The ozone layer is a region of the stratosphere that protects the Earth from the Sun’s harmful ultraviolet B (UVB) radiation. Excess UVB exposure has been shown to disrupt the reproductive cycle of phytoplankton, the tiny but essential foundation of the ocean’s food chain, as well as damage the immune system of human beings. UVB saturation has also been linked to premature skin aging, cataracts and nonmelanoma skin cancers.
In 1985, a trio of scientists published a report in the journal Nature that provided the first evidence that the ozone layer was being depleted over Antarctica. This was primarily due to the emissions of chlorofluorocarbons (CFCs), chemicals commonly used in aerosols, refrigerators and air conditioners prior to 1987. These chemicals were reacting with UV rays and tearing up the ozone layer at an atomic level.
To stop this process, the world’s leading nations signed the Montreal Protocol in 1987, a treaty that required its participants to phase out the use of CFCs. Only now, nearly three decades after the treaty went into effect, has the ozone layer shown signs of healing.
The hole in the ozone reached its largest size in 2006 and has not expanded since. Scientists expect that it will be another decade before it begins to shrink.
While this is generally good news, the story is not altogether a success. After CFCs were phased out, hydrofluorocarbons (HFCs) largely took their place. And while HFCs do not damage the ozone layer, they do contribute to global warming.
As the UN’s assessment panel noted, “Hydrofluorocarbons (HFCs) do not harm the ozone layer but many of them are potent greenhouse gases. They currently contribute about 0.5 gigatonnes of CO2-equivalent emissions per year. These emissions are growing at a rate of about seven percent per year. Left unabated, they can be expected to contribute very significantly to climate change in the next decades.”
Next year, the world’s leading nations will gather in Paris to discuss plans for reducing global greenhouse gas emissions. If they can reach the same compromise they found in 1987, there may still be hope for limiting global warming to 2°C in this century. International leaders are gathering in New York this month in preparation for the 2015 Paris summit, with potentially one million Americans showing their support by gathering in the streets.
You can read the WMO’s latest assessment on the ozone layer here.