In a nutshell: LT stands for long-term and classifies emissions, usually from landfills, which are release into the air or leach to the groundwater more than 100 years after the landfilling happened.
What’s the difference?
LT stands for long-term. An emission is classified as “long-term” if it is released to the environment more than 100 years after the activities considered in the life cycle took place. Decisive for the classification “long-term” is thus the moment at which an emission is released in the environment and not the moment at which it causes its impact. It is, therefore, different from long-term impacts that would be caused, for example, by the bioaccumulation of a pesticide in the food chain.
Why does ecoinvent distinguish between LT and w/o LT?
So far no consensus has been reached among LCA experts if and how long-term emissions should be taken into account. Until the debate is settled, ecoinvent allows users to decide themselves whether to include it. Therefore, long-term emissions are reported separately via two subcompartments explicitly labeled as “long-term”, namely “air, low population density, long-term” and “water, ground-, long-term”. Those exchanges are exclusively present in waste treatment datasets, where it is assumed that the active landfill maintenance ends after 100 years. Since long term emissions are in the environment 100 years less than short term emissions, their CF should be lower. However, most LCIA methods do not provide a distinction of time horizons. Thus, two options are possible:
- Attribute the same CF to both short term and long-term emissions, leading to an over-estimation of the impacts
- Attribute no CF to the long-term emission, leading to an under-estimation of the impacts.
ecoinvent provides the results for both options, allowing you to test the sensitivity of your conclusions. The results without long-term emissions are available in methods explicitly labeled as “w/o LT” or “no-LT”.