Identifying the Source of CO₂

Through measuring carbon isotope concentrations in ice cores, we know fossil fuels are responsible for the rise in CO₂ in the last 150 years. Fossil fuels are derived from fossilized plants. Through the process of photsynthesis plants more readily take up the isotope ¹²C. The preference causes the ¹³C/¹²C ratio to be lower than the atmospheric ¹³C/¹²C ratio. The ¹³C/¹²C ratio of the atmosphere decreases as more CO₂ from burning fossil fuels is introduced. With 'very high confidence' it can be understood that human activities, since 1750, are responsible for the increase in concentration of CO₂ in the atmosphere.