This month, Horizon explores the global challenge of biodiversity loss. Many experts believe we are in the midst of a sixth mass extinction, where human-caused factors such as land use and pollution are causing a decline in biodiversity – something that threatens the future of our own species. We speak to British ecologist Professor Georgina Mace about how bad the situation is and what we can do about it. We explore marine ecosystems, where species relocation outpaces that of terrestrial populations, and examine how we can help these environments adapt, as well as finding out what’s in store for bees – our pollinators. Finally, we investigate the services nature provides for people – from cleaning our water to acting as a carbon sink – and ask whether putting a value on natural capital could help save it.