Greenhouse Effect

Atmosphere

The layer of gases surrounding Earth.

Atmospheric pressure

The force exerted by the weight of air above a location.

Air density

Air density decreases with increasing altitude.

Troposphere

The lowest atmospheric layer; contains about 75% of atmospheric mass and almost all atmospheric water vapor.

Tropopause

The boundary between the troposphere and stratosphere; temperature is approximately constant with increasing altitude.

Stratosphere

The atmospheric layer above the troposphere where temperature increases with altitude.

Mesosphere

The atmospheric layer above the stratosphere; approximately the midpoint of the atmosphere by height, but not by mass.

Thermosphere

The upper atmospheric layer above the mesosphere.

Ozone (O₃)

A molecule made of three oxygen atoms that is concentrated in the stratosphere.

Ozone layer

A region of the stratosphere with a relatively high concentration of O₃.

Photodissociation

The process in which ultraviolet radiation splits O₂, allowing individual oxygen atoms to bond with O₂ and form O₃.

Why does temperature increase in the stratosphere?

Ozone absorbs ultraviolet radiation, releasing heat energy and warming the stratosphere.

Atmospheric composition

The mixture of gases that makes up Earth's atmosphere.

Nitrogen (N₂)

Makes up about 78% of Earth's atmosphere.

Oxygen (O₂)

Makes up about 21% of Earth's atmosphere.

Nitrogen triple bond

The strong bond connecting the two nitrogen atoms in N₂, making it difficult to split apart.

Atmospheric nitrogen

Mostly chemically inert but important for maintaining atmospheric pressure.

Trace gases

Gases present in the atmosphere in much smaller amounts than nitrogen and oxygen.

ppmv

Parts per million by volume.

Argon

An atmospheric trace gas present at about 9,430 ppmv.

Carbon dioxide (CO₂)

A trace gas and important greenhouse gas present at about 425 ppmv in the lecture.

Methane (CH₄)

A trace gas and greenhouse gas present at about 1.9 ppmv.

Greenhouse effect

The warming of Earth caused by greenhouse gases absorbing and re-emitting radiation.

Greenhouse gases

Gases that absorb and re-emit infrared radiation, contributing to the greenhouse effect.

How does the greenhouse effect work?

Greenhouse gases absorb radiation and re-emit it as longwave radiation, warming Earth's surface and lower atmosphere.

Greenhouse effect temperature difference

The greenhouse effect raises Earth's mean global temperature from about −18°C to about 14°C, a difference of about 33°C.

Molecular vibration

Molecules can vibrate in different patterns called vibration modes.

Vibration mode

A specific pattern of molecular motion that allows molecules to interact with electromagnetic radiation.

CO₂ and infrared radiation

CO₂ can absorb and emit infrared radiation because of its molecular vibration modes.

N₂ and infrared radiation

N₂ does not significantly interact with infrared radiation because of its molecular structure.

O₂ and infrared radiation

O₂ does not significantly interact with infrared radiation because of its molecular structure.

Water vapor (H₂O)

A major greenhouse gas with a high atmospheric concentration and short atmospheric lifetime.

Methane (CH₄) and the greenhouse effect

Methane is a greenhouse gas because its molecular vibrations allow it to interact with infrared radiation.

Water vapor and the greenhouse effect

Water vapor is the most concentrated major greenhouse gas but has a short atmospheric lifetime.

Carbon dioxide and the greenhouse effect

CO₂ has a much lower concentration than water vapor but remains in the atmosphere much longer and has been increasing since the Industrial Revolution.

Methane and the greenhouse effect

Methane has a low concentration but a relatively long atmospheric lifetime and contributes to the greenhouse effect.

Water vapor atmospheric lifetime

About 9 days.

Carbon dioxide atmospheric lifetime

About 35–90 years.

Methane atmospheric lifetime

About 10 years.

Water vapor greenhouse-effect contribution

About 36–72%.

Carbon dioxide greenhouse-effect contribution

About 9–26%.

Methane greenhouse-effect contribution

About 4–9%.

Industrial Revolution

The period after which atmospheric CO₂ and methane concentrations began increasing substantially due to human activities.

Keeling Curve

The long-term record of atmospheric CO₂ concentration measured since 1958.

Keeling Curve trend

Atmospheric CO₂ shows a long-term increase with a repeating seasonal cycle.

Seasonal CO₂ cycle

The annual rise and fall in atmospheric CO₂ caused largely by seasonal vegetation activity.

Vegetation and CO₂

Plants remove CO₂ from the atmosphere through photosynthesis during the growing season.

Preindustrial CO₂

Atmospheric CO₂ was about 280 ppm around 1750.

Ice core records

Records of past atmospheric conditions preserved in ancient ice.

Radiation budget

The balance of incoming and outgoing energy in Earth's system.

Shortwave radiation

Incoming solar radiation that peaks in visible wavelengths.

Longwave radiation

Outgoing radiation from Earth that peaks in thermal wavelengths.

Albedo

The reflection of incoming solar radiation.

Transmission

The passage of radiation through the atmosphere.

Absorption

The process in which matter takes in radiation.

Convection

The transfer of heat through the movement of air or another fluid.

Evaporation

The transfer of energy associated with water changing from liquid to vapor.

Re-radiation

The emission of radiation after energy has been absorbed.