Climate Experts Talk Tipping Points

A recent survey published in the Proceedings of the National Academy of Sciences journal asked 14 of the world's top climate scientists what they think the next 200 years have in store for planet Earth. Complete agreement on future scenarios was neither reached nor expected, but the group agreed on one point: at current "business as usual" rates of greenhouse gas emissions, the globe will exceed the worst-case-scenario proposed by the Intergovernmental Panel on Climate Change in its last Assessment Report. Work is currently underway on the IPCC's fifth report, due out in the fall of 2014.

The PNAS survey measures the level of consensus within the climate science community, which has weathered a tough year. (Both Climategate and increasing numbers of skeptics have undermined public response to the threats of climate change.) Science, by nature, is never 100 percent certain about anything, but the survey shows a clear trend among the top researchers working on climate. All agreed the Earth is approaching a tipping point at which significant shifts in the way our climate system functions will be both inevitable and irreversible. Within the next 100 years, the scientists agreed, the globe's average temperature will reach levels we have not seen in the past 10,000 years, around the time human culture became agrarian.

The concentration of carbon dioxide in the earth's atmosphere has now reached about 380 parts per million -- that's about 100 ppm higher than before the Industrial Revolution. According to Dr. Myles Allen, a climate researcher who participated in the survey, our current emissions trajectory will take us to an inevitable height of 1,000 ppm by 2200. Although sobering, there is at least some hope to be found in this dire prediction:

"The emissions that commit you to 1000 ppm in the year 2200 actually occur mostly over the next 50 years," Allen said. "The emissions decisions we make over the next 50 years commit us to the climate we're going to have to deal with (in) 150 years time -- that's the point."

Scientists agree that even if we stopped all global emissions today, the planet would still continue to warm since emissions and temperature, while linked, do not rise simultaneously. (One of the best analogies I've heard was in a lecture by James White, Director of the Institute of Arctic and Alpine Research and professor at the University of Colorado. White compared greenhouse gas emissions and temperature to two prisoners handcuffed together. Ghgs run forward, and yank lagging temperature ahead.)

The good news in Allen's statement is that it is not yet too late to make some positive change. While future warming is inevitable, a 1,000 ppm future is simply unacceptable. It can be prevented, but only if nations work together -- now -- to intelligently and deliberately craft climate policy.