Plants soaking up a third of carbon

by: Tom Arup

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    Australia's landscape soaked up a third of national carbon dioxide emissions from burning fossil fuels over the past two decades, a CSIRO assessment has found.

    The three-year study, published in the international journal Biogeosciences, examined the ability of the Australian landscape to absorb greenhouse gases, including how much carbon dioxide is lost and gained through the ''breathing'' of plants and soil under different climate conditions and as carbon dioxide levels rise.

    It found that between 1990 and 2011 Australian plants on average took up 2.2 billion tonnes of carbon dioxide a year.

The higher carbon dioxide levels in the atmosphere increased the growth and development of Australian plants by 15 per cent compared with pre-industrial levels, allowing the Australian landscape to soak up more gas.

    The study's lead author, Dr Vanessa Haverd, said that the ability of plants and soil to breathe in carbon dioxide from the atmosphere was expected to fall in the future as other factors kick in, such as nutrients and water becoming less readily available.

    The study also found that the amount of carbon soaked up by plants is extremely variable year on year, with the results heavily dependent on rainfall and fire conditions.

In wet years, the Australian landscape breathes in more carbon from the atmosphere than all of the total human-induced greenhouse gas emissions.

    But in dry years nearly the same amount is expelled back into the atmosphere.

    Dr. Haverd said the results would help scientists who were working on a global study trying to reconcile ''top up'' and ''bottom up'' estimates of global carbon budgets.

    She said ''top up'' estimates look at measurements of atmospheric concentrations of carbon dioxide. The ''bottom up'' estimates were a series of land and ocean-based assessments being undertaken over larger regions across the globe.

    ''And together they [the bottom-up studies] should be comparable to what we get from the global top-down estimate,'' she said.

     ''It is a different approach to evaluating the global carbon budget, or in other words the exchanges of carbon between the land surface, the ocean and the atmosphere.''