A new study of three ice cores from Greenland documents the warming of the large ice sheet at the end of the last ice age – resolving a long-standing paradox over when that warming occurred.
Large ice sheets covered North America and northern Europe some 20,000 years ago during the coldest part of the ice age, when global average temperatures were about four degrees Celsius (or seven degrees Fahrenheit) colder than during pre-industrial times. And then changes in the Earth's orbit around the sun increased the solar energy reaching Greenland. Beginning some 18,000 years ago, release of carbon from the deep ocean led to a graduate rise in atmospheric carbon dioxide (CO2).
Yet past analysis of ice cores from Greenland did not show any warming response as would be expected from an increase in CO2 and solar energy flux, the researchers note.
In this new study, funded by the National Science Foundation and published this week in the journal Science, scientists reconstructed air temperatures by examining ratios of nitrogen isotopes in air trapped within the ice instead of isotopes in the ice itself, which had been used in past studies.
Not only did the new analysis detect significant warming in response to increasing atmospheric CO2, it documents a warming trend at a rate closely matching what climate change models predict should have happened as the Earth shifted out of its ice age, according to lead author Christo Buizert, a postdoctoral researcher at Oregon State University and lead author on the Science article.
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