Chapter 1: So Whats Up with the Weather?

Chapter 1: “So What’s Up with the Weather?”

Introduction Chapter 1 provides a broad overview of the scientific evidence for climate change and the forces that can change global climate over time. The aim of the chapter is to “set the scene” for later chapters, giving students who often come from different academic backgrounds an overview of the problem and an introduction to some of the basic terminology needed to understand the following chapters. I continue to use the term “global warming” for changes in temperature that are truly global because they reflect a substantial change in the overall balance of energy measured at the top of the atmosphere. This imbalance drives climate change in the troposphere, which may result in both regional warming and cooling in the short term but overall warming in the long term.

Learning Outcomes • Discuss how global temperature has changed over geological time • Identify some of the principal factors that control global climate over different timescales • Describe the recent historical temperature record • Determine possible causes of recent changes in global temperature • Understand how climate models can be used to project climate change • Evaluate the possible impact of human activity on the atmosphere Discussion The chapter opens with the question “what’s up with the weather?” because many students will not understand the difference between weather and climate. There are many available definitions 1 © 2014 Pearson Education, Inc.(Global Climate Change Turning Knowledge Into Action 1e David Kitchen ) (Instructor Manual) 1 / 4

of climate that are more complete, but I keep mine simple as an introduction. I want to get students thinking about their everyday experience of weather and how this relates to the climate where they live.The image of a forest fire (Figure 1a) highlights how climate change is expected to impact parts of the continental United States because of changes in regional patterns of precipitation. This is an opportunity to start a class discussion about how much climate change is already noticeable in the United States.The graph illustrating the recent record of climate (Figure 1b) shows students how much global temperature has changed since the late 19th century. I use this as an opportunity to discuss the rate of climate change and natural decadal variation. This graph helps students to understand that global temperature has not risen at a constant rate due to the superposition of natural climate variation on top of slow anthropogenic change, a fact that highlights why we study natural climate change in Chapters 3 and 4.I use Figure 1.1c to start a discussion with students about their personal experience of climate change. The changes most of us have observed are not dramatic, but the number of warm weather records broken each year is increasing while the number of cold weather records is decreasing. All this is happening as global temperature is slowly increasing. This is a good opportunity to start discussing rapid climate change and the emergence of critical tipping points.Is the pattern of gradual climate change we observe today the way that climate always changes?Can climate change suddenly and dramatically? The answers are clearly illustrated with many examples in the following chapters.The chapter presents historical evidence that climate change is both natural and normal and introduces students to the Medieval Warm Period and Little Ice Age. These are two 2 © 2014 Pearson Education, Inc. 2 / 4

examples of how climate has changed naturally over time due to natural factors that we understand. This is in contrast to recent warming that can only be explained by a substantial contribution from anthropogenic greenhouse gases.The graph of global temperature change first seen in Figure 1.1 appears again in Figure 1.5b. This time a second graph that illustrates how factors that force climate change have combined to create this record. There is a lot of detail in Figure 1.5b, but draw students’ attention to the impact of the long-lived greenhouse gases (LLGHG) and volcanic eruptions, and then compare these substantial changes to the relatively small changes in radiative forcing from the Sun—a fact that is surprising to many students.Climate models are introduced for the first time in this chapter. Figure 1.7 compares the observed record of climate change with model predictions. The diagram illustrates that the observed changes in global climate cannot be explained without a substantial contribution from human activity. This is an opportunity to start a discussion about climate models and the reliability of their projections of climate change over the rest of this century.The following section focuses on ancient climate change (page 11). If we can understand how Earth has responded to changes in climate forcing in the past it may help us to project what is likely to happen in the near future. I use the Cretaceous Period as an example because the configuration of the continents was close to what we see today, and because levels of carbon dioxide were substantially higher than they are today. In this way the Cretaceous is a model of how Earth might look in the future if we continue to add greenhouse gases to the atmosphere.Students can then contrast the Cretaceous Period with the following account of the Pleistocene epoch and the long ice age that still affects us today. Students gain perspective from the fact that the growth of civilization has been confined to a brief interglacial period that will 3 © 2014 Pearson Education, Inc. 3 / 4

soon change in a geological instant. In the absence of human intervention, the ice sheets are expected to advance again in a few thousand years.Radiative forcing is an important concept that students need to understand before they move on to read later chapters. The concept was first introduced in Figure 1.5 but is explained in more detail on page 12. Figure 1.13 introduces Earth’s atmosphere, cryosphere, hydrosphere, and lithosphere as a climate system where each component is linked like the cogs in a machine, so that changes in one part have an impact on the entire system. This section also introduces the concept of climate feedback and it is worth taking time at this point to illustrate this with further examples. Climate feedback is at the core of the debate about climate sensitivity discussed in Chapter 3 (page 81), and it is important to make sure students have a firm grasp of the concepts involved at this early stage in the course.The section on the timescale of climate change (page 14) reviews factors that impact climate change and the temporal scales involved. This section identifies greenhouse gases in the atmosphere as the only factor capable of affecting the kind of rapid climate change we have observed over recent decades. Other factors that are capable of changing climate over a relatively short period of time such as Milankovitch cycles, solar activity, and the emission of aerosols from volcanic and/or human activity cannot be responsible for warming over recent decades because they all currently cool rather than warm the atmosphere. Ask students what the likely impact on global warming would be if we were not adding industrial aerosols to the atmosphere, if volcanic activity was lower than it is today, and if solar activity were not unusually low. The answer is clearly that the rate and amount of warming observed would be substantially greater than it is today. 4 © 2014 Pearson Education, Inc.

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