WC Archive

A few days ago, a report in Nature from the Max Planck Institute suggested that plants may be responsible for quite a bit more methane than previously believed (methane is, as we know, 21 times more powerful a greenhouse gas than carbon dioxide, but isn't nearly as abundant in the atmosphere). Perhaps unsurprisingly, this report exploded across the newsosphere, usually with headlines suggesting that plants were responsible for global warming, that planting trees to mitigate atmospheric CO2 just made things worse, and otherwise striking an odd balance of "we're doomed" and "it's not our fault!"

We didn't write about it here because we've read enough scientific reports to know when something is very preliminary, and not nearly as big a deal as press reports claim, a decision underscored by RealClimate's take on the report. Today, the researchers who wrote the Nature article issued a new press release trying to get everyone to calm down:

...our discovery led to intense speculation that methane emissions by plants could diminish or even outweigh the carbon storage effect of reforestation programs with important implications for the Kyoto protocol, where such programs are to be used in national carbon dioxide (CO2) reduction strategies. We first stress that our findings are preliminary with regard to the methane emission strength. Emissions most certainly depend on plant type and environmental conditions and more experiments are certainly necessary to quantify the process under natural conditions. As a first rough estimate of the order of magnitude we have taken the global average methane emissions as representative to provide a rough estimate of its potential effect on climate. These estimates... show that methane emissions by plants may slightly diminish the effect of reforestation programs. However, the climatic benefits gained through carbon sequestration by reforestation far exceed the relatively small negative effect, which may reduce the carbon uptake effect by up to 4 per cent. Thus, the potential for reduction of global warming by planting trees is most definitely positive. The fundamental problem still remaining is the global large-scale anthropogenic burning of fossil fuels.

Emphasis mine. The press release includes a brief paragraph explaining in more detail how the estimates were calculated; the amount of methane (CH4) emitted by plants is a tiny fraction of the amount of CO2 captured in the same time frame -- no more than 2g of CH4 for every kilogram of CO2. The greater greenhouse characteristics of methane make the effect of that small amount of methane disproportionately large, but (as quoted above) the overall reduction in carbon uptake is 1-4%.

In short, don't worry. Planting trees for carbon sequestration is still a good idea -- you should just plan to plant 1-4% more of them now.