For years, researchers thought the Antarctic Ozone Hole was increasing despite preventive efforts. A new study says the ozone hole is shrinking.
If the ozone layer were destroyed, life on Earth would stop. Since 1985, when the Antarctic Ozone Hole was discovered, the world recognized the gravity of this threat and worked together to prevent further damage to the Earth’s ozone layer. Now, 30 years later, with reports that ozone layer depletion is still on the rise, a new study from Massachusetts Institute of Technology (MIT) and the University of Leeds researchers sheds new light on the topic and says the Antarctic Ozone Hole may be shrinking in size ÛÒ and has been for years.
A hole in the ozone layer, the section of Earth’s atmosphere containing a high concentration of a gas called ozone, is not a hole at all but a widespread thinning above a certain region of the world. The ozone layer is responsible for absorbing a majority of the sun’s ultraviolet (UV) radiation ÛÒ the radiation that causes sunburn and increases the risk of skin cancer. When the ozone layer thins, more UV radiation is allowed through the atmosphere, causing serious damage to plants and animals.
In 1974, a discovery revealed that chlorofluorocarbons (CFCs) could damage the ozone layer of the atmosphere. CFCs were carried in spray cans, refrigerants and other substances. Damage to the ozone, caused by CFCs, was not a focus point in any important political discussions until 1985, when a group of British Antarctic Survey scientists discovered abnormally low ozone levels in the atmosphere over the Antarctic.
With proof that CFCs caused a real threat to the world, countries around the globe agreed to regulate and phase out the use of CFCs. This led to the Montreal Protocol, a treaty signed by 24 countries. Recently, researchers have questioned whether the treaty was created too late, backing up their arguments with data showing the Antarctic Ozone Hole was still growing and that the 2015 ozone hole was one of the largest since 1991.
However, many scientists were not convinced this was the whole story. Susan Solomon was among them; she is the lead author of a new study investigating the ozone hole. Solomon is the Ellen Swallow Richards professor of atmospheric chemistry and climate science at MIT as well as the former co-chair of the United Nations’ Intergovernmental Panel on Climate Change. She says researchers have not found signs of healing because ÛÏthey have been looking at the wrong time.Û
ÛÏI think people, myself included, had been too focused on October because that’s when the ozone hole is enormous, in its full glory,Û explained Solomon. ÛÏSeptember is a better time to look because chlorine chemistry is firmly in control of the rate at which the hole forms at that time of year.Û
The ozone layer changes thickness throughout the year, effectively changing the size of the hole due to ozone depleting substances in the atmosphere. Chlorine, a persistent threat to ozone in the stratosphere, destroys the molecules most efficiently in the spring, when the weather is largely sunny and cold, causing the ozone layer to be at its thinnest in October. Solomon and her team realized this and started looking at their data from September instead of October.
ÛÏWe used model simulations to look for signs of healing in the Antarctic Ozone Hole and compared the model results with measurements taken by other laboratories,Û said Diane Ivy, research scientist in the Department of Earth, Atmospheric and Planetary Sciences at MIT and one of the co-authors of the study.
These simulations used observed winds and temperatures to recreate what the atmosphere looked like in the past and then added to the model various ozone-depleting substances like CFCs, greenhouse gasses and aerosols. By using their simulations during the September months, the team found data that supported the healing they had hypothesized. ÛÏBy running the model with and without the ozone depleting substances,Û Ivy explained. ÛÏWe could see what affect that had on ozone concentrations.Û
The results were surprising. The team discovered something they did not originally set out to find ÛÒ volcanoes had been skewing the data of previous studies. Large volcanic eruptions can fill the stratosphere with aerosols, small droplets of chemicals dissolved in water that can provide a surface upon which chlorine and other ozone-depleting chemicals can react with ozone, amplifying the depletion of the ozone layer. Most notably, the eruption of Calbuco, a volcano in Chile, was shown to have a direct effect on the abnormally large ozone hole in 2015.
The team ran their simulations with everything they thought would increase the size of the ozone hole and then repeated their simulations without volcanic aerosols. ÛÏThe simulations without the aerosols from Calbuco showed an ozone hole that did not last as long and would not have been a record year,Û Ivy said. This meant that the size of the ozone hole in 2015 may not be proof that the ozone hole was getting worse again, but instead was simply an anomaly. Without the eruptions of Calbuco throughout the year, the data showed that the hole is healing.
ÛÏThe September size of the ozone hole shows this very systematic trend of getting smaller,Û Solomon said. The predicted level of ozone in the atmosphere fell in line with the shrinking trend she had observed over the other years.
Not all ozone researchers are convinced by the study. Some scientists believe the decline of the ozone hole is not as greatly dependent on the amount of chlorine in the atmosphere as the study suggests. Paul Newman, chief scientist for Earth Sciences at NASA’s Goddard Space Flight Center, says the yearly data used to prove Solomon’s hypothesis shows significant variations too great to follow the chlorine trends highlighted in the paper.
Nevertheless, the findings developed by Solomon’s team with the use of data from weather balloons, satellites, and simulations, show that since 2000, the average size of the hole during the September months has decreased by more than 1.7 million square miles, a little more than half of the area of the contiguous United States.
ÛÏThere is still a ways to go until the Antarctic Ozone Hole has fully recovered,Û Ivy explains, ÛÏbut it could possibly be as early as 2050.Û
Josiah Killam is a student at the University of Illinois in Champaign-Urbana studying engineering physics and astronomy. Killam participated in the IEEE Earthzine Writing Club during the summer of 2016.