The Discovery of Global Warming

The Discovery of Global Warming   Spencer R. Weart  Harvard U. Press, Cambridge, MA, 2003. $24.95 (228 pp.). ISBN 0-674-01157-0

Two mountain villages, one Swiss and the other French, are neighbors and only a few miles apart. What divides the communities is the snowy roof mass of Mont Blanc, western Europe’s highest mountain, in the French Alps; so visits between the villages are uncommon. But during the 18th century, as Spencer Weart recounts in The Discovery of Global Warming, both settlements were eager to share experiences when they saw the coarse, glacial ice sheet—always a grim sight for the towns—slowly move nearer their homes.

The elders recalled from village lore how disappointed the people were when their rare exchanges disclosed the threat to every visible wall of shelter on both sides of the mountain. The ice ignored every human appeal, even prayer; only patience and hope offered a defense. The climate was changing, not merely the weather. Climate includes the locally expected weather, such as the valley heat or mountain snow. That a reliable climate also can change may sound like a paradox: Isn’t climate the steady part of changing weather?

Global warming is a worldwide summertime and an unexpected discovery. Of course, ice ages have long belied a fixed climate. At least several millennia ago, mountainous ice caps gripped the world through several cycles. Climate itself has gone through profound, repeated change.

Ice ages have long been recognized as cosmic phenomena caused by interplanetary gravitational interactions that transform any simple elliptical orbit like Earth’s into rosettes. A well-verified astronomical dance creates small but long-lasting deviations in the distance between Earth and the Sun. Sunshine that hits Earth dims and brightens time and time again. The deviations correspond with the main classical epochs of ice-age glaciation. Astronomical in origin, this climate-change puzzle was solved by means that depend on the effects of times and distances so great as to be irrelevant to everyday weather.

Detailed facts about global warming can be found in countless research tables, graphs, maps, and other such records. Yet The Discovery of Global Warming , a thorough history of the subject, has only four graphics in more than 200 pages. But those few graphics are compelling. First, the data in the book stamp a vivid label on one variable: the abundance of carbon dioxide. The large variations in levels of carbon dioxide, which is found in only a few parts in 10 000 of Earth’s atmosphere, are strikingly co-herent. The data reveal changes in carbon dioxide content in Antarctic air measured at different locations over almost 50 years. One set of data show, in two years, continent-wide variations of carbon-dioxide levels, from Antarctica’s icy coast to its far-off South Pole station. Another graph records carbon-dioxide levels from 1958 to 2002 at the high Hawaiian plateau of Mauna Loa. Each year resolves a repeated seasonal rise and fall, with an overall change of 30% in levels of the gas.

Weart is the director of the Center for History of Physics at the American Institute of Physics. His deep engagement with the history of physics informs the book’s guiding summaries of the climate pioneers: Benjamin Franklin, Joseph Fourier, John Tyndall, Svante Arrhenius, John Von Neumann, and Guy Callendar. It was Callendar, an engineer, who cut right to the chase in his 1938 paper to the Royal Meteorological Society about the causes of climate change so decisive in our own history. Callendar advanced data to support his argument that human-made fires in the 20th century generated sufficient amounts of carbon dioxide to raise global surface temperatures. Callendar’s research introduced reasons behind global warming but did not bring clarity to the events overall.

Halfway into the book’s history on global warming, Weart presents a plot of surface temperatures around the world. Described in the book as “the first entirely solid and comprehensive global analysis of average surface temperatures,” the graph reveals a dozen big peaks from global temperature records from 1880 to 1980. The warmest three years, according to a 1986 study of a 134-year record, had all occurred in the 1980s. But cooler weather was what most people recalled during the first years of the warming period.

The disparate details of the climate problem set a tough course for the public. Weart’s figure 3 is a graph that, although somewhat marred by scientists’ reconstruction of old temperatures, documents a swift, strong, credible upturn from the circumstances of the last century. Familiar instruments and complete, meticulous records were valuable to climate scientists and helped bolster their credibility as “the greenhouse gases and the temperature soared.”

The next pages of the book include a metaphor so apt that it seems all but unfair to debate it: “The global climate system,” said geochemist Wallace Broecker in the 1990s, “is an erratic beast, and we are poking it about with a sharp stick.” Insightful and eloquent, Broecker had introduced in his own doctoral thesis 30 years earlier a bold proposition for rapid climate change.

The closing paragraph in Weart’s book sums up the public struggle with the unprecedented changes of climate—changes supported by a rapid increase, from 1900 on, of data, memories, and forecasts from researchers. Figure 3, first published in 1999, is called a “hockey stick” because of the plot’s dramatic upward slope recorded at the very end of the 20th century. The evidence Weart provides has convinced this initially doubtful reviewer of the causes behind global warming. Let us cite Weart’s own words found on the final page of his book, which call upon all of humanity to act: