In particular, while commitments expressed relative to BAU levels can enable a government to commit to reduce emissions without taking on an absolute emissions reduction target, these types of commitments pose particular challenges for emissions accounting. This is because the hypothetical nature of BAU baselines and the possibility of baseline revisions constitute significant additional sources of uncertainty regarding the future target level of GHG emissions. If some post-2020 commitments are expressed relative to BAU baselines, they would need to be accompanied by detailed information on the underlying BAU baseline projection.