Glossary main content.



A body of rock that can contain or transmit water.


Pertaining to the north polar region.


The envelope of gases surrounding a planet, e.g., Earth’s atmosphere consists of approximately 80 percent nitrogen and 20 percent oxygen.


Average weather conditions of a region, including temperature, precipitation, and winds.

climate model

Computer programs that represent processes in the Earth system. Scientists use climate models to investigate the many factors at work in Earth's climate system and to make predictions about how the system could behave in the future.


Information, often in the form of measurements or observations, which can be analyzed.


A collection of data over time.


To turn from a liquid state to a vapor state.

global warming

An increase in Earth’s average surface temperature.

gravitational field

The volume over which an object exerts a gravitational pull.


The force of attraction acting between any two masses.


Fresh water that is stored under Earth's surface in aquifers, layers of sand, gravel, or porous rock; groundwater supplies springs and wells.


The total amount of water on Earth. It includes oceans, lakes, rivers, underground water, and all the snow and ice, including glaciers.

ice sheet

A continent-sized mass of glacier ice that overwhelms the underlying topography.


The transfer of moisture from the atmosphere to the surface of Earth, usually as rain, snow, and ice.

water cycle

The continuous movement of water between the atmosphere, the land, and the sea.

water vapor

The gaseous state of water.