Suggested Citation:
Kendall, Alissa (2012) Time-adjusted Global Warming Potentials for LCA and Carbon Footprints. The International Journal of Life Cycle Assessment 2012 (in press)

The common practice of summing greenhouse gas (GHG) emissions and applying global warming potentials (GWPs) to calculate CO₂ equivalents misrepresents the global warming effects of emissions that occur over a product or system’s life cycle at a particular time in the future. The two primary purposes of this work are to develop an approach to correct for this distortion that can (1) be feasibly implemented by life cycle assessment and carbon footprint practitioners and (2) results in units of CO₂ equivalent. Units of CO₂ equilavent allow for easy integration in current reporting and policy frameworks.

CO₂ equivalency is typically calculated using GWPs from the Intergovernmental Panel on Climate Change. GWPs are calculated by dividing a GHG’s global warming effect, as measured by cumulative radiative forcing, over a prescribed time horizon by the global warming effect of CO₂ over that same time horizon. Current methods distort the actual effect of GHG emissions at a particular time in the future by summing emissions released at different times and applying GWPs; modeling them as if they occur at the beginning of the analytical time horizon. The method proposed here develops time-adjusted warming potentials (TAWPs), which use the reference gas CO₂, and a reference time of zero. Thus, application of TAWPs results in units of CO₂ equivalent today.

Keywords: climate change, cumulative radiative forcing, emissions timing, greenhouse gas, GWP, impact assessment