Climate: Montreal Protocol may have mitigated climate change by protecting terrestrial carbon stores

The Montreal Protocol may have helped to mitigate climate change by protecting plants from UV damage, thereby avoiding a reduction in carbon storage and an increase in atmospheric carbon dioxide levels, reports a modelling study published in Nature.

The ozone layer absorbs UVB light that is harmful to human and ecosystem health, including causing damage to plants that store carbon. Ozone-depleting substances, including chlorofluorocarbons (CFCs) that were used commercially in older refrigerators and aerosols, damage the ozone layer and were phased out as a result of the 1987 Montreal Protocol — an international agreement to protect the ozone layer — and its amendments.

Paul Young and colleagues explored how the Montreal Protocol may have had benefits for the terrestrial biosphere and its capacity as a carbon sink by preventing increases in UV radiation and climate change. They used a modelling framework that integrates ozone depletion, climate change, plant UV damage and the carbon cycle. The simulations indicate that there could have been 325–690 Gt less carbon held in plants and soils by the end of this century in a world without the Montreal Protocol. The authors estimate that the resulting additional atmospheric carbon dioxide could have led to around 0.5–1.0 °C additional global mean surface temperature warming.

These findings suggest a climate system co-benefit of the Montreal Protocol, in addition to the well-known climate protection as a result of a reduction in ozone-depleting substances that are potent greenhouse gases.