Changing Climate

Norwegian scientists have documented a rapid melting of Arctic sea ice http://www.bbc.co.uk/news/world-europe-19508906. If it continues, it is liable to affect global weather patterns, and may already have. What might it mean for western Canada?

Researchers have determined that more and more sea ice is melting in the Arctic every summer, and some of the ice that is not melting is thinner than in decades past. Thinner ice – once the snow has melted – allows sunlight to get through to the water below where some of the energy is absorbed resulting in warming. That warming results in more thinning of the ice, which results in more warming, which results in… well, you get it.

Between the thinner ice and the ever increasing amount of open water, the Arctic waters are warming and are likely to continue warming at an accelerating pace. The consequence of this is that the temperature differential between the Arctic and the equatorial region is decreasing, at least during late summer and fall before the Arctic sea ice reforms.

Why is that important? Well, that difference in temperature is what produces the major jet streams of the northern hemisphere. Jet streams determine where weather systems travel and how fast, and they affect the development of storm systems. They also affect where a ridge of high pressure may form, how intense it may become, and how long it may last.

So what about western Canada’s climate? I’m very reluctant to hazard a guess as to the effects on high pressure ridges over western Canada although I suspect that we will see more ridges meaning warmer and drier weather in late summer and fall. Also, the decreasing temperature differential from the Arctic to the equator will mean weakening jet streams. Weakening jet streams should result in fewer and weaker storm hitting the coast of BC in the fall months.

While it is not unusual for storms to hit the BC coast every 24-36 hours in the fall (often with little or no break between), this frequency should slow down, as should the intensities, meaning less rain and longer breaks between storm systems.

For Alberta and the prairies it may mean a reduction in precipitation in the fall months. Since not a lot of precipitation falls on the prairies during the fall, it should not have a major effect.

These effects, however, are only for the months when the sea ice has melted or is thin. Consequently, by late fall or early winter conditions should return to normal.

In my observances of the climatology of BC, it appears that this effect has already been felt for some time. September and October have become warmer and drier than in decades past, and while November used to be the wettest month in southwest BC, in recent decades that has moved to December. I wouldn’t be surprised to see it move to January in the next few decades.