Al Gore, the former vice president turned environmental activist, was on hand last Friday as Gov. Jon S. Corzine signed legislation requiring the Garden State to achieve ambitious reductions in emissions of global-warming gases. New Jersey became the third state, behind California and Hawaii, to pass a comprehensive greenhouse gas reduction law. The legislation requires the state to reduce global warming gases to 1990 levels by 2020, and to ensure that greenhouse gas emissions do not exceed 80 percent of 2006 levels by 2050. New Jersey is the first state to set global warming targets so far into the future, activists said and the first to require that energy imports adhere to New Jersey’s standards. Eight other states are considering similar legislation, according to Suzanne Leta Liou of Environment New Jersey, while others have started anti-global warming initiatives. Emissions from fossil fuels, such as coal and gasoline, are believed by many scientists to be a leading cause of global warming. Critics of the New Jersey law argued that it would hurt the state’s energy industry and that the act contained no specific proposals to lower emissions. The measure nonetheless enjoyed widespread bipartisan support in the Legislature, passing easily before lawmakers recessed for the summer and advancing to the governor’s desk. Under the new law, the Department of Environmental Protection will conduct an emissions inventory, and based on the results, devise a plan to monitor and reduce harmful emissions.