I can't decide if that'd be better or worse. On the one hand, CO2 fucks up the planet. On the other hand, microplastics fuck up the planet. CO2 is making our planet hotter and less hospitable, while microplastics may be causing a wide variety of issues related to the endocrine system, learning disabilities, cancers, etc.

Then again, there are temporary, albiet extreme, solutions to our climate problems that could be enacted fairly quickly if it came to it. Not that I think world leaders would, they'd generally be very expensive and potentially cause their own ecological issues, but they could be done. However, if we discovered microplastics are the cause of a significant amount of the world's ills, it'd take a while to get rid of it all, even with plastic-eating bacteria.