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Do temperature extremes indicate that climate change is accelerating?

Québec, January 2019 (The Photographer)Québec, January 2019 (The Photographer)Since the beginning of 2019, hundreds of thousands of fish have boiled during the hottest month ever recorded in Australia. Parts of the United States and Canada have suffered much colder temperatures than even in the icy continent of Antarctica. One of the Antarctic’s largest glaciers, the Thwaites Glacier, is melting and threatens to break away from the Antarctic ice cap. There are signs that the Arctic Ocean is warming so fast that it could soon become completely ice-free in the summer for the first time in 700,000 years. Scientists are pointing out that these events are linked: they may all be growing signs of climate disruption caused by global warming.


Jet stream over Canada (NASA)Jet stream over Canada (NASA)As carbon dioxide builds up in the atmosphere—levels are now higher than they have been on Earth for millions of years—the planet gets warmer, and its ice caps start to melt. This has the effect of reducing the difference in temperature between the equator and the poles. Many scientists believe that this causing jet streams to weaken. Jet streams are narrow bands of air that travel at great speed across the sky at high altitude. They are known to have a significant effect on our weather systems.


Jan 2019 heatwave in NSW, Australia (D A R C 12345)Jan 2019 heatwave in NSW, Australia (D A R C 12345)
During the summer, the weakening of jet streams means that zones of high pressure stay around for longer. This causes heatwaves, such as those experienced in the northern hemisphere in the summer months of 2018, and in the southern hemisphere in the summer of 2018-19 (for example, Marble Bar, Western Australia, often called the "hottest town in Australia", experienced highs of 49°C / 120°F in December 2018). 



Chicago during polar vortex of 2014 (stojakovic)Chicago during polar vortex of 2014 (stojakovic)
During the winter, the weakened jet streams break up the polar vortex, the band of strong, high-altitude winds that normally keeps cold air locked into the Arctic region. The break-up allows warmer southern air to enter the Arctic, resulting in the high temperatures recorded in the region last winter. It also allows the freezing polar air to escape southwards (as seen in this temperature map of the globe, below). This was felt in the US in January 2014 and again in January 2019, where temperatures in Minnesota, for example, recently plunged to -50°C (-58°F). Last winter in Europe, escaping polar air was experienced as “the Beast from the East”.

Broken polar vortex, 29th Jan  2019 (NASA)Broken polar vortex, 29th Jan 2019 (NASA)

Despite these extreme winter freezes, the overwhelming global trend is towards higher temperatures. Recent weather satellite data confirm that the past four years (2015–18) have been the warmest recorded. Overall, there is a clear pattern of winters becoming warmer.

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