Of course it was caused by global warming...if you drive your SUV to work everyday Tonga will get wiped out on May 23, 2205.
To be fair, the global warming connection to tsunamis is supposed to be that rising sea levels make places like Tonga more SUSCEPTIBLE to tsunamis, not that global warming CAUSES tsunamis. 'Course, the global warmists play it both ways too, so what the heck!