SINGAPORE - Dozens of people died over the Christmas holiday period as winter storms and intense cold swept across much of the United States, Canada and Japan, knocking out power and causing travel chaos.
While winter storms are not unusual, it was the ferocity and huge amount of snow triggered by the latest storms that alarmed meteorologists and local officials, especially in the US, where the arctic blast affected much of the nation all the way towards the border with Mexico.
The Straits Times looks at some of the likely reasons for the intensity of the storms and whether climate change could have played a role.
1. What happened in the United States and Canada?
At its simplest, intense cold air from the Arctic moved south due to the weakening of atmospheric circulation patterns.
Normally, the Arctic’s freezing weather is locked in by the polar vortex, a large rotating band of cold air that swirls around the far northern latitudes – a bit like a spinning top rotating counter-clockwise. It forms a boundary between the colder air over the North Pole and the warmer air to the south.
But sometimes the vortex can be disrupted. It is accompanied by changes to the jet stream – high-speed winds that run west to east – which develops a wavy, snakelike pattern as it circles the globe.
Sometimes the vortex splits into several fragments that move south, and it can become stretched, like a rubber band.
This is what seems to have happened over the past week, allowing the freezing air to move out of the Arctic across Canada and into the US.
But this can also occur in parts of Asia and Europe.
The large mass of cold air is combined with a rapidly intensifying low-pressure system called a “bomb cyclone” to trigger howling winds and intense blizzards over the Great Lakes and into south-eastern Canada.
2. Is there a link to climate change?
Scientists are still debating different theories.
But one that is gaining support is that a rapidly warming Arctic is disrupting weather patterns. The Arctic is warming about four times faster than most other places in the world, meaning the temperature difference between the North Pole and the tropics is less than before.
Some scientists say the rapid warming is causing disruptions in the polar vortex, through the changes in the polar jet stream. Others say that computer modelling suggests naturally variable factors are driving disruptions.
Dr Judah Cohen, a climate scientist at Atmospheric and Environmental Research, a weather-risk assessment firm in Lexington, Massachusetts, told The New York Times that the warmer conditions create larger and more energetic atmospheric waves that make the jet stream wavier, with greater peaks and troughs.
That affects the polar vortex circulation.
Scientists say they need more data and more evidence to be certain.
But there is far more certainty on the link to climate change and the intensity of rain and snowfall. That is because a warmer atmosphere holds more moisture, and despite the intense cold of the latest winter storms, overall, data shows winter temperatures are becoming milder globally.
In general, climate change has made cold extremes warmer and shorter, Dr Patrick Brown of The Breakthrough Institute, a California think-tank, told New Scientist magazine in December. “In the metrics that look at cold extremes, it’s not getting colder,” he said.
3. And what’s behind the intense cold weather in Japan?
Since Dec 17, a total of 17 people have died and 38 were severely injured in Japan as at Monday, the authorities said, following cold and heavy snowfall, which was accompanied by strong winds and rough seas.
The nation has been hit by separate extreme cold masses. The first was around Dec 17 to 20, and the second around Dec 22 to 26.
Both led to “significantly heavy snowfall” danger warnings in prefectures that are typically used to snow, such as Niigata, Ishikawa and Fukushima.
Some places broke records for 24-hour snowfall, such as Oguni town in Yamagata – 97cm in 24 hours through to 5am on Dec 24.
Snow also accumulated in prefectures not used to it piling up, such as Fukuoka and Kumamoto on Kyushu, and Hiroshima in western Japan. It triggered transport chaos, with cancelled flights and delayed train services, and knocked out power to tens of thousands of homes.
The Japan Meteorological Agency has attributed the bad weather to a “strong and slow-moving winter-type atmospheric pressure pattern”, but there was no mention if it was unusual.
4. What’s likely to happen in the future?
As global average temperatures keep rising, that does not mean an end to winter storms – or freezing temperatures.
Exactly how climate change will affect the polar vortex remains a subject of intense research, but there will certainly be more arctic blasts that will affect North America, Europe and parts of Asia.
“We’re seeing this warming overall in the winter,” Dr Jennifer Francis at the Woodwell Climate Research Centre in Massachusetts told New Scientist. “But we’re also seeing these big cold-air outbreak events happening more often.”
And rain and snowfall intensity is set to increase, so even if blizzards are not intensely cold, they can potentially dump even greater amounts of snow.
Source: University Corporation for Atmospheric Research, NYTimes, New Scientist
- Additional reporting by Walter Sim in Tokyo