CO2 is just one of them, you have a bunch of other gases responsible for climate change like Methane that are way worse than CO2.
I’m surprised this is still on the EPA website Overview of Greenhouse Gases | US EPA
However, plastic are affecting wildlife and, indirectly, also affecting climate. Plastics floating on the ocean are incorporated into the food chain. They also block light and affecting plankton and the other animals they subsequently feed.
Everything we can do to overturn this is welcome. Personally I think both are necessary, taking care of the ocean and of the atmosphere are equally important.