My understanding is that temperature is only part of the problem. Acidification is ongoing, due to increased CO2 in the atmosphere. That's a global problem: the ocean is literally starving for oxygen, everywhere.
If the thermohaline cycle in the Atlantic continues slowing down, there will be significantly less water circulating. There's a risk that bigger & bigger parts of the ocean just sit, don't flow, and thus never get exposed to the air: that they truly deeply & forever run out of oxygen.
The dynamical processes of earth are being disrupted. We talk about extreme weather being the risk, but a lack of weather, a lack of variety, a forever hot, non-humidity bearing (higher temperatures carry less humidity) sit-and-stew earth, just sitting here, baking, is the hell we are headed to. The dynamical processes risk becoming static, stagnant situations. The flow of life & change & systems is being baked off the planet.