The Amazon rain forest may be on the cusp of releasing more carbon than it stores. Until now, the Amazon basin has cooled the planet by removing CO2. Drought and deforestation has led to enormous numbers of trees dying, pushing the rainforest closer to being a source of carbon dioxide rather than sink. Devastated areas threaten the remaining trees by reducing air moisture and keeping rain away from the forest nearby. The Amazon rain forest contains the equivalent of 10 years of emissions from burning fossil fuels.
Davidson E. A. et al. 19 Jan 2012. The Amazon basin in transition, Nature 481, 321–328.