I know CO2 isn’t a heat source. It’s what’s known as a greenhouse gas. The more of it in the atmosphere, the more the heat of the SUN gets retained for longer by the atmosphere and doesn’t dissipate back into space. This warms the earth because every day the sun adds more heat but some of that doesn’t escape at a rate that it used to. Excess heat also warms the water of the sea, which causes damage to coral that evolved to cope within a certain range of heat. Also, warmer water actually absorbs CO2. This causes the water pH to rise causing acidification. This also damages coral.

If you’re trying to claim the Barrier Reef isn’t in decline then I’m sorry to break the news to you. I’ve seen it. The bleaching is widespread. And it’s happened relatively recently, within the last decade.