Abatement. A reduction, decrease, or diminution.
Abiotic. Without life; pertains to nonliving factors of the environment.
Acid rain. Rain or other precipitation containing nitric and sulfuric acids derived from air pollutants, such as industrial and automobile emissions.
Act of God. Legally, an act occasioned by natural forces (hurricanes, earthquakes, floods, etc.) without the interference of any human agency.
Age structure. The percentage of a population according to age levels. The different age levels of population expressed in percentages; often represented graphically as an age pyramid.
Albedo. The reflectivity of a body as compared to the reflectivity of a perfect reflector of the same size, shape, orientation, and distance. Usually given as a percentage.
A micus curiae. A bystander without legal right to appear in a legal suit but who is allowed to introduce argument, authority, or evidence to protect his interests.
Amino acids. Simple molecules that contain an amino group (NH2) along with carbon, oxygen, and other hydrogen atoms, and form the building blocks of proteins.
Anemia. A condition characterized by a decreased oxygen-carrying capacity of the blood due to a deficiency of red blood cells or of hemoglobin.