The amount of carbon emissions caused by world forest destruction is likely far less than the 20 percent figure being widely used before global climate talks in December, said the head of the Brazilian institute that measures Amazon deforestation. Gilberto Camara, the director of Brazil’s respected National Institute for Space Research, said the 20 percent tally was based on poor science but that rich countries had no interest in questioning it because the number put more pressure on developing countries to stem greenhouse gases. “I’m not in favor of conspiracy theories,” Camara told Reuters in a telephone interview on Friday. “But I should only state that the two people who like these figures are developed nations, who would like to overstress the contribution of developing nations to global carbon, and of course environmentalists.”