The Sky Window:
How the Atmosphere Controls to Global Warming
*Audience is the general public – anybody interested in global warming
What is the Sky Window, and Why Does it Matter?
One of the most controversial and ambiguous topics in recent science is global
warming, which is strongly linked to the atmosphere. The atmosphere is composed of gases
like oxygen, carbon dioxide and water vapor, all of which interact with light from both the sun
and Earth. The sky window is a characteristic of the atmosphere related to its interaction with
light. More specifically, it is a range of light that can easily pass out through the atmosphere
without being blocked or reflected. It can be thought of like a screen – if a scoop of dirt is
sifted through a screen, only a specific size can fit through, like only a specific wavelength of
light can pass through the atmosphere. This is important because it is the mechanism that
allows heat (which is actually a form of invisible light) to escape into space, keeping the sun
from burning up our planet! But, this already narrow range of light can shrink as different
gases, like carbon dioxide from fossil fuels, are released into the atmosphere. As the sky
window shrinks, less heat can escape, causing global warming.
Sun-Atmosphere-Earth
Light Interactions
Sun
Atmosphere
Earth
A Quick Explanation of Light
Light acts like a wave, where longer wavelengths correspond to lower energies, and
shorter wavelengths correspond to higher energies. The wavelength determines the property
of the light, ranging from a cancer-causing x-ray to the heat coming off of a warm object.
Visible light is actually only a small portion of the entire light spectrum, and every object
“glows.” Shortwave light corresponds to light from x-rays to visible red light, encompassing all
visible colors. Longwave light corresponds to all of the longer wavelengths, which are
completely invisible and include the light used in microwaves to heat food, and the light that
we perceive as heat.
Range of Wavelengths
Image provided by Brian Litherland on http://www.fabricatingandmetalworking.com/2012/09/tips-forsuccessful-laser-marking-in-job-shops/
All Objects Glow? Really?
Everything produces light, but it usually cannot be seen. The wavelength of light that
an object emits depends on its temperature. The higher its temperature, the higher energy of
light it emits. This explains why the sun looks bright, since it gives off high energy, visible
light, while people are not bright. People have a much lower temperature than the sun, and
the light we give off is perceived as heat.
Different Ways that Light Interacts with the Atmosphere
Every object can interact with light, even when you cannot see it. Three things can happen
when light hits an object (even the air around us is considered an object because it has mass).
The light can be reflected, absorbed, or transmitted.


Reflected: The light bounces off the object. Like when light shines off of a mirror.
Absorbed: The light sinks into a material, but does not go through it. It usually results
in heating the material, like a blacktop on a sunny day.

Transmitted: The light travels through the material. For example, glass allows visible
light to pass through it.
Our atmosphere transmits almost all shortwave light, like sunshine, but reflects almost all
longwave light, like the heat coming from the Earth. This small range of longwave light that
can be transmitted is the sky window, and it can change over time as the atmospheric
chemistry changes.
The Sky Window
If the atmosphere absorbs light, it cannot escape. The sky window is highlighted by the red
lines, showing the long wavelengths of light that will be able to escape from the atmosphere.
The gas molecules responsible for the absorptivity are labeled. This shows that if more water or
carbon dioxide are mixed into the atmosphere, the width of the red lines will shrink, and less
heat can escape. Image adapted from by J. Brownson, from text.
How People can Affect the Sky Window
The atmosphere is composed of gas and particulate matter (very small particles that
float in the air, generally considered pollution), which all interact with light. Each different gas
or pollutant absorbs or reflects light differently, so as the composition of the atmosphere
changes, so does the sky window. Surprisingly, water vapor and carbon dioxide put together
have the biggest effect on the sky window. If their concentration increases in the atmosphere,
the sky window shrinks and less heat can escape the earth. Water vapor comes from water
evaporating, which means that if more carbon dioxide is put into the atmosphere, the earth
gets warmer, and even more water evaporates, also contributing to the problem. This means
that as the earth gets warmer, the problem gets increasingly bigger.
How Scientists Use the Sky Window to Fight Global Warming
To review, the sky window is a small range of light in the form of heat that can escape
from the earth. It is a dynamic characteristic that changes as different gases and particles are
released into the air by people and natural events happening on Earth. It shrinks as more
carbon dioxide and water vapor go into the atmosphere, which is one of the consequences of
burning fossil fuels. Unfortunately, as the sky window closes and the earth’s temperature rises,
more water vapor will form from open bodies of water. This means that the bigger the
problem gets, the faster it gets worse. Although this sounds (and is) very concerning, shrinking
the sky window is reversible and does not symbolize certain death. The sky window can
actually be used as an advantage in combatting global warming and climate change.
Scientists are working on developing materials that release heat, but only the kind that
fits through the sky window. This means that in the future, a roof could be made of special
materials that absorb sunlight and glow heat-light that can escape through the atmosphere.
Heat from a traditional roof would be reflected by the atmosphere and trapped on earth.
Although this does not stop global warming, it could help reduce its impact.