Aug 21, 2021 - Energy & Environment

The unexpected, world-saving side effects of the Montreal Protocol

Visualization ozone hole
A visualization of the Antarctic ozone hole from 1991, two years after the Montreal Protocol went into effect. Credit: NASA/Goddard Space Flight Center Scientific Visualization Studio

A new study finds the 1987 Montreal Protocol, which was negotiated to stop ozone-depleting emissions, also prevented significant climate change.

Why it matters: Former UN Secretary-General Kofi Annan called the Montreal Protocol "perhaps the single most effective international agreement," and its success in both reversing ozone depletion and slowing warming shows why.

What's happening: In a study published in Nature this week, researchers simulated what would have happened to the world if the Montreal Protocol had never gone into effect.

  • The treaty phased out ozone-depleting chemicals like chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs).
  • Previous research has shown the Antarctic ozone hole would have been 40% bigger in the treaty's absence.
  • The new study, though, shows continued use of ozone-depleting chemicals in the absence of Montreal could have led to an additional 2.5 °C of warming by the end of the century.

How it works: Some of that climate change would have been triggered by direct warming caused by CFC and HCFC emissions, which act as a greenhouse gas.

  • But because a damaged ozone layer would let in more harmful UV radiation, plants would have had a reduced ability to store carbon, which would have further contributed to warming.

The big picture: The success of the Montreal Protocol has often been cited as proof the global community can successfully negotiate a solution to a global environmental challenge.

  • But carbon — and the fossil fuels that contain them — is far more central to the global economy than CFCs and HCFCs, which could be replaced with ozone-safer alternatives at a relatively low price.
  • The geopolitical realm is arguably much more complex now than it was in 1987, when large developing countries like India and China — which will be the source of the bulk of current and future carbon emissions — were much smaller and had less of a voice.

The bottom line: The world's governments were unusually far-sighted in negotiating the Montreal Protocol, but climate change won't be as easy.

Editor's Note: This story has been updated to reflect that the Montreal Protocol phased out hydrochlorofluorocarbons (HCFCs), not hydrofluorocarbons (HFCs).

Go deeper