Over the past 540 million years, life on Earth has passed through five great mass extinctions. In each of those catastrophes, an estimated 75 percent or more of all species disappeared in a few million years or less.

For decades, scientists have warned that humans may be ushering in a sixth mass extinction, and recently a group of scientists at the University of California, Berkeley, tested the hypothesis. They applied new statistical methods to a new generation of fossil databases. As they reported last month in the journal Nature, the current rate of extinctions is far above normal. If endangered species continue to disappear, we will indeed experience a sixth extinction, over just the next few centuries or millennia.

The Berkeley scientists warn that their new study may actually grossly underestimate how many species could disappear. So far, humans have pushed species toward extinctions through means like hunting, overfishing and deforestation. Global warming, on the other hand, is only starting to make itself felt in the natural world. Many scientists expect that as the planet’s temperature rises, global warming could add even more devastation. “The current rate and magnitude of climate change are faster and more severe than many species have experienced in their evolutionary history,” said Anthony Barnosky, the lead author of the Nature study.

But equally as strong as the conclusion that global warming can push extinctions is the difficulty in linking the fate of any single species to climate. Policy makers would like to get a better idea of exactly what to expect — how many species will risk extinction, and which ones are most likely to wink out of existence. But scientists who study the impact of global warming on biodiversity are pushing back against the pressure for detailed forecasts. While it’s clear that global warming’s impact could potentially be huge, scientists are warning that it’s still impossible to provide fine-grained predictions.