Managed Global Warming
This issue of Scientific American includes an article titled:
"How Did Humans First Alter Global Climate"
by William F. Ruddiman.
The author points out that three varying cycles occur as the Earth orbits the sun. The Earth's axis of rotation changes direction over time, the distance from the Earth to the Sun at mid-summer varies, and the shape of the Earth's orbit pulsates. These different influences combine, sometimes reinforcing each other, sometimes cancelling each other out. The end result is a repeating pattern of varied amounts of sunlight falling on each region of the Earth during a season. Long sequences of warm seasons in the Northern hemisphere correspond with global warming intervals, while long sequences of cold seasons align with ice ages. This pattern extends back for millions of years.
However, 8000 years ago the pattern broke. The Earth's orbital variations are all acting as expected, and tempertures had begun to fall as expected for the next ice age, then they reversed. The interesting observation is that humans started farming at this time. So the theory is that agriculture has delayed the onset of the next ice age.
We are moving further into an orbital situation that is influencing the Earth to drop its average temperature, while we are pumping out green house gases that cause a temperature increase. If we stop releasing these gases abruptly we will witness a very rapid temperature fall to a level well below today's normal - an instant ice age.
So we don't want to merely stop producing green house gases. We have to reduce them, but just enough to get back to livable levels. We are now stuck with the eternal task of maintaining a constant temperature on a planet where orbital variations tend to change the temperature a lot.