Cloud-radiative forcing and climate: results from the Earth radiation budget experiment
Authors: V Ramanathan
P Minnis
E Ahmad
R D Cess
B R Barkstrom
D Hartmann
E F Harrison
Journal: Science (1989)
Discipline: Multidisciplinary
Keywords: climate; climate change; clouds; radiation balance; cloud-radiative forcing

Abstract:  The study of climate and climate change is hindered by a lack of information on the effect of clouds on the radiation balance of the earth, referred to as the cloud-radiative forcing. Quantitative estimates of the global distributions of cloud-radiative forcing have been obtained from the spaceborne Earth Radiation Budget Experiment (ERBE) launched in 1984. For the April 1985 period, the global shortwave cloud forcing [-44.5 watts per square meter (W/m(2))] due to the enhancement of planetary albedo, exceeded in magnitude the longwave cloud forcing (31.3 W/m(2)) resulting from the greenhouse effect of clouds. Thus, clouds had a net cooling effect on the earth. This cooling effect is large over the mid-and high-latitude oceans, with values reaching -100 W/m(2). The monthly averaged longwave cloud forcing reached maximum values of 50 to 100 W/m(2) over the convectively disturbed regions of the tropics. However, this heating effect is nearly canceled by a correspondingly large negative shortwave cloud forcing, which indicates the delicately balanced state of the tropics. The size of the observed net cloud forcing is about four times as large as the expected value of radiative forcing from a doubling of CO(2). The shortwave and longwave components of cloud forcing are about ten times as large as those for a CO(2) doubling. Hence, small changes in the cloud-radiative forcing fields can play a significant role as a climate feedback mechanism. For example, during past glaciations a migration toward the equator of the field of strong, negative cloud-radiative forcing, in response to a similar migration of cooler waters, could have significantly amplified oceanic cooling and continental glaciation. 

Retracted: No

PubPeer comments:
 I am afraid the article, and many following on the subject, contains a pivotal logical blunder. Delicately it affects the core of climate science and climate models. ![file] There is no further information on how this logic has evolved, or if it was taken from earlier papers. Rather it seems like the authors suggest to only name the obvious, so that there would be no need for any discussion. My subjection is especially on the equation (2), C = H - Hclr. This approach is naturally illicit when dealing with redundant systems. For instance, if A causes an outcome X, and B causes an outcome X and thus X is overdetermined, one could find A does not really affect the outcome. Even if A was not given, the outcome X would still be granted. Asking  what difference does A make would falsely suggest A would not contribute to outcome X. The same of course happens if one asks  what difference does B make . *In sum, redundancy constitutes a challenge for theories of causality. While various amendments have been proposed, both from within and with-out the difference-making framework, an uncontroversial solution is yet to be offered. Finding an appropriate distinction between preempting and pre-empted causes remains an open problem in the philosophy of causation*1 Allocating causation within redundant systems remains an unsolved problem of epistemology. In the above context X is caused by A and B, and there is no way to split up causation among the two factors. And most obviously it would be completely wrong to deny causation by A or B, just because they  would not make any difference . Equation (2) explicitly applies such a logic, by asking  what difference do clouds make . As far as clouds are overlapped with GHGs (and aerosols) in the way they reduce radiative emissions (or expand  radiative heating respectively), equation (2) is blind to the redundant component. Naturally clouds and GHGs are significantly overlapped, which can easily be demonstrated with the help of modtran2. Loading the default preset with a  tropical atmosphere gives an  upward IR heat flux of 298.52W m2. Adding the cloud scenario  Altostratus Cloud Base 2.4km Top 3.0km will reduce emissions to 269.004W m2. Applying equation (2) on this instance will result in a cloud forcing of 298.52 - 269.004 = 29.516W m2. If we set all the six available parameters on GHG concentration (CO2, CH4, T. Ozone. S. Ozone, Vapor, Freon) to zero, the model suggests emissions of 443.682W m2 without clouds. But if we add the same cloud scenario as before, emissions drop to 350.738W m2. Equation (2) now suggests a cloud forcing of 92.944W m2. Accordingly 92.944 - 29.516 = 63.428W m2 of actual cloud forcing are overlapped with GHGs and can not be detected or  seen in the presence of GHGs with equation (2). Despite this being just a model, it does capture a very real problem. Most of (real) cloud forcing is indeed overlapped with GHGs, and applying equation (2) on satellite data will massively underestimate it. Furthermore the erroneous logic implicitly allocates all the causation of the redundant component (only) to GHGs, thereby overstating their significance. Yet one could  excuse this as being just a kind of working hypothesis, with the authors well aware they did not capture  causation correctly here. However, already in the introduction the article is very explicit.. ![file]  Thus, clouds had a net cooling effect on the earth . This conclusion is baseless (and actually wrong). (http: climatemodels.uchicago.edu modtran modtran.html) , 
 * **This approach is naturally illicit when dealing with redundant systems.** * I don t think you know what some of these terms mean or are using them improperly. First, the article does not mention redundancy. Second, a redundant system is typically comprised of components of which some are intended to provide equivalent behavior should one behavior stop being operational. So one were to assume that there is some behavior that you propose to replace clouds that will give the equivalent behavior of clouds should they disappear. Maybe  more clouds is your redundancy, as in the Doritos tag-line from years ago * Crunch all you want, we ll make more * ? ,