気候：南半球の大気循環に変化が生じたことの影響

Changes in atmospheric circulation linked to the recovery of the ozone layer in the Southern Hemisphere are reported in a paper in Nature. The research into these changes suggests that this effect is a direct result of the implementation of the Montreal Protocol.

Human-generated emissions of ozone-depleting substances have contributed to a decline in ozone, which has caused changes in atmospheric circulation in the Southern Hemisphere. The main effects include a poleward shift of the mid-latitude jet stream and the expansion of both tropical circulation and the subtropical dry zone. These changes have been shown to have impacted precipitation and have potentially affected ocean circulation and salinity in the Southern Hemisphere.

Antara Banerjee and colleagues use 1980–2017 atmospheric reanalyses ― a combination of data and modelling ― to show that these trends have paused or reversed since around the year 2000. For example, they found that the Southern Hemisphere jet stream moved poleward until 2000, when it seemed to pause. This timing coincides with Antarctic ozone recovery around the year 2000 and suggests that the decline in ozone-depleting substances, as mandated by the Montreal Protocol, may be responsible for the pause in circulation trends.

These findings indicate that the Montreal Protocol may have also affected other aspects of the Earth system, although the authors note that as carbon dioxide emissions continue to rise, it is unclear whether the pause in atmospheric circulation trends will continue.