In a rare expression of unity from an otherwise cutthroat industry, the world’s automakers pledged Friday to work together on global safety and environmental standards for cars. In a joint statement issued after an auto show in Paris, 13 industry CEOs agreed to work on promoting new technologies and better fuel quality, international standardization of vehicle regulations, and global acceptance of clean diesel technology. The latter might be a tough sell in the U.S., and especially in California, which boasts the world’s strictest clean-fuel standards. Automakers argue that any air pollution losses from diesel technologies would be offset by gains in fuel economy and reduced greenhouse gas emissions. Environmentalists were cautiously optimistic about the cooperative spirit among the automakers, which included BMW, DaimlerChrysler, Fiat Auto, Ford, General Motors, PSA Peugeot Citroen, Porsche, Renault, Volkswagen, Honda, Toyota, Nissan, and Mazda.