Don’t count on trees to store CO2


A NSW program which allows carbon (C) stored by forests to be used to offset fossil fuel emissions may be increasing future atmospheric concentrations of carbon dioxide (C02), according to a Senior Research Fellow from the University of Sydney.

Forests do trap CO2, but for how long? Dr Charles Warren from the University of Sydney School of Biological Sciences says the fact that forests remove CO2 from the atmosphere and store it in wood and soil is not in contention; what is in contention is the definition and longevity of storage.

CO2 can return to atmosphere after 100 years: ‘In our lifetimes, and the 100-year window set by the NSW Greenhouse Gas Abatement Program, storage is real and quantifiable. But this isn’t the case when we consider what happens in our grandchildren’s lifetime. On time scales greater than 100 years much of the supposedly "stored" C will be released back to the atmosphere,’ said Warren.

Decomposing trees quickly release their carbon: He argues that the problem is that C stored in the forests can be released very easily (and rapidly) into the atmosphere. ‘Trees have finite life spans (e.g. hundreds of years for many Eucalyptus), and when they die and decompose "stored" C is quickly released back into the atmosphere.

Fires impact regrowth, future CO2 storage: In the absence of fire, regeneration and re-growth of many Eucalyptus ecosystems is negligible and the amount of biomass and stored C decreases in very old forests,’ he said. According to Warren fire makes "storage" risky and ephemeral, and this is especially the case in Australia. C stored in forests is always at risk of being lost by fire. It is neither feasible nor realistic to keep forested areas fire-free in perpetuity.

Can’t equate fossil fuel emissions and forest carbon: Trading fossil fuel emissions for C "stored" in forests is flawed, because the two are not equivalent. Forests are not stores but part of the actively cycling pool of C, whereas fossil fuels have life spans measured in millions of years.

Burning fossil fuels and planting trees increases CO2: ‘The net result of burning fossil fuels and then planting trees (to offset emissions) is that amount of carbon available in the active carbon pool (the atmosphere and forests) increases. The C in forests can be easily released back into the atmosphere, and thus it is possible that planted forests may contribute to increasing long-term atmospheric concentrations of C02 – the exact opposite of the intended effect,’ said Warren.

Reducing atmospheric CO2 means emission cuts: ‘The only way of reducing atmospheric concentrations of C02 is by reducing emissions or by sequestering C in perpetuity (e.g. geological storage).’

Reference: Media Release, 13 July 2006. For further information please contact the Media Office on Ph: +612 9351 4312 or 0421 617 861.

Erisk Net, 17/7/2006

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