I follow Prof Sobel's logic about the tracking of SST and tropospheric temperature as show in figure 1, but there is a major divergence in the 1991 - 1992 time frame: the tropospheric temperature curve decreased and remained below the SST curve for seveal years. Is there an explanation for this (e.g., Pinatubo)? This does not seem to be addressed in this article, and detracts from the central points (without an explanation, which could clarify the divergence). Thanks!