It never existed.
The trouble is that this energy was not showing up in any measurements which led to Trenberth’s well publicised “travesty” comment in an email published as a result of the “Climategate” leaks which stated: “The fact is that we can’t account for the lack of warming at the moment and it is a travesty that we can’t”.
Knox and Douglass analysed Argo float temperature data for the period from 2003 to 2008 to estimate changes in ocean heat content (OHC). They state that “Our four estimates of the recent OHC trend for 2003–2008 adequately consider interannual variability and we find that the trend is negative”. That is that the ocean heat content has been falling and not increasing.
It is clear from their paper that Knox and Douglass believe that there is no missing energy and that the problem of missing energy is an artifact caused by a “serious overestimate” by Trenberth and Fasullo of the radiation imbalance at the top of the Earth’s atmosphere. Essentially, they are saying that there is no positive radiation imbalance and therefore no need to assume that a store of energy is being built up in the oceans – with the clear implication, although not explicitly stated in their paper, that the Earth may not be not warming.
h/t to Marc Morano