Earlier today, I posted on this issue and a lively discussion ensued. I'm happy to have received several responses. As I recall, each of these took issue with one or more of my posting's claims. An administrator inadvertently deleted the thread of our conversation before this conversation reached maturity. Herein, I attempt to restore this thread and solicit responses on it. It has often been argued that anthropogenic global warming (AGM) is "real" because a "consensus" of scientists support belief in it. Under the methdology of science, though, AGM is an example of a theory. Is this theory a scientific theory? This issue is the topic of this thread. Many people argue that AGM is a scientific theory because it is favored by "the consensus" of scientists. In making this argument, these people invoke the logical fallacy of argument from authority; the authorities are the scientists that belong to "the consensus". Many distinguished scientists and scientific organizations belong to "the consensus." Whether "the consensus" represents the view of most scientists is a topic of debate. This debate is interesting but irrelevant. Under the methodology of science, the mark of a theory is not that it is favored by "the consensus" but rather that it is: a) falsifiable and b) not falsified in repeated trials. Is the theory of AGM falsifiable? The theory of AGM is principally manifested in the climate models that are referenced by the United Nations Intergovernmental Panel on Climate Change (IPCC) in its 2007 report. According to the noted climatologist Kevin Trenberth ( "http://blogs.nature.com/climatefeedback/recent_contributors/kevin_trenberth/" ), these models do not make predictions. It follows that: a) the IPCC's models are not falsifiable and b) the IPCC's models are not scientific models, by the definiition of "scientific." A point of confusion seems to be that the IPCC's models make what the IPCC describes as "projections." A "projection" is a mathematical function that maps the time to the computed global average temperature. A "prediction" is a proposition that states the outcome of a statistical event. The descriptions of a "projection" and a "prediction" differ; only a prediction supports falsifiability. The following fictional example illustrates the difference between a "projection" and a "prediction." Suppose that on December 31, 2020 at 24:00 hours Greenwich Mean Time, the global average temperature is measured as 16.3901. At the same time, a model projects that the temperature is 17.3327. Is this model falsified by the evidence or is it not falsified? This question cannot be answered, for the details of the associated statistical event are not described. Climatology is not about the instantaneous values of variables but rather is about about the average values of these variables over time. In the description of the event that is associated with the prediction of temperature, a starting point is to describe the period over which the temperature is averaged. Let us suppose this period is specified. Then, the model projection of 17.3327 on December 31, 2020 at 24:00 GMT must be compared with the average over this period. Now, let us suppose that, over this period, the measured temperature was 17.3302. Does the computed temperature of 17.3327 falsify the model? This question cannot be answered, for the various outcomes of the associated event have not yet been specified. One possibility is for the outcomes to be defined as temperatures. If this is the case, the model is invalidated, for the computed temperature of 17.3327 differs from the measured temperature of 17.3302. Another possibility is for the outcomes to be defined as ranges of temperatures in the sequence 17.3-17.4, 17.4-17.5... In this case, the model is not invalidated, for the projected and measured temperatures fall within the same range. Hopefully, the foregoing exposition provides a sense of the difference between a "projection" and a "prediction." A projection references a statistical event but a projection does no such thing. Predictions are necessary for a model to be falsified but the IPCC's models make "projections." In the reality of scientific investigation, to define an event entails complexities that are additional to the ones I've addressed. I defer elaboration of these complexities until someone asks me about them. One responder to my posting to the now closed thread takes issue with falsifiability as the criterion by which a theory may be identifed as "scientific" or otherwise. Falsifiability is identified as this criterion by the philosopher of science Karl Popper. As I understand it, Popper's criterion is accepted by virtually all modern scientists and philosophers. If the responder has a different view, I'd like to hear about it. Another responder seems to claim that the thermodynamics of radiative physics prove the anthropogenic global warming hypothesis. In science, though, no theory can be proved right. Theories can only be proved wrong. The thermodynamics of radiative physics are a theory and not a fact. More importantly, thermodynamics is of limited utility in modeling the climate, for thermodynamics describes nature only at thermodynamic equilibrium but the climate system is far from equilibrium. Among the many phenomena at disequilibrium are the albedos (reflectivities of solar radiation) of clouds and the viscosities of fluids.