[DEBATE] : (Fwd) Hydropower no answer for climate change

[Patrick Bond]

Hydropower: a greenhouse gas culprit?
*
*The green image of hydropower may have been seriously overstated, warn 
scientists
1 December 2006
Source: Nature

Hydropower plants have long been a byword for clean energy. But 
researchers warn that tropical reservoirs might release more greenhouse 
gases than fossil-fuel power stations.

Philip Fearnside, a conservation biologist at the National Institute for 
Research in the Amazon in Manaus, Brazil, has shown that in the first 
ten years of operation, a typical reservoir will emit four times as much 
carbon as a fossil-fuel station.

The culprit is organic matter trapped when land is flooded to create a 
dam. As this decays, it releases significant amounts of carbon dioxide 
and methane.

It is a topic of vigorous debate, fuelled by a lack of data for tropical 
dams and the implications for energy strategies in developing countries, 
reports Jim Giles.

It calls into question the wisdom of promoting dam construction in 
developing countries, including a US$5 billion project proposed for the 
Congo river. Another concern is the funding of hydropower projects 
through the Kyoto Protocol's Clean Development Mechanism.

These concerns are likely to influence discussions of greenhouse gas 
emissions at a UNESCO meeting in Paris, France, next week (5-6 December) 
as well as future analyses by the Intergovernmental Panel on Climate 
Change.

***

News

Nature 444, 524-525 (30 November 2006) | doi:10.1038/444524a; Published 
online 29 November 2006
Methane quashes green credentials of hydropower

Jim Giles


Emissions from tropical dams can exceed fossil-fuel plants.

At the time, it must have sounded like a sensible case of sustainable 
development. During the 1980s, about 2,500 square kilometres of 
Amazonian rainforest was flooded to create the Balbina dam to feed the 
energy demands of the Brazilian city of Manaus. A sizeable chunk of 
rainforest was lost, but Brazil gained access to a non-polluting energy 
source. It's a compromise Brazil has made many times; more than 80% of 
the country's domestic electricity is generated by hydropower plants.

Yet the clean, green image of dams may have been seriously overstated. 
Researchers are gathering in Paris next week to discuss greenhouse-gas 
emissions from tropical reservoirs. Some of the latest findings point to 
a disturbing conclusion: that the global-warming impact of hydropower 
plants can often outweigh that of comparable fossil-fuel power stations. 
If that's correct, current energy strategies, particularly in developing 
nations, will need to be rethought.

The problem lies with the organic matter in the reservoir. Large amounts 
are trapped when land is flooded to create the dam, and more is flushed 
in after that. In the warm water of tropical dams, this matter decays to 
form methane and carbon dioxide. Although both are greenhouse gases, the 
main worry is methane, which has more than 20 times the warming impact 
of carbon dioxide over a 100-year period. In the specific case of 
Balbina, there is now a rough consensus: in terms of avoiding 
greenhouse-gas emissions, a fossil-fuel plant would have been better.

But that is where the agreement ends. On one side of the debate is 
Philip Fearnside, a conservation biologist at the National Institute for 
Research in the Amazon in Manaus. His work, based mainly on theoretical 
calculations, looks at water leaving dams. Many dams release water from 
several metres below the surface, so the flow goes through an abrupt 
pressure change. Fearnside calculates that this causes methane release, 
much as carbon dioxide fizzes out when carbonated drinks are opened. His 
latest results suggest that a typical tropical hydropower plant will, 
during the first ten years of its life, emit four times as much carbon 
as a comparable fossil-fuel station.

Lining up against him in a decade-long dispute are Luiz Pinguelli Rosa 
and his colleagues at the Federal University of Rio de Janeiro, who 
accuse Fearnside of exaggerating reservoir emissions. They complain in 
particular that Fearnside has extrapolated from measurements taken on 
the Petit Saut dam in French Guiana; the data were taken in the years 
immediately after the reservoir was created, when the store of organic 
matter would have been greatest.

With few data sets available on tropical dams, the debate has increased 
in acrimony without approaching a conclusion. Environmental groups 
question the impartiality of Rosa's work, which is funded in part by the 
hydropower industry. Rosa strongly denies any bias, and in turn accuses 
Fearnside of seeking to show that "something is wrong with dams".

If these estimates are correct, figures for annual global methane 
emissions need to be increased by a fifth.

The Paris meeting, which runs on 5–6 December and is organized by the 
United Nations Educational, Scientific and Cultural Organization 
(UNESCO), is unlikely to settle their dispute, but researchers will 
discuss new methane data. On 14 November, for example, Frédéric Guérin 
of the Laboratory of Meteorology in Toulouse, France, and his colleagues 
published results on methane release from sites downstream of three 
tropical dams1. They found that so much methane builds up in the dam 
that downstream emissions, which are rarely factored into estimates of a 
reservoir's impact, should account for between a tenth and a third of 
total emissions. Another new paper estimates that, for Balbina, 
downstream emissions alone have the same greenhouse warming potential as 
6% of all the fossil fuels consumed by São Paulo, a city of more than 11 
million people2.

Even without these downstream emissions, the global impact of dams may 
be significant. Danny Cullenward, an energy-policy expert at Stanford 
University, has made preliminary calculations of the impact of 
Fearnside's findings. Cullenward stresses that more data are needed, but 
his estimates suggest that dams release between 95 million and 122 
million tonnes of methane per year. If correct, estimates of annual 
global methane emissions (which do not generally include dam emissions) 
need to be increased by a fifth. Even extrapolating Rosa's figures gives 
Cullenward a total of 23 million tonnes.

Many think enough is known to start acting now. Some worry about the 
huge dam projects tentatively planned for tropical areas, such as a 
$5-billion project on the Congo river. Another concern is the Clean 
Development Mechanism (CDM), a system that allows developed nations to 
fund clean-energy projects in developing nations in return for credits 
that can be used to meet Kyoto Protocol targets. Current rules allow 
certain hydropower projects to be funded under the CDM, a situation some 
scientists and environmental groups would like to see revised.

But matters are unlikely to change without more data, so researchers at 
the UNESCO meeting will discuss which questions to prioritize and how 
best to work together. More substantial progress could begin in 2008, 
when the Intergovernmental Panel on Climate Change (IPCC) will decide 
whether or not to start work on a special report on renewable energy. 
Previous IPCC special reports have had significant political impact, and 
the dams question is likely to fit very well into the scope of the 
proposed energy study, says Bert Metz, a climate-policy expert at the 
Netherlands Environmental Assessment Agency and co-chair of one of the 
IPCC's three working groups.

References

1. Guérin, F. et al. Geophys. Res. Lett. 33, L21407 (2006).
2. Kemenes, A., Forsberg, B. R. & Melack, J. M. in Proc. 8th Int. Conf. 
Southern Hemisphere Meteorology and Oceanography, Foz do Iguaçu, Brazil, 
24–28 April 2006, 663–668 (INPE, São José dos Campos, Brazil, 2006).