Extinctions Increase with Global Warming

This post is by Lisa Moore, Ph.D., a scientist in the Climate and Air program at Environmental Defense.

Earth is home to millions of species. This rich biodiversity isn’t just beautiful, it’s also tremendously valuable. As just one example, consider coral reefs. They support fisheries that are the main source of protein for a billion people, and bring billions of tourist dollars into local economies.

Scientists have warned that climate change puts a large fraction of Earth’s species at risk for extinction. Most of these predictions are based on comparisons between species’ apparent climate requirements to projections of future conditions. A new study [PDF] in the Proceedings of the Royal Society B looks at the relationship between climate and biodiversity from a different perspective: the Earth’s deep past. The study found a long-term correlation between global temperature and extinction.

Biodiversity has increased in the billions of years of Earth’s history, but there have been ups and downs along the way. To find out if climate has anything to do with this variation the scientists compiled records of global temperature and biodiversity over the past 520 million years. They looked at biodiversity at the family level – for example, looking at the sunflower family rather than its 24,000 species. Then they looked at correlations between temperature and three aspects of biodiversity: "standing diversity" (the number of families present at any one time), the rate at which families appeared over time, and the rate at which families went extinct.

There were many interesting patterns, but the result that has received the most attention was that extinction rates tend to be higher during warm periods than cool periods. What does that mean for today’s global warming?

You can’t translate these results into short-term predictions because this study used time steps of 10 million years. That’s hugely different from the decadal time scales that apply to today’s rapid global warming! The authors make that (and other caveats) very clear in the paper. And, like all scientific studies, this one raised a lot of fascinating questions that need further investigation.

On the other hand, even with all the caveats and questions, this study provides little reassurance for the species and ecosystems we love and depend on. As one of the authors said, "If our results hold for current warming – the magnitude of which is comparable with the long-term fluctuations in the Earth’s climate – they suggest that extinctions will increase."