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The human fingerprint in the daily cycle

Posted on 20 November 2010 by John Cook

During the day, the sun warms the Earth's surface. At nighttime, the surface cools by radiating its heat out to space. Greenhouse gases slow down this cooling process. This is why deserts cool so much at night. Water vapour is a strong greenhouse gas and the dry desert air traps much less heat than more humid areas.

A more extreme example is the moon which has no atmosphere. At nighttime, there are no greenhouse gases to trap the outgoing heat. Consequently, the difference between day and night is more extreme with daytime temperatures getting up to around 118°C and nighttime temperatures falling below -168°C. In other words, the stronger the greenhouse effect, the smaller the difference between daytime and nighttime temperatures.

We are currently experiencing global warming. If an increased greenhouse effect is a significant part of this warming, we would expect to see nights warming faster than days. There have been a number of studies into this effect, which confirm that this is indeed the case. One study looked at extreme temperatures in night and day. They observed the number of cold nights was decreasing faster than the number of cold days. Similarly, the number of warm nights was increasing faster than the increase in warm days (Alexander 2006).

Frequency of cold and warm days and nights
Figure 1: Observed trends (days per decade) for 1951 to 2003 in the number of extreme cold and warm days and nights per year. Cold is defined as the bottom 10%. Warm is defined as the top 10%. Orange lines show decadal trend (IPCC AR4 FAQ 3.3 adapted from Alexander 2006).

The difference between daytime and nighttime temperatures is also known as the diurnal temperature range (DTR – the difference between minimum and maximum daily temperature). An increased greenhouse effect should cause the DTR to decrease. Over the last 50 years, DTR over land has shown a large negative trend of ~0.4°C (Braganza et al. 2004). The reason for the falling DTR is because nighttimes have been rising faster than daytime.

The daily cycle also offers interesting insights into climate change over the 20th Century. From the 1950s to early 1980s, global temperatures cooled slightly. A large contributor to the cooling was "global dimming" from 1958 to 1990 where less sunlight made it to the Earth's surface due to air pollution. However, over this period, the nighttime minimum temperature increased. While global dimming was cooling daytime temperatures, the increased greenhouse effect was warming the nights (Wild et al 2007). Even during mid-20th Century cooling, greenhouse warming was percolating away while we were sleeping.

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Comments 101 to 141 out of 141:

  1. Albatross @ 96

    I read the Zhou et al. (2010) paper you linked to. What the paper seems to be saying is that the ALL simulations (ones with both anthropogenic and natural forcing) could not match observed DTR. The model simulations did not have a large enough DTR.

    In this paper they talk about another paper Dai et al. (1999) which I looked up. This paper makes the claim that 80% of the observed DTR can be explained by a slight increase in cloud cover over the time of observation.

    From the Dai article (co-written by you friend Kevin E. Trenberth):
    "The historical records of DTR of the twentieth century covary inversely with cloud cover and precipitation
    on interannual to multidecadal timescales over the United States, Australia, midlatitude Canada, and former
    U.S.S.R., and up to 80% of the DTR variance can be explained by the cloud and precipitation records. Given
    the strong damping effect of clouds on the daytime maximum temperature and DTR, the well-established
    worldwide asymmetric trends of the daytime and nighttime temperatures and the DTR decreases during the last
    4–5 decades are consistent with the reported increasing trends in cloud cover and precipitation over many land
    areas and support the notion that the hydrologic cycle has intensified."

    Link to Dai article.

    On a bigger scale number crunching. I have been entering daily High and Low temperature for Omaha, Nebraska for the past 626 days. I did the Daily high temp minus normal high temp and averaged the 626 days. I came up with -0.65 F. I also did the low temp = the low normal and came up with 2.48 F. The High temps are cooler while the low temps are warmer. Clouds explain 80% of this effect.
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  2. 101, Norman,

    I'm not sure how your Omaha example can be taken to mean anything one way or another. A single, specific location over a period shorter than two years? Crossing the seasons? Including various ENSO events?

    That's like flipping a coin once, and then declaring that coins will always come up heads when flipped, because it did 100% of the time in your sample test.
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  3. Sphaerica @102,

    There are actual physical processes that are taking place that would decrease the average high temperature (compared to normal) yet increase the average lows.

    That is why I linked to the Dai article. They explain that low clouds will lower daytime temperatures but not affect nighttime temps much except in winter months.

    There is always a reason for phenomena, finding that reason can be quite the challenge.

    How many data points are needed to be able to determine a condition? If 626 is too small, what is the magic number?

    How many temperature measuring devices are used to determine the global temp anomaly? How much of Antartic ice is actually bored to gain knowledge of ancient atmopheres?

    Shpareica, there would still be some underlying physical process that would explain why Omaha, Nebraska would have high temps average below normal while low temps averaged above normal. If too many processes can explain this pattern (fronts moving in, etc) then you would need to expand your time frame to eliminate some of the processes that are only short term. Regardless, something is causing this pattern. It could be a short term event and that really does not matter. What matters is what could cause this. I think clouds are a good candidate. More cloud cover the last few years as compared to the long term average.
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  4. muoncounter @ 95

    "You present additional anecdotal evidence: The Dallas data link clearly shows that nightly lows are consistently well above the average. When nights are that much warmer than usual, I don't see how that's greater than normal cooling."

    I obtained that from the DTR of the current Dallas, Texas heatwave. Albatross pointed out that Accuweather data may be tainted (I can't find a monthly NWS listing of July, 2011 temps for Dallas Texas...I could see if the one bad data point could be an error entering the data).

    About AccuWeather data: "AccuWeather's forecasts and services are based on weather information derived from numerous sources, including weather observations and data gathered by the National Weather Service and meteorological organizations outside the United States, and from information provided by non-meteorological organizations such as the Environmental Protection Agency and the armed forces."

    AccuWeather article.

    In my post above (from AccuWeather data) I took daily high temp minus daily low temp to get the daily DTR. I took the normal high temp minus the normal low temp to get a normal DTR for Dallas during this time frame.

    In the current heat wave in Dallas. The daily DTR averaged 21.97 F and the normal DTR is 19.27 F.

    This would be an example of what I am saying.

    On August 3rd the high in Dallas was 111 F, the low was 88 F. The normal high is 97 F and the normal low is 78.

    The DTR for the 3rd was 23 F, the normal is 19 F. If the air cooled at a normal rate of 19 F the low temp would be 92 F instead of 88. To get to 88 from 111 means the air is cooling more than normal.
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  5. Norman, a simple explanation is that it is dry in Dallas and dry air expands the DTR.
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  6. Here is some actual empirical evidence giving a reasonable alternative explanation for the decrease in DTR over the last few decades. It is manmade but not CO2 emissions.
    The effect of decreased DTR is most noticeable over land areas and this article also explains this.

    Scientific explanation for decrease in DTR.

    From this article my DTR change for Omaha Nebraska (Post # 101) as compared to the long term norm makes a lot of sense now.
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  7. Norman#106: Nicely done!

    You seem to be suggesting a strong anthropogenic influence over weather conditions. It is nice to hear such an effective rebuttal to 'its not us.'

    You're also showing direct evidence that high clouds (formed from contrails) are a strong positive feedback:

    Cloud cover subsequently decreased in the west and increased over much of the eastern half of the country during the next two days, producing predominantly negative
    three-day OLR changes in the east and positive values in parts of the west.


    To rephrase, increased clouds in the east resulted in less OLR, ie, more heat retained. That nicely rebuts such silliness as Spencer's magic clouds and the general desire to hang a negative feedback on clouds (largely because its cooler on cloudy days).

    BTW, that also pops the balloon of the GCR argument: if GCRs do in fact stimulate high cloud nucleation (which is not proven), then by the same logic those high clouds contribute to warming, not cooling. You've shown that Svensmark and his adherents have it all backwards!

    And certainly there can now be no doubt that sensitivity is quite high, as there were measurable temperature differences for what must be considered a relatively small causal agent.

    But your 'manmade but not CO2' doesn't do much. Three days with few contrails do not a multi-year trend make.
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  8. muoncounter @107

    I like your clever intellect and how you were able to determine so much from my post. Your post reminds me of the Missouri River flood of 2011. My thoughts were contained in the banks of DTR but yours seem to have topped the banks and entered a lot of other area.

    I would like to question your point. "To rephrase, increased clouds in the east resulted in less OLR, ie, more heat retained. That nicely rebuts such silliness as Spencer's magic clouds and the general desire to hang a negative feedback on clouds (largely because its cooler on cloudy days)."

    There is another possibility you should consider. It may be that more heat is retained but another strong possibility exists to explain the OLR. The cloud cover has cooled the surface of the Earth so there is less available IR being radiated.

    Stefan-Boltzmann calculator.

    To simplify I used a one for emissivity in both calculations. Here is one for you to consider. The area not covered with clouds could reach a warmer daytime temp. I used 80 F in the calculator (after converting to Kelvin) for the cloudless area. The earth would emit 457 watts/meter at this temp and an emissivity of one. For the cloudy sky I used 70 F. In this case the earth would emit 424 watts/meter. I am not saying this was the actual case for your point. I am only using this example to point out that the earth's surface temp has a considerable effect on the OLR measured.
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  9. muoncounter @107

    Another point I would question: "And certainly there can now be no doubt that sensitivity is quite high, as there were measurable temperature differences for what must be considered a relatively small causal agent."

    I am not sure why you feel clouds are a small causal agent. Look at Trenberth's radiation budget. In it he has atmposphere and clouds reflecting 79 watts/meter

    Skeptical Science article by Trenberth.

    The amount of IR a doubling of CO2 will send back to earth for further warming is estimated in the 3 watt/meter range.

    I think a change in cloud cover may actually be much greater than the small casual agent you accept.
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  10. General question. I am not sure how John Cook determined the point of his article.

    John Cook: "During the day, the sun warms the Earth's surface. At nighttime, the surface cools by radiating its heat out to space. Greenhouse gases slow down this cooling process."

    As the sun warms the earth's surface it starts emitting more IR based upon its temperature (which will be warmer than the air above it): "The temperature of desert sand and rock averages 16 to 22 degrees C (30 to 40 degrees F) more than that of the air. For instance, when the air temperature is 43 degrees C (110 degrees F), the sand temperature may be 60 degrees C (140 degrees F)."

    Source of desert quote.

    Since the ground is very hot it will emit a lot of IR during the day (much more than at night) and since the greenhouse effect returns this radiated heat back to the surface, the greenhouse effect will be more pronounced during the hottest part of day (more radiation to return, plug in numbers in the stefan-boltzmann calcualtor using the emissivity of sand). If greenhouse warming were the agent for DTR then it seems by logical conclusion of the physics involved that the DTR should actually increase. The daytime high should be warmer than normal caused by increased CO2 since more IR will return to earth during the hottest daytime temp. The night will also be warmer but the IR being emitted at night will be far less than that during the hot day.

    Point: Hottest time of day would have the greatest greenhouse effect and should be greater than the nighttime effect leading to larger, not smaller DTR's.

    Clouds explain this much better than CO2. Clouds cool the daytime but warm the night causing a smaller DTR which has been observed.
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  11. Why is it so hard to get good empirical data to prove the exact amount of greenhouse contribution of CO2? Climate scientists spend a lot of money on super computers to run the mathematical models and vast amound of time programming in all the many variables. It seems so much more cost effective to develop maybe a hundred or so specialized sensors around the globe under various conditions and climates. You build a sensing device with sensors that only measure the energy emitted by the earth in upwelling IR energy and on the same device you have sensors that only measure the downwelling raditaion. You can put filters on the top sensors to block all wavelengths but the CO2 fingerprint (14 micron). Now you have the energy going up measured directly and you have the energy returning to earth that is the result of CO2. Why is this so difficult to set up?

    If you ran these on clear cloudless nights you would have a very accurate way to determine how many watts/meter CO2 returns to Earth.
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  12. 110, Norman,

    The problem with your scenario/model, as with most attempts to visualize the greenhouse effect with a simple model, is that it is too simple. The interactions are far more complex. Not all of the radiation is "returned" and the return is not one way and immediate. There are many other interactions and factors at work.

    For example, the air over a desert is warmer in the day and cooler at night because it is dry. It lacks the most prevalent and effective greenhouse gas, water vapor, with it's abilities to somewhat neutralize incoming radiation and more importantly to remove heat during the time daytime hours through evaporation.

    At the same time, a desert cools very, very quickly at night exactly because it lacks water vapor in the air above it, and so the greenhouse gas effect there is minimal. A desert is a case-in-point example of what would happen if the earth's atmosphere did not have a greenhouse gas effect, and that the DTR increases without greenhouse gases. More greenhouse effect equals lesser DTR.

    But the answer to your question doesn't lie entire in those details, but rather that the processes of radiation, convection, conduction, molecular collisions, clouds, varying densities of air + CO2 + H2O, etc. lead to a far more complex scenario than your simple hot-in-the-day-so-stronger-GHE-in-the-day implies.

    The bottom line, though, for your scenario is that it is too simple to reliably reach any such conclusions about DTR.
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  13. 111, Norman,
    Why is it so hard to get good empirical data to prove the exact amount of greenhouse contribution of CO2?
    The answer to this question is similar to the previous one.

    The interactions of CO2 are not nearly as simple as a simple, linear "radiation-up-CO2-radiation-down" model. Your sensors at the surface of the earth would detect the radiation being returned by the lowest layers of CO2 only, because CO2 and atmosphere in general is far more dense there. Radiation from higher layers of the atmosphere would be obscured, much as fog obscures your vision.

    There are a few things you have to realize about CO2 in the atmosphere. The first is that while CO2 will absorb IR, and then if given the chance radiate it away, it is more likely (until you reach the more rarefied upper troposphere) that CO2 will collide with an O2 or N2 molecule and pass the energy on that way, heating the atmosphere itself.

    As you get higher and higher in the atmosphere, and the chance of collision becomes less and less, then there is more and more chance of CO2 emitting IR, and even of being excited through a collision with O2 or N2 and then emitting IR, thus cooling the atmosphere at that level (i.e. taking energy from the surrounding O2/N2 and releasing it to space through radiation). This is why greenhouse gases are cooling the stratosphere while warming the surface.

    So if you want to measure IR in the way you describe, to properly observationally quantify it, you need a whole array of sensors at all different altitudes (at different spots around the globe). It's just not nearly as easy as sensors at the surface.

    Beyond this, there is some overlap with various gases and their absorption frequencies. In particular, water vapor overlaps with CO2, so that becomes even more difficult to tease out. And then, of course, water vapor densities vary differently with altitude from CO2 (which is why CO2 has a greater effect where it matters, higher up in the troposphere where the atmosphere actually succeeds in radiating heat into space).

    Does this help clarify things?
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  14. 110, Norman,

    Just an added observation... note that your quote identifies that the temperature of the sand is far above that of the air. Again, it is the lack of H2O as a greenhouse gas that aids this differential. The air can't heat, because the only thing there that can absorb the emitted IR (for the most part) is CO2. There's none of the more prevalent (normally) and effective H2O to absorb the radiation and heat the air. So instead the IR just passes right through to higher up where there is moisture.
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  15. muoncounter @107

    "And certainly there can now be no doubt that sensitivity is quite high, as there were measurable temperature differences for what must be considered a relatively small causal agent."

    I guess I can doubt a high sensitivity.

    Some actual measured graphs of temp vs radiation amounts.

    In these graphs you can get good readings of temp increase with radiation increase. On one graph 110 watts/meter positve radiation gives about a 22 C temp increase. That would be around 0.2 C increase with 1 watt/meter additional energy input. A doubling of CO2 has been calculated to increase downwelling IR by 3.7 watts/meter so the temp increase from the actual graphs would be about 0.74 C
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  16. Norman#108: You brought up the contrail question; I just connect the dots. As I recall, it was a brief period of unusually clear weather.

    The study summarized here suggests contrails are a feedback, not a forcing.

    "This result shows the increased cirrus coverage, attributable to air traffic, could account for nearly all of the warming observed over the United States for nearly 20 years starting in 1975, but it is important to acknowledge contrails would add to and not replace any greenhouse gas effect," ... "During the same period, warming occurred in many other areas where cirrus coverage decreased or remained steady," he added.

    But you must admit some, if not all of the implications:
    - Human influence on climate is a proven fact.
    - High cloud cover can trap heat (contrails and the hypothetical GCR-nucleated clouds, if any exist, are both high cloud forms).
    - If sensitivity was small, why would there be any measurable effect of contrails? They are a small subset of the overall cloud cover.
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  17. Sphaerica @ 112

    "At the same time, a desert cools very, very quickly at night exactly because it lacks water vapor in the air above it, and so the greenhouse gas effect there is minimal. A desert is a case-in-point example of what would happen if the earth's atmosphere did not have a greenhouse gas effect, and that the DTR increases without greenhouse gases. More greenhouse effect equals lesser DTR."

    If I can find an online calculator I will work on the data for this point. You claim it is lack of greenhouse gases that cause rapid cooling in the desert. What about latent heat of moist air? Dry air holds less heat than moist air at the same temperature. The hotter the air the greater this effect is as the warmer moist air can hold a lot more water vapor that needs to be heated but latent heat does not increase the temp. A desert can warm rapidly during the day because the air is dry and hence has little latent heat that slows warming. At night it cools quickly because the air again has little latent heat and cools much quicker than moist air.

    Moist air takes more energy to warm so with equal amounts of solar insolation (even without evaporation taking place), moist air will warm slower and reach lower peak temperatures than dry air and it will cool off slower at night as it has more energy to give up.
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  18. Sphaerica @ 114

    Conduction and convection are also powerful heat transfer mechanisms. The desert air will heat via initially conduction of air in direct contact with the hot sand, then by convection as the heated air becomes more bouyant and rises.
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  19. Sphaerica @ 113

    I believe 14 micron wavelength is the Carbon Dioxide portion of the IR spectrum that water does not interfere with.

    I believe that most temperature sensors that are showing a warming globe are located a few meters above the Earth's surface so this measured warming would be the result of the lower atmospheric contribution of CO2 on warming and should then be measurable. The warming produced by collisions would not return to ground and heat the earth or the near surface air (that the thermometers are measuring). The oxygen and nitrogen that are heated by collisions with CO2 would become lighter and rise and have little empact on SST or global warming sensors or melting ice caps. These phenomena would only be effected by the actual downwelling radiation that returned to earth.

    Since the negative consequences of Global Warming would only take place at the near surface, measuring the downwelling IR in the 14 micron range should still then be able to determine the exact energy CO2 contributes to these negative consequences (melting ice caps, rising sea level etc.)
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  20. 117, Norman,

    I'm not sure what you're saying about latent heat. Yes, certainly air with moisture has a greater ability to retain heat. Latent heat usually raises the temperature of the surrounding air through condensation, and so comes into play at higher altitudes where clouds form (or at cooler temperatures, when dew or fog condenses).

    But you are wrong to say that moist air will warm more slowly and reach lower peak temperatures than dry air. The opposite is true, as demonstrated by desert air temperatures versus those in, say, a rain forest. Simple observation refutes your statement.

    As far as conduction and convection go, if that were the case, you would expect to see desert air being warmer than it is, and that is not the case. That isn't to say that it doesn't happen, but the reality is that heating through radiation is far, far more important and effective than conduction and convection in transmitting heat.
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  21. 119, Norman,

    Virtually all of your statements are incorrect.

    For the overlap between CO2 and H2O, see the graph below:



    Concerning temperature sensors and the CO2 contribution, no. Again, your model is too simplistic. Looking at only the CO2 emissions a few meters above the surface is like looking at the edge of a dense fog. It is not giving you anywhere near the full picture.

    Your statement that "warming by collisions would not return to the ground" is inaccurate because your model is inaccurate and too simple -- it's really neither right nor wrong, but just not a meaningful statement to make.

    Your statement about individual O2 and N2 molecules becoming lighter and rising is flat out wrong. This does not happen. The parcel of air simply becomes warmer. It does not rise because the CO2 is well mixed, and the same thing is happening billions of times all around.

    Your statement that the negative consequences of Global Warming would only take place near the surface is completely wrong. It affects the entire depth of the atmosphere, and it is in fact by raising the altitude at which the planet finally loses radiation to space that greenhouse warming really occurs.

    Again, your own model of what is happening is far too simplistic. I would suggest that you find some sources of information on molecular physics and more details on exactly how the greenhouse effect works. You have some rather simplistic misconceptions about the mechanisms involved. You will not be able to build an accurate mental picture, and structure valid understandings and arguments, until you correct these deficiencies.
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  22. Sphareica @ 112

    "But the answer to your question doesn't lie entire in those details, but rather that the processes of radiation, convection, conduction, molecular collisions, clouds, varying densities of air + CO2 + H2O, etc. lead to a far more complex scenario than your simple hot-in-the-day-so-stronger-GHE-in-the-day implies."

    It might actually be as simple as I suggest. As far as I can tell in your response I do not see how atmospheric complications would effect in any way the energy emitted by the hot sand as IR. I think it is straight physics there. Temperature of substance (hot sand) and its emissivity directly translates to energy emission via the Stefan=Boltzmann law that has been empirically validated.

    The hot sand will emit IR based upon its temp. It does not change its emission with the processes you describe. Only the sand temperature will change the emitted energy.

    In my example I am using the same place, so effects would cancel out. The hot sand emits much more IR than the cooler night sand. If you use the 140 F given above as a possible daytime sand temp and if the sand cools to 100 F by morning (I wish I has some real world sand temp samples, all hypothetical now). 140 F sand would emit 533 watts/meter using the Stefan-Boltzmann calculator (used emissivity of 0.76 for sand). The 100 F would emit far less 403 watts/meter. Lacking the interference of water vapor the CO2 in the air should be sending back much more radiation during the day as compared with the night as much more energy is going up. The effects you mentioned, why would they change from day to night? You would get more collisions during the day but it is not a one way process, the O2 and N2 atoms will collide with CO2, excite it and now it may emit a downwelling IR photon.

    I am not sure that you did demonstrate why the GHE would not be much greater during the day than at night at least in an overall general sense.
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  23. Sphaerica @ 121

    CO2 and H2O absorption.

    The CO2 at 14 microns closes the window on H2O leakage. 4 microns looks like a solo CO2 peak but it is not as broad.

    "Your statement that the negative consequences of Global Warming would only take place near the surface is completely wrong. It affects the entire depth of the atmosphere, and it is in fact by raising the altitude at which the planet finally loses radiation to space that greenhouse warming really occurs."

    But what negative consequences would there be if the air 5 miles up raised temp by 10 C?

    Graph of atmposphere temps.

    (sorry I do not post graphs directly, I have tried without success)

    So from the graph I linked to, you go from -50 C to -40. How is that going to have a negative empact on life on earth? What would the negative consequences be that I am wrong about?

    "Your statement about individual O2 and N2 molecules becoming lighter and rising is flat out wrong. This does not happen. The parcel of air simply becomes warmer. It does not rise because the CO2 is well mixed, and the same thing is happening billions of times all around."

    From how you described the GHE in your 113 post your claim is that collisions with O2 and N2 are more frequent in lower thicker layers. This would mean that lower layers would be warming faster relative to the rate of collisions in the layers above. Being warmer than the air above the air below would then tend to rise.
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  24. muoncounter @ 116

    "But you must admit some, if not all of the implications:
    - Human influence on climate is a proven fact.
    - High cloud cover can trap heat (contrails and the hypothetical GCR-nucleated clouds, if any exist, are both high cloud forms).
    - If sensitivity was small, why would there be any measurable effect of contrails? They are a small subset of the overall cloud cover."

    I could agree to the first one (but the degree of influence is not so certain). Not sure about the GCR debate, looked into it some but not heavily. Last one, the measurable effect of contrails is localized but it can imply clouds (Spencer) do play a significant role in Earth's energy balance.

    Here is a quote from an article:

    "Ongoing debate
    In a study published in 2004, for example, Minnis and colleagues reported that contrails are capable of increasing average surface temperatures sufficiently to account for a warming trend in the U.S. between 1975 and 1994. But some climatologists believe Minnis and his colleagues may have overestimated the contrail warming effect.

    Even if Minnis's estimates are correct, other climate experts feel that any warming from contrails is not something to fret about. In a study published in 2005, James Hansen of NASA's Goddard Institute for Space Studies in New York, and colleagues ran models that increased the contrail coverage in Minnis's study by a factor of five. Even with this significant increase, Hansen's team found that global mean temperature change was in the neighborhood of 0.03°C (0.05°F)—a minute amount."

    Hansen believes it has very minimal effect on the global mean temperature. A cloudy day can cause significant temp difference in a local area but not effect the global temp much.

    Source article for above quote.
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  25. Sphareica @120

    Sorry for the confusion. I used the incorrect term in my discussion. It should be heat capacity of moist air vs dry air, not latent heat. The heat capacity of mosit air is greater than dry air. It will take more energy to heat moist air to a given temperature than dry air. I think your example would confirm this. Desert air warms much faster and reaches a higher peak temperature than moist air given the same energy input.
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  26. Norman "Why is it so hard to get good empirical data to prove the exact amount of greenhouse contribution of CO2?". Because you also need model disentangle the overlaps. The definitive paper is probably Schmidt et al 2010. And reading it will give you idea of complexity of question.
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  27. Schaerica @ 120

    "As far as conduction and convection go, if that were the case, you would expect to see desert air being warmer than it is, and that is not the case. That isn't to say that it doesn't happen, but the reality is that heating through radiation is far, far more important and effective than conduction and convection in transmitting heat."

    It has already been experimentally proven that what keeps the air cooler than the hotter ground is convection. If you stop convection the air above the ground gradually warms to the ground temp. It was done using rock salt instead of glass for a greenhouse. Rock salt does not stop IR (it was thought that the air in a greenhouse warmed up because the glass allowed the short wave energy in but stopped the longwave from leaving). The rock salt greenhouse warmed similar to the glass one. The reason for the warming is because the barrier (glass or rock salt) prevented convection that would move the heated air up and replace it with cooler air keeping the overall air temp much cooler than the ground.
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  28. 127, Norman,

    I've been down this road before too many times in recent months with people who want desperately to find ways that the GHE is inconsequential, rather than wanting to understand it. They start with polite questions, but then when they hear the answers they refuse to accept them, dig in, and argue with Lewis Carrollian nonsense.

    The answers to all of your questions are readily available by studying the vast quantities of material available online, as long as you do so with an open mind and do not immediately dismiss everything you read that you dislike, or stop looking the moment that you find something that seems to appealingly agree with your own misconceptions.

    There is a lot of misinformation out there. You have to dig hard enough to get past your own misconceptions.

    I would suggest starting with Spencer Weart's The Discovery of Global Warming.

    But I'm not going to let this turn into an argument. You asked questions, based on some serious misunderstandings. I explained your mistakes. You have now come back with counterarguments, which tells me that you don't really want to learn and find answers to your questions, but instead wish to try to find ways to ignore known science, which usually happens through the selective, fuzzy mis-application of limited and unquantified science concepts (such as the guessed at effects of convection and conduction).

    Please notice in your own posts how often you say the phrases "I believe," "I think," "perhaps," "maybe," and "it might" and "I am not sure." You are never going to understand things if at these points you do not go and do some hard, open minded research on your own, rather than picking these random possibilities and then clinging to them as if they are facts that must be dis-proven to you before you will move on.

    If you honestly want to understand this stuff, please open your mind, read and learn. Put your energy into studying rather than posting. When something you read doesn't fit with something you think you understand, start from the assumption that you are wrong and that you have more to learn.

    I will not get into another climastrology debate here at SkS right now. I'm tired of them, especially the ones that center around "convection and conduction account for everything" (see the nonsense comments on other threads by Doug Cotton and Rosco).

    This particular flavor of cognitive dissonance has been getting really, really annoying as of late.
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  29. Norman#124: "I could agree to the first one (but the degree of influence is not so certain).

    The first being 'human influence on climate.' Norman, you've given a stock response phrase, more appropriate to the pages in the realm of the uncertainty monster. You brought up the contrail example; 3 days of only a change in the number of airplane flights produced a measurable change in a key climate variable -- the degree of influence is there for you to see.

    "Not sure about the GCR debate, looked into it some but not heavily."

    The point here is not the mechanism that stimulates high clouds; it is the existence of those clouds. Contrail-caused clouds had an effect; GCR clouds (if such actually exist, which I strongly doubt) would have the same effect. Svensmark's mythic effect is overturned on this basis alone.

    "Last one, the measurable effect of contrails is localized but it can imply clouds (Spencer) do play a significant role in Earth's energy balance."

    Yep, these data show that clouds can trap OLR, which is clearly a positive feedback. That is indeed significant. But Spencer's magic clouds are supposed to be a negative feedback, while Dessler finds positive feedback. What data did Spencer produce for the magic cloud argument?

    Norman, the picture keeps coalescing. It is time to abandon those who preach 'we don't know' and 'its not certain' as dead-enders. Take a sheet of paper and make two columns. In one, list the observations one has to reject in order to objectively say 'we don't know.' In the other, list the convoluted explanations needed to explain away those observations - and the supposed observations that support them. When you're done, you should have an approximate outline of the contents of this site. Rather than pick away at the evidence one bit at a time, look at the weight of the evidence. Can you really say with any objectivity 'we don't know'?
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  30. Nice new piece of evidence showing nights warming faster than days and DTR decreasing. Thirty years of hourly temperature data at Mauna Loa makes this detailed analysis possible - and hard to question.





    -- source (tamino analysis of new paper)

    Link to paper: Malamud et al 2011

    Small world: one of the co-authors (Turcotte) was a geophysics prof when I was in grad school.
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  31. muoncounter @ 130

    I looked at the Malamud paper you linked to.

    I do not understand this statement from the article: "Our basic hypothesis is that a large part of the temperature and DTR trends at Mauna Loa can be attributed to changes in CO2. At night, longwave radiation and turbulent sensible heat fluxes dominate heat loss. Increasing presence of greenhouse gases will result in enhanced reradiation back towards the surface and hence warming nocturnal temperatures. During the day time, shortwave radiation dominates, particularly in tropical regions."

    This is my most basic question and the article does not really answer it. What is the meaning of "shortwave radiation dominates"? Shortwave solar energy will have a greater watts/meter flux than upwelling IR but the surface emitted IR will still be greater during the day than at night. Unless shortwave radiation pressure can limit the upwelling IR raditation from being emitted, how does the dominance of shortwave radiation affect the upwelling shortwave radiation (from my physics knowledge, the IR emission is determined by the temperature of the object and its emissivity).

    During the day you will have greater flux of upwelling IR from the surface than at night because of the greater temperature of the surface.

    You should have a stronger reradiation during the day than at night, hence more effective GHE (more IR going up during daytime, more coming back down from the omnidirectional energy distribution of greenhouse gasses).
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  32. 131, Norman,

    If you look at any solar spectrum curve...



    You see that the most energy comes in at short wave lengths (visible light). During the day this "dominates" because it so outweighs any down-welling IR in any calculations.

    At night, there is no such incoming shortwave radiation. Infrared radiation dominates.

    This isn't about "up-welling" at all. It's about what is coming back in to keep the surface warm... short wave sunlight during the day, long wave IR from greenhouse gases at night.
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  33. Norman#131: "During the day time, shortwave radiation dominates"

    This is merely an expression of daytime warming. Since the ground is increasing in temperature, it cannot be in equilibrium (radiated OLR and all other heat loss must be less than incoming solar). Hence you cannot automatically assume that OLR keeps up with apparent temperature.

    This is demonstrated for a number of different surface scenarios here. Example:

    During the day, copious solar radiation is absorbed at the surface, and the ground heats up rapidly. Initially, most of the heat is conducted down into the soil, but as the layer of warmed soil thickens, HS dominates; the heat is primarily transferred to the air. This is promoted by extreme differences (up to 28 K) between the ground temperature and the 2 m air temperature. At night, surface radiative cooling is balanced by an upward ground heat flux. Since the nocturnal boundary layer is very stable, the turbulent heat flux HS is negligible.

    In this example, HS is the 'upwards surface sensible heat flux.' The point is that greenhouse gases appear to slow the net transfer of the energy radiated from the ground back to space. Most of that transfer is taking place at night, because that is when the ground can cool. Added GHGs make that seem as if nights are warming faster than days - perhaps better put as 'nights aren't cooling as fast as they once did.' The upper of the two graphs from the paper shows a mean warming of 0.2C/decade across all hours; nighttime hours at twice this rate.
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  34. Sphaerica @ 132 and muoncounter @133

    Here is an article on ENSO that describes exactly what I am saying. There are many graphs. The ocean is warmer during an El Nino event and the downward longwave radiation is greatest during the El Nino cycle and lowest during the La Nina. During the day the ground is very warmer than at night so it will radiate more long wave radiation. More upwelling longwave radiation will mean more downwelling longwave radiation. So the GHE should be greater during the day. The radiation is additive. You get a 20 F increase in temp from shortwave solar insolation but the downwelling longwave radiation of day should be greater than at night so if night time adds 2 F to the temp, daytime downwelling longwave radiation should be higher and the addition of this energy should not make a smaller DTR but actually a slightly bigger one. That is why I think clouds are the major ingredient of the DTR decrease and it has a logical mechanism. Clouds at day keep things cooler but at night have a warming effect which would decrease the DTR. See my post at 101, based upon a peer=reviewed article.

    Article showing warmer water does produce more Downwelling longwave radiation.
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  35. Norman
    apparently you discovered that the atmosphere is heated from below by the land or ocean surface. You should have quoted Horace-Bénédict de Saussure who in the late 18th century demonstrated the effect.
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  36. 134, Norman,

    To better quantify things, this paper (Philipona et al, 2001) measured between 260 and 420 W/m2 DLR in the daytime over an 8 day period in Oklahoma. The paper also measures a range of 270 to 380 w/m2 DLR at night, so the difference between night and day is minor.

    More importantly, the earth is heating up during the day. It will certainly heat more due to GHGs and increased DLR, but the primary factor is always going to be direct sunlight.

    Remember Stefan-Boltzman: E = σT4

    Because of the T4 relationship to energy emitted, as something gets hot, it becomes harder and harder to make it even hotter. It sheds ever increasing amounts of energy as it heats above and beyond the increase in temperature. Thus, adding more energy during the day, when direct, unimpeded sunlight at noon can deliver 1368 W/m2, is not going to raise temperatures as much.

    But at night, this DLR is going to prevent cooling. Here, when temperatures are lower, the effects of the same increase in DLR are much greater.

    Basically, it is easier to merely keep something warm than it is to make it hotter. It is easier to warm a cool object that one that is already hot.

    As a result, the temperature gain during the day is not increased as much by increases in DLR, while the temperature loss at night is greatly influenced by increase in DLR.

    Your reference to El Nino is not relevant in this case. El Nino is a condition that can last for months. It raises ocean temperatures and so emits more OLR, and so triggers more DLR, but it does so 24 hours a day. It applies at night as well as during the day, so if anything it decreases the DTR in the same way increases in DLR do as a result of the GHE.
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  37. 136, Norman,

    I don't have the time right now, but I suggest you play with the numbers. There's a Stefan-Boltzman calculator here. For the sake of this you can use an emissivity of 1, but if you wish to use other values (see the table on the page), that's fine.

    Try plugging in various temperatures from your own local weather at different times of the day and night. You can estimate inbound solar radiation for different times of the day, maxing out at 1368 W/m2 on the clearest day possible, at noon at the equator. Add estimated DLR from the Philipona paper above, keeping in mind that the daytime/nighttime difference is not as great as you first thought, and that it is also affected by local conditions (e.g. a cloudy day reduces sunlight but might increase DLR).

    So try to figure out how much the earth is emitting around you, using local temperatures at different times of the day. Compare that to the radiation that is at the same time being replaced by different values of DLR (a lower value from before CO2 levels increased, and a higher value later).

    You might even be able to take this a step further, and subtract what goes out and add what's coming in to compute a subsequent temperature, to see how comparatively quickly things warm and cool under different conditions, and so see the DTR effect directly, yourself, quantitatively.
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  38. 136, Norman,

    Just to explain one more thing in this line of thought, consider the fact that the increase in DLR during the day is not a direct, immediate response to increased daytime surface temperatures, due to intense daytime solar radiation.

    Ultimately, DLR is a result of atmospheric temperature. If the atmosphere is cooler, it emits less, warmer it emits more. So the relevant question becomes "how quickly does the atmosphere warm as a result of the day's solar radiation?"

    Your imagined effect of immediate increased back radiation during the day is, I think, exaggerated. Much of the outbound OLR that is intercepted by greenhouse gases is passed to the surrounding atmosphere (O2/N2) immediately through collisions. It heats the surrounding atmosphere, rather than coming "right back down."

    It is this increase in temperature of the atmosphere (which is obviously also affected somewhat by convection and latent heat) which actually increases DLR (which follows, as is already understood, the Stefan-Boltzman relationship).

    Based on this, one might even expect to find the highest DLR values in the evening, when the sun has moved on but the atmosphere has warmed in response to a variety of mechanisms, not all of which act quickly (and since the atmosphere is, for the most part, transparent to inbound sunlight).

    Lastly, remember that a major factor in DLR is clouds. Clouds tend to build during the day, then dissipate (mostly) at night. That means that their effects are minimal until after the sun has gotten lower in the sky, but can persist well into and even completely throughout the night and next day (when they would impeded inbound radiation).

    These are all sort of fudged concepts. Building a clear model of it would involve far more research than I have time. I'm simply trying to suggest to you other factors which greatly complicate the picture beyond your more simple mental model of "more inbound solar radiation in the day must mean more outbound long wave radiation, too."

    A last note: This page might be useful in playing with calculations, although I cannot vouch for its veracity. I just stumbled across it.
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  39. Sphaerica @ 138

    Thank you for your thoughtful and intelligent posts in response to my posts.

    I am not sure if you are playing with me or not, you page link in this post is the same one I linked to in post 115.

    I did find this article that explains why DLR is reduced during the day. I guess a warming atmposphere effects the way radiation is absorbed.

    Quote from article: "It is interesting and very
    important to note that the negative temperature dependence
    of water vapor continuum absorption has a contrasting
    effect on DLR. When warming occurs at the surface and
    consequently in the atmosphere, this mechanism enables
    more emission from the surface to leave the atmospheresurface
    system and simultaneously reduces the downward
    radiation from the atmosphere to the surface. This would
    tend to lower the warming at the surface. Further, this
    mechanism is strongly sensitive to the concentration of
    lower tropospheric water vapor. With increased moisture
    in a warmer climate, the negative temperature dependence
    of the continuum absorption is likely to play a more
    prominent role. It will make the Planck effect more efficient
    in damping the warming of the atmosphere-surface system,
    and will also reduce the radiation emitted to the surface
    from a warmer atmosphere."

    I like the intelligence found on this site, it is food for thought and research.

    Sorry Sphaerica I can't link directly to the article. It loads as an adobe file directly.

    If you want to look at the article then it is the first search in Google with this search words "atmpospheric temperature effect on DLR"

    Have a good day!
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  40. 139, Norman,

    I hadn't realized that you'd supplied that same link. I found it later for an entirely different purpose, when trying to google "atmospheric temperature altitude hour" to try to determine if there's any observational evidence of how the atmosphere warms or cools through the day... although I'm sure I must have looked at it when you sent it.

    I did find the paper you referenced. Here is the link.

    I'll have to read it. It looks interesting. Briefly parsing the section you quoted, it does not seem to have an obvious impact on DTR. It seems instead to be arguing for a factor in lower climate sensitivity (i.e. that a warmer atmosphere has an enhanced ability to "pass through" additional heat coming from the surface).

    But it clearly complicates the picture I've painted and warrants reading.

    FYI, this link is to a PDF for what appears to be a slideshow on the same subject by the same author (Huang).

    This seems to be a favorite topic of his. Searching for "Planck damping" and "Planck effect" primarily yield papers by Yi Huang, including his dissertation.
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    Response:

    [DB] Fixed link.

  41. An uncharacteristically perceptive comment by one of JCurry's 'denizens' in the midst of their agonized debate on the BEST temperature work:

    it is alleged that due to increased green house gases in the atmosphere, heat is trapped that cannot escape from earth. So if an increase in green house gases is to blame for the warming, it should be minimum temperatures (that occur during the night) that must show the increase (of modern warming). In that case, the observed trend should be that minimum temperatures should be rising faster than maxima and mean temperatures. That is what would prove a causal link. -- emphasis added

    This fellow goes on to admit a cherrypick ("my carefully chosen sample of 15 weather stations") of some recent data to demonstrate that in a few locales, DTR is not decreasing. But as we've seen here and here, there is ample evidence of DTR decrease.

    Other references for DTR decrease include Zhou et al 2005:
    Such spatial dependence of Tmin and DTR trends on the climatological precipitation possibly reflects large-scale effects of increased global greenhouse gases and aerosols (and associated changes in cloudiness, soil moisture, and water vapor) during the later half of the twentieth century.

    Zheng et al 2010:
    ... for the later period of 1951–90, the trend in maximum temperature reduces to an insignificant value, while the trend in minimum temperature remains high, resulting in a significant downward trend in diurnal range of 0.10°C/decade.

    From Martinez et al 2009, despite variations due to seasonal effects, an average annual decreasing trend of DTR is found, particularly relevant in autumn (−0.9 °C/decade).
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