Which statement best describes a factor related to human-caused atmospheric change?

• A. Emissions of greenhouse gases trap heat in the atmosphere
• B. Solar radiation from the Sun increases suddenly
• C. Particulates can heat or cool the climate
• D. The atmosphere is unchanged by human activity

Answer: (C)

Particulates in the atmosphere can both heat and cool the climate, depending on their type and properties. When human activities release soot and other black carbon particles, they absorb solar radiation and warm the air, and they can also darken surfaces like snow and ice, reducing reflectivity and accelerating warming in those areas. On the other hand, sulfate and other reflective aerosols scatter and reflect sunlight back into space, which cools the surface and can offset some warming. These aerosols also influence cloud formation and persistence, adding another layer of complexity to how they affect climate.

So this statement captures a nuanced way humans influence the atmosphere: the same general process—emissions from human activity—can produce particles that either warm or cool the climate, depending on their composition. In contrast, while greenhouse gas emissions are a major driver of long-term warming, they don’t inherently include a cooling effect, and a sudden rise in solar radiation is not a typical result of human activity.