If the world continues on a “business-as-usual” trajectory on climate change, global ecosystems including Australia’s will undergo a “major transformation” over the next century.
That’s the warning from researchers who have analysed hundreds of pollen and fossil records from the Earth’s last period of significant global warming, which followed the last glacial maximum around 14,000 years ago.
The study, published today in the journal Science, found that ecosystems that underwent low levels of change were “concentrated in regions where the temperature anomaly was relatively small”.
The researchers used their data to predict the amount of future ecological upheaval that would occur under warming scenarios of 1.5 degrees, 2.4 degrees, 3 to 4 degrees and 5 degrees, by the end of the century.
They found that under a warming scenario of 1.5 degrees — the target set under the Paris Climate Agreement — the chance of “large” structural change to an ecosystem was generally less than 30 per cent, but rose significantly as temperatures increased.
The Intergovernmental Panel on Climate Change (IPCC) predicts that average global temperatures will rise by more than 4 degrees this century under a “business-as-usual” carbon emissions scenario.
Earlier this month, former prime minister Malcolm Turnbull succumbed to pressure to dump plans to legislate Australia’s Paris emissions targets.
Liberal backbencher Tony Abbott has recently been pushing for Australia to withdraw from the Paris Agreement despite signing Australia up when he was prime minister.
More than 40 scientists, including palaeoecology and climate expert Peter Kershaw from Monash University, analysed fossil and pollen records from nearly 600 sites around the world, including Australia, New Zealand and Oceania.
The international team used these records to indicate what types of vegetation existed in each region between 21,000 and 14,000 years ago.
For example, records made up solely of grasses indicate open grasslands, eucalypt and wattle pollen indicates sclerophyll forest and rainforest species are evidence of the existence of a rainforest.
They then compared these records with the vegetation composition and structure from the same sites in the Holocene (present) period.
“There’s only a few parts of the world that haven’t experienced these dramatic changes in vegetation and structure.”
But some places were more heavily impacted than others, according to the researchers.
“These changes were particularly evident … in southern South America, tropical and temperate southern Africa, the Indo-Pacific region, Australia, Oceania and New Zealand,” they state in the paper.
Business-as-usual scenario ‘basically unmanageable’
The early Holocene climate is estimated to be between 4 degrees and 7 degrees warmer than during the last period of glaciation.
While that warming took several thousand years, “business-as-usual” carbon emissions are projected to warm up our climate by a similar amount over the next century.
“These estimates are roughly comparable to the magnitude of warming that the Earth is projected to undergo in the next 100 to 150 years if greenhouse-gas emissions are not reduced substantially,” the researchers state in the paper.
They acknowledge that the study only focuses on temperature, and omits other potential variables.
Increased atmospheric CO2 for instance, may stimulate plant growth to an extent, and is likely to also contribute to ecosystem and vegetation changes in the future.
But despite this, their forecasts are likely to err on the conservative side, according to palaeoclimatology expert Kale Sniderman from the University of Melbourne, who was not involved with the research.
“There is not really an analogue for that in the palaeo record. But it means that basically all the vegetation will be strikingly out of equilibrium with the climate and you really could expect a lot of death — a lot of species to go extinct.”
Although some degree of warming is now locked into the future, the consequences are likely to be vastly different between a temperature rise of around 1.5 degrees, and some of the worst-case-scenario forecasts, according to Dr Sniderman.
“[This research] does try to quantify the difference in peril between those two situations, where one is maybe manageable on a global level, and the other is basically unmanageable,” he said.
“Small amounts of warming have a very different effect.”
Why is 1.5 degrees important?
Limiting warming to 1.5 degrees by the end of the century requires “aggressive emissions cutting”, which many countries are currently failing to achieve.
Australia’s greenhouse gas emissions rose in 2017 for the third consecutive year.
The Paris Climate Agreement target was based on extensive modelling of different temperature-rise scenarios.
The IPCC predict “very high risks with additional warming of 2 degrees Celsius, particularly Arctic sea-ice and coral-reef systems”.
But the effects of warming will not be uniformly distributed.
Southern and northern regions of Australia underwent the most change during the warming that followed the last glacial maximum, according to Professor Kershaw.
“During the Holocene at many sites you had an invasion of eucalypt and wet forest, and then you’ve got that changing into rainforest.”
However, he said, changes were less extreme around the sub-tropical latitudes.
Worldwide, research has shown that animal distribution is already changing.
In the wet tropics region of north Queensland, a number of species are contracting higher up isolated mountainsides, according to tropical biodiversity and climate researcher Stephen Williams.
“Things like ringtail possums, we used to see them at 600 metres, now we haven’t seen them at 600 metres for seven or eight years, and we can only find them now above 700 metres,” he told the ABC earlier this year.
Extinctions are likely to occur for endemic species in that region as their habitat constricts to mountaintops.
“Our models predict that we don’t really get any extinction until about one-and-a-half degrees, and that makes sense because anything that is here now has already survived one-and-a-half degrees in the past,” he said.
“The extinctions don’t really start to kick in until about 2 degrees, and then they start to accelerate rapidly beyond 2 degrees.”
This article was published by ABC News on the 31st of August 2018.
Nick Kilvert is the online environment reporter in the ABC RN science unit. You can follow him on Twitter at @nkilvert