# How to reduce the atmospheric temperature artificially?

Is there any gas/substance which absorbs/reduces atmospheric temperature?

Ozone filters UV rays from the sun light and allows in infrared rays. In my knowledge these infrared rays are the cause of the heat. Do we have any provision to block these infrared rays at least for a targeted area? Does any gas or any other substance, natural or human-made, work in this way?

• – senshin Jun 1 '14 at 17:19
• There's a serious misunderstanding with this question. The vast majority of the energy in the incoming sunlight is in the visible range. The vast majority of the outgoing energy is in the infrared red range. Blocking infrared will do exactly the opposite of what you intend. You want to block incoming sunlight. Or maybe not. There will be unintended consequences to that act. – David Hammen Jun 1 '14 at 22:18
• I am totally confused now. :( – Jashan PJ Jun 4 '14 at 11:31
• Infrared radiation is the result of heated objects re-radiating energy they absorbed at higher frequencies. Dust high in the atmosphere would accomplish your purpose ... that's the basis of "nuclear winter" predictions. – 42- May 22 '16 at 23:32
• Ozone "blocks" uv before it gets here (by absorbing and reemitting the energy), preventing as much of it from getting to Earth. Greenhouse gases "block" ir coming up from earth... preventing as much of it from leaving. – JeopardyTempest Jun 13 '17 at 5:21

Typically temperature reductions in localized regions are not due to reduction of greenhouse gases. Greenhouse gases are well mixed and long lived and so reducing their concentrations has more of a regional or global affect. For a "tageted area" you would want to introduce aerosols into the atmosphere (e.g. clouds) so that the incoming light is reflected before it reaches the surface. Alternatively, you could change the albedo of the surface so that it is mostly white, thereby increasing reflection of visible light at the surface and reducing absorption (which in turn reduces infrared radiation from the surface of the Earth).

• Another way is to artificially alter the albedo. Producing snow, or increasing aerosol concentration would help. – BarocliniCplusplus Feb 12 '17 at 4:59

Ozone does not "filter" UV, it absorbs UV radiation (and undergoes some photo-chemistry reactions in the process). By absorbing those wavelengths it prevents them from reaching us at the surface, but cause a temperature rise in the stratosphere.

We have plenty of gasses that behave this way for terrestrial radiation (however without the photo-chemical reactions). Some of these gases are $\mathrm{CH_4}$, $\mathrm{CO_2}$ and $\mathrm{H_2 O}$, which we term greenhouse gases for their ability to readily absorb and radiate at terrestrial (infrared) wavelengths. If concentrations are high enough, they would reduce some of the infrared spectrum from the sun reaching the surface, but they would also reduce terrestrial emissions into space. Wherever these gases are doing the absorption one would also experience warming.

If you really want to reduce the global temperature solely through radiative forcing, the answer isn't to find and use a gas to absorb infrared radiation. The answer is to reduce the concentrations of greenhouse gases in the region you are concerned with. This will not greatly effect the incoming solar radiation, but it will allow greater radiative losses from the earth and atmosphere (lost to space), resulting in cooling.

You mention that "In my knowledge these infrared rays are the cause the heat". While infrared radiation will make you hot (e.g. when the sun shines on your skin), the peak emission from the sun is in the visible spectrum and the primary energy source is in wavelengths shorter than infrared. This shortwave radiation heats the surface of the Earth which in turn conducts heat to the atmosphere and radiates in the infrared. Without the presence of greenhouse gases, our planet as is (current albedo, etc) would have a global mean temperature around 255 K, which is quite a bit colder than what we experience with greenhouse gases. If you want to reduce temperatures, regionally or globally with a gas, your answer is to remove some of them, not add to them.

I think a brief explanation of how the greenhouse effect1 works is in order here.

• The light coming from the sun has a broad spectrum, which has its peak roughly in the middle of the range that we see as visible light. This is probably not a coincidence - it's likely that our eyes evolved to use this part of the spectrum because it's the most abundant in sunlight.

• The atmosphere is largely transparent to visible light - it has to be, or surface of the planet would be dark all the time. This incoming energy, in the visible spectrum, warms the land and the sea during the day.

• All warm objects radiate electromagnetic energy, and the wavelength of this energy depends on the temperature of the object. In the case of the earth's surface, this temperature corresponds with infra-red wavelengths, and so the surface of the planet gives off infra-red light.

• The atmosphere is much less transparent to infra-red than it is to visible light - it is blocked by so-called greenhouse gases.

So the greenhouse effect is caused by this difference in transparency - by the fact that incoming energy, in the visible spectrum, comes straight through the atmosphere, but outgoing energy, in the infra-red spectrum, is stopped from leaving.

Therefore, if you wanted to change the composition of the atmosphere to reduce the greenhouse effect, you would either need to make it more opaque to visible light (not recommended, although some people have suggested it), or more transparent to infra-red (which is the aim of all the people who want humanity to reduce its greenhouse gas emissions).

1 And I use the term in its most basic sense, without getting into all the complexities of climate change.

Convert infrared energy to matter. Reduces atmospheric temperature. Or pass atmospheric infrared light through Bose-Einstein condensate, and as it loses momentum, the system reduces temperature (decrease in kinetic energy due to momentum loss).

• An interesting answer based on theoretical physics, or possibly a very small scale application, but how could this be achieved practically on a large scale, such as in the Earth;s atmosphere? Links to proven examples of this method being used on a large scale would improve this answer. – Fred Feb 12 '17 at 7:05
• I've since turned on my heels, and recommended converting the infrared wavelength to a portion of the spectrum that is not captured by CO2. Suspended micro gold particulate matter will capture infrared and re-radiate it in the blue spectrum. Which will not be captured and released as light to our outer atmosphere. – Theodore Frimet Dec 31 '17 at 14:03

Add a heat sink. A heat sink is an absorber of heat. So add co2, or dry ice as we usually call it. It is an excellent heat sink.

• Welcome to the site. Answers should go into more detail than one sentence. Also, you've not said how you'd create this dry ice not addressed the long term effects after it thaws and returns to the atmosphere. Finally, dry ice and CO2 aren't heatsinks. – userLTK May 5 '17 at 22:42
• In the temperature range on earth they are heat sinks. Thawed or not, co2 absorbs heat, you cannot argue with that? A heat absorber, which greenhouse theory says co2 is, absorbs heat. A heat absorber is a heat sink. Exactly which part of that do you not agree with? Provide sources in physics to your answer if you don´t agree. Not references from greenhouse theory, because that is circular argumentation. – Emil Junvik May 6 '17 at 15:55
• Atmospheric CO2 does not absorb heat. It reflects specific infra-red wavelengths. For a heat sink to work it needs to be colder than the surroundings and large enough that it can absorb significant heat. CO2 gas simply doesn't do that. Dry ice would, but how would you produce it in such a large quantity? Your answer is not an answer. – userLTK May 6 '17 at 16:40
• This might sound hard, but this comment really makes me worried that climate-science has big problems with the physics-education. The claim is that it "traps" heat. But now you say it doesn´t absorb heat. And, No! It does not reflect infra-red wavelengths, that is exactly what it doesn´t do. And the atmosphere is 33 degrees colder than the surface on average, which makes it an effective heat sink. Co2 is dry ice, spectral distribution observed by satellites show that it emits exactly what dry ice does. We are wasting our time if you don´t read up on physics first. – Emil Junvik May 6 '17 at 17:12
• That CO2 traps heat is often said as a term of convenience. It's 100% true. It traps heat in the Earth's atmosphere. It doesn't trap heat into itself which is how a heat sink operates. You've given 10 times more detail in your comments than your answer. Rather than argue with me, fix your answer. Explain your point. Don't assume people will know what you mean and think a one sentence answer is sufficient. I have no interest in arguing with you, especially about semantics. – userLTK May 6 '17 at 17:34