Across
- 2. of pollution affecting rivers and lakes (5)
- 3. thin layer of gases around Earth (10)
- 6. down trees (11)
Down
- 1. from the sun (6)
- 2. gradual increase in Earth's temperature (7,7)
- 4. substance in the air, water, or soil (9)
- 5. endangered polar region (6)
- 7. use again instead of throwing away (7)
- 8. essential for human survival (6)