Our clock is based on the best science. It considers the two primary and interlinked causes of species extinction: habitat destruction, which already affects 90% of threatened species, and climate change, which will become just as dangerous.
The easiest way to calculate extinction rates is to look to the past, but this significantly underestimates current patterns. Extinctions often occurred without being recorded, especially among less well-known species, and threats to species are now far more widespread and severe. This is why we use predicted extinction rates.
Predictions are always subject to uncertainty, due to use of different information, assumptions, and techniques. Our predicted extinction rates estimate the number of species that will face extinction between 2000 and 2050. We say "faced with extinction" because there is a delay between the onset of threats and the actual death of the last individual of a species, causing an "extinction debt."
Some 5% to 50% of species are predicted to face extinction due to habitat destruction alone between 2000 and 2050. Independent studies on climate change effects predict 15% to 37% of species may face extinction over the same period. The midrange estimate for each scenario is about 25%. Overlap between the 25% of species imperiled by each of these factors is likely, which gives us a midrange predicted extinction rate of around 25% of species by 2050.
Given a conservative estimate of 4 million to 6 million species on Earth today, and incorporating best- and worst-case extinction scenarios, we can estimate how many species will be faced with extinction between 2000 and 2050:
- Midrange estimate: 25% of 5 million species = 1.3 million species, or roughly 1 every 20 minutes.
- Low estimate: 15% of 4 million species = 0.6 million species, or roughly 1 every 44 minutes.
- High estimate: 50% of 6 million species = 3 million species, or roughly 1 every 9 minutes.
The species featured here are not a definitive list, but an example of the variety of species worldwide that are under threat. They include:
Golden-crowned sifaka (Propithecus tattersalli)
Sumatran orangutan (Pongo abelii)
Philippine eagle (Pithecophaga jefferyi)
Lake Titicaca giant frog (Telmatobius culeus)
Red-crowned roof turtle (Kachuga kachuga)
Leatherback turtle (Dermochelys coriacea)
Bastard quiver tree (Aloe pillansii)
African red land crab (Afrithelphusa monodosus)
Giant humphead wrasse (Cheilinus undulatus)
Madagascar baobab (Adansonia grandidieri)
Tiger (Panthera tigris)
Whale shark (Rhincodon typus)
Goliath beetle (Goliathus regius)
1. Baillie et al. 2004. 2004 IUCN Red List of Threatened Species: A Global Species Assessment. IUCN, Gland.
2. Tilman et al. 1994. Nature 371: 65–66.
3. Pimm et al.1995. Science 269 (5222): 347–350.
4. Thomas et al. 2004. Nature 427: 145–148.
5. Novotny et al. 2002. Nature 416: 841–844.