Not being flippant, but you’ll have to ask God what causes El Nino and La Nina. Even large scale glacial stages that last for thousands of years are related to a multitude of constructive and destructive interferece cycles.
Everything has causation and we actually know what causes La Nina and El Nino. Equatorial trade winds. When strong, La Nina. When weak, El Nino. Now what causes these trade wind changes ? Pressure differences between the Eastern Pacific and Western Pacific. These are all known scientific facts.