The Background Rate

To measure today's losses, scientists compare them against the natural background rate — the pace at which species vanished before humans. Fossil records suggest roughly one to five species went extinct each year over most of geological history.

Today's rate is conservatively estimated at hundreds to thousands of times higher. The exact figure is debated: only about two million of an estimated eight to ten million species have been described, and many vanish before discovery. The IUCN Red List has assessed over 150,000 species and found more than 44,000 threatened — a sign the true crisis is likely worse.