Increasing sulfur levels in the upper atmosphere would have the same effect as:

• A. increasing the amount of volcanic ash in the stratosphere
• B. adding more nitrogen gas to the atmosphere
• C. raising the concentration of ozone in the troposphere
• D. decreasing carbon dioxide levels in the atmosphere

Answer: (A)

Verified step by step guidance

1. Understand that sulfur compounds released into the upper atmosphere, such as sulfur dioxide (SO\_2), can form sulfate aerosols that reflect sunlight and cool the Earth's surface.
2. Recognize that volcanic eruptions release large amounts of sulfur compounds and ash into the stratosphere, which leads to a temporary cooling effect by blocking sunlight.
3. Compare the effect of increasing sulfur levels in the upper atmosphere to the known impact of volcanic ash in the stratosphere, which also reflects sunlight and cools the planet.
4. Evaluate the other options: adding nitrogen gas does not significantly affect sunlight reflection; raising ozone in the troposphere affects air quality but not solar reflection; decreasing CO\_2 reduces greenhouse gases but is unrelated to sulfur's reflective effect.
5. Conclude that increasing sulfur levels in the upper atmosphere has a similar effect to increasing volcanic ash in the stratosphere because both increase particles that reflect sunlight and cool the Earth.