By David Shukman
Environment correspondent, BBC News
David Cameron's environmental journey has taken in a trip to the Arctic
To the delight of environmental campaigners, David Cameron has chosen to cast himself in a light that looks a fair bit greener than many might have expected.
Just when he was being criticised for seemingly dropping a cause he had ventured into the Arctic to highlight, he has laid out ideas on tough issues - Heathrow expansion, coal-fired power stations, renewable energy - that could prove more environmentally ambitious than the government's.
Of course, as one Tory frontbencher admitted to me, the party's new Blue/Green Charter is one stage of a "journey" towards finalising the policies that a future Conservative government might eventually implement.
The statements in the charter still have to make it into the yet-to-be-written manifesto, let alone survive the harsher realities of office.
And scrutiny might be more thorough than usual. This is, after all, a time of deepening economic difficulty.
And this is a party whose leader paraded his cycling only to have it revealed that a limousine carried his files.
It is also a party whose mammoth Quality of Life report by green luminaries John Gummer and Zak Goldsmith was seen to be given quite a kicking by less eco-friendly colleagues - plans to charge VAT on domestic flights and for parking at supermarkets were quickly dropped.
Environment or economy?
Yet what is striking, as policy evolves, is that a formidable pocket of climate scepticism within the party appears to have been bypassed.
No less a figure than former chancellor Lord Lawson decries "the new religion of eco-fundamentalism" as economically damaging.
Oil dependency is a major concern to Mr Cameron's Conservatives
But in his latest speech, David Cameron deliberately argues against framing the debate as an apparent choice between the environment and the economy.
In fact, he says, "we can't afford not to go green". We need to overturn "our hydrocarbon dependency" to save money and to boost energy security whether we see global warming as a threat or not - which he says he does.
So what does this mean? The Blue/Green Charter offers a mix of themes on transport, electricity, and research, and some are more specific than others.
There is a target of cutting cars' tailpipe carbon dioxide emissions to 100g/km by 2022 - a relatively modest step beyond the current EU proposal for a limit of 120g/km by 2012 - with a promise of new ideas for spurring research into hydrogen fuel cell and battery-powered cars.
On electricity generation, there is a more radical commitment to copy the Californian model of setting a limit on emissions of 500kg of carbon dioxide per megawatt/hour - the equivalent of a gas-fired station, the cleanest of the fossil fuel types. That would mean that new coal-fired stations - of the sort the government is considering approving now - would be allowed only if they were fitted with devices to capture and store the carbon dioxide, systems that might not be commercially available for a decade. For campaigners, this is very welcome; Al Gore once appealed to young people to link hands around coal-fired stations in protest at their emissions. But for those fearful of a looming energy gap - with gas supplies uncertain and new nuclear stations still distant - a statement this categorical on coal might seem risky.
Are both forms of generation in the picture for the future?
There would be green taxes - though none has yet been identified - which would be designed to change behaviour and would only replace other taxes, not add to the overall tax burden. We are told every additional penny raised from green taxes would go to a Family Fund to finance tax relief for families. This is highly sensitive territory - a leaked internal paper recently warned of the risks of green measures seemingly involving "sacrifice". Left unclear is the party's stand on a planned rise in fuel duty this October.
Decentralised power generation would be encouraged by a so-called "feed-in tariff", a system under which anyone generating electricity is paid for it at above-market rates. This German idea, which Labour questions, is widely supported by environmental campaigners as a way of fostering investment in renewable energy.
Gas and electricity bills would include comparisons of the energy consumption of other households - harnessing the power of so-called "social norms", our desire to act if our neighbours do.
Research into tidal power will get "rocket boosters". Advocates of this technology, who have long felt neglected, will welcome this but will no doubt want to see what it means in terms of promises of hard cash.
There is no guarantee the Tories would agree a third runway at Heathrow
Our national transport infrastructure needs to be "renewed", though only one part of it - the expansion of Heathrow - is explored in detail. Transport policy is a devolved issue, so the Conservatives would have to win power in Scotland and Wales to make an impact across the UK. The Cameron line is that the economic case for a third runway is "flawed", with the economic value of transfer passengers "hotly disputed".
So there is much that remains unspecified, unanswered.
Some in the party will argue that too heavy a green emphasis will alienate voters, especially with fuel prices rising, and could trigger tabloid attacks.
Others will worry that those fears of a backlash will dissuade the leadership from appearing too radical just when the climate science most clearly requires that.
Insiders assert that for David Cameron to have made the low-carbon case at a time of economic slowdown displays courage on the issue.
As one shadow minister told me, the green agenda is now genuinely in the party's DNA - even if we're still some way off knowing exactly what that could mean in practice.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.