Contribution of surface heat to atmospheric warming

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Summary:

GHGs warm the atmosphere, yet they do that in response to LWR from the surface. What is the relative contribution of increased surface LWR to atmospheric warming?

Main Question or Discussion Point

I'm not sure if this should be here or under Earth Sciences.

GHGs warm the atmosphere, but they do that largely in response to LWR from the heated surface. The relative contributions of the major GHGs are known, but I can't seem to find anything about the contribution from surface heat. For example, all things being equal and concentrations remaining unchanged, if surface changes led to greater heat from the surface shouldn't that increase atmospheric temperatures?

Perhaps this is minimal at a global level, but what about at a local level? Here in Australia a lot of land has been cleared for agriculture. With the drought, a lot of land is now dry earth. Regardless of increasing concentrations of GHGs, shouldn't that kind of land change lead to more emitted LWR and more absorption/re-emission by GHGs? And hence local climatic variation on the scale of years/decades?
 

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  • #2
sophiecentaur
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all things being equal and concentrations remaining unchanged, if surface changes led to greater heat from the surface shouldn't that increase atmospheric temperatures?
I think it's fairly well accepted that the melting of snow is leading to more solar energy absorption and a measurable increase in surface temperatures. The same effect is measurable when forest is lost and the local surface temperature rises. It can be a runaway situation when the level of GhG's rises too far.

Read around about climate change (Wiki is a start) and you will find loads of facts (and opinions) about this topic but don't take on board everything that gets posted.
 
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OK, been busy and haven't had a chance to respond till now. So I think you are saying that yes, if the surface warms more, then it follows that the atmosphere also warms more, regardless of GHG concentration. I have read a fair bit about global warming from rising GHG concentrations and know that the climate response to GHG concentration is the subject of a fair amount of research. But I have rarely read anything that quantifies or even identifies the extent to which land use changes contribute. While I know about the UHI, that is more to do with local thermal radiation from artificial structures etc and so is very localised (I understand that it is agreed that homogenisation of records resolves this effect at the global scale). However, land use change is far greater in scale and potential effect. For example, cleared or degraded lands, which in Australia could number in the millions of hectares, must warm the atmosphere more if surface temperatures are greater than historical norms (ie prior to land use activities and hence changes in ground cover which are typically related to agriculture). I would imagine this leads to local increases in hot days (as may be happening here in Australia right now) but given the scale must surely also have an effect at a global scale. Yet it is something I have never come across. So either I am very wrong or I just haven't looked in the right places.
 
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256bits
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Yes, albedo is relevant but from a different angle. But it's a bit of a complex question I think. If an area has high albedo, then it is reflecting a lot of the solar radiation, presumably still in the shorter wavelengths. But the effect of that is different depending on what is absorbing that reflected radiation. The example of the Sahara Desert is given as high insolation, highish albedo, high heat. But I assume the heating depends on the material - a person feels hot there because there is hot sun, hot surface radiating at long wavelengths and also reflected shortwave radiation. A person would be affected by all three, whereas the atmosphere will remain relatively transparent to the shortwave insolation and reflected radiation, but should be warmed by longwave radiation from the heated sand. So high albedo surfaces shouldn't play a big part in warming of the air (except see the paper from Etminen et al regarding previously under-measured methane response), but the extent to which a surface warms from direct insolation will. How much of a difference albedo makes to surface warming I have no idea, for example sand in the sun is very hot, yet Wiki suggests it also has a relatively high albedo.
 

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