Scientists in North America and Britain are working on a massive sun shade they say could be used to stop global warming.

Roger Angel, an astronomer with the University of Arizona, has received funding from NASA to develop a canon that would fire trillions of mirrors into space to deflect the rays of the sun, Britain's Telegraph newspaper reported Friday.

British inventor Tod Todeschini has been contracted to build a scaled-down version of the canon.

Angel said he expects to be ready to launch the mirrors within 20 to 30 years. Researchers at the University of Victoria, Canada are using computer simulations to test the sunshade theory, the report said.