August 17, 2010

Global Warming

David Keith is one of the authors of an international study on climate change. Photo credit: Ewan NicholsonThe world’s top climate scientists say there is a lot of uncertainty about how much the planet will warm because of rising greenhouse gases in the atmosphere, according to an international study.

It is this very uncertainty that bolsters the argument to reduce greenhouse gas emissions, to lower the risk of catastrophic global warming, says David Keith, a professor with the Shulich School of Engineering and one of four authors of the study.

The findings suggest that the United Nations Intergovernmental Panel on Climate Change (IPCC)—the world’s leading scientific body for assessing climate change and its impacts—probably underestimates the uncertainty in predictions about global warming, says Keith who is also the director of the Institute for Sustainable Energy, Environment and Economy’s energy and environmental systems group.

“The study also suggests that uncertainties about climate change will not be resolved for decades,” adds Keith. “But uncertainty is not justification for inaction, any more than uncertainty about the probability of car crashes is a reason to forego seatbelts.

“Just as with car crashes or industrial accidents, it’s the low-probability but high-consequence events that drive the overall risk assessment. The fact that we may be underestimating these risks strengthens the case for action to reduce carbon dioxide emissions.”

The study, which included the U of C, University of Victoria, Carnegie Mellon University and the University of Oxford, involved in-depth, face-to-face interviews with 14 leading climate scientists in Canada, the U.S. and the U.K.

The peer-reviewed research was published in the Proceedings of the National Academy of Sciences—one of the world’s top scientific journals.

Researchers asked the climate change scientists to consider scenarios of low, medium, and high increases of CO2 in the atmosphere to the year 2200, and to offer their expert judgments about the increase in Earth’s average temperature under each scenario.

They were also asked to specify the probability that each of the scenarios would force the planet’s climate system past a “tipping point.” For the high-CO2 increase scenario, 13 of the 14 climate scientists responded that the probability was greater than 50 percent, and 10 scientists said the probability was 75 percent or more.

Such tipping points in the climate system could lead to the loss of a large portion of the Greenland and West Antarctic ice sheets, or the shutdown of currents in the Atlantic Ocean that help moderate climate on a continental scale.

The full study is available at: http://www.pnas.org/content/107/28/12451.full.pdf+html