Question

annual fluctuations in atmospheric carbon dioxide concentrations occur because
a. plants in the northern hemisphere lose their leaves during the winter
b. co₂ emissions increase in the winter
c. humans influence co₂ concentrations
d. photosynthesis stops at night while respiration continues

Explanation:

To determine the cause of annual fluctuations in atmospheric \( \text{CO}_2 \) concentrations, we analyze each option:

• Option A: In the northern hemisphere (where most landmass with vegetation is), plants lose leaves in winter. This reduces photosynthesis (which removes \( \text{CO}_2 \)) and increases \( \text{CO}_2 \) levels. In summer, photosynthesis increases, lowering \( \text{CO}_2 \). This creates annual fluctuations.
• Option B: Winter \( \text{CO}_2 \) emissions (e.g., heating) are not the primary driver of annual fluctuations; natural processes (vegetation cycles) dominate.
• Option C: Human influence is more about long - term trends (e.g., overall increase in \( \text{CO}_2 \)) rather than annual fluctuations.
• Option D: Daily (night - day) changes in photosynthesis/respiration do not cause annual fluctuations.

Answer:

A. Plants in the northern hemisphere lose their leaves during the winter