SAN FRANCISCO — The governors of eight states including California and Oregon pledged Thursday to get 3.3 million zero-emission vehicles on roadways by 2025 in an effort to curb greenhouse gas pollution.Representatives from all eight states were scheduled to gather in Sacramento at 8:30 a.m. to sign a memorandum of understanding that would increase infrastructure and make other changes to help increase market share for electric cars, hydrogen fuel-cell electric vehicles and plug-in hybrids. By 2015, there are expected to be more than 200,000 zero emissions vehicles on the road.“This agreement is a major step forward to reducing the emissions that are causing our climate to change and unleashing the extreme weather that we are experiencing with increased frequency,” New York Gov. Andrew M. Cuomo said in a statement.The other states involved are Massachusetts, Maryland, New York, Connecticut, Rhode Island and Vermont. The eight states together represent about 23 percent of the U.S. auto market.Each state has already, separately adopted rules to require a percentage of new vehicles sold to be zero emission by 2025. California’s mandate alone of 15.4 percent calls for a total of 1.5 million zero-emission vehicles to be on the state’s roads by that time.