What if the Amazon tips from a carbon sink to a source?

By Chris Lang

In the past few years, the Amazon has faced two “one in a century” droughts. Last year’s drought covered a larger area of the Amazon and was even more severe than the 2005 drought. In both years huge amounts of carbon was released to the atmosphere as trees died. During these severe droughts, the Amazon turned from a carbon sink to a major carbon source.

Clearly, this has major implications for REDD.

In a recent short paper in Science magazine, researchers from the UK and Brazil report on “The 2010 Amazon Drought”. They write that the Amazon could be moving towards a tipping point, beyond which it will accelerate climate change, rather than slowing it:

The two recent Amazon droughts demonstrate a mechanism by which remaining intact tropical forests of South America can shift from buffering the increase in atmospheric carbon dioxide to accelerating it.

The researchers estimate that the amount of CO2 released in 2010 could be even more than that released as a result of the 2005 drought. They note that the 2010 drought had three epicentres, in southwestern Amazonia, north-central Bolivia and Mato Grosso state in Brazil. In 2005, there was only one epicentre, in southwestern Amazonia. The drought in 2010 covered a larger area: 3.2 million square kilometres compared to 2.5 million square kilometres in 2005. On 26 October 2010, the river level in Manaus reached its lowest recorded level since records began more than 100 years ago.

The lead author of the Science paper, Simon Lewis from the University of Leeds, said in a press release:

“Having two events of this magnitude in such close succession is extremely unusual, but is unfortunately consistent with those climate models that project a grim future for Amazonia.”

Both droughts were associated with warmer water in the Atlantic and the Pacific oceans. In the Science paper, the authors conclude that “If drought events continue, the era of intact Amazon forests buffering the increase in atmospheric carbon dioxide may have passed.”

In the Leeds University press release, Lewis spells out in more colourful language, what increasing greenhouse gas emissions might mean for the Amazon:

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

New York Times journalist Nigel Pitman was in Peru during last year’s drought. In November 2010, he reported on the impacts of the drought and explained in two sentences how these droughts illustrate that trading the carbon stored in forests would be the riskiest possible strategy for addressing climate change:

Long dry spells like these in Amazonia wither crops and worsen air pollution and cut off whole towns from the rest of the world, when the arm of the river they’re on turns to mud. They also destroy forests. Scientists used to think that if the guys with chainsaws could be convinced to stop cutting down trees, tropical deforestation would just stop. We now know that if all the guys with chainsaws stopped cutting down trees tomorrow morning, Amazonian forests might disappear anyway, thanks to higher temperatures, droughts, and forest fires.

The scale of the emissions from the Amazon is vast. The 2005 drought led to the release of approximately 1.6 billion tonnes of carbon to the atmosphere from the Amazon. In their Science paper, the researchers estimate that as much as 2.2 billion tonnes of carbon could have been released from the Amazon during 2010. That is about one-quarter of global emissions from fossil fuel use.

A year ago, the World Bank produced an “Assessment of the Risk of Amazon Dieback.” This was no ordinary World Bank report. It was carried out with the collaboration of several of institutions, including the Meteorological Research Institute (Japan), Exeter University (UK), the Centre for Weather Forecasting and Climate Change (CPET/INPE – Brazil) and the Potsdam Institute (Germany). The analysis was reviewed by a panel of “internationally renowned scientists and practitioners.” The report concludes that,

With rising atmospheric CO2 concentrations, climate change will lead to a substantial warming in Amazonia during the current century, reaching levels that are highly likely to affect the remaining forests throughout the region.

The report notes that Amazon forest dieback is one of “four major, non-linear, positive-feedback responses to global warming with the potential to create major disruptions in global climate”. (The other three are the slowing of the North Atlantic Thermohaline Circulation, the breakup of the West Antarctic Ice Sheet and methane emissions from melting permafrost.)

The World Bank report is long, and it has some omissions (such as the impact of World Bank projects on deforestation in the Amazon) but the message is clear. The Amazon is at risk due to climate change. Large amounts of the carbon currently stored in the Amazon’s forests could be released – sooner than previously predicted.

Another omission from the World Bank report is the obvious conclusion: trading the carbon stored in tropical forests is an incredibly risky strategy for avoiding runaway climate change. It seems increasingly likely that it would result in the release of the carbon temporarily stored in the Amazon’s forests.