Chancellor Gordon Brown has "a long way to go" to be seen as environmentally friendly following his pre-Budget report, the Green Party says.
Experts say fossil fuel use must be cut to slow global warming
Principal speaker Sian Berry dismissed higher taxes on flights and an increase on fuel duties as "gesture politics".
Mr Brown should focus on encouraging "behaviour that contributes to long-term sustainability", she added.
Friends of the Earth said the chancellor's environmental tax proposals had been "pretty feeble".
In his speech to the Commons, Mr Brown said stamp duty could be abolished for some new "carbon-neutral" homes.
Fuel duty would go up by 1.25p per litre from midnight and air passenger duty from £5 to £10 for most flights from February.
A report by economist by Sir Nicholas Stern for the government, published in October, said that if average global temperatures rise by five degrees Celsius, up to 10% of world economic output could be lost.
Among other measures, he advocated reducing demand for heavily polluting goods and services and making energy supply more efficient
Ms Berry said: "Gordon Brown has a long way to go to gain any real green credentials, and his pre-Budget report will not even start him on the right road.
"This is gesture politics at its worst: he is trying to outflank the Tories on sounding green, when neither party is prepared to take the radical measures needed to prevent climate change."
She added: "What is the point in raising a tax on airline seats when his support for airport expansion will ensure the biggest growth in the aviation sector for a generation?"
Ed Matthews of Friends of the Earth told the BBC: "I would give him probably one out of 10, maybe two out of 10.
"I think it's pretty feeble really. He's got a terrible record.
"For 10 years he's failed to provide a green budget. We thought in the wake of the Stern Review, given the new science demonstrating how bad climate change is, he's got to take action. And he's failed to do so again."
However, the Green Alliance said the chancellor's pre-Budget report "feels like progress".
Director Stephen Hale said: "We welcome his decisions to double tax on aviation and make new homes zero carbon by 2016, and the suggestion that the tax on landfill should rise.
"But we are very disappointed by his timidity on fuel duty. A 1.25p increase does not make up for falling petrol prices."