Mario Molina is famous for discovering that chlorofluorocarbons (CFCs), chemicals once widely used in refrigerators, aerosol sprays, and air conditioners, were destroying Earth’s protective ozone layer. That discovery, published in 1974, earned him the Nobel Prize in Chemistry and helped spark one of the most successful environmental treaties in history.
The 1974 Discovery That Changed Everything
In 1973, Molina joined the laboratory of F. Sherwood Rowland at the University of California, Irvine, as a postdoctoral researcher. Their project seemed straightforward: figure out what happens to CFCs after they’re released into the atmosphere. These synthetic chemicals were considered harmless at the time. They didn’t react with much at ground level, which is exactly why manufacturers loved them.
What Molina and Rowland found was alarming. CFCs drifted intact into the upper atmosphere, where intense ultraviolet radiation broke them apart and released chlorine atoms. Those free chlorine atoms then destroyed ozone molecules in a chain reaction. A single chlorine atom could wipe out thousands of ozone molecules before being neutralized, because the reaction kept recycling the chlorine back into its reactive form. Their landmark paper, “Stratospheric sink for chlorofluoromethanes: chlorine atom-catalysed destruction of ozone,” was published in the journal Nature on June 28, 1974.
The ozone layer acts as Earth’s sunscreen, absorbing most of the sun’s ultraviolet radiation before it reaches the surface. Without it, rates of skin cancer, cataracts, and damage to crops and marine ecosystems would skyrocket. Molina and Rowland weren’t just reporting a chemistry curiosity. They were warning that an entire class of industrial chemicals was quietly eroding one of the planet’s essential shields.
From Scientific Warning to Global Treaty
The response wasn’t immediate. The chemical industry pushed back hard, and it took more than a decade of accumulating evidence before governments acted. A turning point came in 1985, when scientists confirmed a massive “hole” in the ozone layer over Antarctica, exactly the kind of dramatic thinning Molina and Rowland’s hypothesis had predicted.
In 1987, nations signed the Montreal Protocol, an international agreement to phase out CFCs and other ozone-depleting substances. It became the first United Nations treaty to achieve universal ratification, with every country on Earth eventually signing on. The protocol is widely considered the most successful environmental agreement ever enacted. Atmospheric levels of ozone-depleting chemicals have been declining steadily since, and scientists project the ozone layer will return to its pre-1980 condition by roughly the middle of this century.
The Nobel Prize and Other Honors
In 1995, Molina shared the Nobel Prize in Chemistry with Rowland and Paul J. Crutzen, a Dutch atmospheric chemist whose earlier work on nitrogen oxides had also advanced the understanding of ozone chemistry. The Nobel committee recognized all three “for their work in atmospheric chemistry, particularly concerning the formation and decomposition of ozone.”
Molina was the first Mexican-born scientist to receive a Nobel Prize in Chemistry. In 2013, President Barack Obama awarded him the Presidential Medal of Freedom, the highest civilian honor in the United States, calling him “a visionary chemist and environmental scientist.”
Air Pollution and Climate Work
After the ozone work, Molina turned his attention to air quality in rapidly growing cities. In the early 2000s, he led a major interdisciplinary case study on Mexico City’s severe air pollution problem, bringing together experts in health, transportation, and public policy. That effort produced a set of recommendations that formed the foundation for a 10-year air quality management program adopted by the Mexican Metropolitan Environmental Commission. The approach emphasized something Molina had practiced since his earliest advocacy on CFCs: science works best when it directly informs policy.
He also became a prominent voice on climate change. Through the nonprofit Mario Molina Center for Energy and Environment in Mexico City, he developed strategic studies on energy policy and outlined pathways for keeping global temperature rise below the threshold set by the Paris Climate Agreement. He served on the U.S. President’s Council of Advisors on Science and Technology and held a professorship at the University of California, San Diego.
Why His Work Still Matters
Molina’s career is one of the clearest examples of a single scientific finding reshaping global policy. Before his 1974 paper, no one seriously questioned whether everyday consumer products could damage the atmosphere on a planetary scale. His research proved they could, and his willingness to publicly advocate for action helped turn that proof into binding international law. The Montreal Protocol didn’t just save the ozone layer. Recent research has shown it also prevented significant additional global warming, since many of the chemicals it phased out are potent greenhouse gases. Molina died on October 7, 2020, but the atmospheric recovery his work set in motion continues.