A forest is a large area dominated by trees. According to the widely used Food and Agriculture Organization definition, forests covered 4 billion hectares (9.9×109 acres) (15 million square miles) or approximately 30 percent of the world's land area in 2006.

The sea, the world ocean or simply the ocean is the connected body of salty water that covers over 70% of Earth's surface (361,132,000 square kilometres (139,434,000 sq mi), with a total volume of roughly 1,332,000,000 cubic kilometres (320,000,000 cu mi)). It moderates Earth's climate and has important roles in the water cycle, carbon cycle, and nitrogen cycle.

Recycling is the process of converting waste materials into new materials and objects. It is an alternative to "conventional" waste disposal that can save material and help lower greenhouse gas emissions.