Aiming higher to test a bend in the curve of biodiversity loss: the challenge of halt-the-loss targets

Efforts to ‘bend the curve’ of biodiversity loss involve setting targets to halt declines. Here, we propose an empirical test of such targets. This test states the probability that the rate of change in a biodiversity indicator is greater than or equal to zero. We used a combination of real and simulated data to explore factors affecting test performance. We found that while smoothing had a minimal effect, the outcome depends heavily on the variability and number of species in a dataset. This suggests that thresholds for target acceptance should be set on a case‐by‐case basis. Adding data for subsequent years could retrospectively change the outcome in a target year. Assessments made with data only up until the target year should therefore be regarded as interim, with the assessment of the target only finalised once subsequent data are also included. We recommend that simulations are used a priori to choose smoothing levels and to set thresholds for accepting a target has been met.