There is still much to learn about the thinning ozone layer.
Scientists know that ozone-destroying industrial chemicals are the major cause of ozone loss.
However, only about half of the observed ozone loss in the upper atmosphere can be definitely attributed to these chemicals. Other factors, such as climate change, could also be involved. Due to these uncertainties, changes in the ozone layer must be carefully tracked to determine the effectiveness of the actions we have taken to reduce ozone-depleting chemicals. Environment Canada operates a cross-country network of monitoring stations which has kept continuous watch on Canada's ozone layer for nearly four decades. The early records, which were taken before there was any major human influence on the ozone layer, are vital to understanding the changes that are occurring today.