IRISH FORESTRY The role of forests in the global carbon cycle and in climate change policy Kenneth A. Byrne and Carly Green b Abstract It is now widely accepted that increasing levels of greenhouse gases in the atmosphere are altering the Earth's climate system. Forests store and sequester vast amounts of carbon and are therefore a key component of the global carbon cycle. Understanding the nature of that contribution is vital to understanding current and future climate trends. The ability of forests to sequester atmospheric carbon led to their inclusion in the Kyoto Protocol as a means to mitigate greenhouse gas emissions. This paper discusses the role of forest in both the global carbon cycle and climate change policy. The various means by which forests can contribute to reduction of greenhouse gas emissions are also discussed. Key words: Carbon sequestration, forest ecosystems, Kyoto Protocol Introduction The global carbon (C) cycle is a vital component of the Earth's system and consists of various reservoirs (stocks), and the dynamic transfer of carbon between them (fluxes). Both internal, i.e. photosynthesis and respiration, and external forces, i.e. environmental and human disturbance, can cause each of these reservoirs to act as sources and sinks of carbon at various temporal scales. The largest reservoirs of carbon include the oceans, fossil fuel reserves, the terrestrial environment and the atmosphere. Since the onset of the industrial revolution, the burning of fossil fuels has resulted in a large anthropogenic flux of C to the atmosphere. It is widely accepted that this shift in the C balance has largely contributed to the onset of global climate change. Identification of options for mitigating atmospheric C concentrations and development of global climate policy measures has lead to the requirement to report forest related activities under the United Nations Framework Convention on Climate Change (UNFCCC) and subsequently to the Kyoto Protocol, should it enter into force. Such reporting focuses on changes in carbon stocks following afforestation, reforestation and deforestation activities as well as forest management practices. Analysis of current climate change policy indicates a focus towards relatively cheap carbon storage through land use practices. However, available land for increasing carbon stocks through human induced, i.e. afforestation/reforestation activities, is a limited resource and so too is the potential of vegetation management as a mitigation measure. Alternatives which can provide long-term solutions are the a Centre for Hydrology, Micrometeorology and Climate Change, Department of Civil and Environmental Engineering, University College Cork, Ireland. b Forest Ecosystem Research Group, Department of Environmental Resource Management, Faculty of Agriculture, University College Dublin, Belfield, Dublin 4, Ireland. 7