Identify the main concepts in this paragraph.
Global warming is an increase in the earth’s overall temperature caused by a buildup of greenhouse gases in the atmosphere.
1. Global warming
2. Increase
3. Earth's temperature
4. Greenhouse gases
5. Buildup
6. Atmosphere
Complete the following task based on the instruction and optional input provided.### Instruction:
Identify the main concepts in this paragraph.

### Input:
Global warming is an increase in the earth’s overall temperature caused by a buildup of greenhouse gases in the atmosphere.

### Output:
1. Global warming
2. Increase
3. Earth's temperature
4. Greenhouse gases
5. Buildup
6. Atmosphere