An increase in the volume of forests and phytoplankton would lead to a reduction in free "blank" , which in turn could cause a decrease in carbon dioxide in the atmosphere.

Carbon dioxide

Explanation:

The forests and phytoplankton are carbon sinks, which absorbs the green house gas carbon dioxide from the atmosphere for photosynthesis. The carbon dioxide from the atmosphere and water are used as reactant in photosynthesis to yield carbohydrates and oxygen as products. Thus the carbon dioxide level in atmosphere decreases. This is necessary for controlling pollution in the environment and reducing the environmental temperature as carbon dioxide can make the environment warm.

burning fossil fouls really decrease the carbon in the atmosphere so b