Junk science is generally defined as faulty data or incorrect analysis used to promote a false sense of scientific certainty in support of an agenda driven hypothesis. More often than not, the agenda matters only to the researcher and they're simply fooling themselves by seeing what they want to see. If the agenda is widespread, junk science can take on a life of it's own. Intelligent design and free energy physics are examples of junk science that has gone this route. The danger of a shared agenda is that many believe that consensus means correctness and if the science is complex and the agenda widespread, a faith based belief justified by the consensus drives the development of a consensus of believers. The junk science transforms itself into a religion, at which point scientific rigor no longer matters and the views of a heretic carry no weight.
If the scientific arguments supporting the Anthropomorphic Greenhouse Warming hypothesis are examined for the signatures of junk science, the results are revealing. The results are also quite disturbing as they show how AGW pseudo science has already transformed itself to a religious belief.
The foundation of the AGW case is the presumed fact that changes in greenhouse gas concentrations drive the climate and that nothing else matters. Nowhere in the literature is this quantifiably justified by the first principles of physics. None the less, it's universally referred too as an indisputable fact which is beyond debate. Scientists understand that nothing is beyond debate. To paraphrase Einstein, no amount of experimentation can prove a hypothesis right, but a single experiment can prove it wrong. Statements which proclaim no need for debate frequently appear in junk science dissertations and are a futile attempt to mitigate a weak case.
The ice core correlation analysis shows that greenhouse gases are trailing indicators of climate change and not leading indicators. Those AGW proponents who understand the analysis rarely dispute the measured relationships. Instead, they make up math, physics and excuses in order to spin the data to fit their hypothesis. This is yet another common tactic used to support junk science.
Another junk science technique is to start with something that's less controversial and obfuscate a path from it to something else. For example, the IPCC heuristic that predicts about 3.7 W/m^2 of forcing power by doubling CO2 from its baseline value, is loosely based on atmospheric absorption physics and represents a reasonable, yet conservative, upper bound. In contrast, the IPCC's climate sensitivity heuristic converting this forcing power into a temperature change has no scientific basis whatsoever and is actually in conflict with known physics, moreover; the results from models based on this heuristic are held up as the proof that AGW is real. Examining this equation reveals it's meaning to be that temperature changes force additional temperature changes, independent of what caused the change in the first place. Quantifiably, it says that if additional forcing energy increases the temperature by 0.5 degrees, an unspecified empiricly divined amplification factor will increase the temperature by an additional 2.5 to 5.5 degrees. The divined coefficient is derived from the relationship between CO2 and temperature during the transition out of the last ice age assuming that CO2 concentration changes provide amplification of the changes in incident solar energy. The confirming derivation uses the presumed temperature change since the start of the Industrial Revolution to estimate a sensitivity factor assuming that CO2 caused the change and then adds a healthy margin to account for another assumption that there's deferred climate change that's been set in motion by the CO2 increase, but not yet realized. Both methods indirectly set the amplification factor to match that required to make the underlying assumptions true. Using an assumption to make a case to prove the assumption is another clear indication of junk science.
Finally, whenever you confront an AGW proponent with a compelling scientific argument that goes against their beliefs, they get defensive, hostile, belligerent and resort to deprecation and insults. This is the common reaction of any zealot promoting faith based junk science when confronted with evidence to the contrary. To an extent, this is an understandable human reaction, as nobody who is so completely vested in a belief wants to see the foundation of that belief crumble away.
Considering that we are on the verge of spending trillions of dollars on an experiment to verify the validity of a hypothesis supported only by junk science is not only irresponsible, it's insane.