A new simulation has shown that if 193 nations had not agreed to ban ozone-depleting substances, then nearly two-thirds of Earth's ozone would have been gone by the year 2065.
The simulation was developed by atmospheric chemists at NASA's Goddard Space Flight Center, Greenbelt, Maryland, Johns Hopkins University, Baltimore, and the Netherlands Environmental Assessment Agency, Bilthoven.
Led by Goddard scientist Paul Newman, the team simulated "what might have been" if chlorofluorocarbons (CFCs) and similar chemicals were not banned through the treaty known as the Montreal Protocol.
The simulation used a comprehensive model that included atmospheric chemical effects, wind changes, and radiation changes.
Ozone is Earth's natural sunscreen, absorbing and blocking most of the incoming UV radiation from the sun and protecting life from DNA-damaging radiation. s it is moved around the globe by upper level winds, ozone is slowly depleted by naturally occurring atmospheric gases.
It is a system in natural balance.
But, chlorofluorocarbons invented in 1928 as refrigerants and as inert carriers for chemical sprays, upset that balance.
Researchers discovered in the 1970s and 1980s that while CFCs are inert at Earth's surface, they are quite reactive in the stratosphere (10 to 50 kilometers altitude, or 6 to 31 miles), where roughly 90 percent of the planet's ozone accumulates.
UV radiation causes CFCs and similar bromine compounds in the stratosphere to break up into elemental chlorine and bromine that readily destroy ozone molecules. If 193 nations had not signed the Montreal Protocol in 1989, simulations predict that by 2065, nearly two-thirds of Earth's ozone would have been gone, not just over the poles, but everywhere.
By the simulated year 2020, 17 percent of all ozone is depleted globally, as assessed by a drop in Dobson Units (DU), the unit of measurement used to quantify a given concentration of ozone.
Then, an ozone hole starts to form each year over the Arctic, which was once a place of prodigious ozone levels.
By 2040, global ozone concentrations fall below 220 DU, the same levels that currently comprise the "hole" over Antarctica.
By the end of the model run in 2065, global ozone drops to 110 DU, a 67 percent drop from the 1970s.
The ultraviolet (UV) radiation falling on mid-latitude cities like Washington, D.C., would have become strong enough to cause sunburn in just five minutes.
Also, DNA-mutating UV radiation would have gone up 650 percent, with likely harmful effects on plants, animals and human skin cancer rates.
"We simulated a world avoided, and it's a world we should be glad we avoided," said Newman.