Good news/bad news on greenhouse gases

Good news on the greenhouse gas front is rare to find (and not exactly over-reported.) But it turns out that atmospheric levels of methane, an important greenhouse gas due to it having a larger effect than CO2, has stopped increasing. From American Scientist:

This happy development wasn't entirely unanticipated, given that the rate of increase has been slowing for at least a quarter-century. Yet the United Nations Intergovernmental Panel on Climate Change has predicated many of its conclusions on scenarios in which methane concentrations would continue growing for decades to come. Thus the recent stabilization of methane levels is something that some scientists are trying very hard to explain.

Edward J. Dlugokencky, an atmospheric chemist with the National Oceanic and Atmospheric Administration (NOAA), has tracked atmospheric methane for many years. He says that "even as the reduction was happening, people doing emission scenarios weren't accounting for it." Dlugokencky maintains that the evolution of methane levels in the atmosphere mostly just reflects the attainment of a chemical equilibrium, such that methane production is balanced by its destruction. In sum, he says, atmospheric methane "looks like a system approaching steady state."

But now for the bad news. Over at Real Climate, there is a recent post about how much additional CO2 in the atmosphere might be "safe".

As usual with their site, they don't believe in over-simplifying their explanations for easy understanding, but the figures suggested, although appearing fairly "back of the envelope" look pretty bad:

This is a bit of a guessing game, but 2°C has been proposed as a reasonable danger limit. This would be decidedly warmer than the Earth has been in millions of years, and warm enough to eventually raise sea level by tens of meters. A warming of 2° C could be accomplished by raising CO₂ to 450 ppm and waiting a century or so, assuming a climate sensitivity of 3 °C for doubling CO₂, a typical value from models and diagnosed from paleo-data. Of the 450 ppm, 170 ppm would be from fossil fuels (given an original natural pCO2 of 280 ppm). 170 ppm equals 340 Gton C, which divided by the peak airborne fraction of 60% yields a total emission slug of about 570 Gton C.

How much is 570 Gton C? We have already released about 300 Gton C, and the business-as-usual scenario projects 1600 Gton C total release by the year 2100. Avoiding dangerous climate change requires very deep cuts in CO₂ emissions in the long term, something like 85% of business-as-usual averaged over the coming century. Put it this way and it sounds impossible. Another way to look at it, which doesn't seem quite as intractable, is to say that the 200 Gton C that can still be "safely" emitted is roughly equivalent to the remaining traditional reserves of oil and natural gas. We could burn those until they're gone, but declare an immediate moratorium on coal, and that would be OK, according to our defined danger limit of 2°C. A third perspective is that if we could limit emissions to 5 Gton C per year starting now, we could continue doing that for 250/5 = 50 years.

According to a chart that was part of my last post on CO2, the atmospheric level of CO2, on a "business as usual" basis, would be reached by about 2040. (We're already at about 380ppm.)

These figures are not good. However, the argument goes on in the comments section about whether Kyoto is a help or hinderance. Post number 105 comes up with some fairly imaginative ideas about reducing CO2 with self replicating robots and such like, and ends on this note, which neatly summarises conservative's concerns about Kyoto:

..many of the problems associated with CO2 is best solved with wealth. Indeed technology induced wealth solves both CO2-related problems AND all other sorts of nasty problems unrelated to CO2 such as poverty, disease, hunger, misery and disasters. By insisting on strangling economic growth, not only are you robbing the world of the best way to cope with climate change -- technology -- but also robbing the poor of the world the opportunity to cope with just about anything.

I haven't read the Stern report, or many of the articles criticising it yet, so I can't comment helpfully yet. But the main point of this post is just how bad the figures look for how hard it will be to keep that much carbon out of the atmophere.