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?

News
news

Emergency call 'started off dumb, but got pretty serious'

Sport
Erik Lamela celebrates his goal
football

Argentinian scored 'rabona' wonder goal for Tottenham in Europa League – see it here

News
The cartoon produced by Bruce MacKinnon for the Halifax Chronicle-Herald on Thursday, showing the bronze soldiers of the war memorial in Ottawa welcoming Corporal Cirillo into their midst
news
News
peopleFox presenter gives her less than favourable view of women in politics
PROMOTED VIDEO
Voices
Funds raised from the sale of poppies help the members of the armed forces with financial difficulties
voicesLindsey German: The best way of protecting soldiers is to stop sending them into disastrous conflicts
News
The Edge and his wife, Morleigh Steinberg, at the Academy Awards in 2014
peopleGuitarist faces protests over plan to build mansions in Malibu
Property
One bedroom terraced house for sale, Richmond Avenue, Islington, London N1. On with Winkworths for £275,000.
property
Voices
Nigel Farage has backed DJ Mike Read's new Ukip song
voicesNigel Farage: Where is the Left’s outrage over the sexual abuse of girls in the North of England?
News
i100
Arts and Entertainment
Taylor Swift performs at the 2014 iHeart Radio Music Festival
musicReview: 1989's songs attempt to encapsulate dramatic emotional change in a few striking lines
News
Mario Balotelli has been accused of 'threateningly' telling a woman to stop photographing his Ferrari
peoplePolice investigate claim Balotelli acted 'threateningly' towards a woman photographing his Ferrari
Arts and Entertainment
Paul Anderson plays Arthur Shelby in Peaky Blinders series two
tvReview: Arthur Shelby Jr seems to be losing his mind as his younger brother lets him run riot in London
News
ebooksAn unforgettable anthology of contemporary reportage
Voices
Don’t try this at home: DIY has now fallen out of favour
voicesNick Harding, who never did know his awl from his elbow, is glad to see the back of it
Arts and Entertainment
Miranda Hart has called time on her award-winning BBC sitcom, Miranda
tv
Sport
Phil Jones (left) attempts to stop the progress of West Bromwich Albion’s James Morrison on Monday
Chelsea test can be the making of Jones and Rojo, writes Paul Scholes
Arts and Entertainment
Saw point: Bradley Cooper and Jennifer Lawrence in ‘Serena’
filmReview: Serena is a strangely dour and downbeat affair
Life and Style
The Zinger Double Down King, which is a bun-less burger released in Korea
food + drinkKFC unveils breadless meat beast
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

English Teacher

£4848 - £33600 per annum: Randstad Education Manchester Secondary: Outstanding...

Cover Supervisors/Teaching Assistants Secondary Schools in York

Negotiable: Randstad Education Leeds: Cover Supervisors/Long Term Teaching Ass...

Science Teacher

£20000 - £30000 per annum: Randstad Education Leeds: Secondary Science Teacher...

Cover Supervisor

£55 - £70 per day: Randstad Education Leeds: Cover Supervisors needed for seco...

Day In a Page

Wilko Johnson, now the bad news: musician splits with manager after police investigate assault claims

Wilko Johnson, now the bad news

Former Dr Feelgood splits with manager after police investigate assault claims
Mark Udall: The Democrat Senator with a fight on his hands ahead of the US midterm elections

Mark Udall: The Democrat Senator with a fight on his hands

The Senator for Colorado is for gay rights, for abortion rights – and in the Republicans’ sights as they threaten to take control of the Senate next month
New discoveries show more contact between far-flung prehistoric humans than had been thought

New discoveries show more contact between far-flung prehistoric humans than had been thought

Evidence found of contact between Easter Islanders and South America
Cerys Matthews reveals how her uncle taped 150 interviews for a biography of Dylan Thomas

Cerys Matthews on Dylan Thomas

The singer reveals how her uncle taped 150 interviews for a biography of the famous Welsh poet
DIY is not fun and we've finally realised this as a nation

Homebase closures: 'DIY is not fun'

Homebase has announced the closure of one in four of its stores. Nick Harding, who never did know his awl from his elbow, is glad to see the back of DIY
The Battle of the Five Armies: Air New Zealand releases new Hobbit-inspired in-flight video

Air New Zealand's wizard in-flight video

The airline has released a new Hobbit-inspired clip dubbed "The most epic safety video ever made"
Pumpkin spice is the flavour of the month - but can you stomach the sweetness?

Pumpkin spice is the flavour of the month

The combination of cinnamon, clove, nutmeg (and no actual pumpkin), now flavours everything from lattes to cream cheese in the US
11 best sonic skincare brushes

11 best sonic skincare brushes

Forget the flannel - take skincare to the next level by using your favourite cleanser with a sonic facial brush
Paul Scholes column: I'm not worried about Manchester United's defence - Chelsea test can be the making of Phil Jones and Marcos Rojo

Paul Scholes column

I'm not worried about Manchester United's defence - Chelsea test can be the making of Jones and Rojo
Frank Warren: Boxing has its problems but in all my time I've never seen a crooked fight

Frank Warren: Boxing has its problems but in all my time I've never seen a crooked fight

While other sports are stalked by corruption, we are an easy target for the critics
Jamie Roberts exclusive interview: 'I'm a man of my word – I'll stay in Paris'

Jamie Roberts: 'I'm a man of my word – I'll stay in Paris'

Wales centre says he’s not coming home but is looking to establish himself at Racing Métro
How could three tourists have been battered within an inch of their lives by a burglar in a plush London hotel?

A crime that reveals London's dark heart

How could three tourists have been battered within an inch of their lives by a burglar in a plush London hotel?
Meet 'Porridge' and 'Vampire': Chinese state TV is offering advice for citizens picking a Western moniker

Lost in translation: Western monikers

Chinese state TV is offering advice for citizens picking a Western moniker. Simon Usborne, who met a 'Porridge' and a 'Vampire' while in China, can see the problem
Handy hacks that make life easier: New book reveals how to rid your inbox of spam, protect your passwords and amplify your iPhone

Handy hacks that make life easier

New book reveals how to rid your email inbox of spam, protect your passwords and amplify your iPhone with a loo-roll
KidZania lets children try their hands at being a firefighter, doctor or factory worker for the day

KidZania: It's a small world

The new 'educational entertainment experience' in London's Shepherd's Bush will allow children to try out the jobs that are usually undertaken by adults, including firefighter, doctor or factory worker