Researchers say their more reliable projections of global warming estimates at 2100 have narrowed the predicted range of global warming.
Exceeding 6 degrees warming, one of the more extreme estimates, is now unlikely while 2 degrees is very likely for business-as-usual emissions, say Dr. Roger Bodman from Victoria University and Professors David Karoly and Peter Rayner from the University of Melbourne. Western nations have already dropped their CO2 emissions, the United States in particular has slashed its carbon dioxide emissions in energy production by switching from coal to more natural gas. The analysts came up with their estimate by combining observations of carbon dioxide and global temperature variations with simple climate model simulations to project future global warming.
They believe continuing to narrow the range even further is possible - a Bayesian analysis is certain to come up with the correct answer given enough time, for example - significant uncertainty in warming predictions will always remain due to the complexity of climate change drivers.
Their projection found 63% of uncertainty in projected warming was due to single sources – such as climate sensitivity, followed by future behavior of the carbon cycle and the cooling effect of aerosols – while 37% of uncertainty came from the combination of these sources.
"This means that if any single uncertainty is reduced – even the most important, climate sensitivity – significant uncertainty will remain," Bodman said. "Some uncertainty will always remain, meaning that we need to manage the risks of warming with the knowledge we have."
A recent paper in Nature Geoscience (Energy budget constraints on climate response - Nature Geoscience doi:10.1038/ngeo1836) found that since the rate of global mean warming has been lower over the past decade than previously estimated, models might require a downwards revision of estimates of equilibrium climate sensitivity.
Published in Nature Climate Change.