
The weakened ozone layer, which is vital to protecting life on Earth, is on track to be restored to full strength within decades — the latest success of a global effort by nations to stop using chemicals that had been destroying the critical layer in the upper atmosphere. In a report for the United Nations, scientists said Monday that if countries continue to maintain the bans on chlorofluorocarbons and other chemicals, ozone levels between the polar regions should reach pre-1980 levels by 2040. Ozone holes, or regions of greater depletion that appear regularly near the South Pole and, less frequently, near the North Pole, should also recover, by 2045 in the Arctic and about 2066 in Antarctica.