By G.T. Larson
In our last installment, we began a simple overview of the earth’s atmosphere. We will continue now by considering the two key elements in the heated debate of global warming: the source of the heat and the covering that keeps that heat in for our greenhouse home we call Earth.
Our greenhouseʼs heat source, the sun, is a near perfectly round, massive, continuous thermonuclear explosion, radiating tremendous amounts of energy into space. Solar energy enters our atmosphere as short wave visible light; much of it is absorbed by the floor of our greenhouse, the earth’s oceans and land masses. This absorbed heat is, in turn, reradiated back through the atmosphere towards space as long wave infrared radiation. As this infrared radiation is ascending through the atmosphere, much of it is absorbed by an important range of gasses called greenhouse gasses.
The main greenhouse gasses are water vapor (H2O), which makes up between 36 to 72 percent of the total; carbon dioxide (CO2), 9 to 26 percent; methane (CH4), 4 to 9 percent; and ozone (O3), 3 to 7 percent. The remainder is made up of trace percentages of a variety other gasses. These greenhouse gasses reradiate much of the infrared radiation back toward the earth’s surface, heating the earth. This is what is called the greenhouse effect.
A very simple example of the greenhouse effect is parked outside most of our homes. On any sunny day, if you leave your windows up, the sunlight enters the vehicle through the windows and the solar energy is absorbed by the seats and dashboard. As the interior surfaces absorb the solar radiation, it is reradiated as infrared radiation which returns toward the windshield and the windows. Some of this heat escapes through the glass, but much of it is retained and if your vehicle sits in the sunshine long enough with the windows rolled completely up, when you open that car door you will be met with a hot blast of Honda or Ford or VW warming. We leave our vehicle windows cracked a bit to allow some of that build-up of heat to dissipate, thus, to a degree, regulating the vehicles interior temperature. This is an example of an artificial greenhouse effect.
Without a natural greenhouse effect, the average temperature of the Earth would be about 0 degrees Fahrenheit (minus 18 Celsius), instead of its present 57 F (14 C). The temperature controls that regulate our climate are the naturally occurring greenhouse gasses in our atmosphere that absorb infrared radiation from the sun. The greenhouse effect has been in a relative state of balance for millennia, but as we on Earth have become more technologically advanced, we have advanced the dials on our home planets climate controls and they appear to be malfunctioning. Without a correct level of greenhouse gasses there would be no life on Earth. We will look at these greenhouse gasses next time. Aloha Ke Akua.