Assessing Temporary Carbon Storage in Life Cycle Assessment and ...

5 Conclusions
This report summarises the main methodological issues regarding the benefits of temporary carbon
storage and associated metrics that were identified in the presentations and subsequently discussed
throughout the workshop.
Climate benefits of an isolated temporary carbon storage event arise solely when time preferences are
reflected in the method used. This means that accounting for any benefits relies on value-laden
methodological decisions, such as the choice of a time horizon beyond which impacts are not
considered. Indeed, the longer the time horizon adopted for integration of radiative forcing or impacts,
the lower the benefits are from temporary carbon storage. This will only be different if the temporary
storage is repeated, essentially becoming a permanent removal from the atmosphere.
If temporary storage is considered then it is common practice to adopt a 100-year time horizon using
the Global Warming Potential index. Temporary storage benefits are then generally based on the
Moura-Costa and Lashof approaches; assuming that (sequestration and) storage of 1 tonne for 48 and
100 years is essentially equivalent to not emitting 1 tonne.
However, no clear consensus has been reached from these discussions regarding whether or not to
account for temporary carbon storage in general and, if so, which method to employ. The choice of a
100-year time horizon equally remains controversial
Since the benefits given to temporary carbon storage rely on value-laden choices, if considered then it
is important to make them explicit and transparent when using any accounting method. Both short and
long term time horizons should be considered.
It was suggested to do more research in order to improve climate-change modelling in LCA to include
two other indicators (i.e. instantaneous temperature increase and rate of temperature increase), since
they provide information on different types of climate-change impact, and can lead to different
conclusions than the single use of cumulative radiative forcing. Furthermore, research is warranted on
the dynamics of the carbon cycle (e.g. changes in sinks – biospheric, atmospheric and oceanic – are
interdependent and cannot be assessed in the same linear way as fossil emissions with GWP). This is
because any change in biospheric carbon stocks may be partially or totally compensated by the inverse
process from other sinks (e.g. oceans), so this dynamism needs to be addressed.
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