Guardian: The Brazilian government is preparing to pledge a big curb in its greenhouse gas emissions by 2020 as a "political gesture" aimed at pressing rich nations into agreeing to large cuts in carbon. The country’s chief of staff, Dilma Rousseff, said Brazil would take proposals for voluntary reductions of 38-42% by 2020 to the Copenhagen climate change summit next month. The reductions are from projected 2020 emissions levels if no action was taken. "What Brazil is doing is a …