A sincere Global Warming question?

Question

Alright guys, I'm one of those liberal heathens who is worried about global warming and plans to buy an electric car.

But, I had a question regarding the greenhouse effect. So, photons from the sun come down to the earth, hit the earth and are reflected, but then hit the greenhouse gas layer and are directed back to the surface.

The question is- why aren't they just blocked in the first place by that greenhouse gas layer? INstead of penetrating the layer and blocking the reradiation?

The only thing I can think of is perhaps reradiation is in the form of heat, instead of photons of light, and that the greenhouse gas blocks heat but not light.

Am I on the right track?

Answer 1

its like a car on a hot day in the parking lot.. who knows

Answer 2

Good question.  For the most part, portions of the visible spectrum (photos) make it to earth.  These photons are then absorbed by matter, which in turn emit a DIFFERENT type of radiation, infrared.  Infrared is what is reflected differently by "greenhouse" gases back to earth and reabsorbed... like a french fry under a fast-food warming lamp.

To some extent, increasing green house gases will increase the amount of radiation reflected back to space.  The question is if this will be good enough to off-set the heat-trapping component.  Remember, objects continue to give off infrared heat long after the sun goes down.  So, when this energy is retained, the earth cools off slightly less at night... with the long term impact of a warming trend.

Update:  John F is actually incorrect re: new ice age.  A slight cooling trend was noted during the 1950-70s and a couple of scientists came up with an idea of global cooling.  It was never substantiated, never peer reviewed, and never accepted by the broader scientific community, unlike global warming.

Answer 3

You're on the right track, but I've included a few sites I found useful in understanding the process.

Answer 4

You are the perfect example of "Believe in something or fall for anything "

Pick your battles ???  What kind of a fool are you?

Answer 5

Bingo, you got it.  The energy arrives as UV (not blocked), but what's blocked is outgoing infrared (heat).

Technically it's not blocked, the energy is absorbed and re-radiated, in all directions, so some percentage of that energy is radiated to adjacent air (which heats up) while particularly towards the top of the atmosphere, some still escapes to space.  Convection mixes the air and moves the heat around, but not enough to get all the extra heat to the upper, radiating layer (that doesn't simply radiate into adjacent CO2-laden air).  The upper atmosphere actually cools as lower levels trap more of the energy.

Answer 6

Yeah, you are pretty much on the right track

Answer 7

You've kind of answered it with the visible/infra-red thing.

Now think about this.  It takes (about) 1000 times as much energy to heat the oceans one degree as it takes to heat the atmpsphere one degree.  Assuming, for the moment, that we HAVE heated the atmosphere one degree.  What effect has that had on the oceans?

Answer 8

think about it like this; a greenhouse heats up plants so that they can grow during the winter. its like that, the rays go through the layer and turn into heat while in the earth's atmosphere then that gets reflected like the glass of a greenhouse

Answer 9

Basically, yes.  The photons coming from the Sun are primarily in the UV and visible parts of the spectrum, where greenhouse gases are transparent.  Once the photons are absorbed and emitted by the Earth, they're in the form of heat (infrared wavelengths).  Greenhouse gases absorb infrared wavelengths.  See the graphic linked below.

Answer 10

Good question.

A stable temperature requires that the incoming energy equals the outgoing energy. If it weren't for our atmosphere, our planet would be extremely hot during the day and extremely cold at night. Life would not exist on our planet under those conditions.

The reason the energy isn't all reflected back out into space by the greenhouse gases has to do with the wavelengths of incoming energy.

Different colors of light have different wavelengths which allow them to pass through different mediums.  If you shine a white light (which contains all visible wavelengths) through red glass, only the red light will pass through. The other wavelengths will reflect back. Our atmosphere works much the same way.

The incoming energy from the sun consists of a variety of wavelengths. Whenever it strikes something (solid, gas, or liquid) it's magnitude, direction, and/or wavelength will be changed. A certain percentage of the incoming energy is immediately reflected back out into space when it encounters clouds or simply the atmosphere. The rest heats up various parts of the atmosphere or is absorbed by the earths surface.

The reason the earths surface doesn't continually get warmer and warmer, from this energy, is because it emits energy back into the atmosphere in the form of longwave radiation.  Some of this longwave energy goes back out into space (luckily, or we wouldn't maintain a steady temperature), but some is also trapped by the greenhouse gases.  The higher the concentration of greenhouse gases, the more of this energy that is trapped.

Answer 11

No.

In the 1970's the burning of hydrocarbons was supposed to be sending us into a new ice age.  The hydrocarbons were supposed to be reflecting the sunlight back into space.  This was brought up because of the frequent deep snows we'd get.  I find it unlikely that the burning of fossil fuels has now changed properties and it's holding in heat, and not reflecting sunlight back.  

Also, CO2 is a terrible insulator but we can't keep the oceans from evaporating either.

Answer 12

FNA said:

"But, I had a question regarding the greenhouse effect. So, photons from the sun come down to the earth, hit the earth and are reflected, but then hit the greenhouse gas layer and are directed back to the surface.

The question is- why aren't they just blocked in the first place by that greenhouse gas layer? INstead of penetrating the layer and blocking the reradiation?

The only thing I can think of is perhaps reradiation is in the form of heat, instead of photons of light, and that the greenhouse gas blocks heat but not light.

Am I on the right track?"

The sun emits electromagnetic radiation from all over the spectrum--UV, visible, and IR, though mostly near infrared and visible. Greenhouse gases typically do not absorb radiation at visible light wavelengths, so it passes through atmosphere pretty easily. Around 1/3 of incoming radiation is reflected by clouds, ice, light colored sands, aerosols, etc back out into space. The other 2/3 is absorbed by the Earth's surface, warming it. The surface then reradiates the radiation in the form of infrared (not the same thing as heat because all forms of radiation will warm the surface that absorbs them). The various greenhouse gases (H20 in water vapor and clouds, CO2, O3, N20, CH4, and CFCs) absorb most of the infrared and then emits it in all directions, including out into space and downward.

That is a very simplified explanation, but I think it answers your question.

Answer 13

Why do I keep seeing your name all over the place? you must have a ton of questions on here

about the photon thing...maybe its like the dot in Pong...always goes opposite the direction you want it to

Answer 14

The greenhouse layer blocks certain wavelengths and not others.  When the photons come from the sun, they are at lower wavelengths (higher energy) that can get through.  The earth radiates light at a higher wavelength than the sun does, and at these lower energies, they cannot penetrate the greenhouse gases.

Answer 15

GLOBAL WARMING IS'NT CAUSED BY ANYTHING THAT HAS TO DO WITH MAN, IN FACT GLOBAL WARMING IS CAUSED BY A CERTAIN AMOUNT OF BEAMS DIRECTED AT THE SUN FROM MANY PARTS OF THE OCEANS FROM A TECHNOLOGY MUCH, MUCH HIGHER THAN OURS. THIS IS WHY IF WE NEED TO START TO DELETE OUR PROBLEM. WE NEED TO START ASAP. http://www.socyberty.com/Activism/First-...