HAMBURG (Reuters) -- Germany's speed limit-free motorways may fall victim to fears of global warming after the Social Democrats unexpectedly voted on Saturday in favor of introducing a top speed of 130 kph (80 mph).

Studies showing Germany's CO2 output from cars could be cut sharply with a speed limit helped convince a majority of SPD delegates to ignore their leaders at a party congress.

The autobahns were built without speed limits by the Nazis and, after World War II, Germany's influential car industry pressured lawmakers against introducing any national limit.

During the Cold War, West German carmakers used the slogan "Freie Fahrt fuer freie Buerger" (Free travel for free citizens) and they argue high speeds help them sell Porsches, Mercedes and BMWs worldwide -- and protect German jobs.

Opinion polls show about 60 percent of Germans are in favor of a speed limit. Environmental groups have said a speed limit would cut vehicle CO2 output by 5 percent overnight and 15 percent long-term once more fuel-efficient cars were used.

Nobel laureate Al Gore last week criticized Germany in a Berlin speech for not having motorway speed limits.

The SPD is in coalition with Chancellor Angela Merkel's Christian Democrats (CDU). Saturday's non-binding measure has little chance of becoming law any time soon because Merkel is firmly against a speed limit despite her efforts to persuade other countries to cut greenhouse gas emissions.

"It's an important symbolic issue," said Environmental Minister Sigmar Gabriel. "But it will probably be hard to pass into law because we won't find a majority for that with (Merkel's) Christian Democrats."

CDU general secretary Ronald Pofalla said the measure had no chance of becoming law.

"There won't be any such patronizing from the CDU," he said. "It's another scary proposal from the SPD."