At issue is the balance between two natural phenomena. One is beneficial: as carbon-dioxide levels in the air rise, plants grow more quickly, absorbing more carbon in return. Scientists can measure this in the lab, but they don't know how much more fertile the new, carbon-enhanced environment will be for plants.
The other is "a monster in the dark," says Stephen Pacala, an environmental scientist at Princeton. As temperatures rise, permafrost, which holds an enormous amount of carbon from long-dead plants, tends to dry out, allowing decay and a release of carbon into the atmosphere. If this phenomenon, called "outgassing," were to kick in, it could inundate the atmosphere with carbon dioxide, perhaps doubling or tripling the effect of the past century of human industry.
Outgassing is one of the "dangerous anthropogenic warming" effects that the Copenhagen summit is trying to head off. Nobody knows for sure what might trigger it, Meanwhile...As politicians negotiate and the rest are rising quickly at the poles, the north polar ice cap is in retreat, permafrost is showing of us feel good about driving hybrids and using fluorescent bulbs, our fate may be riding on an obscure contest between plants and permafrost. read more at News Week