Washington, July 15: Current climate change models prepared by scientists can explain only half the warming that took place on earth in the ancient past, says a new study.
The study contains an analysis of published records from a period of rapid climatic warming about 55 million years ago known as the Palaeocene-Eocene thermal maximum (PETM).
“In a nutshell, theoretical models cannot explain what we observe in the geological record,” said oceanographer Gerald Dickens, study co-author from Rice University.
“There appears to be something fundamentally wrong with the way temperature and carbon are linked in climate models,” he added.
During the PETM, for reasons that are still unknown, the amount of carbon in earth’s atmosphere rose rapidly. For this reason, the PETM, which has been identified in hundreds of sediment core samples worldwide, is probably the best ancient climate analogue for present-day earth.
But besides the rapidly rising levels of atmospheric carbon, global surface temperatures rose dramatically during the PETM, something that present models cannot predict or have taken into account.
Average temperatures worldwide rose by about seven degrees Celsius — about 13 degrees Fahrenheit — in a short span of 10,000 years.
Many of the findings come from studies of core samples drilled from the deep seafloor over the past two decades. When oceanographers study these samples, they can see changes in the carbon cycle during the PETM.
“You go along a core and everything’s the same, the same, the same, and then suddenly you pass this time line and the carbon chemistry is completely different,” Dickens said. “This has been documented time and again at sites all over the world.”
Based on findings related to oceanic acidity levels during the PETM and on calculations about the cycling of carbon among the oceans, air, plants and soil, Dickens and co-authors determined that carbon dioxide levels in the air went up by about 70 percent during the PETM.
–IANS