Agriculture is essentially a man-made adjunct to natural ecosystems and is weather and climate dependent. It is also a significant source of anthropogenic emissions of greenhouse gases, which are coming under increasing scrutiny as countries seek to meet binding mitigation targets. New challenges are emerging in terms of how we interpret the impacts of warming, how farming systems adapt or are adapted to these changes, and how near-term emissions mitigation requirements can take place in ways that are consistent with longer-term adaptation plans. These increasingly urgent challenges coincide with a process of sector reform in many OECD countries, which is focussed on ways to rebalance the economic, social and environmental objectives for the sector. This process offers a window of opportunity for accommodating mitigation and adaptation options within new agri-environmental arrangements. But all these reforms will affect and be affected by a global agricultural trading system, which is increasingly being required to deliver on ancillary policy objectives (e.g. energy and food security, and poverty alleviation), but which itself is vulnerable to climate shocks.