When President George Bush talked about the US being "addicted to oil" this year, even the hardest-nosed investors took notice.
Mike Appleby, of Morley Fund Management, said it was the "tipping point" for many international investors. Share prices in renewable energy and alternative energy took off.
The London stock market has been fighting to catch up in a sector whose home has previously been Scandinavia, Canada and Germany. Over the past couple of years, London's Alternative Investment Market has seen dozens of companies list which promise to help take us to a future no longer dependent on extraction and the burning of fossil fuels. About 50 companies on AIM are in the sector, although that includes some specialising in water and waste.
The drivers for this industry are obvious. Fossil fuels are finite. Burning fossil fuels produces carbon dioxide, the greenhouse blamed for global warming. And the third reason, which may have been uppermost in Mr Bush's mind: security of supply of the fuel source. While Middle East turbulence could disrupt the flow of oil, wind is not going to suddenly stop blowing.
But how to pick the good from the not-so-promising? All the technology companies in this sector seem to promise they are sitting on a "revolutionary" innovation. Those that could become multibillion-pound businesses have few or no revenues. Here, we pick some of the most interesting that are tackling the fossil fuel problem directly.
But be warned, says Ian Simm of Impax, an environmental fund manager that is listed on AIM. There are parts of the sector where there is a "mini bubble".
He says: "Institutions can afford to take risks but individuals would need to have expertise in interpreting news flow from unprofitable companies. If you are not able to watch these announcements like a hawk, you may be better off investing in a [specialist] fund."
Mr Appleby says in areas such as fuel cells, it is very difficult for investors to pick one company's technology from another. Fuel cells are not commercial yet.
The art of turning garbage into electricity. The company takes methane created by organic rubbish decomposing and uses it to power engines that create electricity. It does this in two ways. Firstly, on about 40 sites in the UK, it drills into "landfill" garbage dumps to extract the methane produced under ground. Secondly, it has a plant in east London, where biodegradable waste goes through "gasification" (using pressure and heat) to turn it into gas, which is used in a generator.
Listed in 2005, Novera should become profitable this year.
D1 plants jatropha trees, from whose seeds oil for refining can be produced. It is also trying to build refineries locally which will turn this oil into biodiesel, for which there is an established and growing demand. It has nascent operations dotted around the globe but is the most far advanced in India.
The small number of trees D1 has planted are maturing only now. It posted annual results this week, when it promised to be profitable next year. The figures revealed just £415,000 of turnover and a loss of £7.5m. D1 boasts an £80m market cap. Risk from a very ambitious business model.
Has created a small fuel cell that can be used in a combined heat and power unit for the home. British Gas has signed a contract to take the product, though this is, as yet, going to be trialled only in homes. The product is powered by natural gas, not hydrogen like many fuel cell technologies, so its feed stock is easily available. It should halve the annual fuel bill for a household.
ITM produces the Electrolyser, which makes hydrogen. By June the group hopes to tell the City whether the device can make hydrogen as cost-efficient as fossil fuels. ITM believes cars and back-up power systems could be among the first to run on hydrogen produced by it. The group believes the market it is targeting will be a trillion-pound market one day. But it is some way off profit. Despite a £200m market cap, it still has zero revenues.
Owns part of the Chicago Climate Exchange and more than 70 per cent of the European Climate Exchange, where the carbon credits established under the Kyoto Protocol can be traded. This area is subject to political risk - the instrument traded is an invention of politicians.
This is a business model based on excrement. Pig excrement to be precise. The company captures the methane that would be given off by piles of animal manure on farms and, using a bio-digester, turns it into carbon dioxide and oxygen. The resulting saving on methane being released into the atmosphere is turned into a carbon credit which is sold to major emitters, such as mining companies.
Some 20 per cent of all greenhouse gases come from agriculture. And methane is reckoned to be 21 times worse for the atmosphere than carbon dioxide. The technology can be applied to any animal excrement, including that of cows and even chickens. Suffered from delays in implementing its business model last year.
Produces a fuel cell that it reckons is 10 times smaller than a conventional unit and at a fifth of the usual cost. The idea is that the fuel cell is made small enough to power electronic devices such as laptops. It is trying to produce a fuel cell that would power a laptop for more than 24 hours.
The company turns vegetable and palm oils into biodiesel, which can then be used either as a pure substitute for conventional diesel or, more commonly, it is blended with regular diesel. Last month, Biofuels announced the first biodiesel had been produced at its Teesside plant. But the company's most recent results showed it was loss-making. City analysts expect it to break into the black by this time next year. On Monday, Michael Buzzacott, a former BP executive, became the company's chairman.
Clipper Windpower, a US wind-turbine manufacturer and wind-park developer, listed on AIM in September. The company, which is based in Santa Barbara, makes highly efficient turbines which can each produce 2.5 megawatts of electricity, sufficient for 800-1,600 homes.
From its 190p-a-share float, it raised £65m which it will use to build up a portfolio of wind farms in the US and the UK. Clipper was formed in 2001 and has since established two US wind projects. Its shares closed at 362.5p yesterday, valuing the company at £225m.
Ocean Power Technologies
OPT is focused on trying to commercialise wave power. This is using the sea to provide a benign source of electricity. OPT's key technology is its PowerBuoy. The device, which has been under development since 1997, bobs along the surface of the water, translating its up and down motion into electricity.
Sizeable waves are important to make the whole process worthwhile, so the technology is not suitable for placid areas such as the Mediterranean coast. The British Isles are certainly suitable, along with most of the western coastline of Europe.
The broker Collins Stewart expects the US-based company to be profitable in the 2007-08 financial year.