Global warming is a complex matter, with many effects interacting. This, of course, makes modeling it accurately a great challenge. Now, a new feedback mechanism has been identified. The quantity of carbon dioxide in the atmosphere is rising. But how does this affect our world?
Recently, a research team has been looking into how higher carbon dioxide concentrations in the atmosphere affect the soil and its ability to take up methane and nitrous oxide, or release these potent greenhouse gases. By gathering data from 49 experiments across the globe, the team went looking for general patterns. They found two strongly emerging patterns:
- More carbondioxide boosted soil emissions of nitrous oxide in all soil types, and
- More carbondioxide also boosted methane emissions from wetlands and rice paddies.
How can this be explained?
By specialized microbial organisms in the soil, that respire nitrate and carbon dioxide, and produce methane (over 20 times more powerful greenhouse gas than carbon dioxide) and nitrous oxide (over 300 times more powerful) (for a comparison of the main greenhouse gases, see table 1). Two possible reasons to explain the flourishing of these microscopic organisms when atmospheric carbon dioxide is high are:
- Higher carbon dioxide concentrations reduce plant water use, making soils wetter and reducing the availability of oxygen in the soil, which is a good thing for these microbes, as they live in oxygen-free habitats.
- Increasing carbon dioxide makes plants generally grow faster, supplying soil organisms with more 'food', and thus energy.
Table 1: Comparison of the main greenhouse gases.
(Source: PEW Center on Global Climate Change)
It was hoped that plants could take up excess carbon dioxide, thereby mitigating the effects of it. But now, it turns out that the more plants take up carbon dioxide, the more microbes release even more potent greenhouse gases. This new finding might mean that previous models could have overestimated the ability of ecosystems to mitigate the greenhouse effect.
Figure 1: Schematic illustration of the greenhouse effect.
(Source: Millenium Energy Solution)
Knohl, A. and Veldkamp, E. (2011). Global change: Indirect feedbacks to rising CO2. Nature. 475(7355), pp. 177 – 178. Doi:10.1038/475177a.