Burning of fuels such as coal and oil.
Explanation
Carbon dioxide (CO2) is a variable gas in the atmosphere that plays a crucial role in the greenhouse effect. Under natural conditions, the global carbon cycle maintains a balance between the release of CO2 (sources) and its absorption (sinks). However, recent anthropogenic activities have disrupted this equilibrium.Analysis of Options:
- Increased respiration by the growing human population. is incorrect: Respiration by the human population is part of the short-term biological carbon cycle. The carbon released through respiration is derived from food sources (plants and animals), which originally fixed carbon from the atmosphere. Thus, it does not contribute to a net increase in atmospheric CO2.
- Burning of fuels such as coal and oil. is correct: Fossil fuels (coal, oil, and natural gas) contain carbon that was sequestered in the lithosphere for millions of years. Burning these fuels releases this stored carbon back into the atmosphere rapidly. This addition overwhelms natural sinks, leading to a steady rise in atmospheric CO2 concentration.
- Reduction in the number of animals releasing carbon dioxide. is incorrect: A reduction in animals would theoretically lower the biological release of CO2, which does not explain the current phenomenon of rising CO2 levels.
- Excessive absorption of carbon dioxide by oceans. is incorrect: Oceans function as a carbon sink, absorbing a significant portion of anthropogenic CO2. While this absorption is increasing (causing ocean acidification), the oceans act to mitigate the rise of CO2 in the atmosphere, not cause the disturbance.
Key Takeaway: The burning of fossil fuels is the primary cause of the increasing concentration of carbon dioxide in the atmosphere, as it releases long-stored carbon that disrupts the natural carbon cycle.