1. 342 W/m2 is the intensity absorbed when averaged over the entire surface of the Earth
where 1370 W/m2 is the solar constant that strikes a circular area of the Earth.
(4x342 W/m2 = 1370 W/m2)
2. 168 W/m2 is absorbed by the Earth, but the energy being radiated from the Earth is
24 W/m2 (thermals) + 78 W/m2 (evapo-transpiration) + 390 W/m2 (surface radiation) =
492 W/m2. How can this be?
3. Notice 324 W/m2 is absorbed by the Earth after being absorbed by greenhouse gases
and re-emitted to the Earth.
4. The total intensity escaping to outer space is 235 W/m2 (infrared) and 107 W/m2
(reflected solar) = 342 W/m2.
Different books use the terms quot;greenhouse effectquot; and
quot;global warmingquot; differently.
In this course, greenhouse effect means the warming of
the earth's surface beyond a 255 K average temperature by
greenhouse gases that occur naturally in the earth's
Global warming means the warming of the earth's surface
beyond a 288 K average temperature because of
greenhouse gases from anthropogenic (human) sources.
That the greenhouse effect makes the earth habitable for
humans has been known in the scientific community for
over a 100 years.
The next slide is the spectrum of
incoming sunlight again
The next slide is the spectrum of infrared
radiated from the Earth at the Sahara Desert
400 wave numbers = 25 m = 25,000 nm
1000 wave numbers = 10 m = 10,000 nm.
Ultraviolet light has wavelengths between 200 and 400 nm.
Radiance is almost the same as intensity.
The next slide shows infrared from the
Earth being absorbed by greenhouse gases
instead of infrared emitted through the
The dark bands are infrared wavelengths
that are being absorbed.