An international team of researchers led by MIT confirms that the hole in the Antarctic ozone layer is healing. They found that since 2000, the size of the ozone hole has decreased by more than 4 million square kilometres, which is equivalent to half of the US.

The team points out that the complete recovery of the ozone hole is delayed mainly because of the volcanic eruptions. Still, they are optimistic that the ozone hole will be healed completely or close permanently by the middle of this century.

The improved state is due to the introduction of the 1987 Montreal Protocol, a law that banned the use of chlorofluorocarbons or CFCs. Previously, CFCs were widely incorporated in air conditioners, refrigerators and aerosol cans.

ozone hole

false-color image showing ozone concentrations above Antarctica on Oct. 2, 2015. Credit: NASA/Goddard Space Flight Center

“We can now be confident that the things we’ve done have put the planet on a path to heal,” says the study’s lead author Susan Solomon, a professor of Atmospheric Chemistry and Climate Science at MIT. “We decided collectively, as a world, ‘Let’s get rid of these molecules.’ We got rid of them, and now we’re seeing the planet respond.”

According to Ryan R Neely III, a lecturer in Observational Atmospheric Science at the University Of Leeds, observations and computer models reflect the ozone hole improvement.  The researchers observed the annual opening of the ozone hole in September from 2000 to 2015.

They also took into account the sulphur dioxide from volcanoes, temperature and wind changes. They found that the observations matched their computer simulations of the ozone hole’s size reduction.

Annual ozone hole depletion begins late August and becomes fully formed by early October. But the team concentrated on September because the chlorine from CFCs is in control of the hole forming rate this month.

Anja Schmidt, also from Leeds, explains that recent volcanic eruptions like the 2015 eruption at Calbuco in Chile in 2015 caused a huge ozone hole that year. Other smaller eruptions also delayed the recovery.

CFCs react with light and the atmospheric temperature, causing it to eat away the ozone. These gases will remain up to 100 years so we still have to wait for some time before the ozone hole heals completely.