The role of land carbon sinks in mitigating global climate change Policy document 10/01 July 2001 ISBN 0 85403 561 3 This report can be found at www.royalsoc.ac.uk Foreword Professor David Read, FRS Chair of the Royal Society working group on land carbon sinks As evidence for the link between atmospheric greenhouse gases and climate change has increased, international efforts have focused on ways in which anthropogenic emissions of greenhouse gases, particularly carbon dioxide, can be reduced. However attempts to commit countries to reduce their emissions though ratification of the 1997 Kyoto Protocol have been hampered by disagreement about the extent to which land carbon sinks should be considered in meeting these reduction commitments. In this report we have examined some of the scientific issues underpinning land carbon sinks that Professor David Read FRS Chair of working group have been of concern to policy makers. Throughout we have drawn extensively on the work of the Intergovernmental Panel on Climate Change, the world’s most reliable source of information on climate change. It is clear to us that the potential to enhance the land carbon sink through changes in land management practices is finite both in size and duration. Further, the amount of carbon that can be sequestered is small in relation to the ever-increasing global emissions of greenhouse gases. It is of concern to us that measurement techniques currently available are not sufficiently accurate to permit the reliable monitoring of any land carbon sinks that may be designated as part of international agreements such as the Kyoto Protocol. We conclude that projects designed to enhance land carbon sinks should not be allowed to divert financial and political resources away from long-term solutions to the problem of reducing the concentration of greenhouse gases in the atmosphere by reduction in the use of fossil fuels. I thank the other members of the working group who have worked extremely hard to complete this report in such a short period of time. We owe a particular debt of gratitude to Rachel Quinn (Royal Society, Secretariat) who has provided support and inspiration throughout the project. Sir Robert May, President There is increasing consensus on the science underpinning predictions of global climate change. Our current knowledge suggests that temperatures will continue to rise, with average global surface temperature projected to increase by between 1.4 and 5.8 oC above 1990 levels by 2100. This increase will be accompanied by rising sea levels, more intense precipitation events in some countries, increased risk of drought in others, and adverse effects on agriculture, health and water resources. It is now evident that human activities are already contributing adversely to this global climate change. The Royal Society has been an active participant in the debate about the science of climate Sir Robert May AC PRS President, Royal Society change and has provided advice on energy policy measures that would ensure that energy supply can meet global demand whilst being economically affordable and sustainable in terms of its global and local environmental impact1,2,3. This report on land carbon sinks is a further contribution to the global discussion on climate change policy and we will continue to facilitate dialogue between scientists and policy makers in this area by convening a major meeting later this year to discuss the current state of knowledge of the science underpinning climate change and what further work must be done in this vital area to ensure that the gaps in our knowledge are reduced. I am grateful to Professor David Read, the other members of the working group and the secretariat for the very considerable effort that has gone into this report. I commend this report to policy makers so that future policy at a global and local level may be based on sound scientific knowledge. It will also be of interest to anyone who is concerned about the issue of climate change and the steps that must be taken to mitigate its effects. Cover picture: An image of the fraction of photosynthetically-active radiation absorbed by land and the concentration of chlorophyll in the sea for June 1998. This image has been produced using data from the Sea-viewing Wide Field-of-View Sensor (SeaWiFS). Such data are used to estimate the size and strength of the land carbon sink. SeaWiFS data are provided by NASA’s Goddard Space Flight Center, Maryland, USA and processed at the Space Applications Institute of the European Commission Joint Research Centre. We thank Frederic Melin, Nadine Gobron, Bernard Pinty, Ruggero Tacchi and Michel M. Verstraete for providing this image. The role of land carbon sinks in mitigating global climate change The role of land carbon sinks in mitigating global climate change Contents page Preparation of this report v Summary vii 1 Introduction 1 2 Global carbon stocks and sinks on land 3 2.1 Carbon stocks 3 2.2 Annual exchange of carbon with the atmosphere 3 2.3 Current perturbation of the carbon cycle 3 3 The current land carbon sink 5 3.1 Factors affecting the land carbon balance 5 3.2 Evidence for the existing carbon sink 6 4 Scope for human enhancement of land carbon sinks 7 4.1 Global estimates of the potential of land carbon sinks 7 4.2 Role of forestry in protecting and enhancing the land carbon sink 7 4.3 Role of agriculture in mitigating climate change 8 4.4 Putting land carbon sinks in perspective 9 5 Quantifying direct enhancement of land carbon sinks 11 5.1 Requirements of the Kyoto Protocol 11 5.2 Methods of quantifying and monitoring land carbon sinks 11 5.3 Measuring trace greenhouse gases 12 5.4 Wider issues 13 6 The future land carbon sink and its permanence 15 6.1 Modelling the land carbon sink 15 6.2 Results from dynamic global vegetation models 15 6.3 Results from coupled climate-carbon cycle models 16 6.4 Common conclusions and key uncertainties from climate modelling 16 7 Conclusions 17 8 References & Notes 19 Annex 1 Land carbon sinks and the international climate change process 23 1.1 Overview of the Framework Convention on Climate Change and the Kyoto Protocol 23 1.2 Issues raised by the inclusion of land carbon sinks in the Kyoto Protocol 23 Annex 2 Examples of management activities to maximise carbon sequestration 25 2.1 Carbon Offset Project in Noel Kempff National Park, Bolivia 25 2.2 ‘Carbon Forestry’- the direct role of forest management 26 2.3 Impacts of changes in agricultural practice or land use on soil carbon stocks 26 Copyright © The Royal Society 2001 Requests to reproduce all or part of this document should be submitted to: Science Advice Section The Royal Society 6 Carlton House Terrace London SW1Y 5AG Preparation of this report This report has been endorsed by the Council of the Royal Society. It has been prepared by the Royal Society working group on land carbon sinks. The members of the working group were: Professor David Read FRS (Chair) Department of Animal and Plant Sciences University of Sheffield Dr David Beerling Department of Animal and Plant Sciences, University of Sheffield Professor Melvin Cannell NERC Centre for Ecology and Hydrology, Edinburgh & Tyndall Centre for Climate Change Research Dr Peter Cox Hadley Centre for Climate Prediction and Research, Met Office, Bracknell Professor Paul Curran Department of Geography, Faculty of Science, University of Southampton Professor John Grace Institute of Ecology and Resource Management, University of Edinburgh Professor Phil Ineson Stockholm Environment Institute & Department of Biology, University of York Professor Paul Jarvis FRS Institute of Ecology and Resource Management, University of Edinburgh Dr Yadvinder Malhi Institute of Ecology and Resource Management, University of Edinburgh Professor David Powlson Agriculture and Environment Division, IACR-Rothamsted Professor John Shepherd FRS Southampton Oceanography Centre & Tyndall Centre for Climate Change Research Professor Ian Woodward Department of Animal and Plant Sciences, University of Sheffield. Secretariat: Dr Rachel Quinn Science Advice Section, Royal Society Miss Marisa Goulden Science Advice Section, Royal Society Dr Rebecca Bowden Science Advice Section, Royal Society The Royal Society The role of land carbon sinks in mitigating global climate change | July 2001 |v Summary • As evidence for the link between atmospheric methane and nitrous oxide is poorly understood and is greenhouse gases and climate change has increased, a priority area for research. Until it is possible to international efforts have focused on ways in which calculate full trace gas inventories we recommend that anthropogenic emissions of greenhouse gases, land carbon sink projects likely to result in significant particularly carbon dioxide (CO2), can be reduced. emissions of trace gases (e.g. the large-scale use of Knowledge that CO2 is stored within and exchanged nitrogen-based fertilisers) be avoided. between the atmosphere and vegetation and soils has led to the suggestion that soils and vegetation could • There is considerable uncertainty associated with the be managed to increase their uptake and storage of estimates derived using the techniques that will be CO2, and thus become ‘land carbon sinks’. Under the required to monitor, quantify and verify land carbon terms of the 1997 Kyoto Protocol, signatories can sinks established under the Kyoto Protocol. There is an meet part of their obligations to reduce greenhouse urgent need to increase the accuracy of these gas emissions from fossil fuel consumption by techniques before land carbon sinks are utilised to any increasing these land carbon sinks. However there significant extent. have been concerns about the permanence of land carbon sinks and the accuracy with which they can be • The permanence of the land carbon sink is uncertain quantified and verified.