In a study titled, “Reaching Climate Objectives-Focussing on the Time Aspects of Bioenergy and Allocation Rules in the European Union’s Emission Trading System”, undertaken by scientists at the University of Gothenburg, efforts are being made to establish that using trees as biofuels can take a long time to achieve carbon dioxide neutrality.
Various biofuels have different time periods ranging from 2 years to 20 years in reaching carbon dioxide neutrality. However, using biofuels will affect the carbon stock in either in a positive or negative manner. Though biofuels, whose carbon emissions are compensated fast, affect the climate lesser, they take a long time to achieve that compensation. This factor is missed out by most countries. As an example, bioenergy emissions have not been given any focus by countries involved in the Kyoto Protocol.
According to Lars Zetterberg who has done a PhD on this topic, using tree stumps for the purpose of bioenergy has a lesser impact on the climate for a longer time period. However, in the short run, using stumps has a greater climate impact than natural gas. Therefore using log residues like branches and tops is ideal since it decreases carbon dioxide emissions both in the long and short run. If regulations and legislations regarding environment lay down conditions that environmental impact be calculated over a period of 20 years, then all biofuels that take a longer time might be considered to be non-renewable. The PhD paper also clearly lays out guidelines as to how the EU Emissions Trading System should be set up so that the use of carbon efficient fuels is encouraged.
Source: http://www.gu.se