The saturation effect, the nonlinear, logarithmic relationship between greenhouse gas (GHG) forcing and increases in atmospheric concentrations of carbon dioxide (CO2), is an important scientific point for the climate debate. Diminishing returns is not as well known as it should be because of a media blackout on its negative implications for CO2 mitigation (reduction) efforts.
The log relationship means that the warming from a doubling of CO2 is not repeated at a tripling but at a quadrupling. This diminishes the fear of future increases that are in severe diminishing returns. This is an optimistic point to not sweat CO2 buildup this century or even next. And if global greening is applauded, the opposite of worry is reasonable.
I asked Randal Utech to do the math on the diminishment of CO2 forcing today (420 parts per million) versus in the late 1980s (at 350 ppm) when the climate debate took off. His result: a metric ton of CO2 reduction today is 18 percent less effective than a metric ton of CO2 reduction made in 1989. And this will continue with future PPM increases.
1) So the CO2 forcing between pre-industrial (280 ppm) and today (420 ppm) is about 2.16 Watts per square meter.
2) The forcing for a 70 ppm change from 280 ppm to 350ppm is 1.19 W per square meter.
3) The CO2 forcing of a 70 ppm increase from 350 ppm to 420 ppm is 0.97 watts per square meter.
The change in 70 ppm forcing going from 2) -> 3) is 82%, so in equivalent, forcing reduction of approximately 18%.
Advocates of mitigation make two points in response. First, GHG forcing is still positive. Second, increasing global CO2 emissions make the forcing line linear.
The fact remains that mitigation is a losing proposition over time, elevating the relative importance of adaptation to extreme weather events (whatever the cause). And as adaption takes place over time, the feared negative externality of CO2 emissions is diminished.
Wealth-is-health free markets, anyone?