Greenhouse gas implications of replacing fish protein with beef in the lower Mekong Basin Ben Galea, * Jamie Pittock * and Steven Crimp † * Fenner School of Environment and Society, The Australian National University, Acton, 2600, Australia. Email: u5568821@anu.edu.au, jamie.pittock@anu.edu.au. † Climate Change Institute, The Australian National University, Acton, 2600, Australia. Email: steven.crimp@anu.edu.au. Abstract: At least 88 new hydropower dams are planned between 2010 and 2030 in the lower Mekong River basin in Southeast Asia as a source of electricity with lower greenhouse gas emissions. Dams result in declines in fish populations that will need to be replaced with other sources of protein for food security. We make the first assessment of emissions should beef production substitute for lost fish in Cambodia and Laos. We assessed two sources of emissions. Replacing lost fish with beef would require as much as 12 million hectares of new pasture. Forest clearing for pastures in Cambodia and Lao PDR would initially emit between 0.859 and 3.015 giga-tonnes of carbon dioxide equivalents (Gt CO 2 -eq.). Methane emissions from additional cattle would add at least 0.0013 Gt CO 2 -eq./year to Cambodia’s total greenhouse gas emissions, equivalent to a 20% increase. In Laos at least 0.0005 Gt CO 2 -eq./year would be released, a 4–12% increase in annual emissions. We demonstrate that activities displaced by hydropower developments could significantly increase emissions. It shows how enclosure of commons at local scales impacts upon other common pool resources at different scales, raising questions for sustainable and equitable transboundary governance. Keywords: fish, food security, greenhouse gas emissions, hydropower, land use change, livestock Introduction There has been considerable debate as to the greenhouse gas (GHG) emissions reduced by sourcing electricity from hydropower or directly emitted from hydropower reservoirs. Similarly, while growing and wealthier populations are increasing demand for meat, the GHG emis- sions from livestock production are considered to be substantial. As both hydropower and live- stock production are expanding, the Mekong region of Southeast Asia is a particular focus for these contested industries. To date, no-one has assessed the risk of hydropower development increasing GHG emissions by displacing food production. The novel objective of this research is to quantify the potential for GHG emissions to increase as livestock production expands to replace fisheries lost to hydropower develop- ment in Cambodia and Laos. Livestock have long played an important role in the provision of food and non-food products for human societies, with increased production often both a result and driver of increased wealth and standards of living. Global meat production has been an inextricable part of the ‘Great Acceleration’, with a four to five-fold increase in supply occurring between 1960 and 2017 to service global demand (Ritchie and Roser, 2017). Currently, Asia is the largest meat pro- ducing region in the world, accounting for around 40–45% of total production (Ritchie and Roser, 2017). When comparing the various food types pro- duced on farm, the average GHG emissions per unit of protein are greatest in the livestock industries. Across the range of possible livestock production types the emissions profile of both beef and buffalo enterprises far exceeds the emission levels of non- ruminant livestock meats like pork and poultry. At a global scale both beef and buffalo production account for two thirds of the global anthropogenic GHG emissions from livestock (Food and Agricul- tural Organisation of the United Nations (FAO), 2018), but livestock also has an important role in Present address: Burnett Mary Regional Group, 193 Bourbong Street, Central, QLD, 4670, Australia. Asia Pacific Viewpoint 2020 ISSN 1360-7456 © 2020 Victoria University of Wellington and John Wiley & Sons Australia, Ltd doi:10.1111/apv.12274