The ozone layer: fragile protection for the Earth

The ozone layer that shields life on Earth from deadly solar radiation is on track to recover within decades, but controversial geoengineering schemes to blunt global warming could reverse that progress, a major scientific assessment warned Monday.

The ozone layer is situated in the stratosphere at 15 kilometres altitude and protects Earth from the Sun’s ultra-violet radiation. Without it there’d be no plants, no animals… none of us would be here!

A natural shield comes under seasonal attack in both polar regions.

This is partly due to the lingering presence of man-made chlorine-based compounds, or CFCs, once widely used in refrigerants and consumer aerosols.

But most damage is caused by very cold weather, when water vapour and nitric acid molecules condense into clouds in the lower stratosphere. These clouds in turn become a “bed” where chlorine molecules gobble up ozone.

Traditionally the layer would thin out from spring until December – but this cycle now continues throughout the southern hemisphere’s summer into February.

Human activity is the source of three quarters of harmful gases currently destroying the ozone layer. Nitrous oxide, a greenhouse gas emitted by many industries, is the biggest threat. But nitrous oxide is also produced and released by soil and marine bacteria found living off tropical islands, salt marshes and peat bogs.

At its most depleted, around the turn of the 21st century, the ozone layer had declined by about five percent.