Hot weather Down-Under

Sydney And Melbourne Copping Record May Heat. The Reason Why Is Scary

Huffington Post,

21 May, 2016

As the world warms, the weather is changing in ways far more dramatic than a little extra heat there, a little less rain there.

Entire weather patterns are shifting, and we're already seeing the results in Australia this autumn.

First up, some dramatic statistics to illustrate the unprecedented Australian temperature anomalies being experienced in Australia this month. Then we'll hear from an expert on why it's happening.

• Sydney is a whopping 4.9 degrees above average for May. Sydney's average May daily maximum temperature is usually 19.5. The average is 24.3 degrees so far this month.
• One more time for emphasis, Sydney is almost FIVE DEGREES ABOVE AVERAGE for a whole month. Wow.
• In fact, the Sydney maximum has topped 20 every day in May so far. Tuesday hit 28. The COLDEST day of the month was 1.3 degrees ABOVE the average.
• Hot streaks do not usually last this long. Not even close.
• Melbourne temperatures are also way up this month. It's May 2016 average of 20.3 degrees (to date) is 3.6 degrees above the long term May daily average of 16.7.
• It's a similar picture across Australia. Canberra is nearly four degrees above average so far this May, Hobart and Brisbane three degrees, Adelaide nearly two degrees, and Darwin and Perth both one degree.
• The fact that it's much warmer than usual across Australia is very much in keeping with the long term Australian trend (depicted below), as well as global data showing that the world just had its hottest ever seven months -- and its hottest April by a huge margin.

The world is warming far quicker in the last year than at any time in recorded human history. This is a well-documented global phenomenon with uniform scientific consensus. But even though warming is accelerating, we're still talking "only" a degree or two warmer than usual in most places.

But four to five degrees above normal in Australia's two largest cities for the first 20 days of a month? Like we said, that's way beyond the norm. So why is that happening?

Agata Imielska is a climatologist with the Australian Bureau of Meteorology. Here's what she told The Huffington Post Australia.

"With climate change one of the things we have been observing is a shift in some weather systems. We are seeing high pressure systems sitting further south and those cold pressure and rain-bearing systems tracking to the south of the continent."

That weather map below? It will help explain what Imielska just said. Don't panic if you can't read a weather map. We'll walk you through this step by step.

See the blue lines with (what look like) shark fins lurking in the Southern Ocean? Those are cold fronts. About the only place they're impacting right now is Tasmania and New Zealand. High pressure systems sit over most of Australia. They typically bring warm, clear weather.

This map is pretty normal for autumn. Most fronts stay south of the mainland in autumn. What's not normal is the map looking like this day after day, after day. A few fronts generally start tracking north during April and May. This has only happened once so far this year.

Ski resort PR teams went gaga when a weak front brought a few centimetres of snow to the Australian Alps last week even though the snow melted by mid morning.

But the weather soon turned warm again.

In 2014, a report called "Climate Change in Australia" was produced jointly by the Australian Government Department of the Environment, the CSIRO and the Australian Bureau of Meteorology.

A key bit is in Chapter 4: Understanding Recent Australian Climate. It spoke of:

• "a tendency for a contraction of mid-latitude storm tracks toward higher southern latitudes", and;
• "global and hemispheric circulation changes providing causality of cool season rainfall declines in Australia", and;
• "Southern Hemisphere circulation warming expanding the tropics, or Hadley Cell circulation, toward the pole."

In other words, this describes exactly what we've been talking about. That the cold fronts -- which bring cooler weather and rain to the southern states in late autumn, winter and early spring -- are arriving less frequently.

These fronts bring not just cooler weather but rain too. Their less frequent visits to the mainland have meant drastic reductions in rain to SW Western Australia and parts of the south-east for at least 20 years now. Conversely, parts of the tropics appear to be getting wetter.

This image shows that really clearly.

Here's one more line in the same chapter of the "Understanding Recent Australian Climate" report that sums all of this up. It says:

"A contraction of mid-latitude weather systems toward the pole... has been attributed to anthropogenic greenhouse gas warming and and springtime Antarctic stratospheric ozone depletion."

In other words, we're causing these problems. And the warm spell in Australia this May can be clearly linked to wider patterns. It's no isolated event.