Australia is continuing to warm. Extreme heat days continue to become more frequent, fire weather continues to ramp up and sea levels continue to rise.
- National and global temperatures continue to rise despite the COVID-induced blip in emissions
- Australia’s climate has now warmed by about 1.5 degrees Celsius since national records began in 1910
- There has been abundant rain in the south-east this year but long-term trends towards wet season drying in southern Australia remain
The latest biannual State of the Climate report, jointly released by the Bureau of Meteorology and the CSIRO, has shown that even the global pandemic with a downturn in industry and transport has not been enough to stand in the way of the relentlessly warming climate.
Senior research scientist at the Bureau of Meteorology Blair Trewin said COVID did have an impact on greenhouse gas emissions.
“Globally, at its peak, emissions were down about 6 percent or so. In Australia, it was about 5 percent,” he said.
Disappointingly, post-Covid global emissions have gone back to near or above pre-Covid levels.
But according to Dr Trewin, Australia is bucking the trend, with levels a little up but still “significantly lower than they were in 2019”.
Sadly though, those changes in emissions have been too small to have any discernible impact on climatic consequences like global temperatures, Dr Trewin said.
“In the normal course of things, we have variations of anything plus or minus 20 or 30 percent in the change of CO2 levels per year just through natural variability.”
Natural variability comes in the form of weather events such as El Niño and La Niña.
“So the sorts of changes we saw in emissions, if they’re confined to a single year, aren’t really going to be detectable in carbon dioxide levels beyond that natural variability,” he said.
“If they were sustained for longer it would be a different story.”
So short of a drastic reduction in greenhouse gas emissions, climate change is something we are going to have to continue to deal with.
Can we expect more floods like this?
According to Dr Trewin, this year’s absolute deluge in the south-east will not be enough to turn around the long-term trend towards less cool-season rainfall in southern Australia.
“It’s perhaps weakened it a little bit in the short term,” he said.
He said many of the rainfall extremes we have seen in recent years have been in summer when there has not been a huge change in southern rainfall.
“We will expect that over time, rainfall extremes will increase, even in areas where average rainfall is decreasing.
“How much that increase depends on how much global warming we see.
“It’s much more obvious in models, at 2C of warming or more than it is at 1.5C.”
“Flooding and flood impacts are about a lot more than just rainfall,” he clarified.
“But the rainfall component of it: we have pretty clear expectations with a warmer atmosphere being capable of holding more moisture, all other things being equal.”
Can we expect more La Niñas?
The report states El Niño and La Niña activity over the past 50 years has been higher and more significant than in the previous 50.
But it is not clear if that is a long-term trend.
“But what we do expect into the future is even if there isn’t a significant change in the frequency of El Niño and La Niña, we do have a fairly high level of confidence that the rainfall extremes associated with El Niño and La Niña will get stronger,” according to Dr. Trewin.
“So more intense rainfall with La Niña and more drought with El Niño.”
The other big factor in the past few years’ flooding has been the triple-dip, with La Niña after La Niña, after La Niña compounding to saturate the soils and fill the dams to overflowing.
Multi La Niñas are rare and Dr. Trewin said there was no clear evidence in the projections suggesting that long-running consecutive-year events would become either more or less common in the future.
“But one of the things about climate change is that sometimes unexpected things happen.
“So it’s certainly something we would be keeping my eye out on.”
Perhaps the most notable difference in this State of the Climate report, compared with previous editions, is the dramatic decline in Antarctic sea-ice coverage over the past few years.
For most of the satellite record, starting in the late 1970s until 2015, Antarctic sea-ice extent was mysteriously increasing, despite global temperatures rising and Arctic sea-ice declining, as would be expected.
“The levels of sea ice we had around 2014/15 were as high as they had been, at any point in the satellite era,” according to Dr Trewin.
“But we started seeing Antarctic sea ice drop away from 2015 onwards. At the time of the last report that hadn’t been going for terribly long, but that trend has continued.
“In fact, in early 2022 we saw Antarctic sea ice extent reach record lows.”
Why the sea-ice was increasing and why it has recently turned around is an ongoing area of research.