for National Geographic News
A team of British scientists contends that, within 200 years, Earth's temperatures may become hot enough to kill off half of all existing plant and animal species.
The researchers from the Universities of York and Leeds in Britain base that dire possibility on a new analysis of the 520-million-year-old fossil record, which links past mass extinctions with cycles of high temperatures.
"We could be in the temperature zone in which mass extinctions have occurred by the end of this century, [or] more likely in the next century," said Peter Mayhew, the study's co-author and an ecologist at the University of York.
A Strong Link
Benton and his colleagues lay out their findings in a paper that appeared in the Proceedings of the Royal Society B.
Measuring in ten-million-year increments, the researchers found a correlation between high temperatures and four of five mass extinctions in Earth's fossil record.
No other research had examined both the entire globe and the entire fossil record, which begins about 540 million years ago. This analysis makes the strongest case yet for a solid link between temperature and changes in the number of species on Earth.
"There have been individual cases where people have shown that some kind of change is detrimental to certain groups," said Michael Foote, a paleontologist at the University of Chicago, who was not involved in the study. "But this is the first time anyone has studied the diversity of animals at a global scale and went back to estimates of temperature over time."
According to the research, Earth is in a process, millions of years long, of moving from colder to warmer temperatures—from the "icehouse phase" to the "greenhouse phase." The Earth will reach the peak of its latest warming phase in the next 60 million years.
It is possible that extinctions don't begin to occur until thousands, or even millions, of years after temperatures begin to rise. And the authors were careful to avoid claims about a causal relation between the rising temperatures and the extinctions.
Other things, such as cycles of cosmic rays from space or carbon dioxide levels, could also have played a role in the past mass extinctions.
Still, the authors say it may be possible to avoid some of the future extinctions if humans work to control temperatures.
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