"Ozone-Destroying Chemical Making Comeback, Scientists Find"

"An ozone-destroying chemical long thought to be on the decline in Earth’s upper atmosphere is making an unexpected comeback, an international team of scientists has found.

Backed by years of global observations including key contributions from a Canadian satellite, researchers reported in the journal Nature on Wednesday that concentrations of hydrogen chloride in the Northern Hemisphere have been edging upward since 2007.

The effect is pronounced enough to slow the recovery of the ozone layer, which helps to screen out harmful ultraviolet radiation from the sun. Ozone thinned dramatically in the past because of the use of chlorofluorocarbons (CFCs), which were phased out after international adoption of the Montreal Protocol in 1987."

Ivan Semeniuk reports for the Toronto Globe and Mail November 5, 2014.