Environment

Extreme times: world's weather is on a weird track that will continue into 2016

If Santa really did reside at the North Pole, he could probably have doffed his thick coat for a few hours this week to dig his sled out of the slush.

Despite being shrouded in darkness since early October, the top of this world recorded temperatures that appear to have  been above freezing point for about six hours on Wednesday, thanks to a huge storm that steered tropical warmth into the high latitudes.

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What's El Nino got in store for 2016?

The giant 2015 El Nino in the Pacific is at or nearing its peak, but it will be months before the world's weather engine takes the heat off Australia.

The Arctic has long been observed as warming at about twice the rate as elsewhere on Earth, but the 30-plus degrees Celsius jump above the average for this time of year was a stunning reading – sending polar temperatures briefly above cities like Chicago in the US and Vienna in Austria far to the south.

Such events made descriptors such as "unprecedented" or "record" almost the bywords for 2015 when it came to weather.

Arctic heat caps off a record hot year for planet Earth.
Arctic heat caps off a record hot year for planet Earth. Photo: Leigh Henningham

The combination of an epic El Niño in the Pacific overlaying the background warming unleased mostly by humans' combustion of fossil fuels jolted the concept of what "normal" conditions mean. It also sets up 2016 for more wild weather.

Even before December brought record heatwaves to regions as diverse as Victoria, the High Arctic and almost all of the eastern US, major meteorological agencies had heralded 2015 as the hottest year for the planet since reliable data gathering began 136 years ago.

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The call was an easy one to make. By November, year-to-date temperatures were more than 0.1 degree higher than the previous hottest year – set just one year earlier in 2014 – with the gap widening, according to the US National Oceanic and Atmospheric Administration [NOAA]:

Of 1630 months tallied by NOAA since 1880, seven of the 10 most usually hot months occurred in 2015 alone.

When the latest data is assessed, it may reveal December to be the first month with a temperature reading a full one degree above the 20th-century average. Last October fell just shy with a 0.99-degree anomaly, NOAA says.

Climatologists have scant doubt which way the climate is changing. In Australia since 2000, for instance, record hot days have been 12 times more common than record cold ones, research published in September showed. 2015 will probably be among the five warmest years for Australia since records began in 1910.

Those trends – and evidence of increasing extreme weather, such as worsening fire risks in southern Australia – were the reason why almost 200 nations agreed last month at the Paris climate summit to try to keep temperature increases "well below two degrees" compared with pre-industrial levels. We are roughly half way there. 

Governments, including Australia's, also backed carbon neutrality – balancing emissions of greenhouse gases to the amounts being sequestered – by the latter half of this century, a pact that will need much more ambitious climate action to limit coal and other fossil fuel use than now being offered.

The global temperature gauge certainly got a kick-along this past year from the monster El Niño in the Pacific, which rivals the 1997-98 event as the most intense on record, and has a big influence on worldwide weather.

Even so, temperatures have been creeping higher for decades, whether it is an El Niño year (red) or its reverse, La Niña (blue), as shown in this NOAA chart:

During El Niños, the typical westward-blowing equatorial winds stall or reverse. Along with a build-up of heat in the central and eastern Pacific, rainfall patterns also shift eastwards away from Asia.

The current El Niño is marked by unusually warm waters covering about 16 million square kilometres, an area bigger than twice the size of Australia and larger than the 1997-98 record event.

Nearing peak?

The 2015-16 version is also showing "no signs of waning", NASA said this week. Australia's Bureau of Meteorology, though, estimates the event is near its peak but says models indicate the unusual heat won't break up until May or later.

Wenju Cai, a CSIRO research scientist who studies how climate change will affect El Niños in the future, says a lengthy breakdown of the event means 2016 could set annual global heat records for a third year in a row.

"It's the release of heat from the ocean that is going to make us hotter," Cai tells Fairfax Media.

Parts of the Northern Hemisphere might welcome a little extra warmth – although less so if it's accompanied by more storms and floods as lately seen in the UK. But in Australia, the extra heat "is coinciding with our peak" in summer, Cai says.

Forests and grasslands have already turned crisp across much of Victoria and elsewhere in southern Australia, prompting fears of a "Black January" if significant rainfall doesn't arrive to add moisture and disperse the heat.

In 2015, south-west Western Australia and parts of inland Queensland, South Australia and much of Victoria and Tasmania had very much below-average rainfall, the bureau said. 

La Niña  next?

The El Niño's demise, though, is unlikely to usher in a new period of climate calm.

As Agus Santoso, a senior researcher at the University of NSW-based Climate Change Research Centre, notes, "extreme La Niñas tend to follow extreme El Niños".

As the climate warms further, "this kind of sequence will happen more", Santoso says. "It's very bad news."

During La Niña years, the world's weather engine flips back to the western Pacific, with rainfall patterns shifting with it. Indonesia, South Pacific and parts of Australia that were relatively dry in 2015 may get excessive amounts of rain in the next year or so.

A comparatively quiet tropical cyclone season for this summer for Australia may revert to a relatively active one in 2016-17.

Research published by Santoso and Cai in 2015 indicates that while the number of El Niños and La Niñas may not alter with climate change, the frequency of the extreme version of such events affecting Australia is likely to quadruple this century if greenhouse gas emissions remain on a rising trajectory.

While "the power of nature is huge" and human activity may not trigger El Niños or La Niñas themselves, the rising atmospheric concentration of carbon dioxide, methane and other heat-trapping gases will make a difference, Cai says.

"In a warming world, the atmosphere can store more water," Cai says. "When conditions for rain are there, it will come down much more vigorously because you have more water."

The climate will become less recognisable to today's population as shifts in the world's weather engine in the Pacific "move further or faster, and stay longer", he says.