Identify and describe an action carried out by humans that could lower carbon dioxide levels in the atmosphere.

Plant trees, trees rid of CO2 and replenish O2 in the enviroment through a process called photosynthesis.

sheep is a herbivore animal whereas grasshopper belongs to the class chordates but both of them feed on greens.  

if grasshopper and sheep feeding on a pasture land, i do not think both of them will have any impact on each other. however, the number of the species can make difference. since sheep feed on greens, there is a possibility there left no pasture land for the grasshoppers or they may get extinct.