Chapter 3 provides an overview of the history of Earth’s climate and how various different geological processes have contributed to climate change in the past. The topics covered include:
|3.1 Changes in Solar Output and in the Earth’s Atmosphere||The sun has increased in intensity by almost 40% since the formation of the solar system 4.57 billion years ago. Because of the presence of life on Earth, and because of changes in the physiology of life forms, our atmosphere has evolved over this time so that a reasonable temperature has been maintained. This has been achieved primarily through changes to the greenhouse gas content of the atmosphere.|
|3.2 Plate Tectonics and Climate Change||Plate tectonics has had a dramatic control over the Earth’s temperature. Some of the important changes include: the distribution of the continents (near to the equator vs near to the poles), the formation of mountain ranges (which promotes weathering and consumption of atmospheric CO2), and changes to the patterns of ocean currents.|
|3.3 Volcanism and Climate Change||Volcanism affects our climate, both on a short time scale (years to decades) because the sulphate aerosols produced by major eruptions block sunlight, and on a much longer time scale (millennia to millions of years) because of the slow buildup of CO2 in the atmosphere.|
|3.4 Earth’s Orbital Fluctuations and Climate Change||Milanković cycles affect the Earth’s climate on the time scale of tens of thousands of years because they lead to changes in much solar insolation is received at different latitudes and at different times of the year. These variations have controlled glacial cycles over the past million years.|
|3.5 Ocean Currents and Climate Change||Ocean currents are responsible for moving heat around on the Earth’s surface. They can vary as a result of changes to the salinity of ocean water and those variations can have significant climate effects on the scale of thousands of years.|
|3.6 Extraterrestrial Impacts and Climate Change||Impacts from large extraterrestrial objects (> 1 km in diameter) are rare, but they can have devastating climate impacts.|
Answers for the review questions can be found in Appendix 1
- Why is the sun getting hotter, and does this have anything to do with climate change over the past century?
- What function of life on Earth has been critical in ensuring that the temperature has remained relatively stable over billions of years, in spite of a warming sun?
- In the context of global temperatures, why does it matter if the continents are concentrated mostly near to the equator or distributed more evenly across the latitudes?
- How does the existence of large mountain ranges affect the composition of the Earth’s atmosphere?
- The Antarctic Circumpolar Current started up at about 35 Ma. How did that affect the climate of Antarctica?
- From a climate perspective, the two most important volcanic gases are CO2 and SO2. What happens to the SO2 in the atmosphere, and what are the climate implications?
- What would it take for the CO2 emissions from volcanism to lead to significant climate change?
- Since the Milankovitch cycles don’t affect how much solar energy reaches the Earth as a whole in any given year, how do they control our climate?
- Based on Figure 3.4.3, how would you describe the trend of insolation at 65° N over the past 10,000 years, and how does this correlate with the actual temperature record over this period?
- The density of sea water is determined by its temperature and by the amount of salt dissolved in it. What are the implications of that relationship for the strength of the Gulf Stream, and might would a weakening of the Gulf Stream affect the climate of western Europe?
- What would be the overall implications for Earth’s climate if the ocean currents were to become generally weaker than they are now?
- Describe what you might have experienced if you had been living the middle part of North America on the first day of the Paleogene. If you did survive that day, what would conditions have been like over the next few months?