The proposed chapters for A Brief History of Earth's Climate are listed here, along with some comments on what each one includes. Of course this may change a little as we go along, but this is the road map for now.
1) What controls the Earth’s climate? The introductory chapter will include an overview of the various processes of climate forcing—both natural and anthropogenic—and an explanation of how positive climate feedbacks can turn seemingly insignificant forcings into major climate changes. There will be a brief discussion of why many of the arguments that are used to deny the existence of anthropogenic climate change can be refuted by an understanding of Earth’s climate history. Because the book deals with processes that have taken millions and billions of years, this chapter will also include an overview of geological time, and how very slow processes can have huge implications.
2) The evolution of an ordinary star Our sun—like billions of others—is evolving over its lifetime from a cold cloud of hydrogen, to a warming main sequence star, to a red giant and finally to a white dwarf. The current process of very slow warming has influenced the climate for billions of years, but through bio-geological mechanisms the Earth has been able to adapt to the changes and maintain conditions that are suitable for life. One mechanism of that adaptation is the storage of carbon in the crust, but we are quickly undoing that now by burning fossil fuels.
3) Sliding plates and colliding continents The Earth is still producing massive amounts of internal heat and that heat drives the process of plate tectonics. The resulting movement of the continents leads to changes in the reflectivity of the surface at various latitudes and that can have implications for the climate because it controls how much of the Sun’s energy is absorbed by the Earth’s surfaces. Continental collisions also lead to the formation of mountain ranges. As those mountains are eroded and weathered, carbon dioxide is removed from the atmosphere, and the climate slowly cools. And finally, the geometry of ocean basins controls ocean currents, which in turn control the climate.
4) Volcanic eruptions Along with the spectacular red-hot lava, volcanoes spew out huge volumes of gases, including water vapor, carbon dioxide and sulphur dioxide. The volcanic water is the basis of life on earth, but the carbon and sulphur can change the climate. Sulphur dioxide from a large eruption can cool the planet by one or two degrees over several years. On the other hand, carbon dioxide from a long period of higher than average volcanic activity can lead to significant warming. The climate has been changed by volcanic eruptions many times in the past, in one case leading to the mother of all mass extinctions.
5) Changes in ocean currents Ocean currents are critical in redistributing the Earth’s heat; without them the tropics would be unbearably hot and the poles impossibly cold. But currents can change over time for a variety reasons, and the results can be dramatic. Other currents vary over periods of several years—El Niño/La Niña for example—and while these short cycles don’t really change the Earth’s climate, they do have significant impacts on the weather and on living organisms.
6) Earth’s orbital variations The Earth’s orbit around the Sun is not only not circular, but its shape changes over time, as does the degree to which the Earth is tilted. These highly regular cycles lead to changes in the distribution of the Sun’s heat on the Earth’s surface, and those subtle changes—amplified by feedbacks—are what have driven the multiple glacial cycles of the past million years.
7) Short-term solar cycles Apart from the long-term evolution of the Sun, it goes through short cycles of changing luminosity that can affect the Earth’s climate. The main cycle is based on the number of sunspots, which varies on an 11-year cycle—with fewer sunspots associated with decreased luminosity. Although this is also too short to affect global climate, there are longer cycles in the average numbers of sunspots over decades, and these have affected the climate in recent centuries. The average number of sunspots has been decreasing steadily over the past four decades, and so the Sun’s output has been decreasing slightly, even as anthropogenic climate forcing has driven the Earth’s temperature to new heights.
8) Catastrophic collisions The Earth has been struck by large rocky or icy objects many times during its history. Depending on the circumstances, such as the size of the object and where it struck, the implications of these events have ranged from minimal to catastrophic for the climate and for life. The best-known collision is the one that marked the end of the Cretaceous Period 65.5 million years ago. The climate implications were immediate and disastrous for all organisms, but especially so for the terrestrial dinosaurs.
9) A plague of humans Homo has existed on Earth for a little over 2 million years but for most of that time we had relatively little impact on our ecosystems and none on the climate. As hunter-gatherers our impacts were small because we lived in small groups and rarely threatened the viability of our food sources. The advent of agriculture about 10,000 years ago changed everything. That, and every subsequent agricultural “leap forward”, has boosted our numbers and our potential to wreak destruction. For the past 300 years our industrial civilization has fed on fossil fuels, and the waste carbon dioxide has been spewed into the atmosphere with little heed for the implications.
10) Tipping points Geological records show that the Earth’s climate can remain stable (or change very slowly) for tens of millions of years at a time, but that there have been some dramatic, rapid and deadly changes in the past, many of which can be ascribed to tipping points caused by runaway climate feedbacks. There were tipping points during the Pleistocene glaciations, and there was a dramatic tipping point about 55 million years ago that led to a major extinction. We don’t understand tipping points fully, but there are many reasons to believe that we are driving the Earth to a tipping-point precipice right now, one that we are too short-sighted to see.
11) What now? Climate change is not coming; it is here now. The symptoms are everywhere, and it requires a strong political conviction or lucrative business interest to deny them. Depending on where and how you live, the consequences can range from irritating to catastrophic to deadly. We know that much more change is coming, but it’s difficult to know how much and impossible to know how close we are to a tipping point. Some advocate for moving full speed ahead with adaptation to a changing climate, and while it would be imprudent not to think about that, we simply cannot, and must not stop working on reducing our collective climate impacts. That includes drastically reducing our emissions related to electricity generation, transportation and consumption, and changing our diets.
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