for National Geographic News
What happens when carbon dioxide levels skyrocket? Most climate scientists think they know the answer: global warming.
But to determine just how high temperatures may climb and how climate patterns may shift, researchers may need to pinpoint, for comparison, a time in our planet's past when a similar carbon dioxide jump happened.
Doing that may have just gotten a lot tougher—a new study says atmospheric carbon dioxide levels haven't been this high in more than two million years.
Fuzzy But Far-Reaching New View
Carbon dioxide, or CO2, is a naturally occurring greenhouse gas that is also released into the atmosphere by the burning of fossil fuels, for example in cars and power plants (causes of global warming).
"We really don't know how high CO2 has been in the geologic past. Thus we don't know how sensitive the surface temperature of the Earth is to CO2," said Don DePaolo, head of the Earth Sciences Division at the Lawrence Berkley National Laboratory in California.
Most global warming predictions are based on fluctuations in CO2 levels and temperature that happened between a relatively recent series of ice ages, said DePaolo, who was not involved in the new study, which will appear in tomorrow's issue of the journal Science.
Chemicals in ice cores, for example, can show how CO2 levels have changed over time, down to five-year intervals.
But ice core records only go back about 800,000 years.
By studying chemicals in long-dead, single-celled plankton called foraminifera, though, the team behind the new study was able to extend the climate record back 2.1 million years (prehistoric time line).
The method doesn't provide as much detail, but it does give a pretty clear picture of what was going on at roughly thousand-year intervals.
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