PLEA Network

14 December 2017, The Conversation, Not just heat: even our spring frosts can bear the fingerprint of climate change. In recent years, scientists have successfully identified the human fingerprint on hot years, heatwaves, and a range of other temperature extremes around the world. But as everyone knows, climate change affects more than just temperature. The “signal” of human-induced climate change is not always clear in other weather events, such as cold snaps or episodes of extreme rainfall. Three new studies, released today as part of a special edition of the Bulletin of the American Meteorological Society, take a closer look at two such events, both of which happened in southern Australia in mid-2016: the frosts that hit Western Australia’s South West, and the extremely wet weather that hit much of southeastern Australia during that year’s winter and early spring. Perhaps surprisingly, WA’s frosts showed a fingerprint of climate change, due to changes in weather patterns. Meanwhile, there was very little climate change signal in the extreme rainfall that hit the southeast. While there is a clear human-driven upward trend in Australia’s average temperatures and the future of southern Australia is projected to be dry in the cool seasons, last year Australia experienced its wettest winter and September on record. Meanwhile, September in WA’s South West brought up to 18 frost nights across the region – the most on record in some locations. An increasing temperature trend would limit the number of extreme cold events, and broadly speaking this is true for Australia. So what caused the record frost risk in South West WA in September 2016? For the northern hemisphere, a “wobbly” jet stream has been proposed as the cause of periodic blasts of extreme cold weather. In this theory, human-driven changes to atmospheric circulation cause Arctic air to temporarily extend southwards over populated areas, bringing Arctic weather in spite of the background warming trend. But this kind of theory hasn’t been examined in depth for Australia. Read More here