on his blog, so I forgive him his 2-3 week advantage in spring bloom time and his later killing frosts (I’m a noble guy). I certainly don’t want my neighbourhood to get more urbanized, so I guess the HBG will just have to make do with the little UHI it has. The last couple of years, however, seem to be getting colder. That is a worry, as is the apparent correlation between sunspot activity and warmth (the Sun appears to be in a deep funk). If, as it seems, global warming was at best a delusion, then Zone 3 gardeners are going to miss it more than most people, except for Phil Jones and his mates, of course.


  1. It was the eerie ice mist that intrigued me this morning - that, and when I opened my front door to get the morning papers from the box it seemed the world was so brittle than even the greenery around the door could snap cleanly in two.

    We have not left the house today.

  2. Hi Garden Ms S:

    That's the way it looked to me too, but I boldly went forth where no Home Bug Gardener had gone before and deposited the cat poo and a full bag of recycling in the garage - entirely because I wanted to be able to brag that I had been out in 40 below weather. Sad, perhaps, but at least I did not adjust the thermometer to make it seem more frigid.

  3. From your title I was afraid that you were somehow going to eliminate my blog.

    I believe we are roughly equidistant from the city centre, so the perceived UHI benefit to my garden is probably the result of the radiant warmth of my aura. Conversely, it is well known that the aura's of Climate Curmudgeons are several degrees cooler..;)

    Merry Christmas!