Hydrogen fuel cells are seen as potentially emissions-free energy sources for everything from automobiles to homes, replacing fossil fuel engines and eliminating the noxious pollutants that damage lungs and build up heat-trapping gases cited in theories of global warming.

But in producing and transporting hydrogen needed to fuel the aspiring technology, roughly 10 percent to 20 percent of the gas can be expected to leak into the atmosphere, the report in the journal Science said.

Quadrupling the levels of hydrogen gas - actually two molecules of hydrogen - in the air from the current 0.5 parts per million would create more water vapor in the stratosphere as the hydrogen combines with oxygen, resulting in more cloud cover, the report said.

Computer models used by study author Tracey Tromp suggested stratospheric temperatures could cool by 0.5 degrees Celsius, slowing the arrival of spring in the North and South polar regions and expanding the size, depth and longevity of the ozone holes.

Less ozone in the upper atmosphere, which allows more of the sun's dangerous rays to reach the Earth and has increased skin cancer risks, is widely blamed on mankind's release of now-banned chlorofluorocarbons, chemicals used in refrigerants and as propellants.

The ozone layer was expected to recover in 20 to 50 years as chlorofluorocarbon levels ease, though an injection of hydrogen into the atmospheric mix might worsen the problem, the report said.

More hydrogen in the air would likely also have a direct impact on the Earth's teeming surface, as it is a nutrient for microbes, it said.