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One day I was sitting in an Atlanta traffic jam wondering about all the engine exhaust heat warming the localised environment. Later that night, things will have cooled down. Where did the heat go? On a global scale, I understand our sun heats the earth via radiation, not conduction as the intervening vacuum of space cannot transfer heat. So if the sun has been beaming gazillions of watts of energy into the earth over the last few billion years, and energy is conserved and the earth does not radiate out daily a material proportion of the radiation it has absorbed, where has all that energy gone?

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    $\begingroup$ earthobservatory.nasa.gov/Features/EnergyBalance/page4.php Also, your only discussing surface temperature, not entire atmosphere temperature. Temperature on the surface can circulate away as well as radiate away. A hot highway might get well over 100 degrees F under mid-day sun, but it cools off within a couple hours with no sun shining on it. $\endgroup$ – userLTK May 15 '16 at 6:39
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    $\begingroup$ Related (almost a duplicate): How does anthropogenic heating affect global warming? $\endgroup$ – Gimelist May 15 '16 at 9:19
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    $\begingroup$ Is a proper interpretation of the NASA article that the earth radiates out to space nearly all of its incoming radiation through infrared? The article uses the word 'heat' and that may be to make it more accessible to readers, but heat does not go back into space, at least not in the common idea of heat in an atmosphere. $\endgroup$ – gwofatlanta May 15 '16 at 10:45
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    $\begingroup$ "Over 99% of outgoing longwave radiation has wavelengths between 4 µm and 100 µm, in the thermal infrared part of the electromagnetic spectrum." @userLTK - That was a fantastic read; it should come with a 'trope warning'. $\endgroup$ – Mazura May 20 '16 at 23:19
  • $\begingroup$ The energy dissipated into space. When a little part of energy can't go-out, the famous "greenhouse-effect" take place which is a cause of global warming. $\endgroup$ – Always Confused Aug 6 '16 at 15:37
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The hotter the Earth gets the more it re-radiates energy back into space.You can see a tiny fraction of this energy by looking at the new moon. The feint glow is just a small part of the re-radiated spectrum.

The long term differential between incoming and outgoing energy is what is causing global warming. It isn't 'a few degrees (Centigrade) every year'. It is currently in the order of about 1.5 degrees per century. That's because of the following reason:

Initially, the carbon dioxide makes Earth emit less radiation than it's receiving. That heats up the air until the oceans are sucking heat out of the air at the same rate as it's being heated by radiation. That process is slowly warming the oceans so they're suck heat out of the air slower so Earth will get hotter. As a result of the higher temperature, the ground will emit radiation at as fast a rate as it's absorbing radiation from the sun and re-absorption from the carbon dioxide. The reason the average temperature is rising is because the amount of Carbon dioxide was increasing.

Notwithstanding some diehard skeptics (who refuse to entertain the facts) the effect of greenhouse gasses in raising the global temperature is now so well verified as to be beyond doubt. Yes, variation in insolation rates and vocanic emissions also plays a relatively minor role, but cannot possibly explain all the evidence of global warming.

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  • $\begingroup$ Thanks, Gordon Stanger. The NASA article seems to state that all of the energy re-radiated by the earth back into space is in the form of infra-red. Would any of that be reflected back from the moon in the visible spectrum? Your comment on greenhouse gasses is noted, but to be clear that was not where my question 'was headed'. I simply didn't understand, nor had imagined, that as much energy as the earth gets each day is nearly completely re-radiated back into space in the form of infra-red. This leads me to asking another question in a separate post. $\endgroup$ – gwofatlanta May 15 '16 at 20:01
  • $\begingroup$ You can't "see it" from the moon, that is reflected sunlight from earth. Earth radiates in the infrared. $\endgroup$ – Kevin Kostlan Aug 26 at 16:03
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A body has to emit as much thermal energy as it absobs to remain in thermal equilibrium. The Earth has been doing the same since its formation, i.e, it absorbs solar shorwave radiation by its atmosphere, solid earth and water body, and releases it in the form of longwave radiation. The amount that is released has to be equal to the amount that is absorbed to maintain same temperature. However, due to much emission of greenhouse gases in to the atmosphere (or according to sceptics of such concept due to solar activity, volcanic emission), some amount that the Earth has to release is absorbed by the gases in the atmosphere and are causing the Earth to warm by few degrees every year.

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  • $\begingroup$ Thanks, GFG. Is it correct that the Earth is warming that fast? The question 'Why is the temperature still rising' has a chart suggesting an average temperature rise of about 1C over 140 years. (Sorry, don't know how to add a link to question) $\endgroup$ – gwofatlanta May 15 '16 at 11:11
  • $\begingroup$ @gwofatlanta a few degrees every year is obviously wrong. 1C over the last 140 is close, but the current warming rate is likely above that. 1.5-2.0 degrees C per century based on the last 35 years is closer to the current rate of increase (global average). On land it's warming faster than over the oceans. As CO2 in the atmosphere increases this rate might go up slightly, but it's difficult to be exact. 1.5-2.0 per century is probably pretty close to the current rate of increase. $\endgroup$ – userLTK May 15 '16 at 17:54
  • $\begingroup$ Thanks userLTK, I accepted GFG answers with this correction. $\endgroup$ – gwofatlanta May 15 '16 at 19:50
  • $\begingroup$ A few degrees every year is put in the context of fraction of numbers not whole numbers. The concept of blackbody radiation and kirchoff's rule ("thermal equilibrium") is enough to understand the concept of a warming body or planets and stars. $\endgroup$ – Gemechu Fanta Garuma May 16 '16 at 15:52

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