Sustaining forest health is critical for sustaining livelihoods, conserving biodiversity, producing biomass and protecting watersheds and river valley systems Prof N H Ravindranath Climate change's impact on physical and biological systems is irrefutable. Forests account for nearly a third of the planet's land surface and over a billion people depend on forests directly for their livelihoods. Forest ecosystems are closely linked to climate change. Tropical deforestation and land use change amount to about 20% of global CO2 emissions. Whereas in order to mitigate climate change, w e need more forests, not less as forests absorb CO2 and act as carbon sinks or storehouses. Climate change will impact forest ecosystems, biodiversity and biomass production. Despite being critical in global and national efforts to address climate change, the forest sector poses a big challenge to the policy makers due to the complexities and lack of adequate knowledge about changes in forest area and carbon sink. Forests are critical for biodiversity and provide timber, fuel wood and various fruits, flowers, honey, gum, medicinal plants, etc. Nearly 200 million people in rural areas depend on forests for their livelihoods. Thus forest conservation and sustainable management is very necessary in the face of changing climate. Forest ecosystems are highly vulnerable to climate change. Studies by the Indian Institute of science show that large parts of forest areas and biodiversity will be very vulnerable to climate change. By the end of the century the forests are expected to lose much of their biodiversity and many species will become extinct. We need planning and implementation of adaptation measures to reduce the vulnerability of forest ecosystems and biodiversity. However, studies are being initiated only now to identify vulnerable forest locations and to develop 'win-win' adaptation measures. Many of the adaptation measures such as halting forest fragmentation, linking protected areas, multi species plantation forestry and fire management are required even in the absence of climate change. Reducing the vulnerability of forest ecosystems is needed to protect forest biodiversity, sustain timber production and livelihoods of millions of forest dependent communities. Using forests, through preservation of existing forest and through afforestation, as carbon sinks is one of the most contentious issues in global negotiations on climate change. While the rules and guidelines for afforestation under the Clean Development Mechanism (CDM) of Kyoto Protocol were agreed over four years ago, no CDM project has been registered so far, while hundreds of energy projects have been registered. Forest conservation, and sustainable management of forests and enhancing forest carbon sink issues are also included in the Bali Action Plan but global agreement on forests is too complex and unlikely due to the lack of agreement on reliable and cost effective methods for measuring, estimation, monitoring and verification of carbon credits. Given the unsatisfactory experience of including afforestation as an option to address climate change under Kyoto Protocol, the future role of forest sector playing a critical role in addressing climate change is doubtfull However, India should be prepared to protect its forests, with a good understanding of the scientific methods as well as policy options. A lot is at stake for India with over 500 million people directly depending on climate change sensitive sectors such as dry land agriculture, forests and fisheries for their livelihoods. Any failure to achieve an agreement for a large global reduction in greenhouse gas emissions will put the lives and livelihoods of these hundreds or millions at risk in the next few decades. India and global community cannot ignore forest sector which contributes to over 20% of global carbon dioxide emissions and sustaining forest health is critical for sustaining livelihoods, conserving biodiversity, producing biomass and protecting watersheds and river valley systems. (The author is with the Indian Institute of Science)