Amazonian droughts can trigger huge CO2 emissions. The tree die-off from the 2005 drought caused the release of 5 billion tonnes of CO2 and the researchers predict CO2 emitted as a result of the 2010 drought will be higher. The United States emitted 5.4 billion tonnes of CO2 in 2009 for comparison. As much as 1.3 tonnes of CO2 are absorbed by the world's rainforests each year, "almost 20 percent of carbon emissions from fossil-fuel burning," noted The Great Beyond blog at Nature.

Above: Drought in the Amazon (1 month assessment period, through 16 October 2010). Source: University College London Global Drought Monitor via WWF.

The new research predicts the Amazon rainforests will not absorb from the atmosphere their usual 1.5 billion tons of CO2 in both 2010 and 2011. A further 5 billion tonnes of CO2 is predicted to be released from the trees killed by the drought as they rot.

"Two unusual and extreme droughts occurring within a decade may largely offset the carbon absorbed by intact Amazon forests during that time. If events like this happen more often, the Amazon rainforests would reach a point where it shifts from being a valuable carbon sink slowing climate change, to a major source of greenhouse gasses that could speed it up," Lewis added.

As part of the new research, Lewis and Paulo Brando, of the Instituto de Pesquisa Ambiental da Amazonia (IPAM) in Belém, Brazil, "used the known relationship between drought intensity in 2005 and tree deaths to estimate the impact of the 2010 drought."

"We will not know exactly how many trees were killed until we can complete forest measurements on the ground," Brando said. "Our results should be seen as an initial estimate. The emissions estimates do not include those from forest fires, which spread over extensive areas of the Amazon during hot and dry years. These fires release large amounts of carbon to the atmosphere."

Unfortunately, Amazonian droughts may become more frequent and intense in coming decades, according to earlier research by Brando.

The 2010 drought reduced rainfall over 1.16 million square-miles (3 million square km) of the rainforests, compared with 734,000 square miles (1.9 million square km) in the 2005 drought, Reuters reported that the study had found. "57 percent of Amazonia had low rainfall in 2010 as compared with 37 percent in 2005", the researchers wrote.

The Rio Negro in Brazil reached a record low in 2010. This tributary to the Amazon, observed by the Earth Observatory at NASA, "is significantly smaller in 2010 than in 2008. The most notable difference is in the braided channels northwest of Manaus. Many of the channels disappeared in 2010, and all are shrunken. The main body of the river near Manaus is narrower. Every body of water in the scene, including the Amazon River, also changed. Tan islands dot the Amazon where water had been in 2008."

Rio Negro in December 2008, source: NASA image.

Rio Negro in December 2010, source: NASA image.

The record low came just 16 months after the river set a record high of more than 97 feet (29.77 meters) that flooded Manaus. In January 2011, far away from Manaus, south-eastern Brazil had massive floods. If wetter areas become wetter and drier areas become drier from climate change, an region that has rainy and dry seasons experience those extremes more intensely with increasing regularity.

Amazonian droughts have grown more frequent and severe, the Global Post reports.

"The ecosystems here have become so dry that instead of a being a barrier to fire, the forest became kindling," said Foster Brown, an environmental scientist at the federal university in the Brazilian state of Acre. "We've changed from a situation where a relatively small part of the region would be susceptible to fire to the entire region being susceptible to fire."

The two extreme droughts fit climate model predictions for the Amazon. "Under the more extreme scenarios, large parts of the forest could turn into a savannah-like ecosystem by the middle of the century with much lower levels of animal and plant biodiversity." Lewis and others are investigating if the droughts are an anomaly or driven by climate change. If the drought's cause is global warming, then it "could quite rapidly move to a much drier Amazon with less forest there," Lewis said.

"If greenhouse gas emissions contribute to Amazon droughts that in turn cause forests to release carbon, this feedback loop would be extremely concerning," Lewis said. "Put more starkly, current emissions pathways risk playing Russian roulette with the world's largest rainforest."

The rainforests' transformation to cerrado, the Brazilian savanna, "may happen faster than that study projected given the droughts of 2005 and 2010," Daniel Nepstad, a tropical biologist at IPAM, told the Inter Press Service.

A year ago, the World Bank predicted "with more certainty than any other prior study" that the Amazon is "very close" to the tippling point of dieback. The Amazon is "very close (about 2-3 percent of total deforestation) to a tipping point of combined events that will lead ultimately to its collapse", the World Bank report found.

A policy of zero deforestation is considered an emergency, although insufficient measure to stabilize the process.  The effects of climate change alone would contribute to the reduction of the extent of the rainforest biome by one third by the end of the century, according to the report. Brazil will depend on others (namely the US and China) to stabilize global carbon density to ultimately to save the Amazon and in turn stabilize a key feedback loop to the global climate.

Between 16 and 17 percent of Amazon rainforests have already been destroyed by deforestation, Mongabay reports. "Logging, clearing, fragmentation, and human-started fires are common occurrences in parts of Amazonian... Although deforestation has slowed recently, it has not stopped. Combined with climate change, these on the ground changes could further push some regions to large-scale forest die-off."

There has been an overall 25 percent decline in rainfall in the southeastern Amazon over the past four years, Nepstad said. The dryness has sparked huge forest fires that cover up to 3,860 square miles (10,000 square km) and the smoke inhibits rainfall, causing more drying the forests.

"Forests diebacks are taking place all around the world. The evidence is quite sobering," Nepstad said.

"I've never seen a year like this," said Mariazinha Yawanawa told the Global Post. She is the first female village chief of the remote Mutum community in Acre in far western Brazil. "Every morning, when all the family members meet, we're asking each other, 'What is happening?'"

"Everything has changed. We don't know when we can plant. We plant and then the sun kills everything," Mariazinha said. "If it continues like this, we expect a tragedy."

And the point she pressed upon her visitors was, perhaps they should be worried, too.

"I ask you," she said, "as someone who lives in the outside world who knows the tragedy that's happening there -- is there anything we can do?"

I think there is much we can do about climate change, but every action we could take involves people change. Perhaps a more pointed question to ask would be -- is there anything that we will do?