When a CFC molecule reaches the stratosphere, it eventually absorbs UV radiation, causing it to decompose and release its chlorine atoms. One chlorine atom can destroy up to 100,000 ozone molecules. Too many of these chlorine and bromine reactions disrupt the delicate chemical balance that maintains the ozone layer, causing ozone to be destroyed faster than it is created.
Because of the Montreal Protocol we have avoided a world where ozone depletion would have led to massive increases of UV radiation. Severe ozone holes would have occurred every year over the Arctic and the Antarctic. By the mid-21st century, severe ozone depletion would have spread across the planet including the tropics. This global ozone depletion would have increased UV-B to levels above anything experienced on Earth with severe consequences worldwide. Let’s explore some of those consequences.
The Vienna Convention for the Protection of the Ozone Layer was adopted in 1985 and entered into force in 1988. Nations that signed the Convention – called the parties – agreed to research and monitor the effects of human activities on the ozone layer...
and to take concrete action against activities that are likely to have adverse effects on the ozone layer.
The Convention did not require countries to take specific actions to control ozone-depleting substances. The specific actions are spelled out by the Montreal Protocol.
The Montreal Protocol on Substances that Deplete the Ozone Layer is a global agreement to protect Earth’s ozone layer by phasing out the consumption and the production of most chemicals that deplete it. The landmark agreement was signed on 16 September 1987 – marked globally as the World Ozone Day - and entered into force in 1989. The Protocol provides a set of practical, actionable tasks to phase out ozone-depleting substances that were universally agreed upon.
The Protocol is unique in having the flexibility to respond to new scientific information. Since its inception the Protocol has successfully met its objectives, and continues to safeguard the ozone layer today.
Although the Montreal Protocol was designed to phase out the production and consumption of ODSs, some replacements of these substances, known as hydrofluorocarbons (HFCs), have proven to be powerful greenhouse gases. In fact, some HFCs are more than a thousand times more potent than carbon dioxide in contributing to climate change.
After several years of effort, the parties agreed on 15 October 2016 to amend the Protocol to include control measures to reduce HFCs (the Kigali Amendment). A successful HFC phasedown is expected to avoid up to 0.5 degree Celsius of global temperature rise by 2100, while continuing to protect the ozone layer.