Not only that, but grass has a special kind of photosynthesis that can survive in a lower CO2 atmosphere than other kinds of plants. Believe it or not, one of the long term hazards for life is too little CO2 for photosynthesis, below 100 ppm. The long term driver of CO2 is geology: weathering of rocks and formation of limestone in the deep ocean remove CO2; subduction zone volcanos return it to the atmosphere. Biosphere carbon is less than one percent of geologic carbon. When the Earth cools down too much to continue plate tectonics in a billion years or so, there will be too little volcanic carbon returned to the atmosphere. Plants and algae will die and so will all animals that eat them. Only chemeotrophic microbes will remain.
Sentient life could halt this process by burning limestone to release carbon. This is how cement is made.
Sentient life could halt this process by burning limestone to release carbon. This is how cement is made.