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23 Degrees heads to Yellowknife Canada

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Stephen Marsh Stephen Marsh | 15:44 UK time, Wednesday, 19 January 2011

d ~ 48'883'200 km: day 19 of Earth's orbit

Today Kate Humble and the 23 Degrees team have travelled deep into the middle of Canada to Yellowknife, the coldest city in North America.

We chose to film on the 19th because it is the day that holds the dubious honour of being on average the coldest day in the northern hemisphere. It's odd that this particular day is the coldest because it's now almost a month since the winter solstice - the shortest day when the northern hemisphere gets the least amount of sunlight. The planet is tilting back towards the sun and we've been getting more solar radiation for several weeks. So in theory, it should be getting warmer. But it's not. It's actually been getting colder. Why? It's all about the balance between heat coming in and heat going out. At the moment we are losing more heat than we are getting. As winter starts the amount of radiation from the sun begins to fall. So the Earth begins to cool down, losing heat from the surface that is radiated into space. But the Earth loses heat slowly, so well into January the northern hemisphere is still cooling down, still radiating heat into space. This cooling effect is more powerful than the warming that comes from increased solar radiation. Not until late January does the increase in solar radiation finally become strong enough to compensate for the heat being lost to space.

The team in Yellowknife will be hitting the highway with ice road trucker Blair Weatherby. As you can guess from the name, he drives not on asphalt roads but roads made from ice. These ice roads are a lifeline for the citizens of Yellowknife because during the summer they are surrounded by hundreds of lakes and impassable bogy tundra. When it freezes ice roads are built across the lakes - linking the community with the outside world and the town comes alive. When cruising along the ice roads with Blair we'll meet some "ice engineers" who build and maintain the roads using snow-ploughs and chainsaws.

Here's a great clip from The History Channel's Ice Road Truckers highlighting how the ice roads are not always safe and extremely unpredictable:

Presenter Kate Humble will also discover why Yellowknife is the coldest city in North America. It's strange that it hold this title because Yellowknife's not in the northern-most part of the continent, and it's not even the most northern city. Barrow in Alaska is around 800 km [500 miles] closer to the North Pole - yet it's not as cold as it is in Yellowknife. So why is Yellowknife colder? The clue is a peculiar detail in Yellowknife's location - it's slap bang in the middle of the continent - a long long way from the sea. And that's the key. The sea absorbs heat from the sun during summer - and holds onto it for a long time. In fact long after the land has lost its heat. So towns like Barrow which are by the sea are kept warmer by the surrounding water even though they are much further north. Poor old Yellowknife is so far inland it loses lots of heat and has no ocean to keep it warm.

Kate will be updating us on the journey soon, so stay tuned...


  • Comment number 1.

    Hi Stephen,

    What is the actual average temperature you refer to?

    Also, is there any marked differences between the northern and the southern hemisphere in terms of variation in temperature, and by extension, weather, throughout the year?

  • Comment number 2.

    Hi JohnTweedie,

    Thanks for your comment. Good question. The temperature I am referring to is the average coldest day in the northern hemisphere.

    Obviously in any given place, the actual coolest day is different every year. To work out the average coldest day scientists measured the temperature all year round all over the planet. They then worked out the average of these temperatures over decades and found that in the northern hemisphere, on average, the coldest day happens about a month after the winter solstice. That gives us our coldest day on the 19th of January.

    Interestingly there is a difference between the hemispheres. Winters are on average are warmer in the southern hemisphere than in the northern hemisphere - but their summers are on average cooler too. This is all due to the amount of land there is in each hemisphere. If you look at the map of the world you'll notice that there's a lot more land in the northern hemisphere than in the southern hemisphere. Land absorbs and loses heat faster than water, which absorbs a lot of heat and holds onto it for a long time. So in the large landmasses in the north, temperatures can get very low because they lose a lot of heat and are so far from any sea to keep them warm. In summer the effect is reversed and the land is far from cooling seas so gets hot. In the southern hemisphere where there is a lot of sea the land never gets cold as cold as in the north because there is so much ocean around it to keep it warmer in winter and cooler in summer. But the cooler summers do mean you get glaciers in place like Tierra del Fuego all year round even though it isn't very high or that close to the south pole.

    cheers stephen

  • Comment number 3.

    Hello Stephen,

    With this entire project, I think you have got to be careful not to slip into a northern-hemispheric point of view. As an inhabitant of the northern hemisphere habitant myself, I know it can be hard. This may sound pedantic but I think it is important to keep a global perspective and to imply the opposite may often being happening on the other hemisphere.

    Perhaps, for instance:
    'the winter solstice' should be termed 'our winter solstice'
    'The planet is tilting back towards the sun ...' should be 'The northern hemisphere is tilting back towards the sun ...'.
    'As winter starts the amount of radiation from the sun begins to fall. So the Earth ...' should be 'Between the summer solstice and the winter solstice the amount of solar radiation hitting the northern hemisphere has been falling. So from the peak summer temperatures it ...'

    I could go on but I am sure you have got the jist.



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