The earth's crust is thinnest at the bottom of the ocean. It has been like that for a long time. Magma will not suddenly cool over 5 years allowing the ocean to cool. Convection currents keep the magma at a more uniform temperature. Further, if the ocean does cool, it would be the area just by the ocean floor that was not monitored.
About the rain, are you suggesting that the amount of evaporation suddenly increased without an associated increase in solar energy reaching the oceans and lakes?
Why in all this supposition did you not conjecture that increased cloud cover reflected more of the sun's rays to space? That is the most obvious and most likely. Instead, you go toward the extreme suggesting sudden changes in magma temperature over short time scales and large increases in evaporation when the temperature has not increased.
