tropical – adj. of, relating to, occurring in, or used in the part of the world that is near the equator where the weather is very warm

continent – n. one of the great divisions of land, such as North America, South America, Europe, Asia, Africa, Australia, or Antarctica, of the Earth

greenhouse gas(es) – n. pollution that causes the Earth's atmosphere to warm

desertification – n. the process by which an area becomes a desert

hydroelectric – adj. of or relating to the production of electricity by using machines that are powered by moving water

replace – v. to put someone or something new in the place or position of someone or something

log(ging) – v. to cut down trees in an area for wood

headache – n. a difficult or annoying situation or problem

cheaper – comparative adj. costing less money than something else

alternative – adj. offering or expressing a choice