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Desertification: Australia


251 - Earth's Tree News


39) Major new research has found a direct link between land-clearing and climate change, and that land clearing triggers hotter droughts. Areas throughout southern Queensland cleared of native vegetation were found to have lost 12 percent of their summer rainfall and to have experienced an average 2C rise in temperatures. The study found that land clearing was just as significant in terms of climate change as greenhouse gas production from fossil fuels. Should these findings hold up and are found to be generalized throughout Australia and other areas globally clearing remaining natural vegetation, it would suggest a major revision in climate change policy-making is due. It is not enough to just focus upon greenhouse gas emissions, but maintaining natural vegetation through preservation, conservation and restoration may be an equally important policy response if global heating is to stopped. While reducing industrial emissions is critically important, we must also stop deforestation, which accounts for roughly 20 percent of all global emissions. Brazil's Amazon, for example, contains 70 billion tons of carbon, but activities such as cutting and burning make Brazil one of the largest carbon dioxide emitters in the world.



Sydney Morning Herald
March 4, 2005

Fewer trees, less rain: study uncovers deforestation equation
By Richard Macey

Australian scientists say they have found proof that cutting down forests reduces rainfall.

The finding, independent of previous anecdotal evidence and computer modelling, uses physics and chemistry to show how the climate changes when forests are lost.

Ann Henderson-Sellers, director of environment at the Australian Nuclear Science and Technology Organisation, at Lucas Heights, and Dr Kendal McGuffie, from the University of Technology, Sydney, made the discovery by analysing variations in the molecular structure of rain along the Amazon River.

Not all water, Professor Henderson-Sellers said, was made from the recipe of two atoms of "common" hydrogen and one of "regular" oxygen.

About one in every 500 water molecules had its second hydrogen atom replaced by a heavier version called deuterium. And one in every 6500 molecules included a heavy version of the oxygen atom.

Knowing the ratio allowed scientists to trace the Amazon's water as it flowed into the Atlantic, evaporated, blew back inland with the trade winds to fall again as rain, and finally returned to the river.

"It's as if the water was tagged," she said.

While the heavier water molecules were slower to evaporate from rivers and groundwater, they were readily given off by the leaves of plants and trees, through transpiration.

"Transpiration pumps these heavy guys back into the atmosphere."

But the study showed that since the 1970s the ratio of the heavy molecules found in rain over the Amazon and the Andes had declined significantly.

The only possible explanation was that they were no longer being returned to the atmosphere to fall again as rain because the vegetation was disappearing. "With many trees now gone and the forest degraded, the moisture that reaches the Andes has clearly lost the heavy isotopes that used to be recycled so effectively," Professor Henderson-Sellers said.

Tom Lyons, professor of environmental sciences at Perth's Murdoch University, said there was now "certainly very strong evidence that changes in surface conditions have an impact on the climate. In some parts of the world the impact is very marked". The Amazon research "helps us understand the mechanism".

Professor Henderson-Sellers said the average water molecule fell as rain and re-evaporated fives times during its journey from the tropical Atlantic to the river's starting point in the Andes mountains. Forests played a vital role in keeping the heavy molecules, and their far more common relatives, moving through the water cycle.

"People will tell you that when you remove the forests it rains less," she said, adding, however, such anecdotal evidence, and even computer modelling, did not convince everyone.

"This is the first demonstration that deforestation has an observable impact on rainfall."

Copyright (c) 2005. The Sydney Morning Herald.

Native trees key to cooling climate
Dani Cooper
ABC Science Online

Tuesday, 30 October 2007

Extensive clearing of native trees is making Australian droughts hotter and is an under-recognised factor in climate change, research shows.

The study by researchers from the University of Queensland and Queensland's Department of Natural Resources and Water shows that land clearing made the 2002-3 drought in eastern Australia 2°C hotter.

The research, published online in the journal Geophysical Research Letters, also found average summer rainfall has decreased by between 4-12% in eastern Australia and by 4-8% in southwest Western Australia because of land clearing.

These are historically the regions in Australia that have been most extensively cleared of native vegetation.

Dr Clive McAlpine, of the university's Centre for Remote Sensing and Spatial Information Science, says about 13% of the Australian continent has been cleared of native vegetation since European settlement in 1788.

However, in many agricultural areas in eastern Australia and southwest Western Australia more than 90% of native vegetation has been cleared.

"This study is showing Australian climate is sensitive to land clearing," he says.

"And our findings highlight that it is too simplistic to attribute climate change purely to greenhouse gases.

"Protection and restoration of Australia's native vegetation needs to be a critical consideration in mitigating climate change."

What's the impact?

Dr McAlpine says the research used the same modelling system as the UN's Intergovernmental Panel on Climate Change to determine the impact of land clearing.

It simulated climate scenarios for the country using data on pre-European settlement vegetation coverage and 1990 vegetation coverage for Australia.

This showed more than 150 years of land clearing had added significantly to the warming and drying of eastern Australia.

He says native vegetation plays an important role in moderating climate because it is deep rooted, which leads to more moisture evaporating into the atmosphere over a longer period.

This is then recycled into the environment as rainfall.

Native vegetation also reflects less short-wave solar radiation into the atmosphere than crops, which keeps the surface temperature cooler and helps in cloud formation.

Looking to the future

McAlpine says the findings should help in the development of policies to deal with the effects of climate change.

"The first thing is we need to protect what vegetation remains," he says.

"We also need to carefully consider in regions such as Queensland where there is a lot of regrowth how we protect that so we are not leaving the landscape vulnerable.

"And we need initiatives in southern Australia to restore native vegetation."