José Mario Molina-Pasqual Henriquez was born and raised in Mexico City. From an early age, Mario was fascinated by the natural sciences. When he encountered his first microscope, he was thrilled to observe the organisms living in a drop of ordinary pond water. His father was a prominent attorney; when Mario was grown, the elder Molina would serve his country as Ambassador to Ethiopia, Australia and the Philippines.
Many of the Molinas were educated professionals, but the only scientist in the family was Mario’s aunt, Esther Molina, a chemist who encouraged his love of the sciences. Young Mario acquired chemistry sets and built his own laboratory in an unused bathroom of the family home. The other major interest of his childhood was music. He played the violin and considered the possibility of a career in music, but found himself increasingly drawn to chemistry, and enjoyed reading biographies of the great chemists. At age 11, he was sent briefly to a boarding school in Switzerland to begin the study of German, a language his parents hoped would be useful to a budding chemist.
He returned to Mexico City to complete his secondary education and went on to the Autonomous National University of Mexico (UNAM), where he studied chemical engineering, a course that provided more training in mathematics than was available in the pure chemistry curriculum. After receiving his chemical engineering degree, Molina enrolled in graduate courses at the University of Freiburg, Germany, where she spent two years carrying out research in the kinetics of polymerization. He had arrived in Freiburg feeling somewhat underprepared in math and physics, and after completing his work at Freiburg, he traveled to Paris for a few months of intensive mathematical study. Molina hoped to pursue doctoral studies in the United States, but returned to Mexico first, to teach at UNAM, where he established the first graduate program in chemical engineering.
In 1968, Molina enrolled in the Ph.D. program in physical chemistry at the University of California, Berkeley. There he expanded his knowledge of physics and mathematics as well as physical chemistry, and joined a research group led by Professor George Pimentel; he would later credit Pimentel as a great influence on his development as a scientist. Under Pimentel’s direction, Molina conducted important research employing chemical lasers. He was among the first to determine that irregularities in laser behavior that had been dismissed as noise were in fact “relaxation oscillations” that could be readily understood through the fundamental equations of laser emission. The Berkeley campus of the late ’60s and early ’70s was still reeling from the tumultuous political events of the preceding years, and for the first time, Mario Molina began to consider the social implications of scientific research, specifically the possible destructive application of laser technology in warfare.
Molina completed his doctorate in 1972, and remained in Berkeley for another year, continuing his research in chemical dynamics, before joining the research group led by Professor Sherwood “Sherry” Rowland at the University of California, Irvine. Rowland offered his young postdoctoral fellow a choice of research options, and Molina’s eye fell on the question of chlorofluorocarbons, industrial chemicals, apparently harmless to man, which were known to accumulate in the atmosphere.
Chlorofluorocarbons (CFCs), of which the most common form were the hydrochlorofluorocarbons, produced by the DuPont Company under the brand name “Freon,” were widely used in refrigeration, as a propellant in aerosol spray cans and in the manufacture of plastic foam. Molina and Rowland were very familiar with the chemical properties of these compounds, but not with their behavior in the atmosphere. What became of CFCs after they were released was an intrinsically interesting problem, although Molina had no reason to believe that the circulation of these gases in the atmosphere posed any particular danger to living things, since they are not toxic in themselves.
Molina learned that these compounds ascend intact into the stratosphere. There, it was expected that solar radiation would destroy them. What Molina found was that CFCs exposed to solar radiation in the stratosphere break down into their component elements, producing a high concentration of pure chlorine atoms. Chlorine, he knew, destroys ozone. A layer of ozone in the stratosphere — between nine and 31 miles above the earth — is what protects living things from the ultraviolet rays of the sun. If sufficient CFCs were released into the atmosphere, the ozone layer would be so depleted that the unfiltered ultraviolet rays reaching the earth’s surface would cause increased rates of skin cancer, cataracts and immune disorders among humans, as well as damage to agricultural crops and to the marine phytoplankton essential to the ecological balance of the world’s oceans. A pure research problem had presented a serious social question. Molina shared his findings with Professor Rowland, as well as other chemists and atmospheric scientists. Everywhere, they found confirmation of their worst suspicions: the volume of CFCs being released into the atmosphere was indeed great enough to damage the ozone layer. What Molina lacked was evidence that such damage had already taken place.
Molina and Rowland published their findings in a 1974 issue of the journal Nature. The alarming conclusion of their study attracted considerable attention, but when they called for a halt to the production of CFCs, they were met with intense criticism and even ridicule from industry interests and from more cautious members of the scientific community. One industrialist was reported as calling their theory “a science fiction tale… a load of rubbish… utter nonsense.” Another wrote to the University of California to complain. Molina took his case to a larger public, and testified before a committee of the U.S. Congress. Despite resistance from industry, the U.S. National Academy of Sciences (NAS) released a report in 1976 that confirmed the essential premises of Molina’s ozone depletion hypothesis, and more resources were assigned to study the problem.
Meanwhile, Molina accepted a faculty appointment at Irvine, where he established an independent program to study the atmospheric impact of other industrial chemicals. The academic duties of this professorship took more time from his laboratory research than he cared for, and in 1982 he transferred to the Jet Propulsion Laboratory at California Institute of Technology (Caltech) in Pasadena, where he could continue hands-on research.
In 1985, scientists of the British Antarctic Survey detected a large and growing gap in the ozone layer over the earth’s Southern Hemisphere. Although the “ozone hole” was centered over Antarctica, its growth appeared to correspond with a dramatic increase in skin cancer rates in Australia and other countries of the Southern Hemisphere. Molina and his group were able to demonstrate that the ice crystals in the polar stratosphere had amplified the ozone-destructive capacity of CFCs. They also determined that chlorine peroxide, a previously unstudied compound, was contributing significantly to the depletion of the ozone layer over the Antarctic.
The announcement vindicated Molina’s hypothesis and galvanized public opinion. By the end of 1985, 20 nations, including most of the major CFC producers, signed the Vienna Convention, which established a framework for negotiating international regulation of ozone-depleting substances. The Vienna Convention was soon amended by the Montreal Protocol, pledging the signatories to end CFC emissions. Industry groups continued to protest that the evidence was unclear. In 1987, representatives of DuPont testified before the U.S. Congress that “there is no immediate crisis that demands unilateral regulation.” Despite this resistance, world leaders, including environmental skeptics such as President Ronald Reagan of the U.S. and Prime Minister Margaret Thatcher of the U.K., signed the protocol in 1987, and more nations quickly followed. Nearly 200 states, including every member of the United Nations, have now ratified the protocol. Production of CFCs has all but stopped. Economically viable alternatives to the offending chemicals have been found, further damage to atmospheric ozone has halted and it is expected that by the midway point of the current century the ozone layer will have recovered completely.
In 1989, Mario Molina returned to academic life at the Massachusetts Institute of Technology, where he continued his research on global atmospheric issues. Dr. Molina received the 1995 Nobel Prize in Chemistry for “contributing to our salvation from a potential global environmental catastrophe.” Asteroid 9680 Molina was later named in his honor. In 2005, Molina moved from MIT to join the University of California at San Diego and the Center of Atmospheric Sciences at Scripps Institution of Oceanography. For the remaining decades he divided his time between San Diego and his native Mexico City, where he created a center for strategic studies in energy and the environment. Much of his later work was related to issues of air quality and development. His center in Mexico is working to improve the notoriously poor air quality of the capital, while his laboratory in San Diego investigated the chemical properties of atmospheric particles.
Dr. Molina was married to Guadalupe Alvarez; his son by a previous marriage is a practicing physician in Boston, Massachusetts. In addition to his academic and research responsibilities, Dr. Molina served on the boards of numerous foundations and on the President’s Committee of Advisors in Science and Technology. In 2008, he served as an environmental advisor on the transition team of President Barack Obama. The President recognized Dr. Molina’s service in 2013 with the Presidential Medal of Freedom, the nation’s highest civilian honor. Mario Molina died in 2020 at the age of 77.
Mario Molina was a postdoctoral fellow at the University of California in 1974 when he published a paper in the journal Nature, outlining the threat to the environment posed by chemicals used in everyday spray cans, refrigerators and air conditioners. Chlorofluorocarbons — CFCs — were destroying the earth’s ozone layer, the atmospheric shield that protects living organisms from the ultraviolet radiation of the sun. Without the ozone layer, animals and plants could not exist on land, and the balance of oceanic life would be destroyed.
For years, Molina’s ideas were dismissed and ridiculed by the chemical industry, but in 1985, a huge hole in the earth’s ozone layer was discovered above Antarctica, and Molina’s hypothesis was vindicated. Today, the nations of the earth have collectively abandoned the use of CFCs, and a global environmental catastrophe has been averted.
Mario Molina was awarded the Nobel Prize in Chemistry for his discovery. He was the first Mexican-born scientist to receive the chemistry prize. For over 40 years, he continued his work in the United States and Mexico, to prevent and repair human-caused damage to the earth’s atmosphere.
Professor Molina, you were honored with the 1995 Nobel Prize in Chemistry for your work dealing with the depletion of the ozone in the earth’s atmosphere. It appears you were always motivated by curiosity about nature, but how did you first become involved in this particular subject?
Mario Molina: When I finished my Ph.D., I moved to Irvine, one of the campuses of the University of California, working with Sherry Rowland. Professor Rowland had a group doing very basic science at that time. But as a postdoctoral student — that’s how I joined his group — we decided to move into a new field for us, which was the chemistry of the atmosphere. And again, it was a question of originating just with curiosity. We knew that there were certain industrial compounds that were being released into the atmosphere. The type of chemicals that were being released were similar to those that we were studying from a very fundamental point of view — chemical properties, and so on. How the reactions take place. But something new happened at that time that I had not done in my earlier stories, which is looking at the natural environment. Looking at the way the world functions as a whole. In other words, we became interested in environmental issues. So it was a new field for me at that time. But it was this basic drive, basic curiosity, to find out how things work. In this case, not how it works, but what is the consequence of society releasing something to the environment that wasn’t there before. Could you do any damage? Perhaps not, but we thought it was important to find out anyhow. So that’s how we got started in that problem, and of course eventually realized that there’s not something we were expecting at the beginning, but we did realize that there were important consequences from this apparently harmless human activity of releasing these gases which are not toxic at all, but eventually they decompose and indeed can affect the ozone layer in very significant ways. So it’s again, just that drive of understanding how things work — in this case, what are the consequences of certain activities of society — that motivated us to solve these problems.
Your findings were not immediately embraced by the rest of the world. You eventually succeeded, but what kind of obstacles did you meet along the road?
Mario Molina: In terms of this issue of these industrial gases affecting the environment, at the beginning the road was not easy, because we were suggesting that society had to change, that industries had to do something different than they were doing at that time. And of course, initially we did not meet with a good reception to these ideas from industry. And even from the scientific community — even though our ideas were well received in the small group of specialists in what we were doing — it was not necessarily well received by the scientific community at large. So we really had to continue doing as good a science as we could, and at the same time trying to well communicate our conviction that it was something important, something that had to change in the way society was functioning.
Once you made this discovery, did you feel a responsibility to get the word out that the world was endangered because of manmade chemicals?
Mario Molina: Yes, it was very important.
It’s a conscious decision that Sherry Rowland and I did, not just to communicate our findings to other scientists, but to actually try to do something about it. In some sense that was taking a risk. Of course, the signs of the ozone layer and the effects of industrial chemicals was not nearly as well established at that time as it is now. We were just convinced that it was very important to find out. On the other hand, we were taking a risk, in that it’s not a normal role expected of scientists. Our peers were perhaps questioning whether we were just seeking publicity or not. But again, we thought it was not important enough just to preserve our image in the scientific community, compared to what we really thought we had to do, which is to find out more about the problem and let the governments know more about it, so that eventually some action could be taken. And that’s indeed what happened.
Did you feel you needed to defend your integrity after receiving this criticism?
Mario Molina: Yes, that was a very important aspect.
It’s easy to exaggerate problems as well, so we have to be very cautious. We have to always preserve our integrity as scientists. Even though we were advocates in terms of trying to get society to do something about it, we had to continue with honesty, in terms of how to express these fears, for example, to the news media. It’s easy to try to exaggerate the problems just to get more attention. So for me, it was very clear that the best way to deal with that was to do the best science that I was capable of doing. Furthermore, to try to distinguish clearly when I was talking as a scientist, in contrast to talking just as a person with value judgments, in terms of thinking that society should do something about it, but that’s not necessarily the scientific issue. That’s more a conviction issue.
Did you ever have any doubts about your work or any worry about failing?
Mario Molina: Shortly after we realized the potential implications of our findings in terms of environmental effects, we were not entirely sure that we were right. We just thought that it was sufficiently important that we had to find out more about it. So that’s the nature of scientific discoveries. When you first sort of get into a new problem, you’re not sure what the outcome is going to be, so you’re always taking risks. In this case, the risk was even larger, because we were suggesting that our findings had to lead to some changes in industry. So that was a big risk, but we thought it was certainly necessary to take it, and again, it was just a conviction of the problem was serious that led us to continue doing good science. And of course, I should point out it’s very important that it’s work that we did with the rest of the scientific community, a small group of scientists, all working in this field. We eventually all worked together, and this community really succeeded in — to do first-rate science, and to establish very clearly that the problem indeed is a very serious one.
Can you recall the moment when you first realized that the ozone layer was threatened? Did it feel anything like the joy a child feels, discovering the world of science for the first time?
Mario Molina: It was indeed something that happened suddenly. Because we had realized that these compounds would actually reach the stratosphere, that they could decompose there, and in fact I even knew without too much trouble that these compounds could actually affect ozone to some extent. But I remember clearly one day — actually doing calculations, finding out how much of these compounds reaches the stratosphere, and comparing that with some natural processes — that I realized that the problem was really potentially very serious. So it seemed, in a sense, a moment of discovery. But it was different from the earlier ones I had as a child, because I was also very worried. It was not also, in this case, the scientific discovery, but also a discovery about something that could damage the environment. So it all seemed to be bad news at that time, and that’s why it has been very rewarding much more recently, not just to have discovered that there was this potential danger, but also to have realized that society can actually do something about it. And so that’s why I sense that, believe it’s really a success story. Very different from that day in which I got very worried, because now essentially the international agreements recognize the problem and call for completely stopping the production of these chemicals that can harm the environment.
Was there a particular calculation you made that led to this conclusion?
Mario Molina: It was, indeed, just putting together all the information that we had, and putting it in context, and realizing that it’s just the way one sets off a scientific hypothesis, a sequence of steps with these very serious consequences. So it’s really just a moment when you put all this information together and realize that you have something important in front of you.
How did you determine that these particular compounds — the chlorofluorocarbons — were threatening the ozone layer?
Mario Molina: It really started asking the question, “What happens to these compounds once released to the environment?” Our starting point was that these compounds have been measured to be throughout the atmosphere. Not just close to cities, but in the Northern Hemisphere, the Southern Hemisphere. That was just a starting point. These compounds are very stable. They are non-toxic, you can even breathe them. So the assumption was that there was no worry, because of the presence of these relatively small amounts — parts per trillion amount — of these compounds in the global environment. So that was just the starting point. The rest was just scientific research. We were asking the question, “What happens to these compounds?” We realized that they would eventually diffuse to the stratosphere, because nothing else would destroy them. In the stratosphere they would be destroyed, but that was not the end of the question. We had to pursue it several steps more. So what? And we had to follow what happens to the decomposition products from these compounds, and that’s of course where the effects on ozone begin. So it’s really taken a complete — an overall — picture of the problem that led us to our discoveries.
You were able to predict the existence of a hole in the ozone layer as early as 1974, but it wasn’t until 11 years later that the hole was actually discovered. Were you at all nervous about that, before the hole was actually found? What was your reaction to that discovery?
Mario Molina: Of course, we were not sure. We realized that the atmosphere is very complicated and that we didn’t know — certainly by far — everything that there is to know about it. On the other hand, pieces of evidence began to come for measurements. Experiments were carried out, and we know that these gases were indeed reaching the stratosphere — the CFCs. We know that the composition products were indeed there, but it was very difficult to measure these actual effects on ozone, because the ozone amounts in the stratosphere fluctuate. On the other hand, we actually did not predict that ozone would be depleted specifically over Antarctica. We just made a very general prediction that these — the composition products — could affect the ozone layer in general terms. So it actually came as a surprise that this large effect was happening in this coldest place on earth. On the other hand, with all the scientific research that had been carried out before the Antarctic ozone hole was found, it was just a matter of a few years for us and the rest of the scientific community to understand — with experiments in the laboratory as well as in the atmosphere — very clearly why is it that specifically Antarctica was the place where this hole appeared. And the reason, of course, is that it’s very cold there, and clouds can actually form over Antarctica that do not form anywhere else in the stratosphere that are sufficiently cold to promote a new type of chemistry that we then investigated in the laboratory. So in other words, what happens is even though our predictions were not very specific, we lay down, together with our colleagues, a foundation and an infrastructure to really understand on a very rapid time scale the nature of all these effects once they became clear.
You faced intense opposition from many sectors, especially industry. Can you recall for us some of the harshest criticism you faced, and how you reacted to that?
Mario Molina: I remember in some scientific meetings, again, arguing about the uncertainties of the problem. And there was not that much disagreement in terms of the science itself with our industry colleagues. It was more either in the public relations arena, or else in terms of whether to advise society to do something about it or not. I remember very well my attitude at that time was that, at the very least, industry should do some research on potential replacements for these compounds. At the same time, of course, we had to know more about the atmosphere, but we had to begin thinking about the possibility of regulating these chemicals. And that’s of course what industry was opposed to do at the beginning, because they wanted more scientific evidence. But eventually we came together on what the scientific evidence indeed was. Very clear. We started to work in a collaborative mode, and that’s what made it possible to reach these international agreements, the Montreal Protocol and so on, on a very short time scale.