the time, however, it was believed that natural forces, such as solar activity and the ability of oceans to absorb and store carbon, were far more important factors and that CO2 had an insignificant influence compared to water vapor. Many scientists believed climate was self-regulating and that small changes to atmospheric composition could not alter climate over brief time periods. Any CO2 that human activity did emit into the air would be absorbed quickly by oceans (and, to some extent, forests and peat bogs)—which was mostly true at the time, when far smaller amounts of fossil fuels were being burned. Some also argued that excess atmospheric CO2 would fertilize plants and create more lush life—which is also true, to a point. Although the notion that human activity, such as burning ever-increasing amounts of fossil fuels, could not affect a self-regulating climate has been thoroughly disproven by modern science, many people still make the same outdated arguments today.
As with earlier scientific investigations, most climate science in the first half of the twentieth century was driven by a desire to explain the causes of ice ages. In the 1950s, scientists started to get an idea of the bigger picture. In 1956, Maurice Ewing and William Donn, at New York’s Lamont Geological Observatory, were also trying to explain ice ages, in particular the abrupt end of the most recent one. In looking at feedback cycles in the Arctic, they speculated that a complex set of circumstances could lead to rapid climate change over the next few hundred or thousand years. But the change they saw was the coming of another ice age.
Their theories were controversial and often criticized, but they did serve to spark a renewed interest in climate science, more testing of theories, and wider acceptance of the idea that changes in Arctic ice sheets and snow cover could cause rapid changes in planetary surface conditions.
By the 1950s, researchers in the Soviet Union were using this growing scientific knowledge to consider ways to deliberately alter local climatic conditions, by “making Siberia bloom by damming the Bering Straits, or by spreading soot across the Arctic snows to absorb sunlight,” according to the American Institute of Physics. This led Leningrad climatologist Mikhail Budyko to examine the ways in which human influences could be amplified by feedback loops. As a result of his studies, he was one of the first scientists to raise concerns about the potential major effects of burning fossil fuels and other human activities. In 1961 and 1962, he published two books warning that growing energy use will warm the planet and cause the Arctic ice pack to quickly disappear, contributing to further feedback cycles.
In the mid-1960s, Budyko developed models that showed relatively small changes in global average temperatures and polar snow cover could cause feedbacks that would cause dramatic increases in temperature and sea levels. Researchers in Sweden, New Zealand, and the U.S. were arriving at similar conclusions. Although many of the studies pointed to a warming planet, some speculated that changes in solar activity or dust in the atmosphere could cause another ice age.
Over the next few decades, climate scientists developed increasingly sophisticated computer models to examine the effects of greenhouse gases on climate—especially as computer technology improved along with scientific knowledge. It also became easier to study other planets, such as Venus, which was covered in an atmospheric blanket of water vapor and CO2, producing a massive greenhouse effect, and to examine past climatic events.
In 1973, a U.S. probe to Mars led the famous astronomer Carl Sagan and others to conclude that the red planet had undergone major shifts between cold and hot. Around the same time, analyses of seabed clay layers showed that Earth’s ice ages had occurred in roughly 100,000-year cycles. Although these roughly matched calculations by Serbian scientist Milutin Milankovitch in the early twentieth century, research also demonstrated that Milankovitch’s theories about the effects of subtle shifts in the earth’s orbit were not sufficient to explain the massive changes. However, natural cycles including ice buildup and flow, warping of the earth’s crust and sea level changes, combined with orbital shifts, could explain the ice age cycles.
Scientists also started looking into the effects of clouds, volcanic dust, smoke, and other aerosols on climate. Some initial studies led researchers such as NASA’s James Hansen to speculate that the world could be headed for a cooling phase. This short-lived theory, which didn’t take into account factors such as ocean circulation, provides ammunition for climate change deniers to this day.
By the late 1970s, many scientists were convinced that Earth was getting warmer, but although many proposed convincing hypotheses, no one was able to accurately and definitively prove the cause. I spoke with science writer Isaac Asimov about it in 1977 on CBC Radio’s Quirks & Quarks.
By the 1980s, computers were becoming sophisticated enough that it was possible to go beyond looking at climatic conditions in isolation to examine the numerous interconnections that can affect systems as a whole. More knowledge was also being gleaned from seabed and ice cap core samples, which allowed scientists to examine regular ice sheet advances and retreats over hundreds of thousands of years. Although exact causes of current warming were still elusive, many experts were starting to agree that the unusually rapid warming they were seeing would bring about increases in the incidence and severity of heat waves, flooding, droughts, and storms—which did indeed start to occur worldwide. Because warming was not uniform but rapid, causes such as solar activity could be ruled out.
By the late 1980s, the theory of global warming and its human contributions had become well established in the scientific community. In 1989, the CBC television show I host, The Nature of Things, did its first global warming program, and I also hosted the five-part radio series It’s a Matter of Survival, which was in part about climate change. The response to the latter (more than seventeen thousand letters in pre-email days) was so overwhelming that my wife, Tara, and I decided we had to do more than just talk about environmental problems; we had to do something. So we gathered a group of people to discuss ideas and, out of that, the David Suzuki Foundation was formed in 1990.
As computer models and research methods improved, along with the body of scientific knowledge, complexity increased. How were biological systems affected by climate and CO2, and how in turn did they affect climate and carbon? What impacts would all of this have on agriculture, forestry, and spread of disease?
By the 1990s, studies of the Arctic showed that twentieth-century warming was far greater and more rapid than anything seen in at least the past four hundred years.
Although scientific models and observations were by this time aligning, and most experts were able to confidently conclude that the planet was warming at an unusually fast rate, in part because of the greenhouse effect, the theories still had their critics. Convinced that natural self-regulation would overcome any human effects on climate over the long run, Massachusetts Institute of Technology (MIT) meteorologist Richard Lindzen set out to challenge the way models accounted for the effects of water vapor. Advances in satellite technology and data would later confirm the climate models and prove Lindzen wrong. He continued to look for flaws in the models, and although much of the modeling data were confirmed, his efforts at least made scientists work to improve models and to confirm data through other methods, including paleoclimate studies.
Numerous models with a wide range of varying parameters all confirmed that adding greenhouse gases to the atmosphere would cause global warming.
Michael Mann and the Hockey Stick Graph
IN 1998, UNIVERSITY of Virginia climate scientist Michael Mann, with Raymond Bradley of the University of Massachusetts Amherst and Malcolm Hughes of the University of Arizona, examined paleoclimatic data by studying ice cores, tree rings, and corals, as well as more recent thermometer readings. In doing so, they were eventually able to reconstruct Northern Hemisphere temperatures going back one thousand years. Mann later worked with the University of East Anglia’s Philip Jones to chart temperatures for the past two thousand years. They found conclusively that global mean temperatures spiked rapidly starting
