The difference in absorbed radiation from the uncovered surface is 136 Wm-2. Using this value, we can now calculate how much desert surface would need to be covered to offset a given level of planetary radiative forcing. This is done by taking the total watts for a given level of planetary forcing and dividing it by 136 Wm-2. Examples are shown in the table below for 2010-2070 as well as for other relevant periods. The areas have been converted to square miles using the factor 2.61 Km2/mi2.

Forcing, Wm-2 Planetary W x 1015 Million Sq. Miles

0.20a 0.102 0.29

0.27b 0.138 0.39

1 0.510 1.4

1.36c 0.694 2.0

2 1.020 2.9

2.48d 1.265 3.6

2.75e 1.403 4.0

5.43f 2.769 7.9

a U.S. Kyoto target for 2012

b U.S. electric power generation 1750-2070 (25% of 20% of 5.43)

c U.S. all forcing 1750-2070 (25% of 5.43)

d all forcing 1750-2000

e all forcing 2010-2070

f all forcing 1750-2070

The U.S. target for Kyoto was calculated by assuming a 25% allocation to the U.S. for all forcing from 1750-2000 or 0.62 Wm-2 and an additional 0.02 Wm-2/year for 2000-2012 with the same allocation or 0.05 Wm-2 for a total of 0.67 Wm-2. Reducing this by 30%, about the equivalent of meeting the Kyoto target, gives 0.20 Wm-2.

Averaged over 60 years and beginning in 2010, the number of square miles per year to be covered to achieve some of these forcing reductions is as follows:

Forcing, Wm-2 Square Miles/Year

0.27 6,500

1 23,333

1.36 22,667

2 48,333

2.75 66,667

5.43 131,333

To offset all new forcing over the period 2010-2070 will require the covering of nearly 67,000 square miles per year, an area about the size of North Dakota or Missouri. By comparison, around 61,000 square miles in the U.S. are devoted to roads and parking lots and 80,000 square miles of U.S. soil is planted in wheat alone each year (120).