That might be a premature threat, though. EU ministers have already accepted European car-makers' joint pledge to cut the total carbon-dioxide emissions from new-car sales by a quarter by 2008. Carbon-dioxide emission is the best measure of a carbon-based propulsion system's energy efficiency, because it reveals both how much fuel is being burnt and how much "greenhouse gas" seeps into the atmosphere.
It's a big problem. The average fuel consumption of new cars sold in Europe is currently 35 mpg on the EU's standardised test cycle, but the agreement will lift this to 50 mpg by 2008. The EU's aim is to see this raised to 80 mpg by 2010; by the law of diminishing returns, that final 30 mpg will be near-impossible to achieve.
There's also the matter of how to divide this pledge between the participants without putting makers of desirable but thirsty sports and luxury cars out of business. It calls to mind the CAFE (Corporate Average Fuel Economy) system set up in the US a while back, which imposes fines on makers whose cars do not, on average, conform to the target.
Small makers of thirsty cars - companies such as Porsche and Britain's most prolific TVR - will be under pressure to merge with a big maker of economical cars so they can shelter under the umbrella of a low overall economy figure. This is how Jaguar (Ford-owned) and Ferrari (Fiat-owned) have managed so far, and it could spell the end of small, independent car-makers.
What we need is the fuel cell. Forget electric cars: their batteries are heavy, their range is limited, recharging them takes ages, and it's a very inefficient use of energy because you're storing power which has already been generated (not necessarily in an environmentally -friendly way) somewhere else.
An electric car is indeed a ZEV (zero emissions vehicle), but only at the point of use. The fuel cell is different. The car (or van, or bus, or truck) is still propelled by an electric motor, but the electricity comes from a stack of fuel cells which combine hydrogen with oxygen, and create a wattage in the process.
The fuel cell was invented by Sir William Grove in 1839, and met an early maturity over a century later in the Apollo space programme. Early fuel cells were unreliable, with highly caustic electrolytes and not suitable for use in a car. Now, though, we have the PEM (proton exchange membrane) fuel cell, which uses a polymer membrane between graphite plates. Hydrogen is introduced into labyrinthine channels in one plate, and while the complete hydrogen molecule can't pass through the membrane, the component nuclei - that is to say hydrogen ions, or protons - can, and an electric charge is created. The ions then combine with the oxygen in the air on the other side of the membrane, and warm water vapour is the sole by-product.
One of the leading fuel-cell protagonists is Mercedes-Benz, which in conjunction with a Canadian fuel-cell company, Ballard, already has three fuel-cell buses in service in Chicago. Ford has now joined Mercedes for further fuel-cell research and development, and several Japanese manufacturers are following parallel paths.
The other major player is General Motors which, like Mercedes-Benz, plans to have a fuel-cell car in production by 2004.
The main barrier to the fuel cell's viability so far has been the storage of the hydrogen. There's plenty of room for hydrogen gas tanks in a bus, but in a car it's a problem. Mercedes' NECAR 1 project (new electric car) was based on a van, and its entire rear was taken up with fuel-cell paraphernalia. NECAR 2, based on a V-class people-carrier, retained all its seats but carried a big pod on its roof.
The breakthrough came with NECAR 3, based on the little A-class, which gets its hydrogen from methanol via an on-board "reformation" process. The methanol, which can be derived from biomass as well as from normal petrochemical and gas products, is much easier to store than hydrogen; you simply fill a tank as you would with petrol or diesel, so it's convenient for the user and easy for current fuel-supply infrastructures to cope with. The downside is a small emission of carbon dioxide, but it's vastly less than an internal combution engine produces and well inside even those 2010 targets.
There's no reason why a fuel cell car shouldn't be pleasing to drive, because electric motors can be powerful and they deliver large amounts of low-speed pulling power. A tankful of methanol could give a range similar to a diesel car's; methanol has a lower calorific value than either petrol or diesel, but a fuel cell is a more efficient converter of energy than an internal combustion engine. The fuel cell produces enough heat to warm the car's cabin, too.
Here, surely, is the future of the car. Even sports cars could be fuel- cell-powered. It's not just a pipe-dream (or a non-pipe-dream as Mercedes wittily describes it in a reference to the lack of an exhaust). For now, though, there are less dramatic but still significant green-hued cars in the offing.
Toyota is showing its Prius hybrid car, which will go on sale here by 2000. It uses both a petrol engine and an electric motor, switching seamlessly between them as deemed optimum for economy and emissions, and keeping the engine working in its cleanest and most efficient speed range. Drive is via a continuously-variable automatic transmission, so you just press the accelerator and let the Prius - a neat four-door saloon - do the rest. It's lively, yet it averages around 57 mpg.
And Volkswagen is revealing its hyper-frugal Lupo 1.2 TDI. The main Lupo range goes on sale here soon, but this version's UK future is not yet known. The 1.2 TDI's significance is that it's the first production "three- litre" car - a figure which clearly refers not to its engine capacity, but to its EU test-cycle economy figure of 3.0 litres per 100km, which equates to 94.5 mpg.
Aluminium components (engine, some body panels and chassis components) save weight, the automatic transmission changes up early to save fuel, and the engine automatically switches off and on whenever it can. Yet the Lupo isn't slow, because its three-cylinder, direct-injection turbodiesel engine produces a remarkable 61 bhp and 103lb ft of torque. Volkswagen has hit the three-litre target now, but other makers are not far behind.
Maybe the car's future isn't so bleak after all.
THE MESSAGE is clear. Cars emit carbon-dioxide and carbon-dioxide is bad. It inhibits the radiation of heat from Planet Earth in what is called the "greenhouse effect", so Planet Earth gets warmer with all the trouble that lies in store as a result.
But carbon-dioxide is not all bad. Plants would be miserable without it because they use it, in combination with water, to grow. Plants are made mainly of cellulose, which is a polymer of glucose, and glucose is the product of photosynthesis. If there are enough plants to absorb it, then, there will be no excess carbon dioxide.
Halting the destruction of tropical forests would help, but Mazda and the Society of Motor Manufacturers and Traders (SMMT), which organises the Birmingham International Motor Show, have set up a slightly smaller but still commendable initiative.
Together with Future Forests, an environmental task force, they commissioned Edinburgh University, which researches "carbon sequestration", to work out how much carbon-dioxide would be used in the setting-up, running and dismantling of the show.
This done, they planted over 5,000 trees in the new Forest of Mercia in the West Midlands. Their carbon dioxide intake will match the show- related emissions and render the show "carbon-neutral". The trees are mainly oaks, chestnuts and beeches. Visitors can fund additional trees for pounds 3 at the Future Forest stand (122).
"This is just one way we can do something to address current carbon dioxide emissions while maintaining our long-term investment in research and development to reduce emissions at source," says Tim Tozer, Mazda Car's UK managing director.