Martine Maron and colleagues assume that a nation's commitment to establishing protected areas of biodiversity provides a suitable baseline for determining the “additionality” of any offset initiative based on habitat protection (Nature 523, 401–403; 2015). The evidence indicates otherwise.

A more realistic baseline would factor in the high probability that national biodiversity commitments will not be fulfilled (see M. Walpole et al. Science 325, 1503–1504; 2009). For example, national conservation commitments can be overridden by development commitments.

Documented trends and local conditions should be used to establish a baseline. Carbon offsets, for example, commonly derive baselines from historical average deforestation (see go.nature.com/rvdx3x). These baselines are typically revised every ten years.

We also disagree that developing countries should withdraw from the Convention on Biological Diversity (CBD) if they are unable to fund protected areas, because that would stop them engaging with other CBD targets. Moreover, honest accounting of offset benefits must occur at the local, regional and landscape levels where conservation is accomplished.

What is most needed in offset programmes is better enforcement, so that they do not become a 'licence to trash' (see A. Villaroya et al. PLoS ONE 9, e107144; 2014).