As you learned earlier, scientists in the mid-1980s recognized that the release of CFCs had depleted the ozone layer so significantly that it was as if a hole had formed. The amount of ozone in the stratosphere is sustained by a balance between its formation, chemical reactions initiated by ultraviolet light from the Sun, and its destruction through a variety of processes. With the release of CFCs, the rate of ozone destruction exceeded its rate formation, resulting in the ozone hole over the Antarctic. Ozone depletion directly threatened human health, because an increase in ultraviolet rays reaching Earth’s surface would increase the incidence of skin cancer.

When we use resources faster than they are replenished, our societies and economies are not sustainable. Because everything that humans need to survive comes from the natural environment, the principle of sustainability is about the wise use of resources to ensure our ability to endure and live healthy lives, without compromising the welfare of future generations. For instance, rather than relying on nonrenewable sources of energy, such as oil and gas, a sustainable strategy incorporates renewable energy such as solar and wind power. When we harvest from wild populations, as is the case in fisheries and forestry, we should do so cautiously in order to allow these populations to reproduce. When we use pesticides on farms, we need to ensure that they do not pollute the groundwater or disrupt the pest control services provided by other organisms. And when we expand cities and agriculture in dry regions, such as the desert Southwest, we will benefit from technologies and policies that conserve water. In short, sustainability is about reducing our ecological footprint in order to make sure that humans and nature can coexist.

On September 16, 1987, President Ronald Reagan and other world leaders made an important step toward creating sustainable policies to protect the ozone layer. Reagan agreed to the Montreal Protocol, which would reduce the production of CFCs and encourage the development of alternative refrigerants and propellants. Reagan, who himself had been treated for skin cancer, recognized the importance of sustainable policies in protecting human health and nature. In the beginning, the Protocol sought only to reduce the global production of the worst CFCs by 50%, but scientists soon recognized that no level of CFC production was sustainable; thus, CFCs were banned completely. Since that time, the Montreal Protocol has been adjusted five times to regulate almost 100 gases, and it is considered one of the most successful global environmental treaties in history, as well as a model for how countries might reduce greenhouse gas emissions. In fact, recent research has even suggested that the reduction in CFCs over the last 15 years has also slowed global warming, which we will later see threatens humans and nature in other ways.

Sustainability provides a pragmatic framework for solving environmental problems. It allows us to set aside differences in environmental philosophies and focus on the common goal of maintaining our health and prosperity, ensuring the survival of future generations.

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