The World Meteorological Organization said Tuesday that the Earth’s fragile ozone layer in the Arctic region has suffered a loss of about 40 percent from the start of winter until late March exceeding the previous seasonal loss of about 30 percent.

The Geneva-based agency blamed the loss on a buildup of ozone-eating chemicals once widely used as coolants and fire retardants in a variety of appliances and on a very cold winter in the stratosphere, the second major layer of the Earth’s atmosphere.