Climate Change: The Science of Global Warming and our Energy Future

One way to think about the difference between weather and climate is to consider the fact that we often dress for the weather but build houses in accordance with the climate. In other words, weather often dictates our day-to-day decisions, whereas our houses are built to withstand the climate in the region where they are located over many seasons and years. This example illustrates the important distinction between weather and climate: the former is the condition of the atmosphere at a given location and instant in time; the latter is the long-term average of the atmosphere within a region (ranging from global to local). Climate, the principal focus of this book, changes in time and space through the dynamic interactions of all parts of the Earth system: the atmosphere, hydrosphere, cryosphere, biosphere, and lithosphere. All these parts are responsible for moving energy and moisture horizontally and vertically about the globe, thus establishing the familiar climate patterns of our planet. The interactions among the various parts of Earth’s climate system vary over many different timescales and can do so in complex ways with important consequences. For example, they are responsible for cycling important chemicals such as carbon dioxide and methane between the atmosphere, ocean, and land surface by processes that collectively make up the carbon cycle. They also produce processes known as feedbacks, or phenomena that enhance or diminish warming or cooling of the planet. Feedbacks have played an important role in changing climates of the past and will play an important role in the future climate as our planet continues to warm.

Understanding climate and its changes requires that we separate facts from fears. We can think of the facts as what we know about how the climate system works—the details of the climate system’s interactions, as outlined in the previous paragraph—and how and why climate changes have occurred in the past. The basic facts that underlie climate change during the past 150 years are that Earth is warming at an accelerating rate, greenhouse gases in the atmosphere have risen exponentially due to human activity, and the link between these two observations is unequivocal. But what about the future? Projecting how changes will occur and what decisions societies will make in light of these changes is an endeavor that is inherently uncertain. Fears regarding climate change therefore can be thought of as what we expect in the future based on how we understand the climate system and what decisions we expect our societies to make. Three examples of fears for the twenty-first century are the magnitude of sea-level rise, the potential for megadroughts over large regions of the globe, and increases in extreme weather events such as heat waves and floods. The extent to which each of these fears is realized ultimately depends on the decisions our societies will make during the twenty-first century. Thus the facts of climate change suggest that our fears are a possibility, but they also imply that many of the direst consequences can be avoided by intelligent action and innovation, which places the future directly in our own hands.

1. The overview contrasts two decisions we make based on either weather or climate: the way we dress on a given day is often dictated by the weather, whereas the type of house we live in is likely related to the local climate. What other aspects of our daily lives demonstrate how either weather or climate impacts our decisions or living environment?

2. The climate changed dramatically in the past due to natural variations, but human-caused global warming is reason for great concern. Chapter 1 points out that the reasons for this concern are that projected changes may be substantial and that organized human societies did not exist during many of the large changes of the past. Are these arguments convincing? Are there other reasons why contemporary climate change should be cause for concern in light of past changes? Are there reasons why it should not?

3. Projecting how climate will change in the future is inherently uncertain, even though scientists know a great deal about the way in which the climate system works. There are certainly open science questions about the details of climate change, but these questions are not the biggest causes of uncertainty in future projections. Rather, human societies’ decisions are the biggest source of uncertainty underlying how the future climate will unfold. What kinds of societal decisions might be the biggest sources of future uncertainty, and what role do these decisions play in affecting climate change?