In addition to loss of trees, the degradation of tropical forests by selective logging and fires causes large amounts of "hidden" emissions.
The slow moving process has remained almost invisible to satellite observations in the Amazon.
Researchers say degradation in Brazil causes additional emissions equivalent to 40% of those from deforestation.
The research is due to be published in the journal Global Change Biology.
The rapid removal of trees in the Amazon rainforest has been a significant source of global carbon emissions for many decades.
It is said to account for around 12% of human induced greenhouse gases, roughly the equivalent of both agriculture and transport.
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