After reading this chapter, completing the exercises within it, and answering the questions at the end, you should be able to:
- Summarize the properties of greenhouse gases and their role in controlling the climate
- Explain the difference between climate forcing and climate feedbacks
- Describe the mechanisms of climate forcing related to solar evolution, continental drift, continental collisions, volcanism, Earth and Sun orbital variations, and changing ocean currents
- Describe the significance of albedo to climate and how the melting of ice or snow and forestry affect albedo
- Explain the roles of the melting of permafrost, breakdown of methane hydrates, and temperature-related solubility of CO2 as positive feedbacks
- Describe some of the ways that our extraction and use of fossil fuels contribute to climate change
- Explain how food production contributes to climate change
- List some of the steps that we can take as individuals to limit our personal contribution to climate change
- Describe the role of climate change in sea-level rise, and why we are already committed to more than a metre of additional sea-level rise
- Explain the link between climate change and the distribution of diseases and pests
The Only Constant Is Change
If one thing has been constant about Earth’s climate over geological time, it is its constant change. In the geological record, we can see this in the evidence of glaciations in the distant past, and we can also detect periods of extreme warmth by looking at the isotope composition of sea-floor sediments, such as those in the core shown in Figure 19.1. Not only has the climate changed frequently, the temperature fluctuations have been very significant. Today’s mean global temperature is about 15°C. During Snowball Earth times, the global mean was as cold as -50°C, while at various times during the Paleozoic and Mesozoic and during the Paleocene-Eocene thermal maximum, it was close to +30°C.
But in spite of these dramatic climate changes, Earth has been habitable from very early in its history — as soon as liquid water was present — right through to the present day. That continuous habitability is perhaps a little more surprising than you might think, as we’ll see.
A significant part of this chapter is about the natural processes of climate change and how they work. It’s critically important to be aware of those natural climate change processes if we want to understand anthropogenic (human-caused) climate change. First, this awareness helps us to understand why our activities are causing the present-day climate to change, and second, it allows us to distinguish between natural and anthropogenic processes in the climate record of the past 250 years.
- Snowball Earth refers to times when Earth's surface is thought to have been frozen from pole to pole, or nearly so. ↵