Global warming

For this week’s reflective writing, we would like you to consider how the albedo changes in each of the following scenarios would change global temperature. Explain your reasoning in each case. In each case, you will need to refer to the following table of typical albedos.

Albedo Approximate Values:
Glacial ice:         a=0.80
Ocean Surface:  a=0.07
Marine Stratus Clouds: Highly variable, but a=0.60 is a reasonable number.
Desert Sand:      a=0.40
Grasslands:        a=0.20
Bare rock:          a=0.30

Scenario #1: As the Earth warms, we observe that most of the glaciers and ice sheets on Earth have been getting smaller. About 10% of the land surface of Earth is covered by glaciers and ice sheets, with most of this ice on Greenland and Antarctica. Suppose that all of this ice were to melt. How would this change the Earth’s albedo? And how would we expect the Earth’s temperature to change as a result of this change in albedo? Why would you expect to see this type of change? (you will need to use some of the numbers in the table to answer this question).

Scenario #2: Many lines of evidence indicate that about 6000 years ago, the Sahara desert was not a desert, but was instead a vast savannah (a grassland ecosystem). Some of the more dramatic evidence of this “Green Sahara” period include fossils of giraffes and elephants, animals that do not live in the Sahara today because it is a desert. When this green savannah ecosystem dried and became the enormous desert that it is today, what effect did this have on the Earth’s albedo? And how do you expect that this change affected global temperatures? Why would you expect to see this type of change?

Scenario #3:  If you have lived in San Francisco for long, you probably know that a thick deck of low-lying clouds often forms over the ocean off the California coast. We call this feature a “marine stratus cloud deck” (stratus clouds are a type of low-lying cloud that have a large horizontal extent and a uniform base height). Stratus clouds tend to be pretty reflective. The albedo of clouds in general is quite variable, and depends on how thick the clouds are, but let’s estimate the albedo of these stratus clouds as a=0.6. Now let’s suppose something were to happen that decreased the amount of stratus clouds that formed off the California coast.  How would you expect this to change the average albedo of the Earth? And how would this change the average temperature of the Earth? Explain your logic. (to answer this question you will also need the albedo of the ocean surface from the table below)

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