There is more than a 10 per cent chance the planet could undergo dramatic warming even if humanity manages to curb emission in coming decades, according to a survey of leading climate experts.
"The possibility of really dramatic climate outcomes is significant," says engineer David Keith, of the University of Calgary, whose survey highlights the large but seldom discussed uncertainty in climate change scenarios.
It is known the climate will warm as a result of the billions of tonnes of carbon dioxide bumped into the atmosphere each year through the burning of coal, oil and other fossil fuels. But it is still not clear how much, says Keith, director of the U of C's Institute for Sustainable Energy, Environment and Economy.
To gauge the risks Keith and his colleagues canvassed 14 leading climate scientists, including two in Canada. Most are on the United Nations Intergovernmental Panel on Climate Change. The scientists were asked for their expert advice on how the climate system will respond to different emissions scenarios. Their responses are detailed in a report published Monday in the U.S. Proceedings of the National Academy of Sciences.
Keith says the most significant finding is that it is "still very uncertain" how the climate will change.
The "risk of rapid or extreme warming are larger than what you would get by reading the IPCC" reports, he says. The UN reports are used at international talks aimed at reducing global CO2 emissions.
But on the flip side, Keith says the survey also found a higher than expected chance of seeing less warming than expected.
In a "medium" emissions scenario, which Keith says will be hard to meet given the increasing global emissions, the level of CO2 in the atmosphere climbs to 550 parts per million by 2200 and stays there. "It's still technically possible but it'd be pretty darn hard," Keith says of the "politically optimistic" scenario. "More than half the experts think there is a more than 10 per chance we'll get five degrees C warming under that scenario," he says. "And five degrees C is gigantic," says Keith, noting it is enough to "knock out" the Greenland and Antarctic ice sheets. The meltwater would eventually raise sea level by as much as 100 metres.
Keith says the level of CO2 will likely climb beyond 550 ppm since emissions keep rising despite years of talk and promises to reduce emissions. Unless humanity puts on the brakes, he says atmospheric concentrations of CO2 could hit 1,000 ppm by 2200.
The experts surveyed said this scenario carries a "substantial probability of the climate warming eight to 10 degrees C" — a heat wave that Keith says would be "stunning." Given the danger, he stresses the need to cut emissions now. "The risk just builds with every extra kilogram of CO2 we put in the air," says Keith, who likens CO2 to nuclear waste. "Even if we stop emitting CO2 completely the impact will still be with us for thousands of years."
The report says the science community needs to focus more on reducing the uncertainty in global warming predictions.
Meantime Keith says policy-makers need to acknowledge the uncertainty and risks. Just like engineers must be aware of structural weaknesses in bridges, he says policy-makers need to come up with strategies for dealing and managing the "worst-case" climate scenario of dramatic and rapid warming.
The Deniers, who have been desperately searching for something to report since the collapse of Climategate (Most Denier Websites are showing a serious decline in traffic.) are already starting to quote mine this report, picking the sentences which stress uncertainty...
But of course the most frightening thing in this article is the 10% chance that we have ALREADY passed the tipping point, and temps will climb no matter what we do from here on out...
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