| By Tim Franks BBC Newsnight |
You have to tell yourself the cows are going to die anyway. 
How biogas is madeInside the abattoir at Swedish Meats in Linkoping, the cows stood patiently, occasionally nuzzling the lens of our camera.
From there, it was a short walk past the white-walled butchery, down the steps to the basement where the raw material for biogas, slid greasily down a chute.
Still bubbling and burping, and carpeting you with an acrid stench, came the organs and the fat and the guts. Enough, from one cow, to get you about 4km (2.5 miles) on the train.
A tanker collects the organic sludge and makes the short journey to the biogas factory, where the stinking fuel is stewed gently for a month, before the methane can be drawn off.
Oil price rising
The world's first biogas-powered passenger train is taking its first passengers between the Swedish cities of Linkoping and Vastervik. And the biogas comes from the entrails of dead cows.
The boss of Svensk Biogas, Carl Lilliehook, is a proper, serious Swede. But his eyes twinkle at the biofuel "revolution", as he calls it. You don't have to look far beneath the number-crunching CEO to find the muesli-crunching environment-lover. 
Yes, he says, the train between Linkoping and Vastervik will cost 20% more to run on methane than on the usual diesel. But the oil price is going up and up, and in any case, Swedes care about being able to pick our mushrooms and their fruit.
Nor is it just trains. In Linkoping, the 65-strong bus fleet is powered by biogas. Indeed the city boasts that it was the first in the world to try out its buses on methane.
The taxis, the rubbish trucks and a number of private cars also fill up at the biogas pump, housed under a dinky green corrugated iron roof.
And if methane doesn't light your fire, you can choose to have your car run on a high-grade biofuel mix. This year, Saab started selling a biopowered version of their 95 model.
Its engine will take a fuel cocktail which is up to 85% bioethanol, made, principally, from Brazilian sugar beet.
Value for money
The experts regard bioethanol and biodiesel as "carbon-neutral", because they spew fewer carbon emissions, and the crops which provide them absorb greenhouse-gas causing carbon dioxide, as they grow.
The Saab executive we spoke to said his company would like to sell the car in the UK but, for the time being, the biofuel infrastructure is not there. Bioethanol - at a 5% mix - only became available from the start of the year in Britain. 
In Sweden, the attraction is not limited just to the large, green consensus. The bio-powered version of the Saab 95 costs around $1,000 (£500) more than the normal model.
But with pump prices for the E85 mix a third cheaper than normal petrol, company car tax breaks, and exemptions for parking and congestion charges, Saab reckons you get that $1,000 back within the first year.
The harsh truth is that, across Europe, transport is not pulling its weight when it comes to meeting the Kyoto targets on cutting greenhouse gas emissions.
Industry is. So, to a lesser extent, are households and agriculture. But now the European Commission - the guardian of the European Union - has weighed in, demanding that transport do more.
It has set binding targets for the amount of fuel use it wants taken up by bio-products by the end of this year, and by 2010.
The UK is set to fall well short of the 2% target for the end of December. The government reckons it is on course for 0.3%. Sweden is likely to be 10 times ahead, at 3%.
By road and by rail, Sweden has a lot to teach the rest of us.http://news.bbc.co.uk/2/hi/science/nature/4373440.stm