This week’s Geneva Motor Show will shine a spotlight on all manner of green vehicles, including hybrids, diesels, diesel-hybrids, electric cars and hydrogen-powered sportsters. But the biggest trend could be small cars. “There’s a downsizing effect,” said Paul Willis, chief operating officer of Kia Motors Europe. “We’re seeing a change in the mix of vehicles.”

As the European Commission is cracking down on greenhouse gas emissions by proposing a reduction of 25 percent from the current levels of 160 grams per kilometer, automakers are realizing that shrinking the size of vehicles is a feasible and practical way to reduce their carbon footprint.

Small fuel-sippers will be featured throughout the show in Geneva. The Ford Fiesta is garnering a lot of attention, as Ford prepares to migrate the efficient European subcompact to U.S. shores. The Fiesta is expected to go on sale in Europe as a 2009 model, before being offered in the U.S. in the following year. The Fiesta engine lineup will include a portfolio of small and efficient powerplants: two gas engines, a 1.3-liter and a 1.4-liter four, and three diesels, including a 1.6-liter diesel with 85 horsepower.

Toyota will feature the tiny iQ concept car, while Saab will introduce a compact crossover utility powered by ethanol. Audi is also expected to show off its athletic little A3 convertible, combining higher performance with lower emissions.