Image: A nuclear bomb test. Nevada Division of Environmental Protection

Updated: Feb. 25, 2011; 11:40 p.m. EST

WASHINGTON — Even a small nuclear exchange could ignite mega-firestorms and wreck the planet’s atmosphere.

New climatological simulations show 100 Hiroshima-sized nuclear bombs — relatively small warheads, compared to the arsenals military superpowers stow today — detonated by neighboring countries would destroy more than a quarter of the Earth’s ozone layer in about two years.

Regions closer to the poles would see even more precipitous drops in the protective gas, which absorbs...

Editor’s note: Simon Wheatcroft lives in Doncaster, England, and has been registered blind since he was 18 years old. That’s because Wheatcroft, now 29, has been diagnosed with retinitis pigmentosa, a degenerative eye disease that essentially breaks down the cells composing the retina, a layer of optical tissue that helps convert light images and visual cues before sending them on to the brain. There is no cure, but that hasn’t stopped Wheatcroft from continuing with one of his great passions: running.

Moreover, Wheatcroft is now committed to running the Cotswold ULTRArace.100, a 100-mile...