When that happens, we will have a warming spiral underway. Ice and the snow that covers it is white in color (colour), which means that it reflects most of the solar energy falling on it back into space. But when the ice melts, it exposes the darker ground beneath it to the sun and this absorbs energy, causing still more warming.
Furthermore, water vapor (vapour) is itself a greenhouse gas. This means that when there is more water in the air because it is warmer, more solar energy is retained so that the temperature gets even warmer.
Global warming operates in the same way as a greenhouse. Ordinarily, solar energy falls on the earth and is then re-radiated into space. It is not reflected into space, but is absorbed first by the earth.
However, the re-radiation back to space takes place at different wavelengths than the primary solar radiation which originally landed on the earth. Greenhouses are hot inside because the panels of glass or plastic allow the solar radiation to enter, but block the re-radiated energy at the different wavelengths from leaving. Thus, energy builds up as heat inside the greenhouse.
Certain gases in the earth's atmosphere act in the same way as the glass panels in the greenhouse. Airborne molecules of these gases allow incoming solar radiation to pass by, but reflect the re-radiated energy back to the ground, so that the earth gets warmer as the amount of these gases in the air increases.
Carbon dioxide is the most important greenhouse gas, it was absorbed by fossil plants during their lifetimes and is released back into the air when fossil fuels, such as oil or coal is burned. Water vapour (vapor) is another greenhouse gas and an especially dangerous one is methane. When dead plants decay in the presence of oxygen, we will get carbon dioxide, but if they decay without oxygen, methane is formed.
Global warming is certainly for real. Each report about it seems to be more ominous than the last. Mountain glaciers are melting all across the world, as well as the glaciers covering Greenland. This is ice that has been there since the last ice age and is only just melting now. And this is going on all across the world. I am a somewhat late convert to global warming, but now do not see how it can possibly be denied.
Global warming will not only produce more powerful storms and raise ocean levels, it will skew climate patterns. Dry areas may become even drier and wet areas wetter. There is no better example of what global warming can do than the planet Venus. There is such a runaway greenhouse spiral caused by the planet's dense clouds that the surface of Venus is actually hotter than that of Mercury, which is much closer to the sun.
I have three things that I would like to add to discussions of global warming that I have never seen before.
First, evergreen trees in high latitudes depend on sunlight reflected at a low angle off the snow. This is simply because the sun is low in the sky. If the sorrounding snow melts, the growth of these trees will be stunted because they will receive less sunlight. This will add to the warming spiral because evergreen trees grow fast and absorb carbon from the air in doing so.
Second, variations in rainfall, as a result of global warming, will contribute to forest fires. If an area receives more rain than usual one year, there will be luxuriant plant growth. But if, in the following year, the area receives less rain than usual, the lesser rain will not be able to sustain the growth of the previous year. The resulting dead and dry plant matter will be a fire hazard.
Third, I consider the real nub of global warming as a kind of competition between two factors. We know that water in the air is a greenhouse gas. Yet, clouds are a potential brake on the warming spiral because if warming causes heavier clouds to form, the white cloud will reflect solar energy back to space.
The big question is: Does the warming spiral caused by increasing water in the air offset the cooling effect due to the reflectivity of clouds when that water condenses into clouds?
In my opinion, the answer is no. The increase in the greenhouse effect caused by more water in the air due to warming is not offset by the cooling reflectivity of the clouds the water condenses into. Part of the reason is that the warming which prompted more water to evaporate also enables the air to hold more water that will not condense into cloud.
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