I remember watching a documentary which talked about feedback loops in the climate. It might have been in the context of history. If the ocean warms up enough, it causes the CO2 in the ocean itself (either in the deposits or the gas saturated in the water) to get released into the atmosphere. Maybe I'm not using the right technical words, but there is a certain amount of CO2 that sits within the ocean that is separate from the atmosphere. In any case, after a certain point it becomes a feedback loop: warmer climate -> more CO2 joins the atmosphere -> warmer climate.
We don't even need the oceans temperature to rise, as the arctic tundra permafrost melts the amount of plant material ready to release its CO2 is massive. Some estimate think it would double the amount of our total emissions if all of it defrosts.
But this did lead to one of the more ridiculous head line from a few years back.
Thawing Permafrost Is Artificially Chilled to Stabilize Alaska Oil Pipeline
Warmer water holds less dissolved gases of all kinds, including CO2. You can see this yourself by heating water in your kitchen. Well below the boiling point, you can observe tiny bubbles, which are composed of nitrogen and oxygen dissolved in the water coming out of solution. The oceans will eventually become carbon sources, not carbon sinks, if they warm enough, but that's not projected to happen this century.
However, there are regions of the oceans which currently absorb lots of CO2 which will absorb much less as time goes on. One important example is the AMOC, which, by turning over lots of water, helps sink surface dissolved CO2 into the deeper ocean. In recent years, oceanographers have observed a weakening of the AMOC, which was predicted but is happening much earlier than expected. This is one of the important planetary tipping points, which could cause a dramatic shift in the planet's climate.
But don't worry -- the Trump administration is defunding programs like the Office of Oceanic and Atmospheric Research, decommissioning the Ocean Observatories Initiative, and is planning to shutter NOAA's research arm altogether -- thus solving the problem once and for all.
And one scary observation related to this is that warm water will also hold less oxygen for marine life, literally throttling that part of our life-support.
