The Convention on Biological Diversity's post-2010 targets are likely to aim for a halt in biodiversity loss by 2050 and for 'more modest' interim targets for 2020 (Nature 461, 1037; 2009). Global aspirations need to be much higher than this to avert the accelerating and catastrophic decline in the variety of life forms on Earth.

A 2050 vision should aim both to arrest this loss and to restore the populations, habitats and ecological cycles that support biodiversity and ecosystem services. A 40-year horizon should be about right, given that the restoration of forests, wetlands, coral reefs and other habitats depends on species and processes that often have decades-long generational periods.

We should, at the very least, aim to maintain biodiversity and the health of ecosystems as they are now — in particular, by setting an intermediate target to prevent further extinctions.

The deadline for achieving 'more modest' targets should be 2015, not 2020. That would synchronise it with the Millennium Development Goals (J. D. Sachs et al. Science 325, 1502–1503; 2009) and with the timeframe of political cycles, which would help to ensure that elected politicians successfully deliver the target to their constituencies.