A new paper published in Nature last week suggests the possibility that the Amazon basin, a major carbon sink, may soon become a huge new source of atmospheric CO2. The paper, with fifteen co-authors from the United States and Brazil, included original research as well as a comprehensive review of relevant literature in order to arrive at a tentative hypothesis that the Amazon basin is losing its equilibrium.
The paper cites a litany of probable causes for the apparently altered Amazon basin carbon cycle, including land-clearing, agriculture, climate change itself and recent exacerbations by El Niņo and La Niņa rhythms causing alternating drought and heavy rain conditions.
The Amazon basin is one of the world’s natural carbon sinks, naturally taking carbon dioxide out of the atmosphere and storing it in other forms, in this case, locked away as plant material. But a carbon sink can also be a carbon source, if something is done to not only interfere with the natural carbon sequestration, but to transform the locked carbon back into carbon dioxide.
Environmental experts have long warned about natural tipping points: critical junctures where change in climate itself begins to affect natural processes in such a way as to initiate or accelerate carbon release or otherwise contribute to warming. The ice sheets, which help cool the Earth by reflecting sunlight back into space, are one such tipping point. Interruption of carbon cycles or the release of static sequestered carbon as a result of increased temperatures or changed weather patterns are another.
The paper notes that for some time now, the Amazon rainforest has been observed to increase its biomass. It’s been hypothesized that it has been doing so as part of a recovery from a previous, unknown disturbance. As long as the total amount of plant material is growing, the rainforest is helping to mitigate emissions, by taking some of the excess carbon out of the atmosphere. However, as soon as this biomass is cleared, whether it is allowed to decompose or is burned, all of the carbon is released back into the atmosphere as carbon dioxide.
Forest clearing for development or agriculture is working against the general tendency of the forest to grow thicker and more massive. But in addition, changed weather conditions, related to climate change, affecting everything from temperature to rainfall are also having a negative effect on the basin’s efficacy as a sink, either by inhibiting growth, promoting forest fire, or killing existing plant life.
The authors of the paper point to changes in water and energy cycles in the basin as evidence that growth is not only slowing down, but may potentially reverse, releasing more and more previously stored carbon into the air.
The results are preliminary and the trend is not certain, but the possibility is frightening. Will we begin to see one major tipping point after another over the next years and decades? The most difficult thing in dealing politically with climate change is the gradual unfolding of its effects. But the changes may be less and less gradual as time goes by.
Photo credit: Jorge.kike.medina