Question

There is a difference between the predicted and observed global carbon budget. The possible reason is:

• A. Higher $\text{CO}_2$ levels stimulate plant growth and productivity, leading to more carbon being sequestered in plant tissues and root systems.
• B. Higher $\text{CO}_2$ levels lead to increased soil respiration rates, releasing more carbon into the atmosphere.
• C. Oceans are absorbing more carbon due to increased temperature, resulting in increased acidification.
• D. The thinning of the stratospheric ozone layer allows higher levels of ultraviolet radiation directly breaking down $\text{CO}_2$ molecules.

Hint:

The "missing carbon sink" is predominantly biological. Increased $\text{CO}_2$ acts as a fertilizer for plants, accelerating carbon capture through photosynthesis and leading to unexpected buffering of global temperature rises.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
This question asks for the possible reason for the difference between the predicted and observed global carbon budget.

Step 2: Detailed Explanation:

• The global carbon budget describes the balance between carbon dioxide emissions and the uptake of carbon by carbon sinks (like oceans and land biosphere).

• Historically, there has been a discrepancy where the observed concentration of atmospheric $\text{CO}_2$ is lower than predicted by standard emission and absorption models. This discrepancy is known as the "missing carbon sink."

• A primary mechanism explaining this sink is the "$\text{CO}_2$ fertilization effect."

• Higher concentrations of atmospheric carbon dioxide stimulate the rate of photosynthesis in many plants (especially C3 plants), enhancing plant growth, forest productivity, and biomass accumulation.

• As a result, more carbon is sequestered in plant tissues, wood, and extensive root systems, as well as being transferred into the soil organic matter.

• This biological response acts as a negative feedback loop that temporarily mitigates the rise of atmospheric $\text{CO}_2$.

• Option B describes carbon release, which would increase atmospheric $\text{CO}_2$, not explain the missing sink.

• Option C describes ocean acidification, but warming actually decreases the solubility of $\text{CO}_2$ in water, reducing physical uptake.

• Option D is scientifically inaccurate because UV radiation does not efficiently photolyze $\text{CO}_2$ in the troposphere.


Step 3: Final Answer:
Therefore, the possible reason is that higher $\text{CO}_2$ levels stimulate plant growth and productivity, leading to more carbon being sequestered in plant tissues and root systems.