03/07/2021

(AU SMH) From Drying Rainforests To Heavier Downpours, Australia’s Climate Is Changing

Sydney Morning Herald - Peter Hannam

Australia’s tropical rainforests will dry out, marine and land heatwaves will become more frequent and intense, and thunderstorms will dump more rain and worsen floods as the globe heats up.

These are among the many impacts from climate change that will blight the nation further unless atmospheric levels of greenhouse gases stabilise, according to the final report of the federal government’s Earth Systems and Climate Change Hub.

’Hub research has shown a clear link between climate change and worsening bushfire weather conditions over the past 70 years,” the centre’s final report finds. Credit: Nick Moir

The work of more than 100 researchers, to be expanded in a new Climate Systems Hub that began operations on Thursday, made advances across fields ranging from bushfire prediction to the rapid identification of the role climate change rather than natural variability plays in an extreme weather.

“It’s clear that climate change is already happening and having impacts,” said David Karoly, the leader of the Earth Systems Hub that ended its work on June 30.

Hub achievements include the “massively successful” improvements to the main ACCESS climate model used by Australian governments and agencies to hone future predictions to a smaller scale than before, he said.

Ancient Gondwanan rainforests in Queensland and NSW, which get as much as 40 per cent of their moisture from being shrouded in clouds, face a drier and hotter future with climate change. Credit: Brian Cassey
The final report said there was “a clear link between climate change and worsening bushfire weather conditions over the past 70 years”, and singled out the World Heritage-listed Gondwana Rainforests as one area of concern.

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The forests, which stretch from north of Newcastle in NSW up to southern Queensland, were hard hit by the 2019-20 Black Summer bushfires and are likely to become drier as clouds and fog that provide as much as 40 per cent of moisture rise in a warmer climate.

“Higher cloud height, especially during the dry season, could lead to a dry climate that is beyond the tolerance of some species, resulting in rainforest community changes,” the report found, adding “even moderate increases in cloud height were found to have significant implications for cloud-water dependent species”.

Professor Karoly said that, while the lineage of the forests dates back many millions of years, changes were underway in a matter of a hundred years, far faster than species could adapt.

Similarly rapid changes were underway in the oceans around Australia although their remoteness from most people’s experiences meant they were not well known.

The Tasman Sea is warming at four times the global average, placing at risk giant kelp forests off the Tasmanian coast. Credit: Craig Sanderson

The Tasman Sea, for instance, is warming four times faster than the global average in part because the East Australian Current is strengthening and dragging tropical water much further south.

Key ecosystems, such as the giant kelp forests off Tasmania, are at risk from more frequent heatwaves.

“A marine heatwave [in the Tasman Sea] similar in intensity to those in 2015–16 and 2017–18 is currently expected to occur approximately once every 20 years,” the report said.

“Under [a global] low-emissions scenario, it is expected to occur once every 15 years by the end of the century, and under the high-emissions scenario, a marine heatwave is projected to occur almost every year.”

Marine heatwave days per year
Source: The Earth Systems and Climate Change Hub

Thunderstorms were another area of interest, including how the number of danger so-called “pyrocumulonimbus” clouds formed out of bushfire plumes.

At least 35 of them were detected during Black Summer, increasing the risk of erratic winds on unpredictable fire behaviour and ignite new blazes ahead of the fire front, the report noted.

Cumulative observed number of fire-generated thunderstorms
Source: The Earth Systems and Climate Change Hub

East coast lows, another big weather event affecting coastal areas from Queensland to Victoria, were among phenomenon undergoing change.

The Hub developed new ways to analyse the complex storms and found the most extreme rainfall near eastern Australia was frequently caused by such low-pressure systems combining with a front and a thunderstorm.

The researchers found short-duration events produced by thunderstorms could potentially increase in intensity by about 15 per cent per degree of global warming.

A line of storms associated with an east coast low sweeping over the Hawkesbury River north of Sydney in July 2020. Credit: Nick Moir

Andy Pitman, head of the ARC Centre of Excellence for Climate Extremes and a Hub advisor, said east coast lows were “one of the least effectively studied phenomena in Australia” even though their impacts can be huge in terms of floods, storm surges and wind damage.

“I worry about how ill-prepared we are for any climate signal for east coast lows,” he said.

Drone vision of Lake Burrendong in the central-west region of NSW in January 2020 when water levels fell to a couple of per cent of capacity. Credit: Nick Moir

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At the other end of the weather spectrum was so-called flash droughts, another of the Hub’s research areas.

These are triggered by lower-than-average rainfall, accompanied by abnormally high temperatures, a dry atmosphere, clear skies and more sunshine, and can be perilous for crops.

The researchers showed the sudden dry spells could be forecast, and they can happen even in winter.

The outgoing Hub cost $23.4 million, with matching contributions from CSIRO, the Bureau of Meteorology and five universities including the University of Melbourne and the University of NSW.

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Its successor has been allocated federal funding of $38 million over six years.       

While welcomed, “we are not investing remotely enough given the scale of the risk”, Professor Pitman said, adding the new funding was “not even one year’s salary of a top soccer player”.

Simon Marsland, a CSIRO senior scientist who will lead the new Climate Systems Hub, said how communities could adapt to the warming impacts still to come will be one priority as will efforts to work closely with Indigenous populations that are often particularly exposed to extreme weather.

Dr Marsland noted the current record-shattering heatwave in Canada, with near 50-degree temperatures recorded even at a latitude as far as 50 degrees north, were “a good reminder that climate change is here now and not something in the far future”.

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