The Greenhouse Effect

What controls climate?

• Energy from the Sun – Radiation!• Consider the 4 inner planets of the solar

system:

SUN

342 W m-22250 W m-2 660 W m-2 150 W m-2

Mercury Venus MarsEarth

Planetary Albedo

• A fraction of the incoming solar radiation (S) is reflected back into space, the rest is absorbed by the planet. Each planet has a different reflectivity, or albedo (α)

• One possible way of changing Earth’s climate is by changing its albedo.

Land has higher albedo than ocean

Clouds have high albedo

Ice and snow have high albedo

The “Greenhouse Effect”

The Earth’s surface thus receives energy from two sources:

the sun & the atmosphere – As a result the Earth’s surface is ~33C warmer

than it would be without an atmosphere

Greenhouse gases absorb longwave radiation – Thus the atmosphere stores energy

Radiation is not evenly distributed over the surface of the earth.

The northern latitudes have an energy deficit and the low latitude/ equator has an excess. But the low latitudes don’t indefinitely get hotter and the northern latitudes don’t get colder.

Why? The atmosphere and ocean transfer energy

from low latitudes to high latitudes(How?)

Greenhouse Effect & Global Warming

• The “greenhouse effect” & global warming are not the same thing. – Global warming refers to a rise in the

temperature of the surface of the earth • An increase in the concentration of

greenhouse gases leads to an increase in the magnitude of the greenhouse effect. (called Enhanced Greenhouse Effect) – This results in global warming