We're besieged almost every day by headlines about climate change, many of them contradictory. One group of scientists warns of significant, potentially devastating human-caused warming in the next half century, but a week later another group says that any changes that may have occurred in the 20th century were caused by natural factors, so not to worry.
If you want to understand what scientists really do and don't know about climate change, and how they have arrived at their present understanding of Earth's climate and the human and natural forces that are changing it, then read The Discovery of Global Warming. It's authoritative, based on more than 1000 peer-reviewed studies; clearly, even elegantly written; and is guaranteed to remain up to date through an affiliated website.
The author, Spencer Weart, traces the history of climate studies back to 1896, when Svante Arrhenius broke with the assumption that Earth's climate was stable over the long run and made the first scientific estimates of how much different levels of carbon dioxide would heat or cool the atmosphere. Over the course of the 20th Century, scientists gradually decoded the history of the ice ages, and came to realize that Earth's climate has changed radically many times. More recently, precision measurements form ice cores, lake beds and cave deposits have shown that the climate can change extremely quickly. For example, ice cores from Greenland show episodes of warming by seven degrees C.--close to 13 degrees F.-within five to ten years.
Since the 1970s, Weart reports, models of Earth's climate have grown from simple paper-and-pencil calculations to enormously complex computer simulations that take into account solar cycles, greenhouse gases, changes caused by wobbles in Earth's orbit around the sun, particles suspended in the atmosphere, ocean circulation, vegetation, Arctic and Antarctic ice, etc. The most sophisticated models are now able to simulate past climate changes, seasonal patterns and regional differences remarkably well. That gives their predictions of how the climate is likely to change over the next century as we continue to pump greenhouse gases and aerosols into the atmosphere considerable and increasing validity.
Weart also does a great job presenting the limitations of science in dealing with the complexities of Earth's climate. He acknowledges that scientists will never be able to prove that human activities are warming and potentially destabilizing the climate, but goes on to point out that the increasingly meaningful provisional answers they are providing are crucial to our decision making. He notes that most of the studies that pushed the field forward were wrong in one way or another, yet, cumulatively, they have created a deeper and more useful understanding of how the climate system works. He also discusses the major critics of global warming, and points out the inadequacies in their arguments and obvious sources of bias, for example being funded by corporations with a vested interest in being able to continue to pump unlimited quantities of greenhouse gases into the atmosphere.
Weart's bottom line is that by the middle of this century, due primarily to human activities, Earth's climate will almost certainly be 1.5 to 5.5 degrees C. (3 to 10 degrees F.) warmer on average. Changes will be greater in certain regions, for example at higher latitudes and altitudes, and will impact different ecosystems in very different ways. There may be a thriving wine industry in England, for example, while some low-lying Pacific island nations may no longer be habitable. He points out that all of human history has taken place in the most stable patch of climate in the past 400,000 years. We simply don't know how resilient our political, financial and cultural systems will be in the face of this degree of change. And, there's a wild card--the potential for far more sudden and drastic changes, for example if melting arctic ice turns off the oceanic "conveyor belt" that warms most of Europe. One scientist compares oceanic circulation to a "capricious beast" that we are "poking with a stick."
If you're like me, by the time you've read the Discovery of Global Warming, you'll agree with Weart's conclusion: "Our response to the threat of global warming will affect our personal well-being, the evolution of human society, indeed all life on our planet." It would be great if America were leading the way toward dealing with this crisis rather than sandbagging the international effort to do something about it.
Robert Adler, Ph.D., author of Science Firsts: From the Creation of Science to the Science of Creation; and Medical Firsts: From Hippocrates to the Human Genome, both published by John Wiley & Sons.
