redOrbit: Scientists said Wednesday that the U.S. has to lead the global fight on climate change by breaking with business-as-usual and setting tough standards for the amount of greenhouse gases it emits into the atmosphere. The National Research Council scientists said the U.S. should set a budget that would limit greenhouse gas emissions to a total of between 170 and 200 gigatons of carbon dioxide equivalent between 2012 and 2050. The report said that limit would correspond to a …