The co-evolution of climate models and the Intergovernmental Panel on Climate Change

As recently as the 1950s, global climate models, or GCMs, did not exist, and the notion that man-made carbon dioxide might lead to significant climate change was not regarded as a serious possibility by most experts. Today, of course, the prospect or threat of exactly this type of climate change dominates the science and ranks among the most pressing issues confronting all mankind.

Indeed, the prevailing scientific view throughout the first half of the twentieth century was that adding carbon dioxide to the atmosphere would have only a negligible effect on climate. Svante Arrhenius, who carried out the first detailed calculations in 1896, thought that doubling atmospheric carbon dioxide levels might take 3,000 years. He was wrong, how wrong remains to be seen, but perhaps wrong by a factor of about 20. He did not foresee the explosive twentieth-century growth in population and fossil fuel use. Like other scientists of that era, Arrhenius investigated the possible connection between carbon dioxide and climate in terms of an explanation for the ice ages. He apparently never regarded it as a candidate climate change mechanism operating on shorter timescales. After Arrhenius, with very few exceptions, the few scientists who seriously considered the issue generally came to incorrect conclusions. Some erroneously thought that the carbon dioxide absorption bands for infrared radiation were already saturated, so that adding additional carbon dioxide would not increase absorption. Other scientists found other reasons to dismiss the effect of rising atmospheric carbon dioxide levels, believing, for example, that water vapour absorption of infrared radiation overwhelmed that of carbon dioxide, or that the ocean would speedily take up any additional carbon dioxide that puny humankind might add to the atmosphere. Today, with the wisdom of hindsight, we know that they were all mistaken.

Thus, in about half a century, the science of climate change caused by atmospheric carbon dioxide changes has undergone a genuine revolution. An extraordinarily rapid development of global climate models has also characterized this period, especially in the three decades since about 1980. In these three decades, the number of GCMs has greatly increased, and their physical and computational aspects have both markedly improved. Modeling progress has been enabled by many scientific advances, of course, but especially by a massive increase in available computer power, with supercomputer speeds increasing by roughly a factor of a million in the three decades from about 1980 to 2010. This technological advance has permitted a rapid increase in the physical comprehensiveness of GCMs as well as in spatial computational resolution. In short, GCMs have dramatically evolved over time, in exactly the same recent period as popular interest and scientific concern about anthropogenic climate change have markedly increased.

In parallel, a unique international organization, the Intergovernmental Panel on Climate Change, or IPCC, has also recently come into being and also evolved rapidly. Today, the IPCC has become widely respected and globally influential. The IPCC was founded in 1988, and its history is thus even shorter than that of GCMs. Yet, its stature today is such that a series of IPCC reports assessing climate change science has already been endorsed by many leading scientific professional societies and academies of science worldwide. These reports are considered as definitive summaries of the state of the science. In 2007, in recognition of its exceptional accomplishments, the IPCC shared the Nobel Peace Prize equally with Al Gore.

Future historians may come to regard the half-century from about 1960 to about 2010 as a period marked by an astounding coincidence in climate change and climate science. In this period, rapidly increasing atmospheric concentrations of greenhouse gases due to human activities led to important observed climate changes and the prospect of even more serious future climate changes. During the same period, the science of climate change underwent a profound transformation, driven and enabled by the invention of satellites, supercomputers and climate models, among other advances. Thus, just at the moment in history when mankind inadvertently became capable of changing the climate, the science required to understand and predict this climate change also came of age.

There is no fundamental reason why humanity might not have evolved somewhat differently since, say, the year 1900. For example, it is perfectly conceivable that during the twentieth century, our species might have increasingly exploited the Earth's reserves of coal and oil and natural gas, while more than tripling global population since 1930, without, however, also inventing the technologies that led to rapid progress in climate science, especially satellite remote sensing and digital electronic computers. In that hypothetical case, man-made global warming in the early years of the current century might have been underway to much the same extent as it actually is today, but our ability to comprehend it scientifically and to describe its causes and project its future would be extremely limited.

In fact, however, the present era is characterized not only by the reality and seriousness of human-caused climate change, but also by a young yet powerful science that enables us to understand much about the climate change that has occurred already and that awaits in the future. The development of GCMs is a critical part of the scientific story, and the development of the IPCC is a key factor in connecting the science to the perceptions and priorities of the global public and policymakers. GCMs and the IPCC have co-evolved and strongly influenced one another, as both scientists and the world at large have worked to confront the challenge of climate change.