New figures show global greenhouse emissions of carbon dioxide increased by the highest amount on record last year. According to the Global Carbon Project, emissions jumped 5.9 percent in 2010 and have soared nearly 50 percent since 1990. Scientists say the increase likely accounted for a half-billion extra tons of carbon released into the air. China is the world’s leading emitter, followed by the United States, where emissions rose more than 4 percent last year.