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Carbon and Forests: The Big Picture

By Jerry Vanclay

Energy generated by burning forestry waste and other biomass sources should be recognised as renewable.

As Australia prepares to pay for its carbon emissions, the challenge is to ensure wise behavioural change rather than “game-playing”. There is a danger that advocates for forests will over-emphasise their capacity for carbon farming, to the detriment of the overall carbon balance.

The two major pools of carbon – in the biosphere and the geosphere – have very different characteristics in terms of cycle time, natural ebb and flow, and reversibility.

In the biosphere – trees, plants and soil – carbon cycles naturally. The volume of carbon cycled globally each year – largely associated with the Northern Hemisphere winter – is about ten times anthropogenic emissions. Trees grow for decades and sometimes centuries, eventually dying to release their carbon. Any carbon flows from the biosphere are reversible because new forests can be created efficiently.

Carbon in the geosphere – oil and coal – tends to remain sequestered for millennia unless it is unearthed by human activity, after which it permanently enters the biosphere. The alternative – commercial-scale geosequestration – is an aspiration rather than a reality. My view is that carbon capture and storage is the new perpetual motion machine: the idea that we can mine coal, burn it and bury the CO2 emissions underground with an efficiency better than a carbon tax is, at this stage, pure fantasy.

As we burn more fossil fuels each year, carbon stored in coal and oil is being dumped into the atmosphere at an unsustainable rate, and these fossil emissions remain irreversibly cycling between the atmosphere and the biosphere. The pool of carbon in the biosphere is relatively small compared with the geosphere, so we need to be cautious about our ability to sequester fossil emissions in plants.

However, as oceans take up about one-third of our carbon emissions and net uptake by plants and oceans represents two-thirds of anthropogenic emissions, a one-third reduction in fossil emissions would stop the problem from getting worse.

It is thus clear that we need to reduce fossil carbon emissions and source unavoidable energy needs from the biosphere rather than from the geosphere.

There are many ways to harvest energy from plants for heat and for fuel. Two age-old methods are burning wood for heat, and brewing alcohol from grain. The former is cosy at the cottage-scale but inconvenient at the industrial scale, and the latter is satisfying for human consumption but inefficient for energy production.

Most bioenergy crops are inefficient, either because they compete for agricultural land needed for food cropping and the energy harvest represents only a small part of plant production, or because the conversion pathway is inefficient.

Some of the most carbon-efficient pathways involve the conversion of biomass residues into energy, either directly into heat, electricity or diesel. Efficiency is gained because, typically, the biomass has already been transported to a central processing facility; because it utilises a residue that may otherwise go to waste; and because the conversion pathway is an efficient way to concentrate the energy density of the residue.

Sadly, current legislation in Australia does not recognise biomass residues as “renewable energy”, thus restricting their eligibility for a range of incentives. While these restrictions may originate from a desire to protect native forest, they may have the perverse outcome of hampering the efficiency of bioenergy, limiting potential reductions in carbon emissions and thus hastening climate change and threatening the forests they hope to assist.

While many people may lament the cutting of a single tree, such a harvest may create opportunities that far outweigh the value of the sacrificial tree. The challenge for policy-makers is to focus on the “big picture” and to create incentives that serve Australia best in the long run.

Jerry Vanclay is Professor of Sustainable Forestry and Head of the School of Environmental Science and Management at Southern Cross University, Lismore.