Climate Change Practice Test

Which statement best describes how forests contribute to the carbon cycle?

They serve as sources of carbon when burned. They release CO2 only during decomposition, never absorb. They act as carbon sinks by absorbing CO2 during photosynthesis, but also release CO2 through respiration; the net effect depends on balance. They have no significant effect on atmospheric CO2.

Correct Answer:

They act as carbon sinks by absorbing CO2 during photosynthesis, but also release CO2 through respiration; the net effect depends on balance.

Explanation:

Forests balance carbon by soaking up CO2 during photosynthesis and storing it in biomass and soils, while they also release CO2 through respiration and the decomposition of organic matter. The key idea is that the net effect depends on which process dominates over time. If growth and carbon storage outpace releases, a forest acts as a carbon sink; if respiration, decay, or disturbances release more carbon than is absorbed, it can become a source. This nuanced balance is what makes forests a major, but not unconditionally fixed, part of the carbon cycle. The other statements are incomplete or inaccurate because they either ignore the uptake during photosynthesis, or assume carbon is released only or always, or claim forests have no significant impact.

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