Greenhouse gas metrics
Overview
Many efforts to mitigate climate change involve tradeoffs between short-lived greenhouse gases (e.g., methane, CH4) and long-lived carbon dixoide (CO2). Equivalency metrics are frequently used to convert emissions of various gases into equal mass emissions of CO2. These metrics are widely used across scales -- from individual technology assessments to global climate commitments -- but questions remain about which ones to choose in different policy contexts and how to best design metrics to link decisions at different spatial and temporal scales.
Our previous work in this area focuses on designing and evaluating metrics for comparing the time-dependent climate impacts of energy technologies, with a focus on natural gas and biofuels. More recently, we are exploring approaches to evaluating the climate impacts energy technologies and systems that have "super-emitter" behavior, where a small number of devices or units are responsible for a large fraction of total emissions.
Approach
This project combines methods in life cycle assessment, energy and climate modeling, and policy analysis. We use these approaches to design new equivalency metrics that reflect how changes in the role of short-lived greenhouse gas reductions in meeting climate policy goals over time. We develop new models (and analytical expressions) to evaluate the consequences of these metrics in use and apply them to quantify the time-dependent climate impacts of energy technologies.
What we’ve found
Time-dependent climate impacts
The climate impacts of energy technologies depend on their time of use. As global temperatures approach a level that we do not want to exceed (for example, the 1.5 or 2°C target set out in the Paris Agreement), technologies with high life cycle methane emissions, including natural gas for electricity or heating, become less favorable.
Role of models in metric testing
Greenhouse gas metrics can lead to unintended consequences when they are used in technology evaluation and policy. By modeling the use of different metrics in technology evaluation and emissions policy, we can understand their potential consequences and make more informed and effective design choices.
Guidelines for choosing metrics
The appropriate climate metric depends on the technology and policy context. For example, some metrics are useful for keeping temperature below target levels, while others are more effective at limiting rates of temperature change. We develop guidelines for choosing metrics to meet different policy objectives.
What’s Next
The environmental impacts of energy technologies vary across locations, over time, and across devices and units. Our new projects focus on evaluating the climate impacts of energy systems in the presence of “super-emitters” and understanding the benefits of policies that measure and fix high-emitting system components.