Global warming may be one of the most important issues influencing your decisions in your lifetime. The decisions you make on energy sources and daily conservation practices will determine not only the quality of your life but also those of your future descendants.

I cannot stress enough how important it is to gain a good understanding of global warming: what it is, why it is happening, how it can be slowed down, why everybody is contributing to the problem, and why everybody needs to be an active part of the solution.

I would sincerely like to thank several of the federal government agencies that research, educate, and actively take part in dealing with the global warming issue, in particular, the National Aeronautics and Space Administration (NASA), the National Oceanic and Atmospheric Administration (NOAA), the Environmental Protection Agency (EPA), and the U.S. Geological Survey (USGS) for providing an abundance of resources and outreach programs on this important subject. I would especially like to acknowledge the years of leadership and research provided by Dr. James E. Hansen of NASA's Goddard Institute for Space Studies (GISS). His pioneering efforts over the past 20 years have enabled other scientists, researchers, and political leaders worldwide to better understand the scope of the scientific issues involved at a critical point in time when action must be taken before it is too late.

I also give special thanks to former congressman and vice president Al Gore and current California governor Arnold Schwarzenegger for their diligent efforts toward bringing the global warming issue to the public's attention. I would also like to acknowledge and give thanks to the many wonderful universities in the United States, Great Britain, Canada, and Australia, as well as private organizations, such as the World Wildlife Fund, that diligently strive to educate others and help toward finding a solution to this very real problem.

I want to give a huge thanks to my agent, Jodie Rhodes, for her assistance, guidance, and efforts; and also to Frank K. Darmstadt, my editor, for all his hard work, dedication, support, helpful advice, and attention to detail. His efforts in bringing this project to life were invaluable. Thanks also to the copyediting and production departments for their assistance and the outstanding quality of their work.


Earth has always exhibited patterns of heating up and cooling down.

At some points in time, many areas of Earth are shrouded in blankets of ice, with ice caps and glaciers dominating the landscape. In fact, certain areas on Earth have been covered multiple times in the past with prominent glaciers for millions of years. Then, during the intervals between these ice ages, Earth's temperatures have warmed up, and the ice has melted and receded. Since the last ice age, which ended just over 10,000 years ago (a short time, geologically speaking), Earth's climate has been relatively stable, with just a few fluctuations—at least until the beginning of the industrial revolution in the 1700s, when the climate began to increase in temperature.

Earth's natural climate is always in flux, adapting and adjusting to internal and external processes. Just as natural processes can have an impact, so can the behavior of humans. Added to this are the external factors relating to variations in solar radiation and cyclic changes in Earth's orbit. All of these inputs—these "forcings"—cause the climate to react in a certain way. The time element is also variable: Some climate changes take thousands of years to take effect; others, only decades. All of the contributing factors of climate, such as temperature, precipitation, atmospheric circulation, ocean circulation, and the distribution of landforms are pieces in the master climatic puzzle, helping shape it over eons of geologic time.

Some of the most commonly studied elements of climate are the ice ages, because ice sheets and glaciers respond so rapidly to the forc ings of climate change. Earth's climate changes whenever the amount of energy stored by the climate system varies. This usually happens when there is a change in Earth's global energy balance—the incoming energy from the Sun being balanced with outgoing heat from Earth. There are some natural conditions that can upset this balance, such as changes in Earth's orbit, changes in the composition of the atmosphere, or changes in ocean currents. Today, however, most of the major disruptions are due to human-caused pollution from the emission of greenhouse gases. When any of these mechanisms are significant enough to change the energy balance, they are said to "force" the climate to change. Climate scientists have adopted the terms climate forcing and forcings to explain these mechanisms' influence on the climate.

Ice ages have also occurred throughout Earth's history in a cyclic pattern and left landforms and other evidence behind, enabling scientists to study them and obtain a detailed, reliable glimpse into the past. By analyzing the repeated advance and retreat of glaciers and the effects and contribution of the environment around it, scientists gain a better understanding of how, when, and why ice ages have occurred. In fact, much climatic research occurring today is related to the glacial and interglacial cycles of the current ice age. Because climate acts as a huge working system, scientists can analyze past evidence and understand the processes that occurred long ago by comparing them to processes that occur today.

As a result of the continuing warmth worldwide, Earth is feeling the effects, though not all results are the same. Some areas are becoming warmer and wetter; some, warmer and drier. Some are experiencing flooding; others, drought. Ocean circulation patterns are changing, wind patterns are altering, and cloud cover is affecting how much solar energy reaches Earth's surface and contributes to the greenhouse effect. Sea ice and glaciers are thinning, and temperatures are expected to keep rising.

Even though the temperature's changing a few degrees may not seem a big concern, it is. During the last ice age, for instance, global temperatures were only about 6.7 to 10° Fahrenheit (4-6° Celsius) cooler than they are today. To get a handle on the climate changes today, it is vitally important that climatologists gain a good understanding of the mechanisms that caused past climate change, putting the Earth repeatedly into and out of ice ages. By understanding these natural cycles, they are better able to compare them to the differences of today's rapid global warming, caused principally by the behavior of humans. This knowledge, in turn, allows them to understand the science of global warming better, a necessary step to solving the problem.

Global Warming Cycles: Ice Ages and Glacial Retreat, one volume in the Global Warming set, focuses on these issues. Chapter 1 looks at what ice ages are and why they occur. Each glaciated period on Earth varies in its intensity, and none is like another. Therefore, if the issue of global warming is such a key topic today, why are some scientists worried about the Earth entering another ice age? My goal is to show you the relationship between the two issues and how a natural cycle can indeed be affected by a human-influenced process. This chapter also presents the many physical factors that shape the Earth's climate and which ones are out of our control and which ones humans have a direct impact on. Finally, we take a look at a well-known, extremely controversial theory called the "hockey stick theory" and present the reasons for the controversy, with the intent that you, as the reader, can decide for yourself what it means.

Chapter 2 focuses on glacial retreat. It looks at the evidence that past glaciers have left, which can clue scientists in today as to what Earth's climate was once like. It looks at how scientists use landform clues from the past to assess global warming and then apply that knowledge to the future in order to help prepare current and future society for what is to come. If scientists do not understand these correlations, there is no way that land managers and politicians will be able to plan ahead and provide for the safety and well-being of towns and cities.

Chapter 3 discusses ice sheets and the phenomenon of isostasy. It looks at research done in Antarctica and Greenland and the consequences of recent breakup of large pieces of the world's largest ice sheets. Both isostasy and the melting of ice sheets affect sea level. This is especially important for every inhabitant worldwide who lives near the coast. If sea levels rise, many populated areas will become submerged and destroyed; therefore, it is important to understand that the consequences of global warming can potentially do extreme damage to present-day developments.

The following two chapters look at the world's oceans as a massive heat transport system. They illustrate how oceans are able to retain so much heat; the role they have played over the years to cancel out the effects of global warming; how they have made some areas on Earth habitable, where otherwise they may not be; and why scientists need to diligently monitor them so that balances do not get easily tipped. I also introduce computer-modeling techniques and other technology available today to help climatologists better predict the conditions of coastlines.

Chapter 6 focuses on the science of abrupt climate change, an issue that has scientists worldwide very concerned with the future of the Earth and global warming. When the film The Day After Tomorrow was released, the thought of, and the potential impacts of, abrupt climate change frightened many people. This chapter looks at what types of things can really happen and, given the condition of Earth today, what the chances are of us experiencing a climate change of significant consequence.

A discussion on tropical cyclones and other severe weather follows, in chapter 7. The rates of incidence will be a consequence of further global warming. Also within the chapter are some fascinating statistics about which areas of the country have the costliest hurricanes and where in the United States you do not want to be if a hurricane makes landfall. The final two chapters, meanwhile focus on what various climate experts have to say on the subject, conclusions, and a glance into the future. Each of the climate research scenarios represented touches on a current aspect of the ocean and global warming being done by leading scientists around the world. Not all scientists agree; disagreement is common in the pursuit of understanding. It is as valuable to know what issues are right as it is to know which ones are wrong; that is how the knowledge base of a scientific field grows. While we learn a great deal from scientists, scientists also learn a great deal from one another. This data sharing is an extremely important role that each good scientist needs to play in order to progress.

Global warming is a huge topic, involving many facets of society: climatology, hydrology, geography, geology, biology, botany, ecology, environmentalism, physics, chemistry, economics, and political science, to name just a few. My goal with regard to this set is to introduce you, the reader, to the entire spectrum of issues so that responsible, knowledgeable decisions can be made in the future. A deep knowledge of global warming can only come one step at a time. As you read, you will make progress toward unlocking the door to understanding the issues, and as the author, I would like to give you the key.

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