Earlier this month, the US supreme court ruled that carbon-dioxide emissions are to be defined as pollutants, a decision that could force carmakers to seriously reduce the levels of CO2 being emitted by vehicles sold in the US. The decision reflects a more drastic situation in Europe, where the government is planning to impose a rule to limit all carmaker’s average fleet C02 levels to just 130g/km.

If any changes do come in, performance makes such as Lamborghini and Porsche will be hit hardest. Lamborghini has the honor of producing the world’s worst C02 offender with its Murciélago supercar. Although it’s unknown how the US Supreme court’s ruling will be interpreted by the US Environmental Protection Agency, it’s highly probable that there’ll be new regulations limiting the allowable levels of CO2 emissions from motor vehicles.

Previously, C02 was deemed as harmless, which meant car manufacturers never focused on reducing its levels as they have done with other smog-forming pollutants. If the allowable level of C02 is reduced, carmakers will be forced to reduce the amount of fuel consumed at the expense of performance.