Alternative Energy Sources

4. Extracting fossil fuels by removing soil and rock overlying the mineral deposit
8. Energy harnessed by the sun
9. An intergovernmental organization that focuses on transitioning into alternative energy sources
11. A system that maintains its own viability for continual use
13. Chemical reaction between two substances that gives off carbon dioxide
14. Energy harnessed from the flow of water
15. Release of harmful gasses into the atmosphere
16. A gas obtained from combustion of coal, natural gas, and oil
19. Energy harnessed from heat sources within the Earth's crust
21. An agency in the US responsible for creating green solutions and renewable energy sources
22. Deposits of tar that is turned into oil

1. Harnessing energy through biological materials
2. Gases released into the atmosphere create this effect that traps the sun's warmth
3. Extracting coal from within the Earth
5. Harmful man-made substances and products in an environment
6. A machine used to harness wind energy
7. A unit of power used to measure electricity
10. A method for generating power using solar cells to convert energy from the sun into a flow of electrons
12. Combustible organic material derived from the remains of former life
15. Any source of usable power
17. Precipitation that contains acid-forming chemicals
18. A way to extract fossil fuels by fracturing rocks in the Earth's surface and injecting chemicals at a high pressure
20. Energy harnessed from ocean tides