Significant scientific contributions
In 1952 I developed a quantitative theory of the damage suffered by living cells when they were frozen and thawed at slow or moderate rates. My experiments had shown that damage was due to the concentration of salt and other solutes when ice separated as a pure substance. Previously it was thought that damage was solely due to the piercing of cells and tissue by ice crystals. I was also able to explain the protective action of glycerol and neutral solutes and predicted successfully that dimethyl sulphoxide would be an excellent protective agent. Later in 1954, I participated in the team that successfully froze and thawed whole animals, hamsters.
My other researches included an investigation of the pathways for the spread of respiratory infection, especially the common cold, and the design of means for its prevention.
Among my inventions are detectors and other devices for use in gas chromatography. The argon detector was the first practical sensitive detector. It realized the potential of the gas chromatography. The electron capture detector was invented in 1956 and is still among the most sensitive of chemical analytical methods in existence. Its use led to the discovery of the ubiquitous distribution of pesticide residues in the natural environment and can be said, along with Rachel Carson's seminal book Silent Spring, to have started the environmental movement.
The same detector was later used to discover and measure the abundance of chlorofluorocarbons and of nitrous oxide in the atmosphere. Another invention was the palladium transmodulator, a device whose use was crucial for the Gas Chromatograph Mass Spectrometer experiment aboard the Viking spacecraft that landed on Mars in the mid 1970s. More recently, I developed a tracer method for mass transport measurements in the atmosphere and oceans. It uses perfluorocarbons as tracers and detects them by electron capture. It has enabled meteorologists to follow the movement of air masses across continents and is now finding use in ocean research.
In 1972 I demonstrated that the summer time turbidity of the air over Southern England and Southern Ireland was man-made not natural by using the simultaneous presence of CFCs as a marker of air from urban sources. In the same year I measured during a ship voyage from the UK to Antarctica and back the abundance and the accumulation of CFCs in the global atmosphere. This data was crucial to Molina and Rowland's hypothesis of stratospheric ozone depletion by chlorine from the CFCs.
On the same voyage I also measured the abundance of dimethyl sulphide and methyl iodide in the ocean and found these natural products to be ubiquitous. In 1974 I made the first measurements of the CFCs and carbon tetrachloride in the stratosphere and showed them to be declining there as the ozone depletion theory required.
I also demonstrated the presence of carbon disulphide in the air and the ocean. In 1975 I reported the first measurements of methyl chloride in the atmosphere. From 1977 until 1980 I established at Adrigole in Southern Ireland, the first monitoring station for atmospheric halocarbons and made the first and essential calibration of the instruments used in this and the other stations of the global network of what later became the GAGE program.
In 1977 I calculated the atmospheric abundance of the hydroxyl radical from my own measurements of the abundance of methyl chloroform, an industrial product. In 1986, together with Robert Charlson, Meinrat Andreae and Steven Warren, we introduced the hypothesis that an important natural source of cloud condensation nuclei was the oxidation products formed in the air from biogenic dimethyl sulphide; this gas came from the decomposition of dimethyl sulphonio proprionate, an osmoprotective agent present in most marine algae.
This work was considered sufficiently important by climate scientists for them to award the four of us their Norbert Gerbier Prize in 1988. Its significance in Geophysiology is mentioned in the next section.
Forty years ago I postulated that the Earth is a self-regulating system able to keep the climate and chemical composition comfortable for organisms. This was the Gaia Hypothesis, which as evidence and mathematical models accumulated has now become Gaia Theory. Biologists and geologists heavily criticised the theory in its first twenty-five years; only climatologists found it useful.
Whether right or wrong, it is a testable theory and capable of making 'risky' predictions. One of these was that there should be a large enough emission of dimethyl sulphide from the oceans to balance the natural sulphur budget. Preliminary confirmation came from my own measurements in 1972; M.O Andreae made complete confirmation independently.
Later, when considering how the Earth system could regulate climate, Charlson, Lovelock, Andreae and Warren proposed that cloud density was modulated by the abundance of atmospheric dimethyl sulphide, and this in turn changed the Earth's albedo and mean surface temperature. This proposal was published as a Nature paper in 1987 and is now generally accepted. Gaia Theory also offered an interpretation of the long-term regulation of carbon dioxide and climate through biologically assisted rock weathering.
In 1999, the eminent evolutionary biologist, William Hamilton, who had been a strong critic, stated in public that he regarded Gaia theory as a Copernican insight. He added that we await a Newton to explain how it works. Gaia theory is now part of scientific conventional wisdom and sometimes called Earth System Science. The name Gaia attracted so much opprobrium from scientists, especially in the U.S.A., that the name is still rejected, as is acknowledgement.
Following the Amsterdam Declaration in 2001, most scientists around the world now accept that the Earth does indeed self-regulate.