Question

why is it commonly believed that carbon dioxide is responsible for global warming? carbon dioxide levels in the earths atmosphere have been steadily decreasing. carbon dioxide has a longer average lifetime in the atmosphere. the warming effect associated with carbon dioxide has remained unchanged. other greenhouse gases amplify the effect of carbon dioxide.

Explanation:

To determine why carbon dioxide is believed responsible for global warming, we analyze each option:

• Option 1 ("Carbon dioxide levels... decreasing") is incorrect as CO₂ levels are rising.
• Option 2 ("Carbon dioxide has a longer... lifetime"): CO₂ has a long atmospheric lifetime (centuries to millennia), meaning it accumulates and persists, trapping heat over long periods, which contributes to global warming.
• Option 3 ("The warming effect... unchanged") is false—CO₂'s warming impact is well - established and linked to rising emissions.
• Option 4 ("Other greenhouse gases... amplify CO₂'s effect") describes amplification by other gases, not why CO₂ itself is blamed for global warming. So the key reason is CO₂'s long lifetime enabling heat - trapping over time.

Answer:

B. Carbon dioxide has a longer average lifetime in the atmosphere.