What is greenhouse effect?

Explanation

**Step-by-Step Solution:**

1. **Definition of Greenhouse Effect**: The greenhouse effect is a natural process that warms the Earth's surface.

2. **Source of Energy**: The primary source of energy for this process is the Sun. Sunlight reaches the Earth and interacts with the atmosphere.

3. **Reflection and Absorption**: When sunlight reaches the Earth, a portion of it is reflected back into space, while the remaining energy is absorbed by the Earth's surface.

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