Comparison of food carbon footprints using 20- and 100-year timeframes

Global Warming Potential (GWP) is a common metric used in life cycle analyses and environmental calculations to quantify the warming of Greenhouse Gases (GHGs) relative to CO 2 over a set timeframe. The Intergovernmental Panel on Climate Change (IPCC) recommends use of both 20- and 100-year timeframes to account for impact of short-lived gases such as methane. However, while GWP over a 100-year period (GWP100) is commonly used in food emission databases, food system data using GWP over a 20-year period (GWP20) that could be essential in political and institutional food policy shifts are not readily available. To address this, we (1) calculate GWP20-derived CO 2 -equivalent emission values for 16 broad food categories and 222 specific food items in a comprehensive database alongside GWP100-derived values, and (2) contextualize GWP differences by comparing emission impacts of different meals at a university dining hall under the two scenarios. We demonstrate that the difference in CO 2 -equivalent emission between generally low and high impact foods widens considerably under GWP20, exemplifying the limitations of a one metric system, and the importance of incorporating the impact of short-lived gases within a shorter timeframe in food emission analyses used for food policy and institutional change.