Almost every day, some claim or counterclaim about climate change and global warming hits the headlines. For most of us this is very confusing. Some people consider every storm, drought, heat wave, and record temperature further evidence for global warming; others dismiss these same events as natural climate variation. Isn’t everyone looking at the same data? How can the same facts be interpreted in such different ways?
When the interpretation of scientific data makes it imperative that we change the ways we create and use energy, the origin of these data becomes controversial and politically-charged. Before we undertake any action that will have a long-term impact on society, we need to understand how and why global climate changes. The geological record shows us that climate change is a normal part of Earth’s history, and while most scientists conclude that recent changes in global temperature and climate are due to the emission of human-made (anthropogenic) heat-trapping greenhouse gases, a small but vocal minority disagrees. In order to project the future impact of anthropogenic emissions accurately, we must understand the different factors that have driven climate in the past and how small changes in global temperature will affect Earth’s climate today.
When you finish this chapter you should be able to:
• 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