Gilbert Norman Plass

Dr. Gilbert Norman Plass (1920/21/22-2004) was the last scientist before Charles Keeling to make important contributions to the study of global warming. He was a Canadian physicist, who obtained his PhD at John Hopkins, and not a climatologist or meteorologist. But it was the publication of his insight into the the reality that increases in carbon dioxide in the atmosphere would increase infrared radiation absorption and global surface temperatures, along with Roger Revelle's work on the oceanic chemistry of carbon dioxide, and Charles Keeling's measurements proving that carbon dioxide was increasing in the atmosphere that established the scientific consensus that humankind's activities could and would warm the climate of the Earth.

Back at the end of the 19th century, Svante Arrhenius made his famous proposal of anthropogenic global warming. But although a few lonely scientists believed him and carried on research in anthropogenic global warming, Knut Johan Ångström carried out experiments in laboratory conditions that appeared to show that carbon dioxide was saturated as an infrared absorber. These experiments were done near sea level, with the higher temperatures and humidity of sea level air. Dr. Plass wondered about the absorption of infrared radiation by carbon dioxide at greater altitudes in the atmosphere, and what increases in carbon dioxide would mean.

A huge hint that Ångström's experiments with carbon dioxide's infrared absorption were not correct had been noted as early as 1890---and yet was ignored. Frank Washington Very and Samuel Pierpont Langley had carried out infrared astronomy for the moon beginning in 1890, and noted that more infrared radiation from the moon was observed when it was near its zenith than when it was near the horizon. These observations proved that carbon dioxide was not saturated in terms of absorbing infrared radiation--it it were, then the absorption of infrared radiation would be the same no matter what altitude above the horizon the moon was. Amazingly, Arrhenius and all climate scientists seemed to have remained unaware of Very and Langley's work for more than 60 years!

Gilbert Plass was either born in1 1920, 1921 or 1922 (my sources disagree) in Toronto and quickly showed strong aptitudes for math and science. After scoring a 168 on an IQ test and having it confirmed, he was allowed to skip years in HS and the government of Canada paid for his education at Harvard where he graduated with a BS in physics in 1941, and earned his doctorate in physics from Princeton in 1947.

After World War II, as part of the United States' rapidly expanding scientific research, the Office of Naval Research. Much of this research was esoteric---who knew what kind of scientific discoveries were to be made, and what impact they could have! The 30 years after World War II were a time when government institutions and Bell Labs supported pure scientific research, and allowed research scientists to follow their own muses, unlike today's more commercial research climate (no pun intended).

The Office of Naval Research was interested in absorption of infrared radiation in the atmosphere as it related to heat-seeking missiles and other weaponry. Beginning in the late 1940s, observations at the Thule (now named Qaanaaq) base in the northwest part of Greenland suggested strongly that variations in carbon dioxide strongly changed absorption of infrared radiation by carbon dioxide. Dr. Plass was a physicist, not a climatologist or meteorologist. However, he was aware of the scientific consensus that carbon dioxide was saturated as an infrared radiation absorber. What if this was not the case?

Dr. Plass was curious about this, and worked on his own time to see if carbon dioxide was really saturated as an infrared absorber. From observations at arctic bases and at high altitude flights were missile tests were conducted, he concluded that it was not. But concluding this was one thing, proving it was another.

In 1953 Dr. Plass moved from Canada to southern California to work with Lockheed on missile testing and guidance. And for the first time he had access to a computer. As a competent physicist, Dr. Plass knew how to craft programs to analyze the absorption of infrared radiation by carbon dioxide using quantum mechanics. Without a computer, he would never have been able to make the calculations. Dr. Plass felt confident enough in his belief that our carbon dioxide emissions would warm the Earth's climate that in 1953 he contributed to an article in Time magazine saying so. But the computers of the 1950s were balky and slow, and he had to do his research on his own time. So it took him more than 2 years to mathematically prove that infrared absorption was not saturated at current levels of carbon dioxide in the atmosphere.

Dr. Plass published his work in the July 1956 issue of American Scientist. Dr. Plass made some errors that oddly enough, cancelled each other out. Dr. Plass underestimated the amount of carbon dioxide humankind was emitting into the atmosphere---he gave a figure of 6 billion tons. We now know it was 8.8 billion tons in 1956. Dr. Plass also overestimated the radiative forcing of additional carbon dioxide in the atmosphere. Dr. Plass estimated that a doubling of carbon dioxide in the atmosphere would yield a radiative forcing of 8.3 watts per square meter under clear conditions, and of 5.8 watts per square meter under cloudy conditions. He only had observational from a few arctic bases and brief airborne tests piggybacking on missile testing. The explosion in the earth sciences generated by the 1957-1958 International Geophysical Year, in which high altitude observations were made in the Andes and Antarctica refined this to 4 watts per square meter, under both clear and cloudy conditions. These refinements came quickly---by 1960 all atmospheric physicists knew that a doubling of carbon dioxide would have the correct, 4 watts per square meter warming. And anyone who still goes by the Ångström experiments of 1901-1902 can be dismissed as an ignorant quack (it is amazing how much Ångström's experiments are still cited by deniers).

Dr. Plass's paper is summarized and discussed here.

Dr. Plass made several simplifying assumptions. He assumed no change in water vapor, and no change in absorption of carbon dioxide by the oceans---as I said he was not a climatologist or meteorologist, or oceanographer. He simply ignored feedbacks in his paper. He also assumed that humankind's carbon dioxide emissions into the atmosphere would remain constant at 6 billion tons per year (and as we know, it was already 8.8 billion tons in 1956.

Dr. Plass made some of these simplifying assumptions because of 'known unknowns'--he knew he was not qualified to assume how water vapor and other feedbacks would behave. Also, in the 1950s, while computers were beginning to be used in science, their power was extremely limited by today's standards.

The assumption that carbon dioxide emissions would remain constant seem more inexplicable. As I have discussed in previous blog entries, in the 1950s long-term economic growth on a planet-wide scale was not a given. Countries such as France, Germany, and Japan had lower industrial output in 1950 than in 1913. The United Kingdom and the Soviet Union were not much better. Yes by the mid 1950s the industrial output of the United States was more than triple its 1913 level, and so were Canada's and Australia's. But among those three, only the United States was emitting carbon dioxide at a globally significant level.

This seems amazing, when we consider than global carbon dioxide emissions more than doubled over the next 15 years. But scientists had no way to know that was going to happen--wars had set back economic growth on a generational scale twice in the recent past, and there was no reason to suppose that would not happen again.

Dr. Plass concluded that carbon dioxide could double over a century and raise global temperatures 1.5° C over the next century, a figure that agrees closely with the definitive Charney report of 1979, which gives a 1.2 °C figure. Dr. Plass also concluded that known reserves of carbon-based fossil fuels would add enough CO2 to the atmosphere to warm the surface of the Earth by 7 °C (12.6 °F) by 3000 CE. At such a planetary average surface temperature, the Greenland and West Antarctic ice sheets would be gone, and the East Antarctic ice sheet would be going.

I must repeat here that Dr. Plass was not a climatologist or meteorologist. He did not try to compute feedbacks such as decreasing albedo or increased water vapor in the atmosphere. He focused on the radiative properties of CO2 only.

During the 1960s, returning to his work on CO2 and the Earth's climate, he concluded that net feedbacks were positive, and that each doubling of CO2 in the atmosphere would increase surface temperatures by 3.6 °C.

It has to be said that Dr. Plass did not optimally research and craft his meteorology papers. His lack of some knowledge of meteorology led him to some errors---he tried to compute atmospheric properties and constants that had been solved by others, sometimes decades previously. And he made some mistakes. Today's research on climate feedbacks produce much larger increases in surface temperature.

But I must also repeat that Dr. Plass's proof that increased CO2 in the atmosphere increases infrared radiation absorption did hold. No meteorologist or climatologist denies that now. Not reputable ones.


Roger Revelle had shown how oceanic chemistry buffers prevent the oceans from absorbing all our carbon dioxide emissions. Plass had proven that carbon dioxide was not saturated in the atmosphere from an infrared radiation absorption standpoint. But were human activities really causing carbon dioxide to accumulate in the atmosphere? That question still remained.

And Charles Keeling was to definitively answer it. But that's for the next blog entry.

Here is a picture of Dr. Gilbert Plass:

Dr. Plass left Lockheed in 1960 to join the research staff of Ford's aeronautical division. Dr. Plass also edited Infrared Physics and Technology, a peer-reviewed scientific publication. Dr. Plass worked there until 1963, when he accepted a position as first professor of atmospheric and space sciences with the University of Texas at Arlington, where he remained for 5 years. In 1968 he joined the faculty of Texas A&M University, ultimately becoming head of the department of physics.