Greenhouse Gas Emissions Timing

Improving LCA and Greenhouse gas (GHG) Accounting

? Current practices ignore when GHG emissions occur in the life cycle of a product, service, or policy

? Ignoring when emissions or sequestration occur can cause bias in comparisons of different technologies or mitigation strategies

? The reality: Time matters

How are GHGs Currently Handled?

? Nearly all methods use the Intergovernmental Panel on Climate Change’s 100-year Global Warming Potential (GWP 100 ) to turn non-CO 2 GHGs into CO 2 -equivalent (CO 2 e)

? CO 2 e emissions over the entire life cycle of the product / service / policy evaluated. This is true not just for LCA, but also for “carbon footprints” and GHG inventories.

? Consider three technologies with the  same total life cycle GHG emissions and a 40 year life time

When GHG Emissions Timing Matters

1. Summing emissions over a long life cycle and presenting as a single outcome

2. When carbon sequestration or avoided emissions occur over many years but is valued today

3. When crediting a material or product with recycling that occurs many years in the future (i.e. future avoided emissions)

4. When amortizing upfront emissions or end-of- life emissions (or credits) over the life of a product

How is this Useful?

? If a tree sequesters approximately 40 kg CO 2 per year for 50 years, how much sequestration credit should it receive?

? Thus when comparing the value of different sequestration credits,timing may play an important role in determining preferences for onestrategy over another.

Why we (Increasingly) Need a Life Cycle Approach for Evaluating Energy and Emissions

How are vehicles regulated?

? GHG emissions are regulated by

? If we wanted to include life cycle emissions we would need to amortize production emissions and recycling credits and make sure we account for time properly

? To do this we can use “Time Correction Factors” for production emission (pTCF) and recycling credits (rTCF)

Vehicle Emissions Intensity Formula

Summary

? Timing of emissions or sequestration is ignored in widely used LCA and carbon footprinting methods

? A number of methods, including those I showed here have been proposed to address this shortcoming

? In the context of incorporating life cycle emissions into vehicle CO 2 e intensity estimates:

? accounting for timing does not have enormous effects,

? but amplifies the importance of production emissions (and diminishes recycling credit value)