The New York Times is reporting today the results of a new study showing global temperatures are higher than they’ve been in the last 4,000 years and are likely to surpass levels not seen since the last Ice Age.
The study‘s lead author, Shaun Marcott of Oregon State University, and his team reconstructed global temperatures over the past 11,300 years, virtually the entire Holocene. They used indicators like the distribution of microscopic, temperature-sensitive ocean creatures to determine past climate.
The Times article sums up the findings:
Their findings confirm previous research that suggests that changes in the amount and distribution of incoming sunlight, caused by wobbles in the earth’s orbit, contributed to a sharp temperature rise in the early Holocene.
The climate then stabilized at relatively warm temperatures about 10,000 years ago, hitting a plateau that lasted for roughly 5,000 years, the paper shows. After that, shifts of incoming sunshine prompted a long, slow cooling trend.
The cooling was interrupted, at least in the Northern Hemisphere, by a fairly brief spike during the Middle Ages, known as the Medieval Warm Period. (It was then that the Vikings settled Greenland, dying out there when the climate cooled again.)
Scientists say that if natural factors were still governing the climate, the Northern Hemisphere would probably be destined to freeze over again in several thousand years. “We were on this downward slope, presumably going back toward another ice age,” Dr. Marcott said.
Instead, scientists believe the enormous increase in greenhouse gases caused by industrialization will almost certainly prevent that.
During the long climatic plateau of the early Holocene, global temperatures were roughly the same as those of today, at least within the uncertainty of the estimates, the new paper shows. This is consistent with a large body of past research focused on the Northern Hemisphere, which showed a distribution of ice and vegetation suggestive of a relatively warm climate.
The modern rise that has recreated the temperatures of 5,000 years ago is occurring at an exceedingly rapid clip on a geological time scale, appearing in graphs in the new paper as a sharp vertical spike. If the rise continues apace, early Holocene temperatures are likely to be surpassed within this century, Dr. Marcott said.
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