Scientists are discussing ways to remove excess carbon dioxide from the atmosphere by increasing the amount that is absorbed by plant life. One plan to accomplish this is to establish giant floating seaweed farms in the oceans. When the seaweed plants die, they will be disposed of by being burned for fuel.
The statement 'Each year about seven billion tons of carbon dioxide are released into the atmosphere but only about five billion tons are absorbed by plant life' would indicate the most serious weakness in the plan above.