Answer: carbon dioxide levels above normal
Step-by-step explanation:
Carbon dioxide is a gas that is available in the atmosphere which is required by the plants for the process of photosynthesis. The carbon dioxide is used as an ingredient along with water in the process of photosynthesis. It is required to produce carbohydrate (glucose) the source of food in the plants.
When the carbon dioxide levels raise above normal the plants play the role of carbon sinks which means their absorption level for the carbon dioxide gas will increase. This means they will be able to produce more amount of carbohydrates as source of food. This will likely to increase the plant growth.