Almost exactly 30 years ago a paper by Farman, Gardiner & Shanklin appeared in Nature describing the loss of ozone in the Antarctic and suggesting that the presence of chlorine compounds high in the cold polar winter atmosphere were responsible.
This finding led to international agreements to reduce the use of man-made CFCs to limit further damage – the ‘Montreal Protocol’ was signed in 1987. But, the original Protocol would only have reduced the growth of stratospheric chlorine – it took later amendments to the agreement in London (1990), Copenhagen (1992), Beijing (1999) and Montreal again (2007) to set the path towards decreasing chlorine amounts, and therefore allow the ozone to recover (see Figure 1).
In addition, as CFCs are also greenhouse gases, this restriction has reduced the radiative forcing by about 0.4Wm-2, so slightly mitigating anthropogenic climate change. The levels of global and Antarctic ozone are now starting to recover (see Figure 2), and this recovery is projected to continue over the coming century.
The fact that it took several international agreements to ‘solve’ the ozone problem is perhaps a lesson for negotiations on similar protocols for climate change more broadly?