To date, no credible, non-fossil fuel-burning car has caught on in any meaningful way and there have been plenty of failures, such as the much-publicised ZAP debacle in California. Most of the ‘green’ vehicles you can currently buy in Europe’s showrooms are still familiarly propelled, the innovation being in fuels not engines, thereby subcontracting most of the problem to the oil companies. Working prototypes and even production cars exist that run on everything from biodiesel to natural gas, bioethanol and liquefied petroleum gas (LPG) as well as more familiar petrol and diesel.

While Honda, Toyota, Nissan, Ford, and General Motors all toyed withelectric vehicles in the 1990s, these companies mothballed development during 2003, when California scrapped its zero-emissions vehicle policy. Since then, electric car enthusiasts have had to look to small independent companies – such as troubled US player ZAP and Norwegian Think, previously made by Ford, and Reva’s G-Wiz in the UK.

Equally significantly, whole sections of the car industry still remain committed to a fossil-fuel future, especially at the luxury level, and its opposite, stripped-down utilitarian end intended for emerging markets. Ford-owned, Swedish luxury carmaker Volvo CEO Fredrik Arp told CNBC European Business that incremental gains from existing technologies was “the highway for us and will continue to be the highway for us.” Meanwhile, ever cheaper and smaller cars, such as Tata’s Nano and the Renault Dacia Logan, designed for emerging markets, rely on cut-price petrol engines.

Another big dilemma now facing the industry is whether it can afford to continue producing large, powerful vehicles, even with correspondingly large, incremental improvements in fuel economy. GM’s Volt concept is conspicuously large and sporty instead of dull and utilitarian. Bob Lutz, GM’s colourful, 76-year-old vice chairman of global product development, insists: “There is and will be room for green and mean. Just because a grocery store is greatly expanding its line of organically grown vegetables, that doesn’t mean it shuts down the meat counter.”

Luxury car maker Bentley emphatically agrees, since otherwise it might be facing the end of the production line. Having previously shunned responsibility for the very high CO₂ emissions of its cars, CEO Franz-Josef Paefgen this year issued a hastily written press release at the Geneva car show claiming that, on a well-to-wheel basis, its fleet of gas-guzzlers could, by 2012, reach a CO₂/km target of 120g. The company’s sales and marketing chief Stuart McCullough told CNBC European Business: “There’s no point showing pictures of polar bears against Arctic sunsets; this is a global problem requiring deep, connected thinking and a long-term strategy.”

Paefgen also announced the development of a new drivetrain to be ready by 2012 – thought to be some sort of diesel or diesel hybrid, drawing down technologies from within the VW empire to which Bentley belongs. Currently, Bentley’s newest model, the Continental GT Speed, achieves fuel efficiency of 16.6 litres per 100km (17mpg) despite being 35kg lighter and slightly more efficient than its predecessor. WhatGreenCar.com, which employs a sophisticated model to assess environmental credentials of new cars, awards the Bentley the worst possible score – 100 out of 100, adding, however, that a handful of Ferraris, Lamborghinis and Hummers are worse still.