A World Avoided.
What if the countries of the world had not agreed to phase out production of ozonedepleting substances?
Were scientists right about predictions of catastrophic ozone loss, which led to the signing of the Montreal Protocol?
To answer these questions, atmospheric scientists at NASA and other research centers decided to create a model using computers to simulate the atmosphere with and without restrictions on ODSs. In the “World Avoided” model, the emissions of CFCs and other ODSs were assumed to grow at a rate of 3% per year, about what they had been doing over the decade prior to the Montreal Protocol’s regulations.
Scientists used an earth system model that accounts for variations in solar energy, atmospheric chemical reactions, temperature changes and winds, and interactions between the stratosphere and troposphere, and let the calculations simulate the atmosphere from 1975 to 2065.
Then, they repeated the simulation, this time using actual and forecast ODS emissions. By the year 2020 in the “World Avoided” simulation, 17 percent of global ozone was destroyed, and an ozone hole formed each year over the Arctic as well as the Antarctic.
By 2040, the ozone hole—ozone levels less than 220 Dobson Units—was global. The UV Index in mid-latitude cities reached 15 around noon on a clear summer day (10 is considered extreme today). By the end of the simulation in 2065, global ozone dropped to less than 110 DU, a 67 percent drop from the 1970s.
Arctic ozone values remained between 50 DU and 100 DU the whole year around (down from 500 DU in 1960).
In the real world, emissions of ODSs ended in 1992. However, their abundance is only now beginning to decline because the chemicals stay in the atmosphere for 50 to 100 years. The peak abundance of CFCs in the atmosphere occurred around 2000, and has decreased by roughly 4 percent to date. Stratospheric ozone was depleted by 5 to 6 percent at middle latitudes, but has rebounded a little in recent years. The largest recorded Antarctic ozone hole was recorded in 2006, with slightly smaller holes since then. The “Real World” simulation predicts the recovery of the ozone layer to above 300 DU by the 2050-2060 time frame.