As Robert Pindyck, recently explained in US National Bureau of Economic Research working paper 19244, "Climate Change Policy: What do the models tell us?": “the physical mechanisms that determine climate sensitivity involve crucial feedback loops, and the parameter values that determine the strength of those feed-back loops are largely unknown.”

And “when it comes to the impact of climate change, we know even less. IAM [integrated assessment model] damage functions are completely made up, with no theoretical or empirical foundation. They simply reflect common beliefs (which might be wrong) regarding the impact of 2C or 3C degrees of warming, and can tell us nothing about what might happen if the temperature increases by 5C or more."

For me, perhaps the biggest deception here is notion that we can concoct statistical artefacts – more accurately “arte-fictions” - like “global temperature” and hoodwink public into believing it can be “measured” to two decimal places, with an accuracy of less than one-tenth of a degree.

http://www.realclimate.org/index.php/archives/2013/09/what-ocean-heating-reveals-about-global-warming/

"Ideologically motivated “climate skeptics” know that these data contradict their claims, and respond … by rejecting the measurements...."