There was a statistically rare, severe 2010 drought in the Amazon rainforest (following on the heels of a previous drought in 2005).

The upshot is that trees die and rainforest carbon dioxide releases go way up as a result (or, conversely, carbon dioxide uptake by the rainforest goes way down).

The possibility of a deleterious feedback loop comes into play: climate change leads to drought which leads to more carbon dioxide release, which leads to more climate change.