The Missing Heat
It is possible for the theory that the climate has a high sensitivity to CO2 (ie that a doubling of CO2 concentrations will lead to global temperature increases of 2.5C or higher) to be correct while still having ten years of flat to declining surface temperatures. That is because Earth's great surface heat reservoir is the oceans, not the atmosphere, and so the extra heat from the greenhouse effect could be going into the oceans rather than into near-surface air.
However, it is NOT possible, as least as we (and by "we" I mean everyone, skeptics and alarmists alike) understand the climate, for CO2 to be holding a lot of extra heat and it not show up either in surface temperatures or ocean heat content. The greenhouse effect does not turn off -- its effects may be masked in the chaotic weather systems, perhaps for years, but if the climate sensitivity to CO2 is really as high as the IPCC says, there has to be new heat going somewhere.
That is why a number of folks, including Roger Pielke, have argued for years that the best way to monitor whether we are truly seeing an additional forcing or heat input to the climate is to look at ocean heat content. Understand, changes in ocean heat content would not tell us where the heat is coming from (e.g. anthropogenic CO2 vs. solar activity). But it is pretty much impossible for us to imagine a new heat input to the Earth's surface, like greenhouse gas forcing from anthropogenic CO2, without observing its effect in ocean heat content.
I will turn over the story to Jo Nova, who has a good post on the new tools we have to measure ocean heat content since 2003. In short, though, we have seen no rise in measured ocean heat content since we started measuring with technology dedicated to the task. This means, if those who believe the climate has a high sensitivity to CO2 are right, something like 50,000 quintillion joules of energy have gone missing since 2003. This is the "missing heat", and though climate scientists sometimes discuss it in private, they almost never do so in public. Ocean heat is the dinosaur bone fossil that the creationists simply don't want to acknowledge.
Read the whole thing. It is very simple and well-written and written.
PS- note in the chart above, the y-axis is mis-labelled a bit, it is not absolute heat content but changes in heat content from some base period. Scientists call this the "anomaly." This is typical of many climate charts.
