Glossary letter G

Gas Oil

A synonym for diesel (see definition).

Gas Pipeline

© Egidi

Pipeline used to transport gas over a long distance, either on land or on the seabed.


A highly sensitive device placed on the ground to record the complex wave trains generated during seismic surveys.



Describes the technology used to tap subsurface heat to produce energy. Low-temperature geothermal energy at very shallow, shallow and medium depths is used to heat homes, public buildings and office and apartment buildings. High-temperature geothermal energy involves collecting very hot water from deep underground and using it to produce power. This water reaches the surface as superheated steam.

Geothermal Gradient

The increase in temperature with increasing depth within the Earth. The gradient averages 3°C per 100 meters, but can vary significantly depending on geographical location.

Global Warming

Global warming, also called planetary warming or climate change, is the rise in the average temperature of the earth's oceans and atmosphere observed in the last several decades. The local effect of global warming is climate disruption. The Intergovernmental Panel on Climate Change (IPCC) has studied the phenomenon continuously since 1988.

Gravity Dam


Massive, thick dam whose weight alone is enough to withstand the pressure of the water pushing against it.

Green Energy

Primary energy is described as "green" or "clean" when only small amounts of pollutants are generated during its conversion. “Clean energy" is a relatively subjective concept and is not a synonym for renewable energy, though many renewable energies are also "clean."

Greenhouse Effect

Natural phenomenon in which a planet's atmosphere is warmed due to the presence of certain gases that have the ability to trap infrared radiation (heat). On Earth, these gases are mainly water vapor and carbon dioxide (CO2) and, in smaller amounts, methane (CH4), nitrous oxide (N2O) and ozone (O3). The greenhouse effect makes life as we know it possible. However, since the Industrial Revolution in the 19th century, human activity has emitted — and continues to emit — large amounts of greenhouse gases, which are the primary cause of global warming and have huge implications for the future of humankind.

Greenhouse Gas (GHG)

Gas with physical properties that cause the Earth's atmosphere to warm up. There are a number of naturally occurring greenhouse gases, including carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), ozone (O3) and, the most common, water vapor. There are also synthetic greenhouse gases: halogenated hydrocarbons — chlorofluorocarbons (CFCs), used as aerosol propellants; hydrochlorofluorocarbons (HCFCs) such as HCFC-22 Freon, used in refrigerators; and perfluorocarbons (PFCs), used in air-conditioning units — and sulfur hexafluoride (SF6), which is used in electrical engineering and metallurgy.

Growth Plateau

When oil prices rise, one of two things occurs. Either prices peak and then drop suddenly, or they stabilize if supply and demand are balanced. This second possibility is known as a growth plateau.

Gulf Stream

A powerful, swift ocean current that originates in the Gulf of Mexico, crosses the Straits of Florida (between Florida, the Bahamas and Cuba) and follows the eastern coastline of North America. The Atlantic Ocean slows the current's flow, at which point it becomes the North Atlantic Drift, which gradually moves warm water to the Arctic Ocean between Greenland and Scandinavia.