Questions about Ozone depletion
Short answers, pulled from the story.
What causes ozone depletion and the ozone hole?
Ozone depletion is caused primarily by manufactured halocarbon compounds, especially chlorofluorocarbons (CFCs) and halons, which release chlorine and bromine atoms in the stratosphere. Each chlorine atom can destroy an average of 100,000 ozone molecules before being removed from the catalytic cycle. The Antarctic ozone hole forms each spring because extreme winter cold creates polar stratospheric clouds that convert stable chlorine reservoir compounds into highly reactive free radicals.
When was the ozone hole first discovered?
British Antarctic Survey scientists Farman, Gardiner, and Shanklin first reported the Antarctic ozone hole in a paper published in Nature in May 1985. Satellite data from the Total Ozone Mapping Spectrometer aboard Nimbus 7 had captured the phenomenon earlier, but the readings were filtered out as errors until the raw data was reprocessed, at which point the hole was visible as far back as 1976.
Who discovered that CFCs deplete the ozone layer?
Frank Sherwood Rowland, a chemistry professor at the University of California at Irvine, and his postdoctoral associate Mario J. Molina proposed in 1974 that CFCs would reach the stratosphere and release chlorine atoms that catalyze ozone destruction. Paul Crutzen had earlier identified how nitrous oxide and nitrogen oxides could deplete ozone. Crutzen, Molina, and Rowland were jointly awarded the 1995 Nobel Prize in Chemistry for this work.
What is the Montreal Protocol and did it work?
The Montreal Protocol is an international agreement signed in 1987 by representatives from 43 nations that froze CFC production at 1986 levels and set a schedule for eliminating ozone-depleting substances. It is considered the most successful international environmental agreement to date. Ozone levels stabilized by the mid-1990s and began recovering in the 2000s, with a 2023 United Nations assessment projecting full recovery to 1980 levels by around 2040 for most of the world, 2045 over the Arctic, and 2066 over Antarctica.
What are the health effects of ozone depletion on humans?
Ozone depletion increases surface UV-B radiation, which causes skin cancer, cataracts, and sunburn. Scientists estimate that every one percent decrease in stratospheric ozone raises the incidence of basal and squamous cell carcinomas by 2 percent. A study in Punta Arenas, Chile, found a 56 percent increase in melanoma and a 46 percent increase in non-melanoma skin cancer over seven years during a period of decreased ozone and increased UV-B. Ozone depletion is predicted to cause hundreds of thousands of additional cataracts by 2050.
Is the ozone layer recovering, and what threatens its recovery?
Global ozone is recovering following reductions in CFC emissions, with the Effective Equivalent Chlorine level dropping about 10 percent between its 1994 peak and 2008. Threats to full recovery include illegal production of banned compounds such as CFC-11 from north-eastern China, the unresolved growth of CFC-113a in the atmosphere, the unregulated greenhouse gas nitrous oxide which is now the most highly emitted ozone-depleting substance, and aluminum oxide nanoparticles produced by satellites burning up on re-entry.