Global warming may very well be one of the most important issues you will have to make a decision on 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 that of your future descendents.

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 give special thanks to Al Gore and Arnold Schwarzenegger for their diligent efforts toward bringing the global warming issue so powerfully to the public's attention. I would also like to acknowledge and give thanks to the many wonderful universities across the United States and in England, 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, and helpful advice and attention to detail. His efforts to bring this project to life were invaluable. Thanks also to the copyediting department for their assistance and the outstanding quality of their work, with a special thanks to Alexandra Lo Re for her enthusiasm and input.


The Earth's climate is always changing. The most obvious changes that have taken place over the course of geologic time are the shifts from glacial (ice age) periods to interglacial (non-ice age) periods. The Earth has had several "ice ages" throughout time, during which ice covered large portions of the Earth's surface, then melted back to nearly nothing. Scientists know the Earth's climate is always naturally changing, but with the amount of human interference today, the questions have become: How are humans changing it? Are they endangering the future? And what will the Earth be like for our children, grandchildren, and future generations? These are the very issues that I would like you—the reader—to ponder as you gain insight into the problem. What long-term effects will our current decisions and lifestyle choices have on future generations? How much hardship are we adding in and above the natural fluctuations in climate that have been normal for the Earth throughout geologic time? For better or worse, our actions today will affect future generations and their standard of living. That is a serious responsibility—not one to be taken lightly.

Climate scientists have repeatedly told us that the 1990s was the warmest decade ever recorded since temperatures began to be consistently kept in the mid-1800s. Scientists around the world support this notion; there are an abundance of data collected worldwide that prove this. Some may argue that the trend has not been a steady upward climb, but that it has had intermittent cooling periods. But, unfortunately, it does not let us off the hook. Although these intervals have occurred every few decades in some locations, the overall trend has been a steady upward climb, coinciding with melting glaciers, rising sea levels, shifting climatic zones, and changing ecosystems worldwide.

Not only were all 10 years of the 1990s among the 15 warmest ever recorded, but also six of them have the distinction of being the warmest years on historical record—ever. When scientists look at this trend, what it tells them right away is that the Earth's atmosphere has become significantly warmer over the past 150 years. This notion then raises other questions, such as the following:

• Has this happened before?

• What effect did warmer temperatures have on the atmosphere?

• What effect did warmer temperatures have on plants and animals?

• How have warmer climates affected humans?

• What do warmer climates do to ecosystems?

• If temperature fluctuations occur, how often and how long do they typically last?

• Did animal species in the past migrate, adapt, or go extinct?

• What can we really expect to happen today?

• Can technology solve all our problems?

These are the questions this volume will address. If scientists can obtain a good understanding of past climate change and how susceptible or resilient the environment has been in response, it offers them the valuable insight they need to understand the global changes happening today in the climate.

One way that scientists are able to study global warming is if they have a baseline to compare it to. This baseline is the Earth's past climate. If scientists can successfully reconstruct the Earth's past climate and determine (1) how often it warmed up or cooled down, (2) to what magnitude it warmed up/cooled down, and (3) what mechanisms triggered the warming/cooling phases, then they are in a much better position to understand what global changes they are seeing today and what they mean for humans and the environment—topics you will be exploring in this volume.

Climatologists have written climate records going back only to the mid-1800s. Luckily for them, the Earth has left a long and detailed record of the past. When scientists study ancient climates, a field called paleoclimatology, they are able to reconstruct the Earth's climate back over long periods of time. By looking backward in time, scientists can find evidence of natural processes that may be currently in effect, causing the global temperature changes we are seeing today. When scientists study warm periods of the past, they can discern vital clues that explain the warming of today and whether this is from natural processes or something else, such as something humans have directly caused.

The goal of this volume is to show exactly how scientists determined what the climate was like at a specific time period and how they inferred what global warming may have been like at another time in the past. For instance, if global temperatures rise, then carbon dioxide (CO2) is released from the ocean. If CO2 is released, it magnifies the greenhouse effect, making atmospheric temperatures warmer. Conversely, when temperatures drop, then CO2 enters the oceans, and the oceans store the CO2 as a sink, lessening the greenhouse effect and cooling the atmosphere. According to the Intergovernmental Panel on Climate Change (IPCC), during the past 650,000 years, CO2 levels have closely followed the glacial cycles. Warm interglacial periods had high CO2 levels, and cold glacial periods had low CO2 levels.

There is also a human factor that each person needs to consider: Almost everything everyone does contributes to the greenhouse effect (such as driving cars, using electricity, buying any manufactured item, using utilities), and it is up to everyone to work toward a solution to conserve natural resources and use less nonrenewable energy. I want to show you how we all leave a "carbon footprint" for which we need to take environmental responsibility.

In order to go back in time and look at the "ecological footprints" that have been left by specific natural processes, climatologists can reconstruct past climates, study them, and then apply what they have learned to present-day observations. Global Warming Trends: Ecological Footprints will focus on how the climate on Earth has fluctuated over time and the various techniques available to scientists today that allow them to study the physical clues left behind by ancient climates and determine when specific changes in climate took place.

Chapter 1 looks at the science of paleoclimatology and how being able to reconstruct the Earth's past climates helps scientists better understand global warming and how it is affecting the Earth today. Chapters 2 and 3 present an overview of significant climatic periods of the Earth's past and introduce the concept of climate proxies—natural indicators that can be used to infer past climate. They also examine the concept of geochronology and how scientists are able to determine the relative ages of objects on Earth. Chapter 4 focuses on the evidence of climate change and global warming that is present in various erosional and depositional features of the Earth's surface and how the study of these landforms and a solid understanding of the processes that created them clues scientists in to what the Earth was like in ancient times. Chapter 5 explores evidence about climate change that can be successfully derived from the ice cores of Antarctica and Greenland and the types of data they contain as well as evidence obtained from marine cores and the preserved secrets held in their sediments at the bottoms of lakes and oceans.

The next chapter dwells on how scientists are able to use pollen, tree rings, plant remains, and other life-forms to make inferences about past climatic conditions. Chapter 7 focuses on how climate has affected the rise and fall of civilizations throughout time, enlightening scientists to the very real issues humans face today with global warming. This volume then looks at two new types of technology and how they are being used to discover the Earth's past climates. It concludes with the most current information from climate experts and how the futuristic role of computer modeling is helping scientists to discover the past and use it to predict the future—something with which you may find yourself directly involved.

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