Im reposting this for those who might not have a solid idea of what global warming is about. And why the scientific community is so concerned. Something I learned in Astronomy 101 at UH: Carbon dioxide is opaque to infrared radiation. For those of you who might not understand the phenomenon of global warming, let me share what I learned in college from one of the classes in which I didnt fall asleep. We all know that sunlight consists of a broad spectrum of wavelengths, from ultraviolet to the infrared. Its why we see rainbows when rain falls in Manoa Valley. What few might appreciate, except for those who have solar hot water heaters, is that when that broad spectrum of light energy strikes a solid object, its absorbed. How fast its absorbed depends on how reflective it is, but in general thats what happens. An object will continue to absorb this energy until it reaches a point of saturation. And then it will release or re-radiate energy it at a much lower frequency (or longer wavelength). And that energy is in the infrared spectrum. We know that energy as heat. If it didnt release the energy, then it would melt or catch fire. But thats the way physics works. Absorb. Reach saturation. Radiate. Simple experiment: Touch a dark-colored car thats parked in the bright sun. Its hot, right? Well, its been absorbing broad spectrum energy all day and is now releasing the excess energy back into the atmosphere. Thats what our planets surface is doing when its exposed to the sun. The exception are areas that are covered by reflective snow or clouds. If we were in the airless environment of space, that energy would quickliy re-radiate back out unimpeded, just like the way a golf ball would bounce back at us if we threw one at a concrete wall. Energy in. Energy out. A level of thermal stasis is acheived. If no sunlight were striking that object, then it would continue to radiate energy and eventually become freezing cold. Hard to believe but thats what happens. Apply this same principle to our planet. The Earths surface gets hit by sunlight. It sheds the excess energy back into space, and the climate continues to be stable. But with an increase of carbon dioxide in the atmosphere, infrared energy radiated by the Earths surface gets trapped by its atmosphere. Why? Carbon dioxide is transparent to shorter wavelengths. The broad spectrum of energy from the Sun passes right through to the surface of our planet, which then heats up, and that energy is re-radiated outward as infrared light. Otherwise known as heat. However, infrared light is blocked by CO2. If theres an increase in CO2, theres an increase in the amount of infrared energy that gets trapped in our atmosphere. The planet gets hotter. And it cant dump the excess heat back into space. Is there a good example of how bad it can get? Again, something else I learned in Astro 101: The planet Venus. Its about the same size and density as Earth. It sits a bit inside our orbit and a little closer to the sun. But astronomers believe that what really heated things up over there was a case of thermal runaway. The suns energy was being absorbed and reflected as usual. But because Venus was a bit closer, there was more energy that needed to be reflected. The warmer temperatures triggered an increase in the release of carbon dioxide into the atmosphere, possibly through various geologic processes. And that, in turn, blocked the usual re-radiation of excess energy back into space. Planetary temperatures increased. More CO2. More infrared radiation blocked. Higher temps. More release of CO2. More infrared radiation blocked. Higher temps. And so on. Thermal runaway. Now surface temps are something like 800 degrees Farenheit. Way more than it takes to melt lead. While Earth might not face the same fate due to its orbital position in our Solar System, things could become increasingly unpleasant in due time. The point is that we have no idea how bad it can get, or what the timescale might be. In my opinion, we are playing Russian Roulette on a global scale. Its better to play it safe than to assume nature might fix things in the long run. We just have to look at our nearest neighbor, Venus, to see an extreme example of how bad it could get.
Posted on: Tue, 14 Oct 2014 10:26:08 +0000
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