Wildlife populations around the world have declined by an average of 73% since 1970. That’s according to the WWF’s new 2026 Living Planet Index – a major estimate, updated every two years, of the changing state of nature. This does not mean that 73% of the world’s animals have disappeared. Rather, it is the average decline in the size of wildlife populations that is being monitored.
The index is one of the metrics used to track progress towards the UN’s biodiversity goals and shapes narratives of biodiversity loss across the world. But the data behind that 73% headline, one of the most comprehensive available, is still far from complete.
Very few, outside of those of us working at the coalface of handling biodiversity data, understand just how poorly wild animal populations are monitored. Though the world faces the joint crises of climate change and biodiversity loss, we can track climate change through thousands of weather stations or measures of atmospheric CO₂. Biodiversity is far harder to measure. Counting wildlife is highly resource intensive, generally can’t be done from space, and systematic monitoring is extremely patchy.
What this means is that, relative to the data we do possess, there are far, far more wildlife populations...