Scotland is lagging badly behind the rest of the UK in the fight against climate change, it has been claimed.
Concern has been expressed globally at emissions
A report by the Scottish Parliament's environment committee says tough targets should be set to reduce greenhouse gas emissions.
It said these should include holding traffic at 2001 levels by 2021 and that some form of road user charging "must" be introduced.
Emissions fell by 5.7% between 1990 and 2002 compared to 15% elsewhere.
The committee called on ministers to set their own aims, rather than simply contributing to the UK's targets.
It wants targets on energy efficiency and more small-scale renewable energy projects.
The report does not come out either for or against nuclear power.
But it wants emission targets to be integrated into transport planning and stresses that vehicle miles are set to grow by 27% over the next 15 years.
Committee convener Sarah Boyack said: "The current rate of progress in reducing Scottish emissions is inadequate to meet both short and long-term targets.
"We need clear and challenging shorter-term targets so that individuals, businesses and the public sector all know exactly what is expected of them.
"There is massive scope for positive change but we must start to act seriously now."
Green MSP Mark Ruskell, deputy convener, said: "In this G8 year Scotland must show global leadership on climate change.
"It's a watershed moment to get our own house in order and set an example to the rest of the world.
"The executive must learn lessons from this report and come back with a climate change programme that is proportionate to the severity of the problem.
"Failure to meet the challenge of climate change is simply unthinkable, and at the moment points to severe embarrassment for Jack McConnell when the G8 comes to Scotland in July."
The report highlights how the executive is "clueless" on how to get transport emissions down, he went on.
'Kicking and screaming'
Mr Ruskell added: "I am pleased that the report does not take the public relations campaign being waged by the nuclear industry seriously."
Criticism of ministers was echoed by ecology campaigners from WWF Scotland.
Richard Dixon said: "Those departments of government which have so far managed to ignore climate change must be dragged kicking and screaming to the table.
Tougher measures are being urged to combat climate change
"The committee's review confirms that, despite their fine words, it is clear that the Scottish Executive as a whole is not taking climate change seriously."
Dr Dixon continued: "Without firm targets Scotland will blunder on building motorways, burning coal and promoting more air travel - instead of getting serious about reducing emissions."
Environmental campaigners from Friends of the Earth urged ministers to "start delivering the cuts needed to halt climate change".
Dr Dan Barlow added: "Progress in cutting Scotland's climate pollution is simply inadequate."
SNP environment spokesman Richard Lochhead argued Holyrood did not have enough power to deal with pollution.
"At the same time, ministers in Scotland are failing to use what little influence they do have," he added.
Clifton Bain, climate change policy officer for RSPB Scotland, said: "We support the findings of this inquiry, particularly the need for clear emissions reduction targets and a strategic approach to planning of renewable energy development."
Traffic levels are adding to the problem
In February, the Scottish Environment Protection Agency (Sepa) warned the committee that climate change could be completely out of control within several decades.
Officials said that nuclear energy and wind farms may be better options than trying to tackle global warming.
Solutions suggested by conservationists included reducing internal UK air travel and boosting electric trains.
The evidence was part of the committee's inquiry into the impact of climate change on Scotland.