I am not a physicist but a retired physician and part time NHS bureaucrat. This paper:

http://pielkeclimatesci.wordpress.com/2005/07/18/what-does-moist-enthalpy-tell-us/

discussed the use of enthalpy as a more appropriate measure of global heat content. It is 45 years since I did A level physics but it seems to make sense to me!
Any thoughts anyone?
Are there data on enthalpy?

Pielke is addressing the topic of latent heat, primarily due to evaporation of water but similar considerations exist where there is ice (and also work done such as photosynthesis). As he points out, temperature is an incomplete measurement of heat. This is usually dealt with by saying that the heat will reappear (possibly in a different location) when the water condenses again, which is true. So while it can make a large short term difference to regional temperature, globally it should average out to zero over time because no significant water leaves the planet.

Of course IPCC modellers and supporters know all this. But only now do they choose to emphasise it a bit more to downplay the importance of temperature measurements when they are not rising as predicted. They also like to give heat quantities in joules because it allows them to quote some big numbers which they think will impress or scare others.

But, but, but....The problem in using heat content/enthalpy is in the calculation: you still need to take temperature measurements, so there is no way to avoid the inherent difficulties. And measurements of the earth's total radiation balance have even bigger uncertainties. So any assertions you see are still based on temperature measurements with some extra calculations and modelling of certain assumptions. It goes without saying that the derived claims are no more reliable (and probably less so) than claims made about temperatures.