Are human technology and activities forces of geophysical scope, capable of affecting the entire planet Earth? Surely not, thought most earth scientists in 1940. But a quarter century later, the consensus was beginning to shift. Several factors were involved in this shift. First of all, unprecedented economic growth. As I noted previously, during the first half of the 20th century, continuous, exponential economic growth was not a given. Two world wars and the Great Depression had interrupted economic growth in many developed countries. In 1950, industrial output was lower than 1913 in several major economic powers, such as Germany, France, and Japan. The Soviet Union and the United Kingdom were not much better. True, the USA had more than tripled its industrial production during that period.
Many scientists in the 1940s and 1950s assumed that carbon dioxide emissions would remain relatively constant. Gilbert Plass assumed that humankind's carbon dioxide emissions would be a flat 6 billion tons annually. (The IEA released a report on May 30, 2011 that humankind's carbon dioxide emissions soared past 30 billion tons for the first time in 2010, q.v.).
By 1965, humankind's carbon dioxide emissions were greater than 12 billion tons annually, and rising by more than half a billion tons per year. The assumption that carbon dioxide emissions would remain relatively low was incorrect.
Second, the work of Drs. Roger Revelle and Gilbert Plass showed that the oceans would not, could not, absorb all of humankind's carbon dioxide emissions, and that additional carbon dioxide would increase absorption of infrared radiation.
And then, Dr. Charles Keeling proved through his meticulous measurements of atmospheric carbon dioxide, and his isotopic analysis, that humankind's activities were increasing carbon dioxide in the atmosphere. During the first couple years of his measurements, it was postulated by some scientists that there could be a natural cycle that causes carbon dioxide concentrations to fluctuate, and it was possible that he was observing the uptrend of a natural cycle. And in fact there is such a natural cycle---the ENSO cycle does cause carbon dioxide concentrations to fluctuate by a few parts per million. But as carbon dioxide concentrations continued to rise each year, by 1962/1963 there was no possible doubt. Atmospheric carbon dioxide concentrations were rising, and humankind was responsible. For the past 50 years, no serious scientist has doubted that.
This graph shows the Keeling measurements for atmospheric carbon dioxide from 1958-1966. I would have preferred a 1958-1965 graph to dovetail with what the scientists at the "Causes of Climate Change" conference knew, but it is close enough for my blog, and the trend was clear:
Although the conference was organized by Dr. Revelle, the inspiration for it happened in 1963 Dr. Revelle had a conversation with astrophysicist and atmospheric physicist Dr. Walter Orr Robertsm who founded the National Center for Atmospheric Research in 1960. Dr. Roberts pointed out the aircraft contrails in the sky early one morning, and said that they would be indistinguishable from natural cirrus clouds in a few hours. They had a morning meeting, and when it broke for lunch, Dr. Revelle and Dr. Roberts went outside and could see the contrails from earlier, smearing out. By the time they finished lunch, the contrails looked just like cirrus clouds. Dr. Roberts wondered if adding cirrus clouds to the atmosphere could change the climate. Dr. Revelle wondered too.
The National Center for Atmospheric Research. The futuristic buildings served as a set for the comedy classic Sleeper, directed and written by Woody Allen.
Also in 1963, Dr. Ried Bryson (1920-2008), meteorologist and geologist, and one of the few scientific opponents to anthropogenic global warming, noticed on a flight across India to a scientific conference noticed that although the sky was cloudless, he could not see the ground, with all the smoke from brush and cooking fires. He noticed similar hazes in Brazil and sub-Saharan Africa. Dr. Bryson thought that global dimming would trigger global cooling--and that was the major threat that humankind's activities would have on the environment, a view that influenced Dr. Isaac Asimov (1920-1992) during the 1960s and 1970s.
During the last few years of his life, Dr. Bryson revised his views and concluded that global warming from the greenhouse gases humankind emits are the greater threat.
An aside on global dimming. It is a legitimate scientific viewpoint, and in fact during the 1950s and 1960s, the rise in global temperatures did pause, and increased pollution in the industrialized countries coupled with increases in tropical haze from cooking fires and brush fires and fires set to clear forest land may have had enough of an impact to blunt the rise in global temperature. Since the 1970s, increased pollution controls in the most advanced countries coupled with the relentless rise in concentrations of atmospheric carbon dioxide have clearly overwhelmed any cooling effect from aerosols in the atmosphere which promote global cooling.
To save time and effort, I am not going to go into every scientist that attended the conference, or go into everyone's theories or what they said. The main purpose of the Boulder conference, at least officially, was to discuss the mechanisms of natural climate change.
Until the 1950s, it had been believed that there were four major ice ages over the past 2 million years. And this viewpoint persisted in most of the general scientific community until the 1970s. In fact, the four ice ages are referred to in Dr. Arthur C. Clarke's novel 2001: A Space Odyssey (1968). [There are not many references to the novel, which was released in July 1968. There are many references to the film, of course.] This went with the reassuring uniformitarian mindset that typified earth science studies from the time of geologist Dr. James Hutton to the mid 20th century. Over the past 50 years, the realization that changes in the Earth's environment can be sudden and far reaching has led to a more neo-catastrophism mindset, of which the extinction of the dinosaurs by the impact of a comet/asteroid is the most prominent example.
Discoveries in the 1950s lead to the realization that ice ages and interglacials were far more frequent--more than 20 glaciations were identified by 1965, although this new knowledge took a long time to diffuse into the general scientific community. This work had been done by Drs. Harold Urey and Cesare Emiliani (q.v.) Their discoveries also indicated that climate change could have been rapid, although this discovery was resisted. However, in the early 1960s, work by Dr. Wallace Smith Broecker (Wally) (1931-) on ancient tropical corals also showed evidence that climate could change rapidly. [Dr. Broecker will be the subject of a forthcoming blog entry.] Also, Dr. Edward Lorenz (1917-2008) discussed his work on computer simulations of weather patterns, which was proving to be chaotic. Dr. Lorenz wondered whether climate states could also prove to be chaotic.
The implications were becoming clear. Climate had changed more rapidly in the past than had been believed before. Most of the scientists who attended the Boulder Conference on Climate Change were convinced of that by the time the conference was over. But it took a long time for this new consensus to diffuse into the general scientific community. To use an analogy, the discoveries of the 1950s had planted the seed of the possibility of rapid climate change. The 1965 conference was when the seed sprouted.
The work by Dr. Charles Keeling (q.v.) had shown definitively by 1965 that humankind's activities were measurably and significantly increasing the amount of atmospheric carbon dioxide. Dr. Gilbert Plass had overthrown the old belief that increases in atmospheric carbon dioxide would not increase the amount of infrared radiation trapped by the atmosphere---additional atmospheric carbon dioxide clearly would. So would humankind's carbon dioxide emissions trigger a sudden change in the Earth's climate? That question left the attendees of the Boulder conference uneasy.
The minutes of the conference published in 1966 contain this interesting statement: "We are just now beginning to realize that the atmosphere is not a dump of unlimited capacity but we do not yet know what the atmosphere's capacity is"*
*National Academy of Sciences, Committee on Atmospheric Sciences Panel on Weather and Climate Modification, Weather and Climate Modification: Problems and Prospects. 2 vols. (Washington, D.C., National Academy of Sciences, 1966), col. 1, p. 10.