On NOVA lastnight they were discussing how air-borne pollution in the atmosphere is dimming the sunlight and having a measurable affect on the amount of heat reaching us from the sun. Some were of the opinion this was good because is counters global warming...but one leading researcher has a theory that it has made us underestimate how sensitive the planet is to CO2 & other greenhouse gases. We have been measuring the net rate of global temp changes, not the amount from greenhouse gases by themselves. As CO2 levels continue to rise as sunlight blocking pollutants level off, there could then be a sudden increase in global temps, resulting in not 1-3 ft ocean level increases, but more like 10-25 meter rises in the next 50 years. At a certain global average temp, the polar permafrost will thaw and decay, releasing extremely large quantities of CO2. As ocean temps rise, there will be a point where vast amounts of methane will be relesed from the sea floor...methane is much more potent at trapping infrared.

The real question is: are we approaching, at or past the tipping point...?