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 in the early twentieth century, just as industrial and other human activities were releasing ever-increasing amounts of CO2 and other heat-trapping gases into the atmosphere.
The graph they created, which was used in the IPCC’s Third Assessment Report, in 2001, looked like a hockey stick, with a long, steady line that took a sudden jump upward at the end. Although many other scientists confirmed the results, Mann’s work became a target for those opposed to prevailing theories of anthropogenic climate change. Attackers included politicians, pundits, a few scientists, and two Canadians: former mining company executive and consultant Steve McIntyre and economist Ross McKitrick. Although subsequent research found that the Canadians were correct in pointing out some statistical errors, the failings were minor and did not significantly affect the overall results. Several studies found more serious errors in McKitrick and McIntyre’s methodology, and dozens of subsequent studies using various methods and records have since confirmed Mann’s original analysis, with only slight variations.
Another report by aerospace engineer Willie Soon and astronomer Sallie Baliunas, published in the journal Climate Research, claimed that the Northern Hemisphere was warmer during the medieval period than Mann estimated, but their methodology and data, and the publication’s peer-review process, were found to be lacking, leading to the resignation of several of the journal’s editors and an admission by the publisher that the article should not have been accepted as is. Soon has received much of his funding from fossil fuel companies, and Baliunas has been affiliated with a number of fossil fuel–funded organizations.
As Mann told Scientific American in 2005, “From an intellectual point of view, these contrarians are pathetic, because there’s no scientific validity to their arguments whatsoever. But they’re very skilled at deducing what sorts of disingenuous arguments and untruths are likely to be believable to the public that doesn’t know better.”4
The IPCC and Global Efforts
IN RESPONSE TO the increasing knowledge—and alarm—about global warming, the World Meteorological Organization and UN Environment Programme set up the Intergovernmental Panel on Climate Change in 1988 at the request of member governments. According to the IPCC website,