The primary consequence of human-driven CO2 emissions is to

• A. Enhance the greenhouse effect
• B. Cause global cooling
• C. Neutralize ocean chemistry
• D. Increase atmospheric oxygen

Answer: (A)

The main concept being tested is how increasing CO2 affects the Earth’s energy balance. CO2 is a greenhouse gas that absorbs infrared radiation and traps heat in the lower atmosphere and near the surface. When humans burn fossil fuels, atmospheric CO2 levels rise, strengthening this trapping of heat and leading to a warmer global climate. This warming is the primary consequence of human-driven CO2 emissions.

Other options don’t fit because CO2’s overall effect is to warm, not cool the planet; cooling would require factors like reflective aerosols or reduced solar input. CO2 does not neutralize ocean chemistry; in fact, increased CO2 causes the ocean to become more acidic through dissolution, altering seawater chemistry rather than neutralizing it. Finally, CO2 emissions do not increase atmospheric oxygen; oxygen levels stay relatively constant, with any changes being much smaller than the long-term warming signal from higher CO2.