The ozone layer has seen unprecedented damage in the Arctic this winter due to cold weather in the upper atmosphere. By the end of March, 40% of the ozone in the stratosphere had been destroyed, against a previous record of 30%.
The ozone layer protects against skin cancer, but the gas is destroyed by reactions with industrial chemicals. These chemicals are restricted by the UN's Montreal Protocol, but they last so long in the atmosphere that damage is expected to continue for decades.
"The Montreal Protocol actually works, and the amount of ozone-depleting gases is on the way down, but quite slowly," said Geir Braathen, a senior scientist with the World Meteorological Organization (WMO), which co-ordinates ozone data globally.
"In the meantime, we have some winters that get much colder than before and also the cold periods last longer, into the spring," he told BBC News.
"So it's really a combination of the gases still there and low temperatures and then sunshine, and then you get ozone loss."
Dr Braathen was one of a number of scientists presenting the findings at the European Geosciences Union (EGU) annual meeting in Vienna.