Brazil's new pledge to slash its national carbon footprint by 43% by 2030 sounds like exactly the kind of aggressive commitment that environmentalists have been clamoring for ahead of December's United Nations talks in Paris to reach an international climate treaty to replace the Kyoto Protocol.
It's far more ambitious than the Obama administration's plan to reduce US emissions by 26-28% by 2025, never mind Beijing's goal of "peaking" Chinese emissions by 2030.
Unveiling the pledge at the UN on Sunday, Brazil's President Dilma Rousseff said her country was "contributing decisively" to the global fight against climate chaos.
There's just one problem with Brazil's plan: it relies heavily on hydroelectric power from dams in the Amazon, which some independent experts say have huge greenhouse gas emissions that officials fail to acknowledge.
Rousseff said Brazil would increasingly replace fossil fuels with wind and solar power while maintaining 66% of its growing electricity generation from hydroelectric power. Her administration plans to bring 12 new mega-dams on line in the Amazon by 2024.
The Brazilian government diverts attention from the dams' controversial impact on biodiversity, and on the indigenous communities they uproot, by claiming they have a negligible carbon footprint.
"It does not emit greenhouse gases," Rousseff insisted when unveiling one rainforest dam. "That means that we have a renewable energy project."
Philip Fearnside, an American professor at Brazil's National Institute for Amazon Research, who has spent decades studying the problem, says this is not true.
"The fact that they are emphasizing hydro is very worrisome," he told VICE News. "These dams have tremendous carbon impacts."
The problem, comes from the thousands of square miles of uncleared tropical rainforest flooded by the dam reservoirs. As the vegetation rots, it emits massive quantities of greenhouse gases that are ignored by dam planners and government officials who do not include them in their calculations of national emissions.
The dead trunks above the water release carbon dioxide, the principal cause of the climate crisis, but what goes on under the surface may be worse. At the bottom of the reservoirs, the dead jungle gives off methane as it decomposes in anaerobic conditions. The greenhouse effect of methane is up to 36 times more potent than that of carbon dioxide.
The numbers are complicated, and depend on the specific conditions at each dam. Fearnside has calculated that one existing Amazonian dam, Tucurui, has a larger carbon footprint than Sao Paulo, the world's ninth largest city.
Meanwhile, the controversial $22-billion Belo Monte complex of dams, currently under construction, will give off 11.2 million tons of carbon per year, Fearnside said. The scientist said it will take 41 years for emissions from the complex to finally fall below those of a fossil fuel power plant of equivalent capacity.
The emissions from many — but not all — of the dams do fall over a period of years or decades. But the initial spike falls exactly within the brief window that scientists say humans have to dramatically slash the world's carbon footprint in order to avoid catastrophic climate change.
Paulo Barreto, a forester with Imazon, a Brazilian think tank specializing in Amazonian conservation, said putting new roads through virgin rainforest to build the dams will also draw economic migrants, and encourage settling on the jungle frontier. This, he said, means that the dams indirectly trigger more deforestation, with each lost acre releasing as much as 150 tons of carbon into the atmosphere.
"Brazil needs to think harder about the impacts of climate change on Brazil, rather than just meeting our international climate obligations," Barreto said.
Campaigners say that a strong deal in Paris committing large nations to drastically reduce their greenhouse gas emissions may be our last chance to avoid catastrophy.
"Brazil is putting these dams into the energy mix, without so much as looking at their carbon footprints," said Brent Millikin, the Brazil-based Amazon program director for International Rivers, a US environmental group. "The dams are a disaster every way you look at it."
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