Blistering heat across Australia but frigid conditions across much of the continental US – what’s going on?
As Sydney braces for 38-degree heat and a total fire ban on Friday and some inland towns of NSW face their sixth heatwave since October, regions of north-eastern United States are digging themselves out of two metres of snow or more.
The challenge, says Matt England, a leading climate scientist at the University of NSW, is to avoid confusing day-to-day weather events with the longer-term climate trends under way. In the case of the massive US snowstorms – handily striking a region that’s home to major media outlets ensuring wide coverage – “you’re looking at a weather-scale event”, Professor England said.
“It’s early blast of winter weather”, he said, adding that “it’s crazy stuff to call it an end to global warming”.
Indeed, the Northern Hemisphere, including North America, has been generally much warmer than average this year. Andrew Watkins, the head of climate prediction services at Australia’s Bureau of Meteorology, also said the snow was a local event. ”The cold in the US … it looks like a local or regional climate phenomenon, rather than a hemisphere-wide one,” Dr Watkins said. Professor England and other scientists point to larger, longer-term trends that are more significant than unusual weather-scale events. These include an Arctic region that is warming faster than almost anywhere on the planet, which is causing Arctic sea-ice cover to thin out and shrink and the Greenland ice sheet to melt. (A study published in Nature earlier this year linked increased snowstorms to that ice loss.)
The US National Climatic Data Centre released its global readings for October on Thursday and confirmed earlier conclusions from the Japan Meteorological Agency, which declared last month to be the hottest October in more than a century of records by a wide margin. Continental US had its fourth-warmest October on record, the centre said earlier this month. The NCDC says that November and December need only to the 10th warmest on record to make 2014 the hottest year on record. Given oceans, which continue to set monthly highs – land temperatures in October were merely the fifth warmest – an annual record seems more and more likely. The years to beat are 2005 and 2010.
Meanwhile, much of Australia is about to experience another burst of early-season heat. Is that just weather too?
“There’s a global warming signature in pretty much everything that we see these days,” Dr Watkins, from the bureau, said. ”The trouble is, teasing out what’s natural variability and what’s the global warming signature is very difficult.” However, Australia has seen a regular pattern of unusual heat roughly every month for the past two years, Dr Watkins said.
Over the past 15 years, the frequency of very warm months in Australia has increased five-fold compared with the period 1951-1980, the bureau said in its State of the Climate 2014 report released earlier this year. The frequency of very cool months, meanwhile, has dropped by one-third. What is notable is that the more recent heat over the past 24 months or so has occurred without the usual kick to Australia’s famously variable climate that comes from El Nino events forming in the Pacific. El Ninos can add 0.1 degrees or more to the global average and typically set southern and eastern Australia up for warmer and drier than normal conditions – and bad bushfire seasons. Earlier this week, the bureau raised its estimate of the likelihood of an El Nino forming in coming months to at least 70 per cent.
For Gavin Schmidt, director of the NASA-Goddard Institute for Space Studies, it’s the broader warmer weather – and not this week’s cold snap in the US – that people should be watching. ”The extraordinary thing is that this is not an El Nino year, despite a lot of discussion about El Nino emerging,” Dr Schmidt told The Washington Post.
“And so you’re looking at a situation where you’ve got a neutral year and you’re still close to breaking records,” he said. “That’s telling you something about the whole shift in the baseline of temperatures.”