It is generally assumed that clouds affect climate by reflecting sunlight back to space and therefore decreasing the total warming of the Earth. However, stratospheric ice clouds are said to have a net warming effect, due to (I think) the insulation properties of clouds and the low reflectivity of ice clouds.

How do various clouds affect climate? Specifically, what is the relative energy balance effect clouds have as you go up in the atmosphere? Is it just stratospheric ice clouds that have a net warming effect? What really are the insulation properties of a cloud and how do they compare to the reflectivity?

  • $\begingroup$ Actually, iirc clouds are one of the biggest uncertainties in future climate in the latest IPCC. Their effect varies based on a number of factors. $\endgroup$ – casey May 30 '15 at 20:34
  • $\begingroup$ Could you edit the question to address those ideas? $\endgroup$ – farrenthorpe May 30 '15 at 21:00
  • $\begingroup$ Possible duplicate of earthscience.stackexchange.com/questions/22/… . $\endgroup$ – David Hammen May 31 '15 at 4:25
  • $\begingroup$ I don't think so... I'm asking information about how different types of clouds affect climate... not what the net effect of clouds in the future will be. $\endgroup$ – farrenthorpe May 31 '15 at 4:43
  • $\begingroup$ There's a fair bit written on this since the the IPCC assessment reports 3 and 4 (and perhaps 2 as well), all drew attention to clouds being the biggest unknown in climate change modeling. This answer touches on your question: skepticalscience.com/clouds-negative-feedback-basic.htm and many articles are google-search available, but it would take some digging, at least based on what I reviewed, to find answers in relation to specific cloud types. $\endgroup$ – userLTK Nov 9 '15 at 8:38

There are a few things that come into play when you talk about the radiative forcing of clouds, or their effect on the climate budget. "Cloud" is a pretty wide-sweeping definition. Scientists are still trying to fully understand and quantify these effects. Clouds do not vary only in where they are in the atmosphere but also in their phase (ice versus mixed phase versus water) and their depth--the combination of these two affect the cloud's optical depth. All of these different properties affect the net effect (whether positive, negative, or neutral) of clouds on the climate system.

High clouds are generally ice crystals, yes, because they are in areas of the atmosphere that are far colder than the freezing level. They are also generally geometrically thin. These high clouds have little effect on the shortwave energy and instead mainly reduce the amount of longwave radiation leaving the planet.

Clouds in the middle parts of the atmosphere are usually tall cumulus clouds that are full of liquid and mixed phase precipitation. These will be very bright to shortwave radiation and thus reflect much of that incoming radiation. They also provide some trapping of longwave emission from the surface and radiate less longwave radiation for a given level in the atmosphere than would normally be the case. The anvil regions of these clouds, on the other hand, are full of ice crystals which again don't reflect much shortwave radiation but do reduce the amount of longwave radiation leaving the planet.

Compared with the high atmosphere, completely ice phase clouds near the surface are thicker and their shortwave reflection is therefore a bit stronger than their thinner counterparts in the middle and upper atmosphere; they also trap longwave radiation from the surface. Mixed and liquid phase clouds' effects have similar effects as ice phase but are stronger in both the short- and longwave spectra.

Another thing special about clouds near the surface is because of that proximity they can actually have a strong influence on the surface which can cause a climate feedback. If you have a deck of clouds overlying a bright surface, it can actually warm the surface a bit since it is reflecting less shortwave than the highly reflective underlying surface would otherwise. For example, it has been hypothesized that the Greenland Ice Sheet melting is enhanced when cloud cover is present.

A good resource on this topic is available here. There have been many hypotheses over the years as to how these clouds and their effects will change in a changing climate. You can search for things like the "Iris hypothesis"--and subsequent refutation--as a good example of this still-evolving science. Climate models are still struggling to cope with correctly representing all of the feedbacks associated with clouds, which causes such high uncertainty in cloud effects in the IPCC reports.

One last thing to keep in mind is that these forcings are relative to a column with no cloud in the current climate. But what if our distributions or regimes of clouds greatly shift? If the planet warms so much that ice clouds can never exist, the relative forcing of ice clouds in that climate would then be null. So akeep in mind the point of reference you are using when thinking about the forcing of clouds.

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Water is one of the main absorbers of sunlight in the atmosphere. Electromagnetic radiation from the sun is the heat source and water and soil absorb this radiation. Liquid water does not act like a mirror. A mirror will reflect almost all of the sun's light and radiation. Water almost does the opposite. Ice can reflect light and some radiation back. The atmosphere acts like a greenhouse trapping the the heat.



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    $\begingroup$ this is incorrect... water vapor is mainly transparent in the visible spectrum. The question is about clouds... not liquid water. There are many different types of clouds, all with varying optical properties... this doesn't talk about any of them. $\endgroup$ – farrenthorpe Dec 5 '15 at 22:40
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    $\begingroup$ Water vapor and liquid water are good IR (radiant heat) absorbers and emitters, but bodies of water and droplets (mist, as in clouds) actually are rather good reflectors or scatterers of visible light. $\endgroup$ – Eubie Drew Dec 5 '15 at 23:41
  • $\begingroup$ @ Aabaa Kawad and farrenthorpe-Please take time to read the links I posted.And the subject is focused on climate changes due to clouds,Clouds consist purely of water droplets and water absorbs light and solar radiation.And I told you already light is reflected at best only in a angular position and that happens twice a day for a hour at the most.Solar Radiation causes the HEAT,The light from the sun does not. $\endgroup$ – user5434678 Dec 6 '15 at 4:35
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    $\begingroup$ @TheVoid the light from the sun is radiation, just as is the infrared emission (what you are calling HEAT). Radiation across a huge spectrum is emitted by the sun and how this interacts with things in the atmosphere is strongly dependent on wavelength (e.g. our sky is blue). Clouds (liquid water) strongly scatter visible wavelengths (they look white). Water vapor strongly absorbs and emits infrared radiation (greenhouse gas). Thin cirrus clouds (ice) transmit visible wavelengths (you can see the sun though them). The question is complex and your answer doesn't really address it. $\endgroup$ – casey Dec 28 '15 at 20:03

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