The World We Avoided by Protecting the Ozone Layer

By Michael Carlowicz, with contributions from Rebecca Lindsey Design by Robert Simmon May 13, 2009

The year is 2065. Nearly two-thirds of Earth’s ozone is gone—not just over the poles, but everywhere. The infamous ozone hole over Antarctica, first discovered in the 1980s, is a year-round fixture, with a twin over the North Pole. The ultraviolet (UV) radiation falling on mid-latitude cities like Washington, D.C., is strong enough to cause sunburn in just five minutes. DNA-mutating UV radiation is up more than 500 percent, with likely harmful effects on plants, animals, and human skin cancer rates.

Maps of ozone concentrations for the world avoided and projected based on current regulations.
These maps show computer model predictions of the state of the ozone layer in 2064 without (above left) and with (above right) the effects of international agreements to curb ozone-destroying chemicals in the 1980s and 90s. (NASA images by the GSFC Scientific Visualization Studio.)

Such is the world we would have inherited if 193 nations had not agreed to ban ozone-depleting chemicals, according to atmospheric chemists from NASA’s Goddard Space Flight Center, the Johns Hopkins University, and the Netherlands Environmental Assessment Agency. Led by Goddard scientist Paul Newman, the team used a state-of-the-art model to learn “what might have been” if chlorofluorocarbons (CFCs) and similar chemicals had not been banned through the 1989 Montreal Protocol, the first-ever international agreement on regulation of chemical pollutants.



Photograph of Paul Newman standing in front of NASA's DC-8 research aircraft.
NASA’s Paul Newman led the interdisciplinary team that modeled the “World Avoided.” His team envisioned what the Earth would have looked like with high concentrations of ozone-destroying chemicals in the atmosphere. (Photograph courtesy Paul Newman.)

“Ozone science and monitoring have improved over the past two decades, and we have moved to a phase where we [scientists] need to be accountable,” said Newman, who is serving as a co-chair for the latest “state of the science” assessment report required by the terms of the Montreal Protocol. “We are at the point where we have to ask: Were we right about ozone? Did the regulations work? What kind of world was avoided by phasing out ozone-depleting substances?”

Ozone Chemistry

Ozone is Earth’s natural sunscreen, absorbing most of the incoming UV radiation from the sun and protecting life from DNA-damaging radiation. The gas is naturally produced and destroyed by sunlight-driven chemical reactions in the stratosphere, between about 10 and 50 kilometers above the Earth’s surface. Ozone is made when oxygen molecules (O2) absorb ultraviolet light and split into individual atoms (O), which join with other O2 molecules to make O3—ozone. Ozone is destroyed when molecules containing nitrogen, hydrogen, chlorine, or bromine catalyze reactions that pair a single O atom with ozone (O3) to make 2 molecules of O2. It is a system with a natural balance.

But chlorofluorocarbons—invented in the early 1890s, and first used in the 1930s as refrigerants and propellants for chemical sprays—upset that balance. While CFCs are not reactive at Earth’s surface, they become quite destructive when they are exposed to ultraviolet light in the upper stratosphere. There, CFCs and their bromine-based counterparts break up into elemental chlorine and bromine that repeatedly catalyze ozone destruction. Worst of all, such ozone-depleting chemicals can reside for several decades in the atmosphere before breaking down.

Graph of ozone hole measurements from Halley Bay and Satellite.
In the late 1970s, a springtime “hole” (areas with total ozone below 220 Dobson Units) developed in the ozone layer above Antarctica. British researchers stationed on the ice of Halley Bay, Antarctica, discovered the hole with ground-based measurements (red). NASA satellites corroborated the discovery (blue) and mapped the extent of the hole. (NASA graph by Robert Simmon, based on data from the British Antarctic Survey and GSFC Atmospheric Composition Team.)

The chemical phenomenon opened up a springtime hole over Antarctica in the 1980s. Each winter, stratospheric temperatures are cold enough to form clouds, even though the air is very dry. Chemical reactions on the surfaces of the cloud particles convert chlorine from a relatively unreactive form into highly reactive form. The September sunrise over Antarctica triggers ozone-destroying reactions by these reactive kinds of chlorine, and the ozone concentration over the South Pole drops from about 300 Dobson Units to as low as 100 Dobson Units. (See “What is a Dobson Unit?”) By late spring, the rising temperature stops the ozone destruction cycle. The ozone layer rebounds over summer and fall. The ozone hole phenomenon opened the eyes of the world to the effects of human activity on the atmosphere.

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