Some of Australia's iconic and unique natural ecosystems may disappear for good
if we keep emitting carbon at current rates, climate experts warn.
on the effects of and adaptation to climate change, Australia can expect more
hotter days, fewer cold ones, more extreme fire weather, and heatwaves on land
and in oceans under 1.5 to 2C of global warming above pre-industrial
levels.
The world is currently at an average of about 1C of warming, and, exacerbated by
other human actions, this is already modifying Australian ecosystems, says
Griffith University climate and environmental scientist Brendan Mackey.
"We know how the climate has changed in the last 100 years in Australia, and we
have some evidence now for how ecosystems have been impacted by those changes."
Professor Mackey was a coordinating lead author for the Australasian chapter of
the IPCC report, which outlined nine key climate risks for the region.
Four of those risks focused on ecosystems at risk
of severe damage — or even collapse — under climate pressures.
So let's take a tour of the continent and have a look at what's at stake — and
they're not necessarily the ecosystems you might expect to see.
Up high in alpine regions
When we think of alpine regions, often the images that spring to mind might be
the snow-covered peaks of Europe or the Himalayas.
Though much lower, Australia's alpine regions host some of the most unique
biodiversity on the planet — mountain pygmy possums, corroboree frogs, spiny
crayfish, snow gums, and myriad plant species.
But the short stature of our mountains is their Achilles heel.
Many species have adapted to living in the cooler climes found on our
mountainsides above 1,000 metres or so.
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Mountain pygmy possums need snow cover to insulate them from the
freezing air while they hibernate over winter.
(Supplied: Victorian Department of Environment, Land, Water
and Planning)
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As the climate warms, those animal and plant species are forced to migrate
further and further up the mountains to find a suitable, cooler habitat.
But there's not very much further for them to go, according to Professor
Mackey.
"If you're in New Zealand, as you go up in elevation, they have real mountains
with pointy tops.
"In New Zealand, the alpine vegetation can potentially grow uphill a bit, and
any plants or animals that are dependent upon that habitat can go with it.
"But in Australia, the top of our alpine zone, there are no peaks above
it."
The IPCC singled out Australian alpine regions for special mention in the
latest report.
There's predicted to be a sharp increase in extinctions in these regions as
warming goes beyond 1.5C toward 2C.
On the latest predictions, we're
forecast to hit 1.5C around 2030.
In Australia's tropical north, species have already been observed pushing
further up mountains, according to Steven Williams from James Cook University.
"The lowland species are moving into the midlands, the midlands species are
declining," Professor Williams said.
"A lot of the endemic [bird] species … most of them have already declined by
up to 30 per cent, some to 60 per cent."
For mammal species like possums, he said it seemed to be the increase in
extremely hot days that had been doing the most damage.
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Green ringtail possums are already declining in the Queensland
wet tropics.
(Getty Images: Auscape)
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"The ring-tailed possums endemic to the area have already declined by 50 per
cent," he said.
"Two other species are declining badly.
"The paper that we’re about to bring out on the possum shows that most of the
possum species will be in really serious trouble by 2050.
"Some of the birds, based on their observed decline so far in the last
10 years, would be in similar deep s*** by 2040-2050."
But so far Australia's southern alpine regions are yet to feel the real brunt
of climate change, according to Ary Hoffman from the University of Melbourne.
Mt Buller's mountain pygmy possum population appears to be healthy, for
instance.
Its key threat today, according to Professor Mackey, is logging.
In the southern alpine regions more generally, Professor Hoffman said the
biggest threat right now is from weeds and ferals like the wild brumbies.
But the changes will come, he said.
"There is no doubt about it. There are plants you only find in snow patches,
and they will disappear," Professor Hoffman said.
"Animals associated with the wetlands and the bogs will start disappearing;
frog species like the corroboree frog and Baw Baw frog, they’ll be in
trouble."
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The southern corroboree frog is critically endangered, with fewer
than 200 wild individuals left.
(Taronga Zoo: Michael McFadden)
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But he said it's the unexpected interactions between species that create the
most uncertainty.
Scientists suspect warmer temperatures and longer drought in the Australian
alps are responsible for a boom in longicorn beetles, for instance.
The beetles in turn are causing an extensive and sudden dieback in our snow
gums — trees a few hundred years old have been dying en masse as they're
essentially ringbarked by the beetles.
"That's the problem with climate change — you get these unexpected things
happening," Professor Hoffman said.
The race to save five Australian species from extinction 29min 35sec
Some forests on land …
Speaking of snow gums, forests of southern and south-west Australia were also
singled out as Australian ecosystems at risk of the one-two punch of climate
change and human mismanagement.
But not the eucalypt forests of Victoria and NSW that were decimated in the
2019-20 bushfires … at least not immediately.
That's mainly because those trees are known as "sprouters", and store tiny
buds under trunk and branch bark which are ready to grow out as green shoots
should a fire go through the area, Professor Mackey said.
"So most of our native eucalypt forest is well adapted to wildfires."
The forests at risk are of towering jarrah and mountain ash, found in the
continent's south-west and south-east corners respectively, as well as gnarled
snow gum woodland and Tasmania's pencil pines.
And each is affected slightly differently by a warming world.
In southern Western Australia, winter rainfall would normally replenish
underground reserves of water, which the deep roots of jarrah trees tap into
to keep going over summer.
But regional winter rainfall has steadily dropped over the past 30 years, and
their subterranean reservoirs haven't been topped up as much.
On the other side of the country,
mountain ash trees are
"seeders". Older trees can cope with intense bushfires, but seedlings must
grow for around 20 years before they can reproduce.
"So if you start getting catastrophic wildfires more than two to three times
every 10 years, that's faster than it takes the ash forest to grow," Professor
Mackey said.
"And if you have a commercial logging regime that's keeping ash forest at a
young age — so rather than letting the trees grow to be 400 years old, you're
harvesting them between 48 years old and 46 years old — they're younger trees,
they're more vulnerable, and they're more likely to be killed by fire.
"The more of these catastrophic fires we have, the more we risk going
into a downward spiral."
More fires, more often, affect snow gums in a similar way. These trees
resprout from the base, where they keep a stock of starches and sugars for
this purpose.
"But if you increase the frequency of catastrophic fire events ... and snow
gums get hit too often, they don't have time to replenish the energy stock
they use to regenerate," Professor Mackey said.
Pencil pines (Athrotaxis cupressoides) can live for 1,300 years.
(Getty Images: Ted Mead)
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And Tasmania's ancient pencil pines haven't had to deal with catastrophic
fires — until recently.
Bushfires in 2016 razed swathes of pencil pine forest, and even six years on,
large areas are not recovering well, Professor Mackey said.
"If it got hit by another extreme wildfire event like that, it's going
to be in very serious trouble."
So what would happen if these forests disappeared?
They wouldn't leave a barren plain. Rather, a different type of forest would
grow in its place.
For instance, if snow gums disappeared, they might be replaced by woody shrubs
that can regenerate after fire quickly — something that's already happening in
parts of the country.
And this, Professor Mackey says, results in an overall loss of biodiversity.
"You lose something that was particular to a local environmental condition,
and it's replaced by something which is more common elsewhere."
… and forests beneath the waves
When Gretta Pecl started diving in the kelp forests off the east coast of
Tasmania in the mid-1990s, towering stands of giant kelp stretched from seabed
to surface.
"By around 2005, I started noticing changes," said Professor Pecl, now a
marine ecologist at the University of Tasmania and a lead author on the
Australasian chapter of the IPCC report.
Different and diminutive kelp species started moving in while the long ropey
strands of giant kelp dwindled.
"And when you consider the kinds of [kelp] habitats and systems that we had in
the late 90s and early 2000s to what we've got now, they actually look like
two different ecosystems."
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Tasmania's giant kelp (Macrocystis pyrifera) forests have
declined by more than 90 per cent since the 1960s.
(Getty Images: Nigel Marsh)
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Indeed, the IPCC report states "less than 10 per cent of giant kelp in
Tasmania was remaining by 2011 due to ocean warming".
The loss of kelp forests in southern Australia and south-east New Zealand —
highlighted as a key risk — is already severe, Professor Pecl said.
"But it could be reduced substantially by rapid, large-scale and effective
mitigation and adaptation strategies", such as transplanting more
heat-tolerant types.
So what happened to the once-dominant kelp forests?
Giant kelp is sensitive to temperature and thrives in the cold, nutrient-rich
water that laps at the Tasmanian coastline.
But on the east coast, this has been replaced by water that's warmer and
comparatively devoid of nutrients.
This warm water is shuttled down by the East Australian Current, which has
moved 350 kilometres south since the middle of last century, Professor Pecl
said.
"That extension of the East Australian Current, as shown in the working group
1 IPCC report, is largely driven by warming over the Pacific."
This underlying ocean warming is separate to marine heatwaves — days-long
bursts of particularly warm seawater.
Kelp must also contend with overgrazing by nibbling fish and sea urchins that
are moving southward with the East Australian Current.
"They literally eat kelp out of house and home," Professor Pecl said.
"We know that at the global level, around half of plants and animals,
including marine species, are moving poleward … and changing where they live
now as a function of climate.
"Effectively everything is moving at the same time, but at different rates.
"Connections are being broken apart and new connections are being formed … and
the kelp forests around Australia are a victim of that."
But worst affected will be coral reefs
By now we've all heard how climate change is going to kill a lot of coral.
We've already seen several mass bleaching events on the Great Barrier Reef
since 2016.
According to the latest report, we're expecting to see bleaching conditions on
the reef at least once every five years by 2035, even if we aggressively cut
emissions from today.
That's likely to increase to every year by around 2050.
Without long periods in between bleaching events for the coral to recover,
mass mortality is a near certainty.
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In March 2020, the Great Barrier Reef endured its third mass
bleaching event in only five years.
(Supplied: Victor Huertas)
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At 1.5C of warming, the IPCC predicts we'll lose between 70 to 90 per cent of
coral diversity. At 2C, that rises to more than 99 per cent.
But the problem is far bigger than losing pretty corals. The corals are merely
one part of a massive food web that provides nutrients for marine species well
beyond the reef itself, according to Scott Heron from James Cook University.
"Coral reefs cover less than one-tenth of 1 per cent of the ocean floor," Dr
Heron said.
"But they support more than 25 per cent of oceanic fish species.
"When we talk about punching above weight, corals are really punching
above weight."
Losing 90 per cent or more of coral species is going to have a profound effect
on fish abundance, including on many of the commercial fish species that we
rely on.
Then there is the physical buffering that reefs provide our coastlines.
Reefs help dissipate wave action, sheltering our coastal communities from the
worst impacts of storms and cyclones.
"That's all the more important in an era where we're seeing storm intensity
increase," Dr Heron said.
"We're not necessarily seeing more tropical cyclones, but we're seeing more
severe tropical cyclones."
Despite the dire predictions for our reefs, Dr Heron says he thinks they're
still worth fighting for, and that we need to make an equitable and rapid
transition from greenhouse-gas-emitting technologies.
"The number of options and ideas that we have available to us are rapidly
diminishing," he said.
"The question is: what are we doing this decade so that we minimise the
impacts?"
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