The theory is so simple yet so apparently wrong. Firstly, conservation of energy. The input from the sun never changes outside its own variations. There is a limit to the amount of heat 'generated' by holding what goes in and stopping it from coming out. Surely this alone creates huge warning bells as the moon, with no effective atmosphere, can reach 100F at the equator simply by absorbing the heat by convection. Not turning as our planet does it is daytime the whole time and a good control sample of the temperature on a body without a greenhouse effect. Climatologists appear to have forgotten what I could call the 'direct heating effect', one we also share here every single day before the sun goes down.
Secondly, there is simply no known example in past records where a rise in temperature from all causes creates a corresponding rise in water vapour, which then produces a feedback loop. In fact this relies on a massive dwell time for water vapour (answers needed here), and apparently ignores the actual water cycle where the water evaporates, forms clouds and then falls back as rain. So in reality we already know the routine where from all evaporating sea a proportion dwells as water vapour (how much and how long for?) while the rest falls back as rain.
Thirdly what does water vapour make? Clouds. One of the greatest causes of negative feedback. Stormy weather involves warming of the sea, the fast evaporation causing storm clouds, and within an hour or so (the observable dwell time and cycle by anyone on a hot day) falls back as a storm. How much of a not 1C but maybe 10C rise stays up there while the rest falls back almost immediately in climate terms? And the usual slow version produces white fluffy clouds which before they rain (if they do) block out the sun and reflect the heat back to space, as negative feedback. Current research admits the lack of knowledge on cloud formation from evaporation so pretty much a wild card, yet Hansen acts as if it doesn't exist (try measuring the temperature in the shade compared to the sun, that is wilful blindness to the extreme).
On top of this, Hansen's theory relies on the sea storing heat and having some sort of as yet unknown delay mechanism stopping it from releasing it as it is gradually heated by what he thought would be global warming. Simply watching puddles after a storm gradually evaporating shows that if a body of water evaporates evenly over an observable period that is what it always does. The sea hasn't changed its physical properties over a certain area, and he hasn't actually tried to claim it has, but the storage effect he claims implies just that, and could still be used as the final excuse why no feedback has ever been observed over 150 years. Also there was never a delay built in to his predictions. The feedback was supposed to be steady, following standard Newtonian laws of heat transferring from a warmer body (the sea) to a cooler one (the air) until an equilibrium was reached. Therefore any delay breaches any of Newton's laws you care to mention.
The knowns here appear to have already sewn up Hansen's theory. He has a PhD, not in climatology but computer modelling (much in the realm of astrology), and has cobbled this simplistic childlike view and convinced the world's powers it is 99% accurate although my O level physics and a little further research makes it look virtually impossible. The small amount of water vapour from a 1C rise can be measured roughly (help please!) and then fed into the water cycle to use the known amounts of returning rain and remaining vapour to pretty well work out the total feedback if any. The cloud cover is only likely to cancel the mechanism altogether, and observation shows with the 50% rise of CO2 the IPCC assign half the 0.8C to that, the rest being natural. Any CO2 greenhouse effect has clearly not just found no feedback but a slightly negative one, yet the authorities are acting as though current observations mean nothing while Hansen's goldmine is the one everyone has accepted unchallenged.
I will add this particular colon also has an appendix, something possibly added in desperation in case more people realise the first theory (literally) holds no water. The idea that methane stored in polar ice will be released when it melts, thus adding a far more powerful greenhouse gas, is also so different from the truth it bears no merit on close scrutiny. Methane is quite unlike CO2. It is not measured in parts per million, but parts per billion. Unlike CO2 it is pretty quick to react with oxygen, releasing CO2 (so little as not to be significant) and water. That is why there is so little in the atmosphere, as however fast the relatively minuscule amounts are released, the air simply mops most of it up. However, the second part of the theory relies on melting ice at unprecedented rates. Melting ice requires higher temperatures, not vice versa, and without a significant rise (2-3C according to the IPCC) it won't be happening in our lifetimes or our childrens' (again, the IPCC are looking to around 2100 and that is only their personal computer model, the actual results so far are well below it since the early 1990s). So the methane is truly a red herring anyone seriously involved with science should steer well clear of.
Update, the 2013 IPCC report has now removed the threat from methane.