Over the last 15 years, we've been told that human CO2 emissions would cause global warming to accelerate to new dangerous levels, and this "unequivocal" warming would generate fantastic, catastrophic climate change disasters - the IPCC's climate models told us this, and truth be told, they were absolutely and spectacularly wrong.
As the U.S. has baked during the hot summer of 2012, the rest of the globe has been treading water, so to speak. As the HadCRUT global temperature chart above shows, the large growth in atmospheric CO2 levels continues. Yet the 15-year trend of stable to a slight global cooling remains.
This extended 180-month period of non-warming was not predicted by a single global climate model.
The IPCC's climate models obviously have very serious, fundamental issues that can't just be 'tweaked' away. The most serious issue is their being CO2-centric, thus minimizing other factors (i.e., forcings) that influence temperatures and climate. Water vapor and solar variation don’t even make it into the IPCC computer climate models.
From recent experience, it is quite clear that the climate models' sensitivity to CO2 levels is likely to be way overstated - in other words, the climate is not as sensitive to CO2 as the programmers thought.