Increasing levels of carbon dioxide in the air, which have occurred mainly in the past 50 years, he says, are a byproduct of deforestation and the burning of fossil fuels.
(Increasing levels of carbon dioxide in the air; have occurred mainly; T:in the past 50 years) (he; says; are a byproduct of deforestation and the burning of fossil fuels) (Increasing levels of carbon dioxide in the air, which have occurred mainly in the past 50 years; are; a byproduct of deforestation and the burning of fossil fuels)
Increasing levels of carbon dioxide in the air he Increasing levels of carbon dioxide in the air, which have occurred mainly in the past 50 years
have occurred mainly says are
T:in the past 50 years
are a byproduct of deforestation and the burning of fossil fuels
a byproduct of deforestation and the burning of fossil fuels