Escaping the most severe effects of global warming will require quick, steep cuts in greenhouse gas emissions, a new government-funded study finds.
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Cutting emissions by 70 percent by the end of the century would cause the Earth to warm by an average of about 2 degrees Celsius, versus 4 degrees if emissions continue growing at their current rate, according to computer simulations run by researchers at the National Center for Atmospheric Research in Boulder, Colo.
And that would give the world its best chance to avoid massive loss of Arctic sea ice and permafrost and limit sea level rise, the scientists said. Future changes in snow and rainfall patterns and the incidence of heat waves would be about half as intense as they would be without the steep emissions cuts.
The study, which will appear in the April 21 issue of Geophysical Research Letters, was funded by the Energy Department and the National Science Foundation.
Its authors based their findings on computer simulations that examined the degree to which climate change's effects can be limited by human actions.
"We can no longer avoid significant warming during this century," lead author Warren Washington, an NCAR climatologist, said in a statement. "But if the world were to implement this level of emission cuts, we could stabilize the threat of climate change and avoid catastrophe."
The world has already warmed by an average of 1 degree Celsius over the last century. The level of carbon dioxide in the atmosphere has risen from 284 parts per million in the pre-industrial era to 385 ppm today. That level could rise further, the study warned, to 750 ppm by the end of the century if greenhouse gas emissions continue on their current track.
Cuts could stabilize CO2 level at 450 ppm
In contrast, the greenhouse gas emission cuts outlined in the new study would stabilize atmospheric CO2 at 450 ppm by 2100.
The scenario is similar to curbs outlined in President Obama's current budget proposal and in draft legislation that House Democrats released last month, which both seek to limit emissions 83 percent below 2005 levels by 2050.
It also tracks with the climate debate in Europe, which has largely focused on limiting global warming to just 2 degrees by 2100. That would "limit massive and irreversible disruptions of the global ecosystem," the Council of the European Union said in a 2007 statement. That means cutting global emissions at least 50 percent below 1990 levels by 2050, E.U. Environment Commissioner Stavros Dimas said last week in Stockholm.
A handful of scientists, including NASA climatologist James Hansen, have suggested that an even tougher target is needed to prevent catastrophic climate change. Hansen has argued that the world should cut atmospheric CO2 levels to just 350 ppm -- below today's level of 385 ppm (ClimateWire, June 24, 2008).
But even the 450 ppm target could be a reach, White House science adviser John Holdren said Monday at an event held at the Massachusetts Institute of Technology.
Choices: 'mitigation, adaptation and suffering'
"Climate change is now happening faster than almost anyone previously predicted," said Holdren, who categorized the world's choices for dealing with climate change as "mitigation, adaptation and suffering." Greenhouse gas emissions, land and ocean temperatures and the average sea level are all rising more rapidly than predicted by scenarios developed by the Intergovernmental Panel on Climate Change, he said.
Stabilizing atmospheric concentrations of greenhouse gases at 450 parts per million of CO2 equivalent appears "prudent," he said.
"It is still no guarantee against increasingly difficult to manage consequences" of climate change, Holdren added. "It is probably in the range of the best that is practical, given where we are starting."
Meanwhile, a poll of climate experts commissioned by the London Guardian has found that nearly 9 out of 10 respondents believe the world won't be able to reach the 2-degree-Celsius target by the end of the century.
The poll, reported by the newspaper yesterday, surveyed more than 1,500 scientists, policymakers, social scientists and business leaders who attended last month's Copenhagen Climate Congress. Of the 261 respondents, who included 200 climate scientists, 86 percent said they believed the 2-degree-Celsius target won't be achieved by 2100.
That doesn't mean it's impossible, according to those surveyed. Sixty percent of respondents felt that limiting temperature rise to 2 degrees Celsius is "still technically and economically possible," the Guardian said yesterday. But nearly half of those polled, 46 percent, said they believe the world will only be able to limit warming to 3-4 degrees Celsius by the end of the century.
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