A new study published in the journal Nature, has found that international co-operation through the Montreal Protocol helped not only to restore the ozone layer in the southern hemisphere, but also restore the southern jet stream to a normal state after decades of disruption.
The Montreal Protocol, signed in 1987, is a landmark international agreement between 197 parties to phase-out the use of ozone-depleting substances. It placed legally binding restrictions on the use of chemicals and aerosols that contain chlorofluorocarbons (CFCs) which deplete the ozone in the upper layers of earth's atmosphere, which protects all living things from most of the harmful ultraviolet rays from the sun.
The southern jet stream is a powerful wind that affects weather patterns and currents in the oceans in the southern hemisphere. Since the hole in the ozone layer formed in the late 1970s, the jet stream has been moving southward towards the Antarctic at a rate of one degree of latitude each decade, affecting wind patterns up until about the year 2000.
The article states that pre-2000 wind circulation trends affected rainfall over South America, East Africa and Australia, likely to causing increased droughts in those regions, and potentially ocean circulation and salinity of the ocean water. The study anticipates that the effects of the Montreal Protocol and the associated stratospheric ozone recovery might manifest in weather patterns across the whole World.
Lead author of the published article, Antara Banerjee said: "It's a success story. There is more evidence that the Montreal Protocol has lead to the recovery of the ozone layer."
However, the restoration of ozone is not enough to push southern hemisphere weather patterns back to normal (as they were prior to industrial emissions) due to the greenhouse gas emissions which still impact the jet stream and force it in opposite direction.
Banerjee added: "There is a tug of war between ozone recovery and increasing CO2. That's why we are seeing a pause. In the near future, the ozone factor could dominate and the jet stream will move back towards the equator. But once the recovery is complete, CO2 could push it southwards again."
