By Dr. Adam Fenech, UPEI Climate Research Lab

The PEI winter of 2014 brought the most snow in 42 years, and colder than average temperatures. But why? I have never seen so much discussion about the polar vortex, nor the blame it received for our cold and snowy winter. There was also discussion later in the season about climate change being the possible cause of our severe winter. So who is to blame? The easy answer is climate variability – climate is nature’s carousel that goes up and down so we should experience variations in our winters – some warm and dry, and others cold and snowy. But variability is the easy answer and too general to explain the winter of 2014.

Some people blame the polar vortex for our most recent cold and snowy winter. The northern polar vortex is a large region of air that circles the North Pole (counter-clockwise) in the high atmosphere dripping high colder air to the surface of the Earth. The northern polar vortex is kept in place by the northern jet stream, a west-to-east warmer wind that flows around the Earth between the upper and lower atmospheres driven by the differences between the cold north and the warmer south. Sometimes the northern jet stream meanders like a stream causing a piece of the polar vortex to break off and plunge to the surface over Canada bringing cold air and snow. This happened in Manitoba and influenced our Atlantic region. But is the polar vortex to blame for this winter’s cold? It is more a symptom than the cause.

Others blame climate change for our severe winter. I know this sounds counter intuitive as “global warming” is supposed to bring warmer not colder temperatures. But here is how the theory goes – rapid Arctic warming and reductions in northern sea ice will weaken the difference in air temperatures between the north (Arctic) and the south (mid-latitudes) forcing the northern jet stream to meander across North America as it did this past winter. I asked the proponent of this theory, Jennifer Francis of Rutgers University, at a recent meeting in Ottawa as to the evidence for her theory. She said that it is still premature to blame climate change as the jury is awaiting ten more years of monitoring and examination of the data.

We need to focus on the meandering northern jet stream to get at the cause of PEI’s cold and snowy winter of 2014. The United Kingdom’s Meteorological Service has put the blame on increased rainfall over Indonesia associated with higher than normal ocean temperatures in that region. This caused the Pacific jet stream to continually interfere with our northern jet stream causing its meandering (known as Rossby waves) or being knocked out of its usual place of trapping the northern polar vortex.

So to connect the dots – heavy and continuous rainfall in Indonesia with higher than normal western Pacific ocean temperatures pushes the south Pacific jet stream more north bumping into the northern jet stream forcing it to meander like a stream across North America allowing the northern polar vortex to drop further south into Canada. Boom-boom-boom and behold, a colder winter for PEI.

I suppose what is emphasized most by this discussion is how interconnected global processes like these are, how they change regularly and how they might be influenced by human activities in the long run. What I find most intriguing is that enhanced rainfall halfway across the world can have serious implications for our way of life here on Prince Edward Island. The world is certainly a weird and wonderful place.

Notes:

• Our month of April 2014 was just below normal in terms of temperature (average of 2.9 degrees Celsius) and about 30% wetter than normal (135 mm of rain and snow).
• If you missed the launch of the 2015 PEI Weather Trivia Calendar, they can still be purchased at peiweathercalendar.ca or at your local Murphy’s Pharmacy.