SAJC Cluster 3.2 Lecture 9 Notes (Natural factors influencing climate change)

St Andrew’s Junior College H2 Cluster 3: Sustainable Future and Climate Change H2_Cluster 3 Lecture 9_2025/pg1 Lecture 9 The Science of Climate Change (II): Natural Factors influencing Temperature Variability KEY QUESTION: Can natural factors fully account for contemporary climate change? With the completion of this lecture, attached readings and tutorial, you should be able to understand the: • Natural factors influencing temperature variability in the Quaternary period • Influence of these natural factors on temperatures through feedback mechanisms Lecture Outline 9.1 Introduction 9.2 Natural Factors Influencing Temperature Variability in the Quaternary Period 9.2.1 Changes in Solar Output Box 1: The Maunder Minimum 9.2.2 Changes in Thermohaline Circulation Box 2: The Younger Dryas – A Warning from the Past 9.2.3 Changes in Ice Sheets: Milankovitch Cycles (a) Eccentricity (b) Obliquity (c) Precession Box 3: Can the Milankovitch cycles explain contemporary climate change? 9.3 Feedback Mechanisms 9.3.1 Positive Feedback Loops 9.3.2 Negative Feedback Loops 9.4 Conclusion

St Andrew’s Junior College H2 Cluster 3: Sustainable Future and Climate Change H2_Cluster 3 Lecture 9_2025/pg2 9.1 Introduction • As we have seen in Lect. 8, Earth’s climate has undergone significant variation over the course of its existence. The Quaternary Period, for instance, consisted of a cold Pleistocene epoch, and a warm Holocene epoch. • Since human activity associated with the modern human ( homo sapiens ) only arose about 200,000 years ago, the factors that caused temperature variability prior to that are likely natural. (But in Lect. 10, we will learn that humans play a bigger role today.) • While examining the list of factors affecting temperature variability, it is important to understand that they do not operate independently but simultaneously. This might therefore mean that while one factor leads to warming, another might counteract or enhance that warming. 9.2 Natural Factors influencing Temperature Variability in the Quaternary period 9.2.1 Changes in Solar Output • The sun is Earth’s only s ource of heat and light, so it is natural to assume that changes in the global temperature must be related to changes in the solar output. • For centuries now, scientists have known that the solar output (irradiance) varies over time. Periods of slightly higher solar output are associated with the appearance of sunspots , and astronomers have been recording the number of sunspots since the 1600s. The abundance of sunspots rises and falls usually in a 11-year cycle. • The so-called “Little Ice Age” (see Lect. 8 Fig. 1) that affected parts of Europe and North America for several centuries ending in the 1800s is thought to have been caused (at least in part) b