Nature News | April 29, 2009 | Richard Monastersky
The climate situation may be even worse than you think. In the first of three features, Richard Monastersky looks at evidence that keeping carbon dioxide beneath dangerous levels is tougher than previously thought.
In 2007, environmental writer Bill McKibben approached climate scientist James Hansen and asked him what atmospheric concentration of carbon dioxide could be considered safe. Hansen's reaction: "I don't know, but I'll get back to you."
After he had mulled it over, Hansen started to suspect that he and many other scientists had underestimated the long-term effects of greenhouse warming. Atmospheric concentration of CO2 at the time was rising past 382 parts per million (p.p.m.), a full 100 ticks above its pre-industrial level. Most researchers, including Hansen, had been focusing on 450 p.p.m. as a target that would avoid, in the resonant and legally binding formulation of the United Nations Framework Convention on Climate Change, "dangerous climate change". McKibben was aware of this: he was thinking of forming an organization called 450.org to call attention to the number, and his question to Hansen was by way of due diligence.
As he thought about McKibben's question, Hansen, who runs NASA's Goddard Institute for Space Studies in New York, began to wonder if 450 p.p.m. was too high. Having spent his career working on climate models, he was aware that in some respects the real world was outstripping them. Arctic sea ice was reaching record lows; many of Greenland's glaciers were retreating; the tropics were expanding. "What was clear was that climate models are our weakest tool, in that you can't trust their sensitivity in any of these key areas," he says. Those warning signs — and his studies of past climate change — led Hansen to conclude that only by pulling CO2 concentrations down below today's value could humanity avert serious problems. He came back to McKibben with not 450 but 350. In 2008, he published a paper spelling out his rationale for that target.
The difference between 350 and 450 is not just one of degree. It's one of direction. A CO2 concentration of 450 p.p.m. awaits the world at some point in the future that might conceivably, though with difficulty, be averted. But 350 p.p.m. can be seen only in the rear-view mirror. Hansen believes that CO2 levels already exceed those that would provide long-term safety, and the world needs not just to stop but to reverse course. Although his view is far from universal, a growing number of scientists agree that the CO2 challenge is even greater than had previously been thought.
Several recent studies, for example, indicate that it may be exceedingly difficult to cool the climate down from any eventual peak or plateau, no matter what CO2 concentration is chosen as a target by the international community. And by looking at the problem in a new sort of way — by tallying the total amount of carbon injected into the atmosphere across human history — two papers in this issue of Nature reveal how close the world has come to the danger point (pages 1158 and 1163). "It's tougher than people have appreciated. We have less room to manoeuvre," says Malte Meinshausen, an author of one of the papers and a senior researcher at the Potsdam Institute for Climate Impact Research in Germany.
This video was createdby Michael McGee, with filming by Alan Walton, to introduce what Bill McKibben calls "the most important number on the planet," and to say why it needs to be at the heart of our climate policies and economic planning. It was submitted to the Davos Debates 2009, an online forum for discussing and debating global issues in the lead up to the 2009 World Economic Forum (AGM) in Davos Switzerland. The video answers the following Davos Debates question: Will the environment lose to the environment in 2009?
The Davos Debates forum was the product of a collaboration by YouTube, LLC and the World Economic Forum. The "gas station scene" in the McGee video was used by YouTube in a video it created for the World Economic Forum in January 2009.
A practical global strategy almost surely requires a rising global price on CO2 emissions and phase-out of coal use except for cases where the CO2 is captured and sequestered. The carbon price should eliminate use of unconventional fossil fuels, unless, as is unlikely, the CO2 can be captured. A reward system for improved agricultural and forestry practices that sequester carbon could remove the current CO2 overshoot. With simultaneous policies to reduce non-CO2 greenhouse gases, it appears still feasible to avert catastrophic climate change.
"If humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted, paleoclimate evidence and ongoing climate change suggest that CO2 will need to be reduced from its current 385 ppm to at most 350 ppm."
Global warming is the result of the unnatural rise in the concentration of greenhouse gases in the Earth’s atmosphere. Carbon dioxide the greenhouse gas most responsible for the global warming trends that are happening and projected into the future.
The question we need a clear answer to is this: what concentration of CO2 and other greenhouse gases is safe for us and for future generations? For an answer to the question based on paleoclimate science, there is a single report, the Hansen report. In April 2008, ten scientists published Target CO2: Where should humanity aim? The lead writer is James Hansen, head of the NASA Goddard Institute for Space Studies in New York. The report states that a safe level of atmospheric CO2 has a ceiling of about 350 parts per million (ppm) and that the functioning of the planet will be at risk of remaining at elevated, rising levels for too long. Here is an excerpt:
If humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted, paleoclimate evidence and ongoing climate change suggest that CO2 will need to be reduced from its current 385 ppm to at most 350 ppm, but likely less than that.
The Nobel-winning International Panel on Climate Change implies a need to stabilize the concentration of greenhouse gases at levels below present levels. Here is an excerpt from the AR4 2007 Synthesis Report:
In order to stabilize the concentration of GHGs in the atmosphere, emissions would need to peak and then decline thereafter. The lower the stabilization level, the more quickly this peak and decline would need to occur. [p. 66]
During 2008, US environment writer Bill McKibben and colleagues established the climate activist group 350.org, with the aim of spreading the message that policy targets need to reflect the scientific imperative.
The campaign has harnessed many people and organisations' collective energy and has been successful in the United States, and internationally at such forums at COP14 in Poznan, in helping to educate people that targets such as 450 ppm (per million) carbon dioxide in the atmosphere are not acceptable, that the current level of carbon dioxide (387 ppm) is too high for a safe climate, and so our action must be zero emissions and a cooling of the planet.
The important question now is whether 350 is a target based on the science, or one that is judged to be politically appropriate.
David Spratt's full blog entry can be read at Climate Code Red:
By David Spratt | March 7, 2009 | Reposted from Climate Code Red
The “25-40/2020” scenario was published in the IPCC’s 2007 Fourth Assessment Report Working Group III report, in Box 13.7 on page 776, “The range of the difference between emissions in 1990 and emissions allowances in 2020/2050 for various GHG [greenhouse gas] concentrations for Annex I and non-Annex I [Kyoto] countries as a group”, where targets were given for stabilisation at 450, 550 and 650 ppm CO2e.The targets for 450 CO2e were:
Region: Annex 1 countries
2020: –25% to –40%
2050: –80% to –95%
Region: non-Annex 1 countries
2020: Substantial deviation from baseline in Latin America, Middle East, East Asia and Centrally-Planned Asia
2050: Substantial deviation from baseline in all regions
The following excerpts are from 
