By Richard Black
Environment correspondent, BBC News website
There is a feeling of maturity about the British government's proposed Climate Change Bill.
The government hopes other nations will jump on the climate bus
Ten years ago, even five years ago, the buzz-phrase was "reducing emissions". Now it is all about moving to a "low-carbon economy".
The concepts are of course closely related; but the newer model, unveiled by Environment Secretary David Miliband with support from Tony Blair and Gordon Brown, speaks of a future where we can do pretty much the same things as we do now with the hair shirt tucked safely out of harm's way. It is broader, bolder, wiser.
There are even echoes of Harold Wilson's "white heat of technology", if you look for them.
The Climate Change Bill sees a future where governments define the progress to be made, and entice industries and consumers towards good environmental habits with a combination of new technologies, carbon pricing, and the carrot of lower energy bills.
Businesses will seamlessly embrace energy efficiency and renewable technologies. Domestically, enough of us will see, in the soft light of our energy-efficient bulbs, the need to fill our cars with biofuels and buy a home microgeneration unit.
And if the country does not deliver, it will take itself to court; because the targets of a 60% reduction by 2050, and between 26% and 32% by 2020 (all compared to a 1990 baseline) are legally binding.
So far, so impressive; Britain may not have the most vivid ambition in terms of emissions cuts and energy transformation (those belong to California and Iceland respectively), but it is the first country to enshrine its low-carbon vision in law.
And here is one of the big holes in the plan.
Is there a real target for legal action if emissions do not fall?
Normally the law works like this. If I do something which you do not like - whether it is planting too high a hedge between our gardens or planting an axe in your head - there is a powerful third party (the state, in some guise or other) which will intervene, apportion blame, and punish.
With the Climate Change Bill, it is not at all clear what happens should a future UK government not meet its legally binding emissions target. The consultation document - for this is draft legislation - says that "...a government which fails to meet its targets or stay within budget would be open to judicial review".
This is perhaps the sort of sanction which a future government might decide it can withstand, particularly if elements of the low-carbon economy turn out to be unpopular.
There are plenty of examples, not just in Britain, of carbon targets which have been missed when they proved difficult.
Labour is set to miss its 1997 election manifesto pledge of a 20% reduction in CO2 emissions by 2010, probably by a significant margin.
The Kyoto Protocol targets are supposed to be legally binding too; but a number of countries are currently way off achieving them, and the Canadian government has decided it is not worth even attempting to reduce emissions as its predecessors promised.
THE UK EMISSIONS 'CAKE'
British carbon dioxide emissions by source for 2004
Total amounts to 153.0m tonnes (carbon equivalent)
Figures do not include emissions/removals from land use changes and forestry
Another important issue going out to discussion is carbon offsetting.
This is where a business, or indeed a government, can choose to pay for emissions reductions somewhere else - usually in a developing country - rather than cutting its own greenhouse gas output.
The government is keen on offsetting. Official and ministerial flights are offset, as was the 2005 G8 summit in Gleneagles.
But there is growing doubt about its real worth, about whether all the schemes brokered by NGOs and private companies lead to real emissions cuts. So doubtful is the government that it is already consulting on setting a code of practice for the industry.
The draft bill does not make clear how much offsetting should contribute to the five-yearly, 2020 and 2050 targets. Businesses will be lobbying for as much leeway as possible, environmental groups for the tightest constraints.
Geographically, Britain may be an island - in fact several - but in climate terms, it is not.
This Climate Change Bill and forthcoming energy legislation have to dovetail with the European Union's plans, announced last week, for a 20% cut in greenhouse gas emissions and a 20% renewable share of the energy mix by 2020.
Mechanisms are unclear, as - again - are sanctions for missing the targets.
Then there is the global context, where, through the G8 and the United Nations, European leaders are pursuing the dream of a global emissions deal.
But putting the UK and EU actions together, it is possible to begin to sketch out what a low-carbon Britain might look like.
Gordon Brown has pledged measures on household emissions
Emissions from electricity generation and heavy industry are the easiest to tackle, because there are relatively few players and because much of the technology is proven.
By 2020, assuming everyone plays ball, we would see a spread of renewable energy generation, with perhaps one-fifth of Britain's electricity coming from onshore and offshore wind turbines and a smaller slice from whichever marine technologies prove the most efficient and economic.
Gordon Brown spoke on Monday of measures for households, and if he follows through we would see insulation and microgeneration spreading into homes and communities, though not nearly as fast as some lobby groups would like.
Fuel pumps will presumably be dispensing mixtures containing fair proportions of biodiesel and perhaps ethanol, with cars equipped to run on a range of fuels as they are currently in Brazil.
Flights are another matter. The EU is determined to have them included in its Emissions Trading Scheme - but with a number of UK airports embarking on expansion plans, it is difficult to see that Britons will be flying less by 2020.
And the impact of Britain's adventure on the rest of the world?
Politically, it is likely to be well received in many European capitals and by the US Democratic party. How it will play with the major developing world governments is another matter; some may love the investments that offsetting can bring, without seeing any need to follow suit.
Tackling emissions globally, as Mr Brown acknowledged this week, requires some kind of global deal. And that, even with Britain cutting a dash on the world stage with its shiny new climate legislation, remains elusive.