Could we be wrong about global warming?
Could the best climate models -- the ones used to predict global warming -- all be wrong?
Maybe so, says a new study published online today in the journal Nature Geoscience. The report found that only about half of the warming that occurred during a natural climate change 55 million years ago can be explained by excess carbon dioxide in the atmosphere. What caused the remainder of the warming is a mystery.
"In a nutshell, theoretical models cannot explain what we observe in the geological record," says oceanographer Gerald Dickens, study co-author and professor of Earth Science at Rice University in Houston. "There appears to be something fundamentally wrong with the way temperature and carbon are linked in climate models."
During the warming period, known as the “Palaeocene-Eocene thermal maximum” (PETM), for unknown reasons, the amount of carbon in Earth's atmosphere rose rapidly. This makes the PETM one of the best ancient climate analogues for present-day Earth.
As the levels of carbon increased, global surface temperatures also rose dramatically during the PETM. Average temperatures worldwide rose by around 13 degrees in the relatively short geological span of about 10,000 years.
The conclusion, Dickens said, is that something other than carbon dioxide caused much of this ancient warming. "Some feedback loop or other processes that aren't accounted for in these models -- the same ones used by the Intergovernmental Panel on Climate Change for current best estimates of 21st century warming -- caused a substantial portion of the warming that occurred during the PETM."
In their most recent assessment report in 2007, the IPCC predicted the Earth would warm by anywhere from 2 to 11 degrees by the end of the century due to increasing amounts of carbon dioxide in the atmosphere caused by human industrial activity.