The Ozone layer the last 30 years

Emissions of ozone-depleting substances have weakened the ozone layer over the past 30 years. Gases that deplete ozone in the stratosphere contain chlorine or bromine, and are long-lived, so that they can be transported into the stratosphere.

The main ozone-depleting substances are CFCs.  The CFCs with the highest concentrations today are CFC-11 and CFC-12, which have a life of 45 and 100 years, respectively. CFCs were later replaced by HCFCs, which are better for the ozone layer. HCFCs have a lifespan of around 10-20 years and but also break down ozone, so that these gases are now often replaced by HFCs. All of these chlorinated fluorocarbons are greenhouse gases and are covered by the national greenhouse gas monitoring programme that NILU conducts on behalf of the Norwegian Environment Agency

Read more: Greenhouse gases, NILU's observatories

The ozone layer over Norway weakened by about 2.5% during the period 1979-2009. This is an improvement compared to 1979-2008, and measurements in recent years suggest that ozone amounts over Norway are now starting to build up again. The decrease in ozone over Norway was mainly due to reduced ozone levels in the spring. Globally, the ozone layer is 3% lower than the long-term mean for the northern hemisphere and 6% lower for the southern hemisphere. According to the WMO / UNEP, it is expected that the ozone layer will be rebuilt by the middle of this century, around 2050. But there is some uncertainty about this, as a result of other changes in the atmosphere. These include climate change, changes in water vapour and emissions of gases that are not regulated by the Montreal Protocol, such as nitrous oxide (N2O). It is not clear how the ozone layer will respond to these factors.