In the fight against global warming, Prof. Hasem Akbari says changing all the roofs in the world would be the equivalent of getting rid of all the world's cars for 20 years. (CBC)

All new roofs would be white under a Montreal borough's proposed bylaw aimed at taking advantage of a white roof's cooling effects.

Mayor François Croteau of Rosemont-La Petite-Patrie wants to make white roofs mandatory on new buildings. Roofs requiring repairs would have to be painted white as well.

Croteau's idea is supported by a Concordia University engineering professor, who says all the world's roofs should be changed to cooling colours.

"Ten metres squared of white roof is equivalent, in cooling the globe, the equivalent to one tonne of [carbon dioxide]," Prof. Hashem Akbari says.

Akbari is trying to persuade 100 of the world's largest cities to switch to light-coloured roofs. Changing all the roofs in the world would be equal to getting rid of all the world's cars for 20 years, he says.

If Croteau gets his way, many of his borough's roofs will be white within about 15 years.

The bylaw would not apply to buildings with peaked roofs, which many residential houses have.

Croteau said making the switch to white roofs would be more expensive in the short term. But, he said, the cost would be offset eventually because white roofs are more durable.

Councillors in Rosemont-La Petite-Patrie will vote on the proposal in October.