Laurence Frost and Agnieszka Flak

For years, carmakers kept pace with European Union CO2 goals by shrinking engine capacities, while adding turbo chargers to make up lost power. Three-cylinder motors below one liter have become common in cars up to VW Golf-sized compacts; some Fiat (FCHA.MI) models run on twin-cylinders.
 
 These mini-motors sailed through official lab tests conducted – until now – on rollers at unrealistically moderate temperatures and speeds. Carmakers, regulators and green groups knew that real-world CO2 and nitrogen oxide (NOx) emissions were much higher, but the discrepancy remained unresolved.
 
 All that is about to change. Starting next year, new models will be subjected to realistic on-the-road testing for NOx, with all cars required to comply by 2019. Fuel consumption and CO2 will follow two years later under a new global test standard.
 
 Independent testing in the wake of VW’s exposure last year as a U.S. diesel emissions cheat has shed more light on the scale of the problem facing automakers.