Drought is killing off trees in Brazil's fragile Amazon rainforest and depleting the region's carbon reservoirs - an ecological double-whammy with devastating implications, according to a new study.

The Amazon's lush vegetation in a typical year absorbs nearly two billion tonnes of carbon dioxide.

But a 30-year study published by the journal Science found that the world's largest tropical rain forest is surprisingly sensitive to drought, and that the resulting loss of vegetation will have a greater-than-anticipated effect in causing a sharp spike in greenhouse gases.

The Amazon tree canopy, which absorbs massive amounts of greenhouse gases, often succumbs to the effects of dryness, thereby accelerating global warming by not absorbing CO2, say scientists.

Drought also accelerates the depletion of the region's carbon sinks, natural reservoirs that accumulate and store the chemical compound for an indefinite period.