Scientific Errors in the Fearnside Comments on Greenhouse Gas Emissions (GHG) from Hydroelectric Dams and Response to His Political Claiming

Abstract

In the September 2004 edition of Climatic Change (N • 66), an editorial comment was published by Philip Fearnside, jointly with an article written by ourselves (Rosa et al., 2004) reporting on a broad-ranging project through which we measured CO 2 and CH 4 emissions at eleven Brazilian hydroelectric dams, from Itaipu, with the largest installed capacity in Southern Brazil, northwards to Tucuruí in Amazonia.This comment reflects a long-standing controversy over the estimates presented by Fearnside and the experimental results that we have obtained so far on greenhouse gases emissions by hydroelectric dams in Brazil (Rosa et al., 1996;Fearnside, 1996).The key issue in this latest comment by Fearnside is based on the fact that the water intake for the Tucuruí hydroelectric dam turbines is located at an average depth of 35 m, with a high methane concentration at a pressure of around three atmospheres 1 and an estimated temperature of 15 • C. This water pressure is suddenly eased after running through the turbines to the tailrace, flowing downstream from the hydroelectric dam, while it is drawn into the spillway at a depth of no more than twenty meters, far shallower than the water intake point for the turbines.The author of these comments uses the data published by us (Rosa et al., 1997) on the methane concentration measured by Tundisi 2 , who worked in cooperation with our research group. Fearnside commits a series of errors: he is confused about the transformation of units to express the Henry's constant, obtaining a value that is completely wrong; he errs when calculating the methane concentration in the water Climatic Change (2006) 75: 91-102

Hydropower – A Green Energy? Tropical Reservoirs and Greenhouse Gas Emissions

“…CH 4 is still emitted [20]. The scattering of the data is significant for the same reasons mentioned above, and it must be pointed out that significant quantities of field data do not show any ebullition.…”

“…The total GHG emissions of 942 kg MWh -1 CO2 eq. exceed the emissions of comparable energy production form the use of coal by a factor of 2.6, calculated for a coal emission of 25.6 t TJ -1 C and a conversion factor of 0.0036 MWh TJ -1 [20].…”

Greenhouse Gas Emissions from Hydroelectric Dams: Reply tO Rosa Et al.

“…pressure (i.e., in the tailrace) is lower than I calculated, then one should conclude that more (not less) CH 4 is released when water that is super-saturated with methane emerges from the turbines. Even if the value for the Henry's Law constant were the value suggested by Rosa et al (2005), the estimates of CH 4 release presented in my editorial comment would remain the same. Both the discussion of Henry's Law and of soft drinks in my editorial comment were illustrations of the principles involved in methane release.…”

“…The actual calculation of the amount released, however, was based instead on published measurements of CH 4 concentrations above and below real dams. Rather than a theoretical calculation from temperature and pressure changes, the bottom line, which Rosa et al (2005) think "absurd," is based on a more direct line of evidence. Rosa et al (2005) suggest that the argument for a rapid release of methane when water emerges from the turbines of a hydroelectric dam is somehow invalidated by the difference between the "few seconds" mentioned in my paper as the time necessary for release of gas bubbles from a bottle of Coca Cola and the half hour they refer to for the last bubbles to emerge from a leisurely consumed bottle of Brazil's politically correct soft drink -Guaraná.…”

“…In the case of methane in the water from the spillway at Tucuruí, this is best considered to be completely released because the water is pulverized into tiny droplets as it falls 58 m to a reinforced-concrete dissipation basin, including a "ski-jump" device that launches the water skyward half-way down its decent (see Fearnside, 2004a). Rosa et al (2005) have apparently misread the description of the CO 2 portion of my calculation. They state that I add the "CO 2 emissions not only from the hydroelectric dam tailrace, but also from the water surface."…”