Re: Antactica is melting too
Positive forcing refers to the AGW theory that CO2 concentration will reach a tipping point where the earth's climate will "run away". Part of the theory involves the water cycle. A doubling of CO2 results in 1°C increase in temperature. That means from 200ppm to 400ppm results in 1°C increase. 400ppm to 800ppm results in another 1°C increase. 800ppm to 1600ppm add another 1°C increase.
AGW is attempting to convince us that somewhere between 400ppm and 800ppm the temperature increase will be much larger than 1°C due to other effects, such as an increase in evaporation which increases water vapor in the air. Water vapor, which is a much more potent greenhouse gas than CO2, will then cause the global mean temperature to increase much faster and eventually "run away". Currently the water cycle acts to moderate global temperatures. The water cycle/temperature is stable (negative forcing). AGW is trying to convince us that there is some critical mean global temperature at which the water cycle will become unstable (positive forcing) and cause all of these global catastrophes.