"over the past few decades, researchers have observed declining numbers in two species of penguins native to the west antarctic peninsula. new evidence is pointing to a decline in their food supply as the primary cause for the recent drops in their numbers. these penguins feed on krill, small animals that grow and develop under ice masses. the graphs below show data related to two factors: atmospheric carbon dioxide (co2) levels and antarctic ice mass. the diagram of a generalized antarctic food web illustrates the role of the penguins.

state one specific way in which humans might have caused the changes in atmospheric co2 levels"