Question

without phytoplankton in the oceans performing photosynthesis, the amount of carbon dioxide in the atmosphere would ____ and the atmospheric temperature would ____.
○ decrease, increase
○ decrease, decrease
○ increase, decrease
○ increase, increase

Explanation:

Phytoplankton perform photosynthesis, which takes in carbon dioxide ($\ce{CO_2}$) from the atmosphere. If there were no phytoplankton doing this, the $\ce{CO_2}$ in the atmosphere would not be removed as effectively, so its amount would increase. Carbon dioxide is a greenhouse gas; more of it traps more heat, leading to an increase in atmospheric temperature.

Answer:

D. increase, increase (assuming the options are labeled A to D with the last option being "increase, increase")