I hope you were trying to say grass can combat global warming, not exactly true.
As all living plants do actually emit co2 during the night, without going down the rabbit hole. Yes they absorb co2, however over a full year this is pretty negligible when you take into account summer and winter etc.
Saying trees would be a better idea, as they store co2 within the timber. But again planting trees will never be the panacea solution.