Original PowerPoint file available for download: bonn_ghg.ppt (184k)

Dams and Global Change

Objective : how can the available science inform decision-making ?

• Draft report on GHG emissions from reservoirs
  (Prof Pinguelli Rosa & M.A. dos Santos, COPPE, Rio de Janeiro)
• Submisssions from interested parties
• Reviewed by scientists, NGOs, industry
• Workshop of 20 scientists, utilities and NGOs from Canada, Brazil, France, Finland and USA
• Tucurui case study (Brazil)

Role of the Commission

• These findings reflect the results coming out of the work programme and derive from the available science
• They are not the Commission’s views
• The Commission also addresses economic, social and ecosystem issues, that are not reported here
• The Commission wishes to share these inputs in a timely manner with others debating dams and global warming

Findings (1)

• All 30 reservoirs studied so far emit GHGs
• Natural lakes studied emit GHGs
• Natural habitats may be either sources or sinks

Conclusion 1 : a reservoir causes a net change in GHGs from pre to post-impoundment and it is this net change that should be assessed for its contribution to global warming.

Emissions from different sources

Hypotheses for Emissions over Time

Findings (2)

Conclusion 2 : carbon is flowing into the reservoir from the catchment (and perhaps from the atmosphere)

Conclusion 3 : long term studies are essential to look at full life cycle emissions over reservoir lifetimes

Comparing Emissions: Alternatives

Comparing Emissions

• To make proper comparisons a full life cycle assessment is needed
• Observed emissions per square metre of reservoir need to be converted to emissions per TWh generated
• Both hydropower generation and emissions from reservoirs fluctuate from year to year
• Gross emissions from some reservoirs are so low that the difference between gross and net is unlikely to change the conclusions
• Gross emissions from other reservoirs are at similar levels to the thermal equivalent, but the net emission, and the life cycle are unknown

Calculating Emissions

Advice to Commission

• Hydropower cannot, a priori, be automatically assumed to be a ‘cleaner’ technology than thermal alternatives with respect to GHG emissions. Research is needed on a case by case basis to make this claim.
• In boreal climates (like Canada and Scandinavia) available studies so far suggest that emissions from hydropower reservoirs are very low.
• For Brazil, of ten dams studied, emissions vary from dam to dam with a 500-fold difference between lowest and highest. The lowest emissions are similar to Canadian lakes and reservoirs, the highest gross emissions may be in the same range as thermal energy plants.
• More research is needed

Assessment needs

• A pre-dam assessment of GHG emissions/sinks from the natural habitat and basin (baseline).
• An assessment of GHGs released from water passing through the dam (turbines and spillway)
• The observed GHG emissions from the reservoir surface. Inflows of carbon from upstream in the river basin.

Dams and Kyoto

• Reservoirs have been shown to emit GHGs - but this in itself is inconclusive
• If the objective is to ensure that dams only get the credits for the real emissions avoided, not the assumed emissions avoided, the work compiled by the WCD provides background
• The final report of WCD (Nov 2000) will give additional insights on the global experience with social, environmental and economic impacts of large dams

Research Needed

• More measurements on a wider range and diversity of reservoirs (including turbine emissions)
• More measurements on a wider range and diversity of natural environments in countries that are currently building dams.
• Improve the understanding of the role of transient carbon in reservoirs and natural lakes.
• What role do oceans play as repositories of carbon in sediments and how is this role affected by dams?
• What is the fate of carbon in an undammed catchment compared to a dammed catchment?