Overview
The world is warming up very quickly. Since the 1970s, surface temperature has risen about 1 Celsius in a nearly unbroken linear trend. Warming is substantially faster on land than over oceans. Sea ice is melting very quickly and the ice sheets of Greenland and Antarctica are getting smaller. Increasing evaporation over warmer oceans and the greeter water-holding capacity of the air has produced unmistakable upward trends in atmospheric water vapor, a strong greenhouse gas that amplifies global warming. Global precipitation has increased too, but regional differences in rainfall show that some regions experience more and some experience less. The frequency of very heavy rainfall has increased. The distribution of temperatures has shifted and temperatures that were unusually hot a few decades ago are much more common now
Learning Objectives
Upon completion of this module you should be able to:
- Describe the global distribution and magnitude of observed changes in temperature, precipitation, water vapor, ice and snow, and sea level that have been observed around the world over the past century.
- Explain why there has been more warming in some parts of the world than others.
- Give examples of regions that have experienced increases and decreases in precipitation associated with warming.
- Explain the occurrence and impact of changes in extreme rainfall in some regions of the United States.
- Compute changes in means and extremes; describe how small changes in means can lead to significant changes in extremes.
Readings
Module 6: Recent Climate Change [PDF]
Observations [Schmittner OER Chapter 2]
USGCRP, 2017: Climate Science Special Report: Fourth National Climate Assessment, Volume I [Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart, and T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, 470 pp, doi: 10.7930/J0J964J6.
- Pages 185-194 (Chapter 6)
- Pages 207-215 (Chapter 7)
Slide Deck / Lecture
Review Questions
- What is the Intergovernmental Panel on Climate Change (IPCC)? What is the US National Climate Assessment (NCA)? How are the two groups similar and different? What are some of their key conclusions?
- Compare/contrast the rate of warming on land vs over the oceans. What physical mechanisms can explain the difference?
- How much global warming in the past few centuries is attributed to changes in greenhouse gases and pollution particles, as opposed to natural cycles or other causes?
- How much has global average sea levels risen in the past couple of centuries?
- By about what percentage has the extent of summer sea ice cover in the Arctic Ocean decreased over the past century?
- Propose a mechanism for the observed trends in the amount of water vapor in the atmosphere. What does the observed trend tell us about climate feedback and sensitivity?
- Describe some geographic patterns in temperature and precipitation trends around the world.
- Explain what statisticians mean by the “normal distribution,” and use the concept to describe observed trends in summertime temperatures over land in the past 60 years.
- Annual average temperatures in the United States increased by about how much over the past century?
- Describe changes in the frequency of very heavy rainfall in the United States and explain why they are happening.
