Of late, there has been a lot of discussion about the validity of the IPCC warming forecasts because global temperatures, particularly when measured by anyone but the GISS, have been flat to declining and have in any case been well under the IPCC median projections.
There has been a lot of debate about the use of various statistical tests, and how far and for how long temperatures need to run well below the forecast line before the forecasts can be considered to be invalid. Beyond the statistical arguments, part of the discussion has been about the actual physical properties of the system (is there a time delay? is heat being stored somewhere?) Part of the discussion has been just silly (IPCC defenders have claimed the forecasts had really, really big error bars, such that they can argue the forecasts are still valid while at the same time calling into question their utility).
Roger Pielke offers an alternative approach to validating these forecasts. For quite a while, he has argued that measuring the changes in ocean heat content is a better way to look for a warming signal than to try to look at a global surface temperature anomaly. He argues:
Heat, unlike temperature at a single level as used to construct a global average surface temperature trend, is a variable in physics that can be assessed at any time period (i.e. a snapshot) to diagnose the climate system heat content. Temperature not only has a time lag, but a single level represents an insignificant amount of mass within the climate system.
What he finds is a hell of a lot of missing heat. In fact, he finds virtually none of the heat that should have been added over the last four years if IPCC estimates of forcing due to CO2 are correct.