The role of carbon sequestration and the tonne-year approach in fulfilling the objective of climate convention

Abstract

Carbon can be sequestered from the atmosphere to forests in order to lower the atmospheric carbon dioxide concentration. Tonne-years of sequestered carbon have been suggested to be used as a measure of global warming impact for these projects of finite lifetimes. It is illustrated here by simplified example cases that the objective of the stabilisation of the atmospheric greenhouse gas concentrations expressed in the UN Climate convention and the tonne-year approach can be in contradiction. Tonne-years generated by the project can indicate that carbon sequestration helps in the mitigation of climate change even when the impact of the project on the CO₂ concentration is that concentration increases. Hence, the use of the tonne-years might waste resources of fulfilling the objective of the convention. The studied example cases are closely related to the IPCC estimates on global forestation potentials by 2050. It is also illustrated that the use of bioenergy from the reforested areas to replace fossil fuels can in the long term contribute more effectively to the control of carbon dioxide concentrations than permanent sequestration of carbon to forests. However, the estimated benefits depend on the time frame considered, whether we are interested in the decadal scale of controlling of the rate of climate change or in the centennial scale of controlling or halting the climate change.

Introduction

The ultimate objective of the United Nations’ Framework Convention on Climate Change (UNFCCC) is to stabilise the greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system (Article 2) (UNFCCC, 1992). Increased concentrations of greenhouse gases change the radiation energy balance of the Earth by hampering the transfer of infrared radiation from the Earth to space. This is assumed to lead to global warming. The perturbation of the radiation energy balance is called radiative forcing.

The Kyoto Protocol can be seen as the first step in the practical application of the UNFCCC. In the Protocol, the industrialised countries (listed in Annex B of the Protocol) commit themselves to percentual reductions in their anthropogenic greenhouse gas emissions (UNFCCC, 1998). In the control, several greenhouse gases are considered simultaneously; in addition to carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) some halocarbons (HFCs and PFCs) and sulfur hexafluoride (SF₆) are included. According to the Protocol text the carbon accounting includes provision for greenhouse gas sinks and sources of due to terrestrial ecosystems, but limited to the impacts of land use changes, caused by direct human induced afforestation, reforestation and deforestation activities (ARD), as well as some additional human induced activities.

In order to meet the reduction targets some additional mechanisms are allowed and these are referred to as international emission trading (IET), joint implementation (JI) and the clean development mechanism (CDM). The CDM permits projects implemented in the non-Annex B countries (developing countries) within the Protocol, and IET and JI enable co-operation between the Annex B countries on emissions reduction. JI and the CDM operate in principle at project level. Sinks are included in JI and CDM under certain limitations.

The practical application of the Kyoto Protocol including the definition of detailed accounting rules, baselines and method of verification is to some extent open and is to be agreed in the subsequent Conferences of the Parties (COP) to the UNFCCC. At present the proposed accounting principles are under lively discussion among scientists, governmental officials and various interest groups. One important contribution to this process is the Intergovernmental Panel on Climate Change (IPCC) special report on land use, land use change and forestry (LULUCF) accepted in May 2000 (IPCC, 2000a, IPCC, 2000b). Presently IPCC is preparing Good Practise Guidelines for the LULUCF sector, but the final decisions on the rules will be made under COP.

The method of inventory to account for emissions from fossil fuels is relatively straightforward, whereas the treatment of greenhouse gas sinks and in general the carbon balance of terrestrial ecosystems, as provided by the Articles of the Protocol, is a very complicated task especially if soil carbon is to be included. Detailed but pragmatic carbon accounting rules need to be developed. The accounting system has to meet various criteria concerning transparency, consistency, comparability, completeness, accuracy, verifiability, and efficiency (Gustavsson et al., 2000). One prerequisite for the accounting rules to be applicable is that they are simple enough. This is important particularly in the case of those Kyoto mechanisms, which will be implemented at project level; an example could be the potential forestation projects under CDM. Their transaction costs, e.g. due to delicate measurements and verification, could otherwise be so high that actually no project activities would be built up. An interesting and important aspect that needs to be considered when formulating these rules is the duration of projects aimed at carbon sequestration through afforestation and reforestation. It can be asked what is going to happen after finishing the project, who will take the responsibility of the carbon pool sequestered, when and how will the carbon sequestration be credited, and what is the overall impact on global warming if the pool is emitted back to the atmosphere. A requirement for permanent sequestration implies indefinite commitment periods, whereas practical projects are more likely to have a finite duration.

An accounting method known as the ‘tonne-year approach’ has been proposed with the apparent aim of promoting the positive contribution to carbon sequestration made by forestry projects of relatively short duration. The method has been given particular attention in the IPCC Special Report on LULUCF (IPCC, 2000a) and accounting methods based at least partly on the tonne-year approach have been described and advocated in the scientific literature (e.g. Marland et al., 1997, Chomitz, 1998, Fearnside, 1995, Fearnside et al., 2000, Tipper and de Jong, 1998, Moura-Costa and Wilson, 2000, Fearnside, 2002). In essence, the tonne-year approach involves giving credit for quantities of carbon stocks attributable to forestry projects for each year that the carbon stock is maintained. The very raison d’etre of the tonne-year approach is, therefore, to give credit to projects for carbon sequestered from the atmosphere for a finite period.

In this paper, we consider the tonne-year approach as a measure for greenhouse impact of carbon sequestration projects, and which consequences its application could have for the ultimate objective of the UNFCCC to stabilise greenhouse gas and particularly CO₂ concentrations in the atmosphere. Our analysis in the following shows that there can be a contradiction between the target of the concentration stabilisation and the incentives afforded by the tonne-year approach. For background information we consider in Section 3 also carbon cycle in general, and in Section 7, we compare the calculatory scenarios used in this paper with the IPCC (1996b) and IIASA/WEC (1998) carbon sequestration and bioenergy scenarios.