(p. 38) . . . the repeated inventions and spread of agriculture around the planet affected not only the surface of the Earth, but its 100-kilometer-wide (60-mile-wide) atmosphere as well. Farming disturbed the soil and increased CO2. Some climatologists believe that this early anthropogenic warming, starting 8,000 years ago, kept a new ice age at bay. Widespread adoption of farming disrupted a natural climate cycle that ordinarily would have refrozen the northernmost portions of the planet by now.
Source:
Kelly, Kevin. What Technology Wants. New York: Viking Adult, 2010.
(Note: ellipsis added.)