The remaining substances will be phased out over the next 15 years. As a result, the ozone layer is projected to recover by the middle of this century. In addition, because many ozone-depleting substances are also potent greenhouse gases, ozone protection efforts have significantly helped to mitigate climate change by averting more than 135 billion tonnes of carbon dioxide equivalent emissions. Other important continuing issues include prevention of illegal trade in ozone-depleting substances and the sound management of those substances still in use, such as in refrigerators, air conditioners and firefighting equipment.