Question

question 9
1 pts
carbon dioxide levels are increasing because
○ humans have begun releasing carbon that was formerly sequestered in fossil fuels into the
atmosphere.
○ the huge growth in the human population and domestic livestock has increased the amount of carbon
dioxide being released through respiration.
○ holes in the ozone layer have reduced the total amount of photosynthesis occurring in the biosphere.
○ human agriculture has greatly increased the amount of carbon dioxide given off by plants during
respiration.

Explanation:

• Option 1: Burning fossil fuels (like coal, oil, and gas) releases carbon that was trapped in them for millions of years. This is a major contributor to the increase in atmospheric \(CO_2\) levels.
• Option 2: While human and livestock respiration does release \(CO_2\), it is a natural cycle (plants take in \(CO_2\) for photosynthesis). The increase from this source is negligible compared to fossil - fuel burning.
• Option 3: Ozone layer holes are mainly related to issues like increased UV radiation reaching the Earth's surface. They do not directly reduce the total amount of photosynthesis in a way that would significantly impact global \(CO_2\) levels.
• Option 4: Plant respiration is a part of the natural carbon cycle. Agricultural practices may have some minor impacts on local plant - related \(CO_2\) fluxes, but it is not a major cause of the global increase in \(CO_2\) levels.

Answer:

humans have begun releasing carbon that was formerly sequestered in fossil fuels into the atmosphere.