More CO2 is generally good for photosynthesis. Higher temperatures are generally bad for photosynthesis. Which dominates depends on a lot of factors including

More CO2 is generally good for photosynthesis. Higher temperatures are generally bad for photosynthesis. Which dominates depends on a lot of factors including base temperature, C3 versus C4 photosynthesis, etc. And then there's the changes in rainfall. Personally I wouldn't be particularly surprised if the first .5 C of global warming was a net benefit for humanity. I'd be pretty surprised if the second was, though, and very very* surprised if the third was. And that's just what takes us to our current target for limiting warming.