The U.N.-sponsored body also includes solar photovoltaic, wind power, geothermal and ocean wave technologies as among the renewable sources. But the bulk of the estimated contribution of renewables to global energy supply in its future scenarios is achieved by estimating the energy derived from traditional biomass, according to the "Summary for Policymakers" and charts published by IPCC.
Primitive vs. modern practices
The latest IPCC report estimates that in 2008, the renewable energy sources under their review contributed 12.9 percent of the world's main energy supply, measured in a thermal energy output unit called an exajoule. Half of that is from traditional biomass, the IPCC admits, and the group offers little justification for including this most primitive source of energy in its calculations.
IPCC researchers say their estimates show traditional biomass usage shrinking over time, to be gradually placed by more modern biomass generation, whereby trees felled are actually replanted. But charts showing the possible scenarios of the growth of renewables' share of energy still show biomass as the top source, even out to 2050.
The IPCC's blending of charcoal production with modern practices like biomass cogeneration on farms or wood waste burning near cities makes it difficult to determine how much traditional practices are to be replaced by more modern ones. But the IPCC admits that traditional biomass's share is larger, and the report suggests that its consumption will only fall slightly over the coming decades while modern biomass's share expands gradually.
"The number of people without access to modern energy services is expected to remain unchanged unless relevant domestic policies are implemented," IPCC officials explain.
Still, the group largely defends its future estimates. Although the other renewable technologies each separately represent a much smaller proportion of sources today as compared to traditional biomass, the scenarios laid out by the IPCC's calculations predict a threefold increase in their contribution by 2050 on the low end, and a tenfold expansion in its most optimistic outlook.
Experts say traditional biomass is likely the world's largest source of primary energy, due to widespread poverty in the developing world and the fact that nearly one-fourth of the world's population lacks regular access to electricity, according to the International Energy Agency. But the use of charcoal and felled trees and bushes for cooking food or heat is not celebrated by most environmentalists.
Indoor pollution hazards
The U.N. Environment Programme calls traditional biomass one of the most inefficiently used sources of energy in the world, and several U.N. agencies have been battling the negative health effects of indoor wood burning for years.
"Traditional use of biomass, especially charcoal, is often linked to degradation of forests and woodland resources as well as soil erosion," UNEP experts say in an earlier assessment of biomass's role in climate change mitigation. "Studies have shown that the inefficient use of bioenergy results in significant exposure to indoor air pollution. Women, children and the elderly face higher risks due to long hours spent around solid fuel based fires."
The Belgium based nonprofit Alliance for Rural Electrification estimates that traditional biomass is the main source of fuel for close to 2.4 billion in the developing world, but argues against its use, as "such traditional use of biomass fuels is typically inefficient, relying largely on low-cost sources such as forests and other natural vegetation," it says.
A 2006 study of biomass burning in India and Bangladesh by the Institute for Global Environmental Studies concluded that the practice was a top source of indoor air pollution and a major health problem.