Charles David Keeling

Climate scientist who first charted the rise of greenhouse gases

Although over many thousands of years man's destructive impacts on the Earth have often been far-reaching - from the wiping out of the giant animals that stalked the landscapes of Australia and South America, to the cutting down of the great pine forests that once clothed the Scottish highlands - none has actually put the Earth at risk. The American climate scientist Charles David Keeling measured and showed the world what will probably turn out to be the most deadly impact of all, the one which does indeed put a question mark over the future of the planet itself: the accumulation of carbon dioxide gas in the atmosphere from the burning of fossil fuels, now widely accepted to be causing global warming, with potentially catastrophic effect.

Charles David Keeling, chemist, oceanographer and atmospheric scientist: born Scranton, Pennsylvania 20 April 1928; Research Fellow, California Institute of Technology, Pasadena 1953-56; Assistant Research Chemist, Scripps Institute of Oceanography, University of California, San Diego 1956-60, Assistant Professor of Oceanography 1964-68, Professor of Oceanography 1968-2003 (Emeritus); married 1955 Louise Barthold (four sons, one daughter); died Hamilton, Montana 20 June 2005.

Although over many thousands of years man's destructive impacts on the Earth have often been far-reaching - from the wiping out of the giant animals that stalked the landscapes of Australia and South America, to the cutting down of the great pine forests that once clothed the Scottish highlands - none has actually put the Earth at risk. The American climate scientist Charles David Keeling measured and showed the world what will probably turn out to be the most deadly impact of all, the one which does indeed put a question mark over the future of the planet itself: the accumulation of carbon dioxide gas in the atmosphere from the burning of fossil fuels, now widely accepted to be causing global warming, with potentially catastrophic effect.

Keeling's scientific legacy is illustrated in an image of unforgettable, ominous simplicity: the jagged, remorselessly rising line marking the increase in atmospheric CO ₂ from 1958, when his measurements began, to the present day. There seems little doubt now that the so-called "Keeling curve", plotting his data from the observatory on the top of Mauna Loa, an 11,000ft extinct volcano in Hawaii, will be one of the key images in human history, as recognisable and as full of instant meaning as the crucifix or the swastika.

The Swedish chemist Svente Arrhenius realised as long ago as 1896 that an increase in the trace gases in the atmosphere would cause more of the sun's heat to be trapped, as if behind the panes of a greenhouse; yet he thought the process would take thousands of years to have a discernible effect. Although a steadily increasing amount of coal, gas and petroleum had been burned since the industrial revolution, many assumed that the resultant CO ₂ would be absorbed by the earth's so-called "carbon cycle", dissolved into the oceans or taken up by plants during growth.

Keeling's observations showed for the first time that this was not happening, and that a large fraction of the CO ₂ being produced on such a scale by industrialisation was actually remaining in the atmosphere, and that the total amount was increasing. Before large-scale industry and the invention of the internal combustion engine the natural concentration of CO ₂ is now thought to have stood at about 280 parts per million by volume (ppm); when Keeling began his measurements at Mauna Loa he found it stood at 315ppm.

Then, as economies around the world surged forward in the great post-war growth spurt, and thousands more power stations were built and everybody bought a car, it began climbing upwards on Keeling's graph at a steadily increasing rate. The speed at which it was happening made it clear that the prospect of global warming which Arrhenius had comfortably located millennia into the future was actually just around the corner - and so it has proved.

Despite the scepticism of the Bush administration in the United States, the majority of climate scientists and national leaders, including Tony Blair, now believe that global warming, directly caused by the increase in greenhouse gases, has begun, and that its consequences in terms of droughts, agricultural failures, weather extremes, flooding and the spread of disease are potentially disastrous for the whole world.

Arguments continue over exactly how much warming the increased CO ₂ will generate, and by when, but there has been no disputing Keeling's scrupulously careful and precise measurements. (The CO ₂ level has now reached nearly 380ppm.) His data set is one of the most important in history and stands as the base on which all modern climate change science is built.

Charles David Keeling - C.D. Keeling on academic papers but Dave to his family, colleagues and friends - was born in Scranton, Pennsylvania, in 1928. He graduated in chemistry at the University of Illinois in 1948 and received his PhD in chemistry from Northwestern University in 1954. His move into atmospheric studies began in 1956, when, as a post-doctoral fellow in geochemistry at the California Institute of Technology, he was recruited by Roger Revelle, the eminent Director of the Scripps Institution of Oceanography, at La Jolla, part of the University of California, San Diego.

Revelle was a far-sighted oceanographer who had seen the possibility of an enhanced greenhouse effect caused by industrial carbon dioxide emissions, and had already instituted a research programme. Under his guidance Keeling established the long-term CO ₂ monitoring on the top of Mauna Loa because it was in a pristine environment where measurements were unlikely to be skewed by industrial sources in the vicinity - and proceeded to run it, based at Scripps, for nearly half a century.

A friendly and popular man, in the course of his career Keeling garnered a huge collection of American and international awards for his work (including the National Medal of Science in 2002), but still found time for a crowded family life - he and his wife of 50 years, Louise, had five children and six grandchildren. He was almost as distinguished a musician as he was a scientist and loved the outdoors, frequently retreating to his cabin in Montana.

It was at his Montana home that he died last week, of a heart attack after a hike. And it was in Montana that The Independent reached him last October, after we had noticed that the annual increase in global CO ₂ levels, detailed in his measurements, had for the first time exceeded two parts per million, for two years running. We wanted Keeling to comment on whether or not this might be a sinister change in the rate of increase itself - perhaps due to some sort of global warming feedback mechanism slowing down the carbon cycle - and discovered something else just as sinister.

In the course of a long, off-the-record conversation, the grand old man of CO ₂ explained in disturbing detail the pressure that the Bush administration was now putting on US climate scientists to keep quiet about any inconvenient facts or research that might support the idea that global warming was happening. The usual threat, he said, was a simple but dire one - your funding would be cut. Keeling did not want that to happen to him: even though he was then 76, he was still in active charge of the Carbon Dioxide Research Group at Scripps. At the end of our talk he said: "Give me 24 hours to think about it."

The following day he had made his choice: he would speak on the record. The increase in the rate of CO ₂ accumulation was a real and worrying phenomenon, he said - and the story went round the world.

Keeling knew that what he had been recording so tellingly for nearly half a century was far too important for all our futures to keep quiet about; history will surely bear him out.

Michael McCarthy