He has over 20 years of experience in the field of greenhouse emissions and climate change and has sat on more than ten advisory panels or task groups. He spent six years working for the Ministry for the Environment as Senior Adviser on climate change and has also worked for the Inter-governmental Panel for Climate Change in the UK and in India. He is a Coordinating Lead Author for the International Panel for Climate Change Fifth Assessment Report (AR5) and is a New Zealand representative for the Global Research Alliance Livestock Research Group. He is a member of the Agricultural Greenhouse Gas Inventory Advisory Panel to the Ministry of Primary Industries, Member and New Zealand representative on the Scientific Programming Group of the Asia-Pacific Network for Global Change Research (APN), and Member, Task Group on Data and Scenario Support for Impact and Climate Analysis for the Intergovernmental Panel on Climate Change (IPCC). He is a member of the Royal Society New Zealand.