44 Climate Management Issues
consistently experienced an ice age. Since the last ice age, CO
2
levels remained
fairly constant, however, until the Industrial Revolution, when billions of
tons of extra CO
2
began to be added to the earth’s atmosphere.
The turning point was the use of fossil fuels—coal, oil, and gas—made
from the carbon of plants and animals that decomposed millions of years
ago and were buried deep under the earth’s surface, subjected to enormous
amounts of heat and pressure. When this carbon is converted into usable
energy forms and is burned as fuel, the carbon combines with oxygen and
releases enormous amounts of CO
2
into the atmosphere.
According to NASA/GISS, CO
2
levels have not been as high as they are
today over