Major banks in the United States last year started offering green credit cards that use about 1 percent of the amount of customers’ purchases to offset their emissions. So far, the cards seem to be taking off, benefiting credit card companies and, arguably, the planet. The cards come complete with hokey names like GreenPay MasterCard, GE Money Earth Rewards MasterCard, and Brighter Planet Visa. As customers spend, no doubt on eco-friendly purchases, they accumulate points toward offsets or carbon-mitigation projects. The going rate is roughly one ton of carbon offset for about $1,000 in credit card purchases. Green credit cards have earned scorn from some critics who argue they foster the illusion that a few offsets will solve the world’s environmental woes and encourage carbon frivolity. But credit card execs disagree, saying the cards are just one more way consumers can lighten the planet’s environmental load. “We don’t pretend to be the only answer,” said Bank of America’s Michael Rhodes.