It’s true that climate change does contribute, but it’s also worth noting that without human disruption of natural biogeochemical cycles (like the nitrogen cycle), even with climate change, we’d see significantly fewer harmful algal blooms. Algae do like the warm water, so when combined with excess nutrients the algal blooms only get worse. It’s just not really reasonable to point to climate change without mentioning nutrient pollution, which is far more impactful on algal blooms.