Secondly, Lin disagrees with Lindzen’s proposed physical model of the clouds themselves. “Deep convective clouds very strongly reflect sunlight back to space,” he states, “but their relative area of coverage is small.” Cirrus clouds, on the other hand, are very extensive and cover large areas. They can be thin enough to allow sunlight to pass through, or they can also have a high reflectivity. Cirrus provides a much larger “canopy” over the tropics so, from a radiative perspective, those clouds are actually more important than deep cumulus clouds.
The third major disagreement between Lin’s and Lindzen’s
experiments pertains to the amount of heat escaping from cloudy regions. CERES
measurements reveal that 155 Watts per square meter escaped the atmosphere over
cloudy, moist regions, which is significantly more than the 138 Watts per square
meter that Lindzen’s team assumed (Lin et al. 2001).
Different types of clouds have different effects on the balance of energy received and emitted by the Earth. In areas covered by the cumulus towers of a thunderstorm’s convective core (left) almost all the Sun’s energy is reflected. The cold cloud tops radiate very little energy out into space. Cirrus clouds (the cloudy and moist region, center), on the other hand, reflect some shortwave energy, but let some through to the surface. Likewise, they emit some heat (longwave energy) but redirect some back to the surface. Clear and dry regions (right) are almost the inverse of convective cores— most of the solar energy is absorbed by the surface, much of which is eventually emitted as thermal infrared radiation back out to space. In the clear regions, reflected energy increases as low level clouds increase, while as humidity increases less longwave energy is emitted. (Image by Robert Simmon)
In summary, Lindzen’s team suggests that higher sea surface temperatures lead to less cloudy, moist skies and a corresponding increase in clear, dry skies. Lin disagrees with Lindzen’s interpretation of the cloud physics. In their paper, Lin’s team wrote that the much smaller albedo and lower outgoing heat flux assumed by Lindzen exaggerated the cooling effects of the outgoing radiation over cloudy, moist regions while minimizing the warming effects of incoming sunlight through regions covered by cirrus (Lin et al. 2001). Based upon CERES data, Lin’s team concluded that the reduction in cloudy, moist skies allows extra sunlight to warm the surface by up to 1.8 Watts per square meter—a small but positive net energy flux (Lin et al. 2001).
“Our results are based upon actual observations that are used to drive global climate models,” Lin concludes. “And when we use actual observations from CERES we find that the Iris Hypothesis won’t work.”
In the graphic on the left, “L” refers to Lindzen’s team and “C” refers to Chambers and Lin. Both teams used the same equations to predict climate change, but they used different data sources and made different assumptions for the values of some variables that model the behavior of clouds. The table at left shows the contrasting values used by the teams. The most important differences were in the cloudy and moist region. Lindzen et al. used an albedo of 0.35 while Chambers et al. used an albedo of 0.47. Values of net flux for the region were 123 W/m2 for Lindzen and 46 W/m2 for Chambers. (Table by Robert Simmon)