What kinds of things could decrease Earth’s temperature?

Greenhouse gases are important. Without them, the Earth would lose heat too quickly and life as we know it would be impossible to sustain. Greenhouse gases, which include water vapor and carbon dioxide, absorb heat in the lower atmosphere and reflect it back to the Earth.

Or

Aerosols are tiny particles that float in the air, and they usually have the opposite effect of greenhouse gases: as the concentration of aerosols increases, surface temperatures decrease.

Explanation:That's because aerosols generally reflect incoming sunlight, increasing Earth's albedo.

Explanation:

basically reduce greenhouse gasses in the atmosphere, and have more reflective buildings, roads ect..