Posted in Emissions

Burn bush, reduce emissions: evaluating costs and benefits of prescribed burning

By Matthias Boer, University of Western Sydney and Ross Bradstock, University of Wollongong

Bushfires are, together with cyclones and flooding, among the most important natural hazards affecting Australian communities. They also make a significant contribution to Australia’s greenhouse gas emissions.

Australia has bushfires because of our inherently flammable vegetation types, the recurrence of severe droughts, and a high incidence of hot, dry weather conditions.

Management agencies cannot control climate and weather. Consequently, fire hazard reduction focuses primarily on reducing bushland fuel.

Starting fires to stop fires

In most of Australia’s fire-prone environments, “burning off” – more formally known as prescribed, or fuel-reduction burning – is the preferred method to reduce the density and spatial continuity of fuels.

By burning under controlled conditions, fuel loads can be reduced over large areas at relatively low cost. These burns generally target the understorey vegetation and surface litter, while aiming for minimum damage to overstorey trees.

Depending on the type of fuel, its accumulation rate and the intensity of the burn, fuel loads may take months to decades after a burn to recover to pre-treatment levels. If the fuel accumulation rate is high, burns need to happen frequently to keep fuel down to acceptable levels.

When fuel loads are relatively low, bushfires are generally less intense. This provides more opportunities to suppress the fires and reduce the severity of their ecological impacts.

However, when weather conditions are severe, differences in fire behaviour between treated and untreated areas can become negligible or irrelevant, as seen during the 2009 bushfires in Victoria.

Besides hazard reduction, prescribed burning is carried out to meet objectives such as biodiversity conservation, forest regeneration or management of water resources. These objectives require different frequencies, intensities, sizes, or seasons of fire to hazard reduction.

There are other ways of reducing bushland fuel. But methods such as mowing, thinning, or chaining tend to be used only in small areas (such as roadsides), where prescribed burning is deemed either too dangerous, expensive or undesirable (for example, because of smoke pollution).

Releasing emissions to prevent emissions

Burning biomass inevitably releases CO₂, CH₄, N₂O and other greenhouse gases (GHG) to the atmosphere. Emissions from vegetation fires account for about 3% of global GHG emissions.

Bushfires in Australia burn over 500,000 km² annually, mainly in the northern half of the country. They account for about 6-8% of global fire emissions and contribute significantly (about 3%) to the nation’s net GHG emissions.

So can prescribed burning help reduce carbon emissions from fire-prone environments?

jarrah forest
Prescribed burning has been used for over 50 years to manage fuel loads in Western Australia’s jarrah forests (Cristina Ramalho)

Recent studies from North America and Europe claim that prescribed burning could produce major reductions in emissions from forest fires.

These claims need to be evaluated for Australia. Our initial assessment suggests there is good potential for mitigating carbon emissions with prescribed burning in tropical savannas, but probably little or no such potential in temperate forests of southern Australia. This is because there are fundamental differences in fuel dynamics and fire behaviour between the two environments.

Prescribed burning will only reduce carbon emissions from a landscape if it reduces the extent of unplanned fire and if it burns less fuel per hectare than an unplanned fire would.

Good potential for the savanna, uncertainties for the forest

Analysis of historical fire records shows that prescribed burning does much more to reduce unplanned fires in tropical savannas than it does in temperate forests.

In the tropical savannas, every hectare of prescribed burning yields about one hectare reduction in the extent of wildfires, on average.

Planned savanna fires also burn less fuel than wildfires would in the same area. They are usually conducted early in the dry season, when fuels are moist, while unplanned fires are more frequent later in the dry season when fuels have thoroughly dried-out.

The feasibility of mitigating carbon emissions from flammable tropical savannas through prescribed burning is already being demonstrated in the West Arnhem Land Fire Abatement Project.

In the forested regions of southern Australia prescribed burning is less effective in mitigating unplanned fire. To get a hectare less of wildfire you have to burn three to four hectares with prescribed fire.

To reduce emissions under these circumstances, fuel consumption rates of planned fires have to be a very small fraction of those of unplanned fires.

So far, we can’t tell whether that’s the case, though future research should produce the numbers to make that call.

Matthias Boer received funding from The Bushfire Cooperative Research Centre and The Australian Research Council

Ross Bradstock receives funding from the ARC.

The Conversation

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Does the Chinese emissions ‘error’ matter?

By John ED Barker, Murdoch University

Recent analyses that China’s carbon dioxide (CO₂) emissions might be 1.2 gigatonnes or 20% higher than previously estimated have generated something of a feeding frenzy in the media; and not just the daily tabloids. Even The Scientific American has jumped on the bandwagon, adding a few more factoids to increase the alarm.

It is understandable that we could be alarmed by a figure of 1.2 gigatonnes; that’s a mighty big figure. It’s equivalent to the total of Japan’s annual emissions, the SMH repeated, without providing the more useful fact for its readers that it is also about three times all of Australia’s annual emissions.

It reminds me of the caption of a famous Punch cartoon, after it was announced that the postwar census of elephants in Burma suggested that many thousands were missing: “are you sure you’ve looked everywhere?”.

Three questions come quickly to mind: Is it true? If so, why? If so, so what?

First, is it true? The original Nature article is an impressively detailed analysis, which finds the discrepancy between the aggregate (national) Chinese emissions and that of the 30 provinces. According to Guan et al, energy accounting is poor in China, particularly in the myriad of small enterprises in the provinces.

Very few people would be in a position to corroborate the analysis; however, Professor Wang Yi, director of the Climate Change Research Centre of the Chinese Academy of Sciences in Beijing has immediately counter-claimed that the official figures may be overstated by 10-20%. He claims that the authors of the Nature article have not taken into account the differing calorific content of the different grades of coal used across China.

This is understandable; the energy content of coal can vary from less than 10MJ/kg for wet brown coal (lignite) to almost 40 MJ/kg for dry, clean anthracite. Australians are very familiar with this situation when Victorian coal is compared with Queensland coal. China is a mix of all of these types. So a familiar situation is emerging; dispute between experts in the light of inadequate data.

Even if the Guan analysis is correct, does it matter? It does, to the extent that if emissions abatement is attempted in China via a carbon tax, then the figures would be skewed and there would be free-riders. But this is no different to Australia, where the Gillard government is only going to tax the top 500 (or so) carbon emitters. The whole abatement business is very approximate, so a 10-20% error is not significant.

On a global scale, the “error” of 1.2 GT or 20% of China’s emissions is not as impressive as the media announcements make it out to be. China emits about 24% of the global total, so even taking the top end estimate of a 20% “error”, China would be emitting about 28% of the total; that is, another 4% of the global total. In perspective, China’s emissions are increasing at an annual rate similar to this; possibly 5-8%. So the “error” amounts to an adjustment of perhaps several years; meaning China is emitting at a rate now that we thought that they would be emitting perhaps two years hence.

So what is the fuss about? Certainly, accurate data is always desirable, but does it change anything? China is leading the world in most areas of renewable energy manufacture and is rapidly increasing its domestic use. Its energy intensity is dropping dramatically.

I suspect that the media attention paid to the Guan et al paper is partly justified; we need to get the numbers right. But it is also partly due to what I see is a persistent inclination by the media to portray China and its achievements as lacking credibility. For example; China announces its quarterly economic outcomes quicker than the ABS and each quarter our pundits disparage their data, only to find year-on-year the data is as good as ours (is the ABS disparaged for its quarterly revisions?).

But as always, as soon as the buzz-words of “gigatonnes” and “Chinese error” are splashed across the media, the caravan moves on, leaving The Conversation to try to make some sense from it all.

John Barker has no direct connection with any organisation mentioned in this article.

The Conversation

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