The Gorilla in the Room: Radiation
Radiation? Why is it important to Global Climate Change? Well---we need to understand radiation to discuss climate change, but the good news is that we already know everything we need to know from everyday experience.
Turn your backside to a campfire on a cold night and the warmth you feel (ouch, if you stay that way too long) is radiation from the fire. Everything that has any temperature at all radiates energy to everything around it. When the radiation hits us we feel that energy as warmth. If we move away from the fire we feel less warm as the radiation is spreading out and becoming less intense.
The part of our body turned towards the fire feels warm, but the air still feels cold. The radiation from a fireplace doesn’t directly warm the air in the room, but first warms walls and furniture, they in turn warm the air. So we already know from experience that radiation warms us, but mostly passes through the air.
Sunlight is also radiation. It just happens to be radiation we can see (good planning on our parts). This happens to me a lot, but if I’m trying to catch some rays it always seems that the only cloud in the sky will always move between me and the sun. You don’t need to be a scientist to quickly learn that clouds (made up of small water drops or ice crystals) block sunlight.
It is common experience that clear nights seem to be colder than cloudy nights, but why? Well---we know that clouds block the sunlight (darn those clouds) so it isn’t a stretch to guess that clouds also block radiation from the warm earth from going away forever into the vastness of space. Some of that blocked radiation returns to earth which helps to keep the earth warm.
But if clouds covered all the earth, the earth would be a pretty cold, wet and inhospitable place for us as most of the sunlight would never make it to the ground. So how does it all work? What is the key to keeping the earth at a temperature that keeps us alive?
Remember I wrote that “radiation mostly passes through the air.” The word “mostly” is the key to life as we know it. There are certain gases in the air (water vapor, carbon dioxide, methane) aka greenhouse gases (gulp) that let the sunlight through, but when the radiation (a longer wavelength) from the earth tries to escape to space these gases partially block the radiation and return some to the earth. Without the dreaded greenhouse gases Earth would be a lifeless and cold planet. There would be no Lady Gaga, Big Macs, Enumclaw, or warming our backsides by a campfire.
So it turns out that we already knew how the earth keeps warm, but we just didn’t know we knew it. Sunlight passes through the air and heats up the earth, the greenhouse gases keeps some of the radiation from the warm earth from escaping back into space, and the earth supports life as we know it. Clouds block some of the sunlight from reaching the earth, but also help stop radiation from escaping. All of this results in a temperature that supports life (though the recent out of season tornados would hardly qualify as life supporting).