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Published online 5 March 2009 | Nature | doi:10.1038/news.2009.136
News: Briefing
Climate change crisis for rainforests
Drought could turn carbon sinks into sources.
The tropical forests of South America, Africa and Asia take up and release huge amounts of carbon each year. On the whole, they are a significant 'sink' for atmospheric carbon dioxide, but their future role in sequestering the greenhouse gas is uncertain.
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In a forest, new plants grow in each year and the growth of plants is a process of net carbon absorption. How can forests become a carbon source?
@Hilstein Huang: When trees die, the carbon that has been absorbed over time, is released. When many trees die at the same time - here as a result of drought - more carbon is released than is absorbed at the same time by regrowth (and by trees that have survived), and the forest becomes a net carbon source.
The irony of it all is that human impact on the natural hydrological cycle may be an important but underestimated causative factor of droughts. Just look at what we have done e.g. Hoover Dam, Three Gorges, etc.
Also, a dry rain forest has the potential to become fuel for a (Rain)forest fire. Regarding human endeavors of the hydrological: dams reprise a fraction of the water from a region. It's extremely difficult to associate dams with a drought in the current state of climate change, i.e. ocean (3.6x10^8 km^2) temperature/current fluctuations. It's probably a more sound case to consider aquifers/ecology for each damn first, rather than large-scale climate predictions based on land-based (1.5x10^8 km^2) hydrological changes until more supercomputers are dedicated to such data collection and computation.