...and the problem of the non-linear warming caused by CO2.
In any reasonable scenario, carbon dioxide can’t cause catastrophic global warming by itself. This is because the absorption of infrared radiation by CO2 is non-linear. The first 20 parts per million of CO2 in our atmosphere account for about one-half of the greenhouse warming from CO2. Adding more carbon dioxide has a diminishing warming effect. Doubling atmospheric CO2 from 280 ppm to 560 ppm, whether from natural or man-made causes, would by itself increase Earth’s surface temperature by only about 1.2oC.So how do the climate models reach their alarming conclusions? They assume that positive feedback from water vapor will cause additional warming. The argument is that, since warmer air can hold more moisture, water vapor will increase in the atmosphere as Earth warms. Since water vapor is a greenhouse gas, additional water vapor will add additional warming to that caused by CO2.The assumption of positive feedback from water vapor has been integral to the climate models since the 1960s, when Dr. Syukuro Manabe developed one of the first models. As part of his model, he assumed that global relative humidity remained constant as the atmosphere heated up. This meant that the atmosphere would hold increasing amounts of water vapor, adding additional greenhouse heating to that of carbon dioxide.But, satellite data shows atmospheric water vapor to be relatively constant over the last 30 years. In addition, peer-reviewed papers by Lindzen and Choi (2011) and Spencer and Braswell (2010) show that climate system feedbacks are likely to be low or even negative. Rather than adding to the warming, water vapor and clouds may even act to reduce warming from rising atmospheric CO2.