A week or so ago I explained how researchers had discovered that plants are a source of methane: that a new study led by Frank Keppler of the Max Planck Institute in Germany calculates that all the world’s living vegetation (forests included) emit between 62 and 236 million tonnes of methane per year. This is apparently equivalent to between 10 and 30 per cent of annual global methane emissions.
Now the same researchers are claiming that their findings have been misinterpreted:
The most frequent misinterpretation we find in the media is that emissions of methane from plants are responsible for global warming. As those emissions from plants are a natural source, they have existed long before man’s influence started to impact upon the composition of the atmosphere. It is the anthropogenic emissions which are responsible for the well-documented increasing atmospheric concentrations of methane since pre-industrial times. Emissions from plants thus contribute to the natural greenhouse effect and not to the recent temperature increase known as ‘global warming’. Even if land use practices have altered plant methane emissions, which we did not demonstrate, this would also count as an anthropogenic source, and the plants themselves cannot be deemed responsible.
I guess this approach is consistent with the United Nations Framework Convention on Climate Change which defines ‘climate change’ as that which is attributable directly or indirectly to human activity, click here.
So according to Keppler et al. plants are not responsible for what they emit. I guess this means that they are not responsible either for sequesting carbon dioxide. However, we do count carbon sequestration (post 1990) in national greenhouse inventories, so shouldn’t we also count methane emitted from the same plants in the inventory?
Interestingly, in the Nature paper, Keppler et al. state:
In pre-industrial times, that is, without anthropogenic emissions, the relative contribution of methane to the atmosphere by direct plant emissions may have been even larger than today. This could have far reaching implications for the interpretation of atmospheric methane levels and climate signals in the past.