The chancellor's pre-Budget report fell far short of measures needed to tackle global warming seriously, an influential committee of MPs has said.
The Greens say only they are prepared to make the CO2 cuts necessary
Environmental Audit Committee chairman Tim Yeo said the report was "grossly inadequate" and that "steep cuts" in emissions were needed.
Among measures expected in this week's Budget is an increase in taxes on "gas-guzzling" cars.
The Green Party said it alone would take the "radical cuts" necessary.
Mr Yeo criticised the pre-Budget report, published in December, for not addressing the concerns of the Stern Review - which warned of the devastating consequences of climate change.
He said: "The pre-Budget report was a grossly inadequate response to the hardening evidence of the increasing risks of major and irreversible impacts from climate change.
He added that its "lack of boldness" raised major doubts about the Treasury's "seriousness about implementing Stern's recommendations on domestic policy."
Mr Yeo's committee has published a review of the pre-Budget report every year since 1997.
It warns that the government's own target for reducing carbon dioxide emissions (by 60% from 1990 levels by 2050), fell short of Stern's recommendations (nearer 80%).
It said the recent doubling of air passenger duty (APD), from £5 to £10, had only brought it back in line with levels of five years ago.
And it suggested that APD should be levied per flight, not per passenger - to include empty and freight flights - and that it should take account of emissions.
It also said a rise in fuel duty already announced was only in line with inflation - leaving it 15% lower in real terms than in 1999.
The Treasury replied that the government continued to "lead international action" on climate change - including pushing for an EU Emissions Trading Scheme.
A spokesman added: "The government has taken action domestically too, and thanks to the right combination of tax and non-tax measures introduced since 1997, the UK is one of the few countries on course to meet its Kyoto commitments."
But for the Lib Dems, Chris Huhne said Mr Brown had been "spooked" by the fuel protests of 2000, since when green taxes had been falling as a percentage of income.
He added: "When the chancellor has modestly raised green taxes, he has given them a bad name by failing to guarantee that the revenue will be handed back in tax cuts elsewhere."
Meanwhile, the Green Party has released its own "carbon-costed" budget - aimed at helping to lower UK emissions by about 90% by 2050.
This was needed, it said, to "have a fighting chance of staving off devastating climate change".
They have outlined tough measures to reduce carbon emissions by 7.5% in 2007/8, such as raising APD to £100 and spending the proceeds on VAT cuts and environmental measures.
They say they would also charge £1,800 in tax for the worst "gas-guzzlers", double the climate change levy on businesses, spend £3bn on buses and cheaper rail fares and boost renewable energy grants by £500m.