Prehistoric polluters

Did early man turn the outback into a barren desert? Kate Ravilous meets the scientists scouring Australia for clues about climate change

Once upon a time, Australia had a lush, green interior where grazing animals roamed, shrubs grew and the rain fell. Then, about 55,000 years ago, man arrived and started hunting the animals and burning the vegetation; ultimately, he drove the rain away and turned Australia's interior into the harsh, red, desert landscape that we see today.

Once upon a time, Australia had a lush, green interior where grazing animals roamed, shrubs grew and the rain fell. Then, about 55,000 years ago, man arrived and started hunting the animals and burning the vegetation; ultimately, he drove the rain away and turned Australia's interior into the harsh, red, desert landscape that we see today.

There is no doubt that Australia's environment and climate has changed dramatically, but was man responsible? Gifford Miller, from the University of Colorado at Boulder, thinks so, and he and his colleagues have discovered convincing evidence to back up their theory.

The story starts at Lake Eyre, a huge salt flat covering one-sixth of Australia's landmass. Miller has been working with John Magee, of the Australian National University in Canberra, to drill down through the layers of mud, sand and salt at the site to uncover Lake Eyre's past. Going back 125,000 years, they have found that it used to be a vast freshwater lake, covering 35,000 square kilometres - an area the size of Taiwan. Rains used to swell the lake every year, following the patterns of the Australian monsoon. Then, about 14,000 years ago, "the monsoon stopped penetrating into the interior of Australia and Lake Eyre started to turn into a salt lake, like it is today," says Miller.

While he was looking for reasons as to why the monsoon could have failed, Miller discovered that the Australian environment had suffered other dramatic changes in the past. "About 50,000 years ago, some 60 different species of animal went extinct," he says. Miller's work focused on the demise of an ostrich-sized flightless bird called Genyornis newtoni. Measuring amino acids in the fossil eggshells of these birds and using radiocarbon dating, Miller and his colleagues found that Genyornis suddenly disappeared about 50,000 years ago. Meanwhile, other scientists have recorded that a host of other creatures, including a giant horned tortoise (the size of a small car) and a hippopotamus-sized relative of the wombat, were also snuffed out.

And animals were not the only ones to suffer. Pollen records suggest that many species of tree also vanished at this point. "Some of the most fire-sensitive plants, such as rainforest gymnosperms [plants whose seeds are not encased and thus protected from fire], disappear and never come back," says Miller. The evidence was circumstantial, but Miller became suspicious that all these sudden environmental changes were linked. He believes that early man may have pushed the natural balance too far by burning large areas of vegetation on a regular basis. The burning was probably used to hunt animals, promote new plant growth and exchange signals, but eventually it changed the environment irreparably. As well as burning plants and forcing animals to extinction, Miller thinks that man may be indirectly responsible for the monsoon failure - by removing the vegetation that sucked the rain into Australia's interior.

Miller and his colleagues have been looking at the link between Australia's vegetation and its climate, and using climate models to better understand the pattern of Australia's monsoons. Matching up pollen records with the Lake Eyre data has indicated that vegetation and climate used to be strongly linked. "Prior to 50,000 years ago, the vegetation beat to the same rhythm as the monsoon," says Miller. The lake data shows that Australia's monsoons followed precessional cycles, related to the tilting of the Earth as it spins on its axis. Over a 22,000-year period, the Australian monsoon swung from being a deluge to a drizzle and back again. Similarly, the vegetation swung from being dominated by lush rainforest to being made up of higher proportions of shrubby plants and grass, and back again.

"The earliest humans arrived in Australia about 55,000 years ago, at the tail end of one of the stronger monsoon periods. There would have been lots of animals and plenty of green plants," says Miller. But that didn't last. By 45,000 years ago, Lake Eyre sediments show that the monsoon entered its weaker phase and became more of a dribble. At the same time, the Earth entered an ice age, making the planet cold and dry. It wasn't until about 14,000 years ago that the ice retreated and the monsoon rains started again. But, unlike on previous occasions, the strong monsoon rains never returned to the Australian interior. "We would have expected the climate to stay quite dry until about 14,000 years ago, but then the heavy monsoon should have reappeared," says Miller. Instead, the Lake Eyre sediments show that the interior of Australia continued to remain dry.

Using general circulation models (GCMs - climate simulators), Miller and his colleagues have been testing how sensitive the Australian monsoon is to changes in vegetation. They have found that plants appear to be the key to holding on to monsoon rainfall. When the model is run with vegetation covering the Australian interior, it gets twice the rainfall compared with a model run with no vegetation. "The GCM suggests that rainfall in the interior would be about 600mm per year when trees and plants cover the ground, compared with about 300mm per year when the ground is bare," Miller says.

Vegetation is likely to be important because it helps to recycle the rain via evaporation and transpiration. "Plants collect moisture and hold onto it. Without any vegetation the rain either evaporates, or sinks into the ground and disappears," explains Miller. Trees also add "surface roughness" to a landscape, which is thought to promote convection and to encourage rain-cloud formation. If Australia's earliest human inhabitants burnt enough vegetation, Miller believes that this could have tipped the balance and prevented the monsoon rains from reaching the interior.

Today, northern Australia still receives an annual monsoon, dousing cities like Darwin with more than 1,600mm of rain a year. The GCM models have shown that Australia's monsoon is connected to the northern-hemisphere climate and the Asian monsoon. "Early man didn't have enough influence to affect the global monsoon pattern, but it appears that localised burning was enough to produce a continental-scale change in the water balance and climate," says Miller.

It is unlikely that we can turn the clock back for Australia. In principle, trees could be planted to entice the moisture back, but thousands of years of desert weathering has left Australian soil very low in nutrients, making it almost impossible for trees to get a grasp again. "Physics is working against us right now. Perhaps we could try planting in another 11,000 years, when we are in a strong monsoon period again," says Miller.

If Miller and his colleagues are right about Australia's past, it provides a sobering lesson. Rainforest is being felled all over the world at an unprecedented rate and ecosystems pushed way out of kilter. What kind of effect will this have on the world's climate? Are we leaving a legacy to future generations of desert landscapes and unpredictable rainfall?

Voices
On the last day of campaigning before the polling booths open, the SNP leader has written to voters in a final attempt to convince them to vote for independence
scotland decidesIs a huge gamble on oil keeping First Minister up at night?
Arts and Entertainment
Rosalind Buckland, the inspiration for Cider with Rosie died this week
booksBut what is it like to be the person who inspires a classic work of art?
Life and Style
techApple has just launched its latest mobile operating software – so what should you do first?
News
A male driver reverses his Vauxhall Astra from a tow truck
newsThe 'extremely dangerous' attempt to avoid being impounded has been heavily criticised
PROMOTED VIDEO
Arts and Entertainment
Lionel Messi in action for Barcelona
filmSo what makes the little man tick?
Arts and Entertainment
tvReview: An undercooked end (spoiler alert)
News
i100
News
ebooksAn unforgettable anthology of contemporary reportage
Arts and Entertainment
Pharrell dismissed the controversy surrounding
musicThe singer said 'the last thing I want to do is degrade'
Sport
Cesc Fabregas celebrates his first Chelsea goal
footballChelsea vs Schalke match report
Arts and Entertainment
Toby Jones (left) and Mackenzie Crook in BBC4’s new comedy The Detectorists
tvMackenzie Crook's 'Detectorists' makes the hobby look 'dysfunctional', they say
Life and Style
fashion

Olympic diver has made his modelling debut for Adidas

News
i100
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Maths Teacher

£110 - £200 per day: Randstad Education Leeds: Secondary Maths Teacher for spe...

Maths Teacher

£90 - £160 per day: Randstad Education Leeds: Secondary Science Teacher (mater...

Maths Teacher

£110 - £200 per day: Randstad Education Leeds: Secondary Maths Teacher for an ...

Maths Teacher

£22000 - £37000 per annum: Randstad Education Leeds: A West Yorkshire School i...

Day In a Page

Mystery of the Ground Zero wedding photo

A shot in the dark

Mystery of the wedding photo from Ground Zero
His life, the universe and everything

His life, the universe and everything

New biography sheds light on comic genius of Douglas Adams
Save us from small screen superheroes

Save us from small screen superheroes

Shows like Agents of S.H.I.E.L.D are little more than marketing tools
Reach for the skies

Reach for the skies

From pools to football pitches, rooftop living is looking up
These are the 12 best hotel spas in the UK

12 best hotel spas in the UK

Some hotels go all out on facilities; others stand out for the sheer quality of treatments
These Iranian-controlled Shia militias used to specialise in killing American soldiers. Now they are fighting Isis, backed up by US airstrikes

Widespread fear of Isis is producing strange bedfellows

Iranian-controlled Shia militias that used to kill American soldiers are now fighting Isis, helped by US airstrikes
Topshop goes part Athena poster, part last spring Prada

Topshop goes part Athena poster, part last spring Prada

Shoppers don't come to Topshop for the unique
How to make a Lego masterpiece

How to make a Lego masterpiece

Toy breaks out of the nursery and heads for the gallery
Meet the ‘Endies’ – city dwellers who are too poor to have fun

Meet the ‘Endies’ – city dwellers who are too poor to have fun

Urbanites are cursed with an acronym pointing to Employed but No Disposable Income or Savings
Paisley’s decision to make peace with IRA enemies might remind the Arabs of Sadat

Ian Paisley’s decision to make peace with his IRA enemies

His Save Ulster from Sodomy campaign would surely have been supported by many a Sunni imam
'She was a singer, a superstar, an addict, but to me, her mother, she is simply Amy'

'She was a singer, a superstar, an addict, but to me, her mother, she is simply Amy'

Exclusive extract from Janis Winehouse's poignant new memoir
Is this the role to win Cumberbatch an Oscar?

Is this the role to win Cumberbatch an Oscar?

The Imitation Game, film review
England and Roy Hodgson take a joint step towards redemption in Basel

England and Hodgson take a joint step towards redemption

Welbeck double puts England on the road to Euro 2016
Relatives fight over Vivian Maier’s rare photos

Relatives fight over Vivian Maier’s rare photos

Pictures removed from public view as courts decide ownership
‘Fashion has to be fun. It’s a big business, not a cure for cancer’

‘Fashion has to be fun. It’s a big business, not a cure for cancer’

Donatella Versace at New York Fashion Week