Most likely culprit is the sun imo. Not sure of the how. We just wrapped up a solar maximum. Headed toward solar minimum now. Beleive sun flips its poles every 11 years and does all kinds of crazy stuff. Im no expert, but I know it has to play a big role on not just our atmosphere, but also tectonic plates, earth magma etc.
I think we rightfully so try to annalyze sea surface stuff alot, like mjo, mountain torgue, base state, etc. But there is so much that goes on underneath the indian and pacific ocean, geo magnetic wise that probably change sea temps, which in turn drive weather patterns. Just thinking out loud here.