Germany's environment ministry is proposing an emissions certificate be displayed on new cars that would alert potential buyers to heavily polluting vehicles, a ministry spokesman said.

Under Environment Minister Sigmar Gabriel's proposals, car dealers would have to show the certificate next to the price sticker on new vehicles, rather like the efficiency "passports" found on European household appliances like refrigerators.

The certificate would detail carbon dioxide emissions and give an indication of the car's fuel consumption relative to its class, on a scale running from red to green, the Welt am Sonntag newspaper said in a version of an article to appear on Sunday.

"This climate passport would show the consumer how environmentally damaging the car is," an environment ministry official, Astrid Klug, told the newspaper.

Social Democrat Gabriel has proposed a similar energy efficiency certificate for homes and apartments in order to alert potential buyers and tenants to heating and energy costs.

The suggestion for a car certificate is likely to meet resistance from some quarters of Chancellor Angela Merkel's right-left governing coalition and from Germany's auto industry, which is a major employer.

Christian Democrat (CDU) politician Dirk Fischer said the proposals had not yet been agreed by the coalition government and warned against introducing measures in Germany that were not replicated in other European markets.

"We need to know what this means for manufacturing and for the domestic market if we are going to unilaterally introduce this," he was quoted as saying by the newspaper.

Germany 's transport ministry welcomed the environment ministry's proposals, a spokeswoman said on Saturday.

A suggestion by Transport Minister Wolfgang Tiefensee, also a Social Democrat, that emissions' measurements should take into account a vehicle's payload was being considered, she said.

This would mean that heavier polluters such as SUVs would fare better than under the environment ministry's initial proposals that purely measured the carbon dioxide output of an engine, the newspaper said.

Car makers are under pressure to manufacture cleaner engines because the European Union wishes to reduce the bloc's carbon dioxide output. Manufacturers must cut average emissions of their new car ranges to 130 grams per kilometer by 2012.