National Environmental Policy Act (NEPA)
A 1969 U.S. law that established environmental protection as a guiding policy for the nation and required that the federal government take the environment into consideration before taking action that might affect it. (Chapter 24)
natural capital
The wealth of resources on Earth. (Chapter 6)
natural gas
A gaseous fossil fuel composed mainly of simpler hydrocarbons, mostly methane. (Chapter 19)
natural interest
Readily produced resources that we could use and still leave enough natural capital behind to replace what we took. (Chapter 6)
natural selection
The process by which organisms best adapted to the environment survive to reproduce, leaving more offspring than less well-adapted individuals. (Chapter 11)
negative feedback loop
Changes caused by an initial event that trigger events that then reverse the response (for example, warming leads to events that eventually result in cooling). (Chapter 21)
net primary productivity (NPP)
A measure of the amount of energy captured via photosynthesis and stored in a photosynthetic organism. (Chapter 10)
New Urbanism
A movement that promotes the creation of compact, mixed-use communities with all of the amenities for day-to-day living close by and accessible. (Chapter 25)
niche
The role a species plays in its community, including how it gets its energy and nutrients, what habitat requirements it has, and what other species and parts of the ecosystem it interacts with. (Chapter 8, 10)
nitrogen cycle
A continuous series of natural processes by which nitrogen passes from the air to the soil, to organisms, and then returns back to the air or soil. (Chapter 8)
nitrogen fixation
Conversion of atmospheric nitrogen into a biologically usable form, carried out by bacteria found in soil or via lightning. (Chapter 8)
noncommunicable diseases (NCDs)
Illnesses that are not transmissible between people; not infectious. (Chapter 5)
nondegradable
Incapable of being broken down under normal conditions. (Chapter 7)
nonpoint source pollution
Runoff that enters the water from overland flow and can come from any area in the watershed or enters the air from dispersed or mobile sources. (Chapter 15, 20)
nonrenewable resource
A resource that is formed more slowly than it is used, or is present in a finite supply. (Chapter 1, 19)
nuclear energy
Energy released when an atom is split (fission) or combines with another to form a new atom (fusion). (Chapter 22)
nuclear fission
A nuclear reaction that occurs when a neutron strikes the nucleus of an atom and breaks it into two or more parts. (Chapter 22)
nutrient cycle
Movement of life’s essential chemicals or nutrients through an ecosystem. (Chapter 8)