In his brilliant 1991 design for Frankfurt's Commerzbank, the tallest office building in Europe, he brought off the seemingly impossible feat of building a supertower that could use natural ventilation (as against fuel-gobbling air conditioning) during 60% of the year.

CNN: ASIANOW - TIME Asia

Also, the test is done without air-conditioning, which reduces fuel economy, and without any popular options that add weight to vehicles, thereby making them less efficient.

FORBES: Fuel Economy Sticker Shock

In Eco mode, parameters such as the throttle map and air conditioning are controlled for minimal fuel and electrical consumption.

ENGADGET: VW unveils CrossBlue plug-in SUV with iPad mini headrests and 85MPGe efficiency (eyes-on)

Just as air-conditioning increases a car's fuel consumption, so does a plasma scrubber.

ECONOMIST: Diesel engines

Other incremental improvements range from solar panels that run the air conditioning during stand-still, so fuel is not used to cool down the car, to small electric motors tucked away in the doors and powered by batteries that are charged when a car is braking.

BBC: Electric motoring: a quiet revolution

Mr Liddell argues that the increased use of air conditioning, particularly in summer, is also leading to much higher fuel bills.

BBC: NEWS | Business | Cracking down on energy waste

Joseph Sartiano, a Pentagon official, says this treatment halves the energy needed for air-conditioning and pays for itself within three to six months, depending on how the price of fuel is reckoned.

ECONOMIST: Monitor