Weather for Gardeners - Greenhouse gases and the Greenhouse Effect
Living in a greenhouse is a gas?
Carbon dioxide, nitrous oxide, water vapor and methane have always been a part of the composition of our Earth's atmosphere. Without them, our planet would be too cold to sustain life as we know it. The way they interact with heat radiated from the Earth's surface facilitates the maintenance of the temperature regimes that make life here so diverse and possible. How, exactly, do these "greenhouse gases" function in this role, and in what way are humans affecting this function?
Each of the greenhouse gases has a similar characteristic, and that is the capacity to absorb and emit infrared, or longwave, radiation. This type of radiation does not come directly from the Sun, but from constituents of the Earth's surface that have first absorbed the solar radiation. The Sun's radiation shines through the atmosphere, striking plants, trees, soil, buildings, and everything else on the surface of the Earth. Infrared radiation is then emitted from the surface, and this radiation heads for space. Without the greenhouse gases, that radiation would go right out into space and allow the surface of the Earth to become a deep freeze at sunset, as on other planetary bodies with little or no atmospheres. Instead, the molecules of these gases intercept and absorb the infrared radiation, thereby increasing their energetic vibration. In the process of time, the molecules emit the infrared radiation and return to their lower energetic state. Some of this newly emitted radiation goes out towards space, and a small percentage of it actually makes it into space. However, a larger percentage strikes other molecules, or the surface of the Earth, and is reabsorbed. In this way, the heat energy accumulates rather than being lost to space..
The Cold of Space?
Now I wish to take a moment to point out that planetary bodies without greenhouse gas atmospheres do not become deep freezes at night because space is cold. The states of coldness and warmth require molecules to be present, and molecules are in very short supply in the vacuum of space. The real reason for the chilling of these planets is the loss of the infrared radiation, not the intrusion of the supposed "cold of space". Space is neither cold nor warm because it is a vacuum. Objects in space will lose heat in the form of infrared radiation unless something is present to redirect that radiation back to the object. That redirection is exactly what the greenhouse gases do, and is why they are called "greenhouse gases". Like the glass or plastic panes on a greenhouse, these gases act to delay the escape of infrared radiation into space.
What can make a difference?
Several factors can limit the greenhouse effect, or the process whereby more infrared radiation is trapped by the atmosphere than is lost to space. One factor is reflection of sunlight by ice packs and clouds. Both ice and clouds appear white because they are reflecting so much sunlight. This sunlight just passes right back into space. A second factor is a decrease in greenhouse gas concentration that would also increase the amount of infrared radiation that could make it into space successfully. A third factor would be particles in the atmosphere, such as volcanic dust, which act to reflect sunlight back into space before it can reach the surface and produce infrared radiation. In fact, major volcanic events can result in a temporary case of global cooling as a result of the ash projected into the atmosphere.
When a small change makes a big difference
Since the Industrial Revolution began, human activity has added measureable amounts of carbon dioxide, methane and nitrous oxide to the atmosphere. Higher concentrations of these greenhouse gases enable less infrared radiation to escape into space. The actions of humanity are making a change in the parameters inherent in the planetary climate. The initial change itself may be small, but the reiteration throughout the system can amplify the effects of that small change.
To illustrate this, consider the following example: the basic Mandelbrot Set fractal equation. This very simple formula has just two variables, one fixed and one changing. The equation is z x z + c = z, where c is a fixed quantity and z changes with each iteration (recalculation) of the equation. Starting with no alterations to the basic equation, an image is iterated with a fractal generation program. A selected portion of the result looks like the picture to the left. Now, subtract 1 from one of the "zs" in the basic equation as follows, z x (z-1) + c = z, and run the equation through the program again. The new result is shown by the respective portion of the new image, as illustrated on the right. See how a small change can make a significant difference? Remember how simple an equation this is, with just one changing variable. Then consider the Earth's very complex weather system, with its many changing variables, some of which have been wittingly or unwittingly altered without thought to what changes in the patterns will result.
Some effects, such as the melting of the north polar ice, won't affect people as much as the changes in local weather. Examples of changes that can result are heavier and more frequent rains, the onset of droughts in areas that have rarely seen them, and a more rapid breakup of polar and glacial ice packs. These effects, and others, are already being observed, reported and recorded.
One of the topics of debate is the time frame within which effects will manifest. This is where the unpredictable outcome aspect of changing fractalic parameters comes in. If we could predict it, it wouldn't be unpredictable! For that reason, I believe surprises await us in the near future, regardless of what the experts have to say about it.
Photo credit: Public Domain Clip Art and my own fractal images
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