Claims that a “critical flaw” has been discovered in carbon accounting are somewhat exaggerated, and substantial bioenergy resources – subject to well-understood checks and balances- are available to tackle climate change, argue a group of scientists.
The full list of authors can be found at the end of this opinion piece.
Many expert scientists have studied the global carbon cycle over the past thirty years or more, reaching a high degree of consensus, so we feel weary every time a ‘new’ claim is made that diverting low-value forest products for bioenergy use will create a ‘carbon deficit’ or ‘carbon debt’ lasting decades or centuries, which does not fit the urgent timescale for mitigating climate change.
To reduce the facts to their most simplistic, if the carbon emitted by the use of bioenergy worldwide (together with emissions involved in its production, harvest, etc.) is less than the net photosynthetic production of its supply chain, then there is a net withdrawal of carbon from the atmosphere and hence no carbon debt.
The amount of carbon fixed annually worldwide as chemical energy in biomass is equivalent to between four and five times the world’s total primary energy consumption at present, so we are a long way off exceeding this limit. However, it is important to do this carbon accounting over appropriate time scales and spatial scales. This is a complex subject, and the fine details are not always apparent to campaigners and policy decision-makers alike.
It is misleading to focus upon the carbon emitted at the point of bioenergy use. In a well- managed system of forestry rotation, every tonne of biomass that is harvested and burnt will be balanced by a tonne of new biomass that is growing somewhere else nearby.
If we look at such an area of managed forest supplying a bioenergy power plant, and measure it on a timescale appropriate to forestry practice (e.g. 1–5 years), it is often found that the rate of harvest is at least equalled by the rate of regrowth.
Suitable data may be available from national forest inventories to assess whether overall standing biomass stocks are indeed static or increasing across a region.
Humanity has exploited the products of forests for centuries, sometimes well, sometimes poorly (as indeed was pointed out for 19th-century Europe), but more recent history has shown that large-scale construction timber and paper pulp production is able to co-exist with healthy forest carbon stocks, just as bioenergy can, both now and in the future.
Prof. Iain Donnison, Institute of Biological, Environmental & Rural Sciences, Aberystwyth University
Prof. Leif Gustavsson, Department of Built Environment and Energy Technology, Linnaeus University, Sweden
Dr. H. Martin Junginger, Professor of Bio-Based Economy, Utrecht University
Dr. Jonathan Scurlock, Visiting Fellow, The Open University
Prof. Nilay Shah, Department of Chemical Engineering, Imperial College London
Prof. Richard Templer, Grantham Institute for Climate Change and the Environment, Imperial College London
Dr Jeremy Woods, Senior Lecturer in Bioenergy, Imperial College London