Global Warming: Plants Are Not To Blame

By Catherine Brahic
First published in SciDev.Net - 20 January 2006

Plants are not to blame for climate change, according to a statement issued this week (18 January) by the researchers who reported eight days ago that plants emit up to a third of the methane — a potent greenhouse gas — in the atmosphere (see The latest threat to the world’s climate?).

Surprised by the wave of media attention generated by their study, the authors have hastened to add that because these previously unsuspected methane emissions come from a natural source, they are not the culprits in contemporary climate change.

"They existed long before man's influence started to impact upon the atmosphere," the team write. "The fundamental problem still remaining is the global large-scale burning of fossil fuels."

Following the media interest, Frank Keppler at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany and colleagues received numerous emails from scientists and concerned members of the public. Some asked the team whether it was safe to stand near plants or visit the Amazon rainforest.

Speaking to SciDev.Net, Keppler said he wanted to make three points clear to the public.

First, their findings do not mean that reforestation programmes should be condemned. Trees absorb carbon dioxide, the most important greenhouse gas, so planting them is still beneficial.

When the methane emitted by trees is taken into account, says Keppler, the benefits of planting trees to absorb atmospheric carbon dioxide diminish by just one to four per cent — a negligible effect.

Secondly, changes in the overall amount of methane emitted by plants — including changes that could worsen global warming — are likely to be caused by human activities such as deforestation.

Finally, they say that much more research is needed to discover how methane emissions from plants vary according to species, temperature, humidity, sunlight and other factors, as well as how these emissions might change as the environment does.

"From a scientific point of view, this is fascinating," says Keppler. "We wanted to share this. It could be one piece of the puzzle which is important for the future."

To those who are wondering if they should start chopping down trees, Keppler says they should imagine a world without any trees. "What do we have, then?" he asks.

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