Daniel Bezte has a special interest in farm weather, which he follows from a small farm near Winnipeg, where he has his own computerized weather station. He has been a regular contributor to other farm publications including the Farmers’ Independent Weekly and the Manitoba Co-operator. Daniel has a degree in geography, specializing in climatology, from the University of Winnipeg.
He welcomes questions and comments at [email protected]
In the last article we finished by introducing the idea of a positive feedback loop. One of the reasons that the Arctic is so cold (besides low sun angle and little to no sunlight in the winter) is that a good portion of this region is covered in ice and snow. Both of these substances are highly reflective, or have what is known as a “high albedo.” Most of the sunlight that does make it to the surface gets reflected away (about 80 per cent) and does very little to help heat the area.
If we reduce the area of the Arctic that has a high albedo, then more of the sun’s energy will be absorbed, allowing the region to heat up more – the extra heat further reduces the area with high albedo, so even more of the sun’s energy is absorbed – a positive feedback cycle. One change feeds back on itself, creating a bigger change.
If the Arctic was only land area I don’t think people would be getting as excited about what is going on. But the Arctic contains a lot of water, most of it in the form of the Arctic Ocean. What’s the big deal about all the water?
Well, water can absorb a great deal of the sun’s energy (around 80 per cent). Water can also move that energy around. Finally, water can also store the sun’s energy (heat) for much longer than land. So, if the amount of sea ice drops, then a lot more energy, or heat, can be added to the Arctic, leading to our positive feedback cycle.
MEASUREMENTS HAVE IMPROVED
Now just how much sea ice is there in the Arctic and what is its current state? Before satellite records began, measurements of Arctic sea ice came in the form of reports from ships in the region, explorers and scientists, and the different indigenous groups living in the Arctic. While a lot of good information can be gathered from these reports we can’t really create a reliable record of monthly or even yearly sea-ice amounts until the early 1970s. This is when NASA launched a microwave-imaging satellite that passes over the Arctic several times a day collecting daily data on sea ice.
Then in 1978, NASA launched a new multichannel microwave-imaging satellite, seen as the beginning of really useful satellite data. This means that fairly reliable continuous records of Arctic sea ice only go back 31 years – not bad, but not great.
What patterns have we seen in the Arctic sea ice over this period? Well, unless you are a conspiracy theorist and believe that NASA and everyone else looking at this data is in on some massive coverup, it is pretty evident that the amount of sea ice in the Arctic is going down. I have included two graphs showing average monthly sea ice in March (month with maximum ice cover) and September (month with minimum ice cover). From the graphs you can definitely see that while there is yearly variation in the amount of ice cover, the overall trend (depicted by the blue line) is a downward one.
Looking at the September minimum graph we can see that over the last 30 years, ice cover has dropped from around 7.5 million square kilometres to around 5.5 million. That is a change of about 2.0 million square kilometres or about a 30 per cent decline!
In our next article on Arctic sea ice we’ll explore the current ice conditions and what factors have possibly been influencing this rapid decline.