Australia's first full carbon budget assessment, presented at an ecosystem research symposium in Canberra on Wednesday, looked at carbon production and reduction in Australia over the past two decades and compared them with the past 100 years.

It found Australia exported two and a half times more carbon in fossil fuels in 2009-2010 than it caused by burning fossil fuels within the country.

The landscape had absorbed one third of carbon produced by burning fossil fuels in Australia over the past 20 years.

Lead author Dr Vanessa Haverd said in wet regions of Australia, plants absorbed carbon, while in temperate regions where conditions had been dry, including in Canberra, plants were breathing carbon out.

But increased carbon production from burning fossil fuels was also fuelling plant growth, which in turn helped to offset the amount of carbon in the atmosphere, in a process called the CO2 fertilisation effect.

The fertilisation effect was overriding the negative impact of drier conditions on the level of carbon in the atmosphere.

''We'd be in far worse shape if ecosystems weren't providing that service, but that doesn't mean that we're not creating serious consequences by continuing to emit high amounts of carbon into the atmosphere,'' she said.

The study, funded through the Australian Climate Change Science Program, found about 2.2 billion tonnes of carbon was taken up by plants each year in Australia over the past two decades and more carbon was absorbed by dry and grassy regions than woody regions.

The study considered the impact of fire on the level of carbon in the atmosphere, and found there were both positive and negative results.

Fires across Australia produced a similar volume of carbon emissions to the burning of fossil fuels, but the net impact of fires on the amount of carbon in the atmosphere was a lot less, because fires burned fuel that would have eventually decomposed and released carbon anyway.

After fires there is also significant regrowth of plants, which in turn absorbed carbon.

''Although the gross blocks of fire in the atmosphere due to fire is very large, the net impact is relatively small, but that's not to say it's not important,'' Dr Haverd said.

Dr Haverd said that the study helped understand how the Australian landscape stored carbon as the climate went through droughts and floods.

''We expect these sorts of numbers is what should go into informing good policy and indeed should inform any actions aimed at reducing Australia's contribution to global carbon emissions,'' she said.

She said future work would look at the impact of changing intensities of fires in Australia on the carbon budget.