Saturday, August 2, 2014

Why does CO2 cool the stratosphere & warm the troposphere? Warmists don't agree on an answer

A paper published today in the Journal of Climate uses "a chemistry-climate model coupled to an ocean model" to arrive at a number of seeming contradictory conclusions about the opposing radiative effects of the greenhouse gases CO2, water vapor, ozone, and halocarbons (CFCs) depending upon the levels in the atmosphere where each of these are present.

Conventional AGW theory proposes the existence of a mid-troposphere "hot spot" and an overlying cooling of the stratosphere because heat is "trapped" in the "hot spot" and therefore can't make it to the stratosphere. However, despite millions of weather balloon and satellite observations over the past 60 years, the "hot spot" has still not been found and thus questions the fundamental theory of anthropogenic global warming climate change. The formation of a "hot spot" would also require a physically impossible reduction of entropy in the mid-troposphere and thus violate the second law of thermodynamics which requires maximum entropy production. 

According to the abstract below, the net radiative effect of these greenhouse gases in the troposphere vs. tropopause vs. stratosphere are:

GHG                          troposphere        tropopause       stratosphere

CO2                          warming              warming            cooling

water vapor                      ?                   cooling              cooling
ozone                              ?                   warming            warming
CFCs                         warming                  ?                  cooling?

I've been asking CAGW believers for years why CO2 and other greenhouse gases have opposite radiative effects upon global temperatures depending upon where they happen to be located in the atmosphere, and have yet to receive a satisfactory answer. Even the warmists themselves can't seem to agree on this fundamental question underlying CAGW theory. Wikipedia propagandist William Connolley disagrees with Gavin Schmidt and RealClimate on why increased greenhouse gases would cause the stratosphere to cool. 

RealClimate links to this site (update: link broken, but this is a mirror site) for their explanation, which upon examination makes no sense, violates basic physics including the 1st and 2nd laws of thermodynamics and maximum entropy production, contains contradictions, and then concludes "We now know that stratospheric cooling and tropospheric warming are intimately connected and that carbon dioxide plays a part in both processes. At present, however, our understanding of stratospheric cooling is not complete and further research has to be done.":

Excerpt in blue text from the site Gavin & RealClimate claim has the definitive answer to the question "why does the stratosphere cool?" [emphasis added]:

Why does the stratosphere cool?

There are several reasons why the stratosphere is cooling. The two best understood are:

1) depletion of stratospheric ozone
2) increase in atmospheric carbon dioxide

Cooling due to ozone depletion

The first effect is easy to understand. Less ozone leads to less absorption of ultra-violet radiation from the Sun. As a result, solar radiation is not converted into heat radiation in the stratosphere.  So cooling due to ozone depletion is simply reduced heating as a consequence of reduced absorption of ultra-violet radiation.  Ozone also acts as a greenhouse gas in the lower stratosphere.  Less ozone means less absorption of infra-red heat radiation and therefore less heat trapping.
At an altitude of about 20 km, the effects of ultra-violet and infra-red radiation are about the same.  Ozone levels decrease the higher we go in the atmosphere but there are other greenhouse gases present in the air which we have to consider.

Cooling due to the greenhouse effect

The second effect is more complicated. Greenhouse gases (CO2, O3, CFC) absorb infra-red radiation from the surface of the Earth and trap the heat in the troposphere.  If this absorption is really strong, the greenhouse gas blocks most of the outgoing infra-red radiation close to the Earth's surface.  This means that only a small amount of outgoing infra-red radiation reaches carbon dioxide in the upper troposphere and the lower stratosphere.  On the other hand, carbon dioxide emits heat radiation, which is lost from the stratosphere into space.  In the stratosphere, this emission of heat becomes larger than the energy  received from below by absorption and, as a result, there is a net energy loss from the stratosphere and a resulting cooling.  Other greenhouse gases, such as ozone and chlorofluorocarbons (CFC's), have a weaker impact because their concentrations in the troposphere are smaller. They do not entirely block the whole radiation in their wavelength regime so some reaches the stratosphere where it can be absorbed and, as a consequence, heat this region of the atmosphere.

3. Stratospheric cooling rates:  The picture shows how water, cabon dioxide and ozone contribute to longwave cooling in the stratosphere.   Colours from blue through red, yellow and to green show increasing cooling, grey areas show warming of the stratosphere.  The tropopause is shown as dotted line (the troposphere below and the stratosphere above).  For CO2 it is obvious that there is no cooling in the troposphere [or warming!], but a strong cooling effect in the stratosphere.  Ozone, on the other hand, cools the upper stratosphere but warms the lower stratosphere.  Figure from: Clough and Iacono, JGR, 1995; adapted from the SPARC Website.

Where does cooling take place?

The impact of decreasing ozone concentrations is largest in the lower stratosphere, at an altitude of around 20 km, whereas increases in carbon dioxide lead to highest cooling at altitudes between 40 and 50 km (Figure 3).  All these different effects mean that some parts of the stratosphere are cooling more than others.

4. Cooling trends at different altitudes in the stratosphere.  source: Ramaswamy et al., Reviews of Geophysics, Feb. 2001

Other influences

It is possible that greenhouse warming could disturb the heating of the Arctic stratosphere by changing planetary waves.  These waves are triggered by the surface structure in the Northern Hemisphere (mountain ranges like the Himalayas, or the alternation of land and sea).  Recent studies show that increases in the stratospheric water vapour concentration could also have a strong cooling effect, comparable to the effect of ozone loss.


We now know that stratospheric cooling and tropospheric warming are intimately connected and that carbon dioxide plays a part in both processes.  At present, however, our understanding of stratospheric cooling is not complete and further research has to be done.  We do, however, already know that observed and predicted cooling in the stratosphere makes the formation of an Arctic ozone hole more likely. 

[end excerpt]

Note the quote above "In the stratosphere, this emission of heat [proper term is radiation] becomes larger than the energy received from below by absorption and, as a result, there is a net energy loss from the stratosphere and a resulting cooling."

Basic physics question: How can CO2 increase emission of radiation to space if it is absorbing less radiation from below? This would violate the 1st law of thermodynamics which requires conservation of energy.

Secondly, the graph above [from an AGW model] shows that CO2 greatly increases cooling of the stratosphere but has essentially zero effect warming or cooling on the troposphere [below the dotted line]. Therefore, this graph indicates a net cooling effect of CO2 upon the atmosphere.

Therefore, can anyone please provide a plausible explanation that does not violate the laws of thermodynamics as to why increased CO2 allegedly warms the troposphere and cools the stratosphere? And why the model output above shows CO2 has a strong cooling effect in the stratosphere, but essentially zero warming or cooling effect in the troposphere? And if the stratosphere cools thus increasing the temperature gradient between troposphere and stratosphere, why that would not increase heat transfer from the troposphere to stratosphere (thus cooling the troposphere)?

The climate impact of past changes in halocarbons and CO2 in the tropical UTLS region

Charles McLandress1
Department of Physics, University of Toronto, Toronto, Ontario, Canada
Theodore G. Shepherd
Department of Meteorology, University of Reading, Reading, UK
M. Catherine Reader
University of Victoria, Victoria, British Columbia, Canada
David A. Plummer
Canadian Centre for Climate Modelling and Analysis, Victoria, British Columbia, Canada
Keith P. Shine
Department of Meteorology, University of Reading, Reading, UK

A chemistry-climate model coupled to an ocean model is used to compare the climate impact of past (1960-2010) changes in concentrations of halocarbons with those of CO2 in the tropical upper troposphere and lower stratosphere. The halocarbon contribution to both upper troposphere warming and the associated increase in lower stratospheric upwelling is about 40% as large as that due to CO2. Trends in cold-point temperature and lower stratosphere water vapor are positive for both halocarbons and CO2, and are of about the same magnitude. Trends in lower stratosphere ozone are negative, due to the increased upwelling. These increases in water vapor and decreases in lower stratosphere ozone feed back on lower stratosphere temperature through radiative cooling. The radiative cooling from ozone is about a factor of two larger than that from water vapor in the vicinity of the cold-point tropopause, while water vapor dominates at heights above 50 hPa. For halocarbons this indirect radiative cooling more than offsets the direct radiative warming, and together with the adiabatic cooling accounts for the lack of a halocarbon-induced warming of the lower stratosphere. For CO2 the indirect cooling from increased water vapor and decreased ozone is of comparable magnitude to the direct warming from CO2 in the vicinity of the cold-point tropopause, and (together with the increased upwelling) lowers the height at which COincreases induce stratospheric cooling, thus explaining the relatively weak increase in cold-point temperature due to the CO2 increases.

UPDATE: See also the German Science Skeptical Blog with a more complete figure of that above showing the atmospheric cooling profile:


  1. "Therefore, can anyone please provide a plausible explanation that does not violate the laws of thermodynamics as to why increased CO2 allegedly warms the troposphere and cools the stratosphere?"

    First, please note that the atmosphere is not at equilibrium, therefore does not have the behavior expected in thermodynamic equilibrium. There is no explanation for your question as posed since there is no thermodynamic equilibrium. The stratosphere is at best "non local thermodynamic equilibrium".

    Given this caveat, here is the explanation.

    Gas molecules have discrete energy levels. If a gas molecule is excited it will after a sufficient period of time time emit the energy and lose it. The rate of this process is given by the Einstein coefficient of radiation, in a time on the order of h-bar/delta energy. Excitation can occur from either absorption of a photon or from a collision with another molecule. If the molecule is not subsequently excited, it will radiate its energy until it reaches a state consistent with absolute zero.

    At issue is the balance between excitation and deexcitation by radiation and collision processes.

    At lower altitudes where density and temperatures are higher, collisions deexcitation is relatively more likely than direct radiation, so absorbed radiation gets dumped into the kinetic heat of the neighboring molecules. But at higher altitudes where density and temperatures are lower, radiation of energy is more likely than collision, and an indivicual molecule the intercepts radiation from a collision can radiate its heat and become colder than its neighbors.

    1. Essentially what you are referring to is that the troposphere is dominated by convection and thermodynamics, not "radiative imbalance." The primary greenhouse gas water vapor reduces the adiabatic lapse rate by half, cooling the surface, proving that the primary greenhouse gas acts as a cooling agent, not warming. CO2 has little warming or cooling effect in the troposphere as shown in Fig 3 above, but a big cooling effect in the stratosphere, along with ozone.

      Thus, increased CO2 does cool the stratosphere by increasing the radiative surface area to space, but has essentially no effect on the troposphere.

  2. classic paper on CO2 cooling

  3. Stupidity squared. CFC destruction of ozone in the stratosphere caused the cooling an d allowed more UVB radiation to hit earth. Doesn't seem to be many real scientists anymore. Bob Ashworth

  4. This post is both outdated and grossly inaccurate in its details. It first confuses two issues in the climate literature--namely the tropospheric "hot spot" and the observed cooling in the upper layer of the atmosphere (the stratosphere). These are mostly unrelated concepts that merit separate treatment. The former describes the reduced lapse rate in the tropics due to higher concentrations of water vapor in this region, while the latter refers to the observed cooling trend in the stratosphere from an influx of CO2 released in the troposphere (and is among the clearest fingerprints of anthropogenic forcing).

    Since the title of the post calls attention to the latter, let's discuss it. It should first be noted that stratospheric cooling stands as a fine example of an earlier prediction being vindicated by later observation. It was predicted way back in 1967, per Manabe & Wetherald 1967.

    The inverse relationship between tropospheric warming and stratospheric cooling can be derived from fairly basic physics, and the 'Anonymous' poster above elucidates this nicely. (I recommend reading it again.) There are two primary reasons we see cooling in the stratosphere when we increase tropospheric CO2: 1) lost IR energy via collisional deexcitation from an increase in stratospheric CO2 and 2) less overall IR energy available to the stratosphere due to said increase in tropospheric CO2.

    1) is dominant and can be summarized thusly: Stratospheric CO2 generally moves in lockstep with tropospheric CO2: an increase in the lower atmosphere will be mirrored by an increase in the upper atmosphere. However, due to the extremely different properties of these layers, changes in CO2 concentration produce inverse effects on temperature. The stratosphere is much thinner (less dense) than the troposphere, so there is much less CO2 overall, even though the concentration of CO2 in the stratosphere relative to N2 and O2 is the same as in the troposphere below. The density component is key for understanding the disparate effects of CO2 in these layers.

    An increased CO2 concentration in the stratosphere creates greater opportunity for those CO2 molecules to collide with N2, O2 or other CO2 molecules, which will result in “excited” CO2 molecules as kinetic energy (KE) is transferred. All entities, including atoms and molecules, prefer the unexcited state to the excited state (hello, entropy). So these CO2 molecules will deexcite by emitting IR radiation (heat energy) through the thin atmosphere and out into space, thus lowering stratospheric temperature. Now, the reason this does not happen in the troposphere is because, due to higher pressures and shorter distances between particles (i.e., higher density), any emitted radiation gets immediately absorbed by another nearby CO2 molecule, which deexcites and whose IR energy is absorbed by its CO2 neighbor, and so on and so forth.

    2) As tropospheric CO2 increases, more heat is trapped within the troposphere and less heat escapes into the upper atmosphere, resulting in less heat available for the stratosphere—a net energy loss. From Robert Guercio's article: "The energy that remains in the absorption band after the IR radiation has traveled through the troposphere is the only energy that is available to interact with the CO2 of the stratosphere. At a CO2 level of 100 ppm there is more energy available for this than at a level of 1000 ppm. Therefore, the stratosphere is cooler because of the higher level of CO2 in the troposphere."

  5. If you want to combine these two causes in a single sentence: More CO2 released at the surface means more heat trapped in the troposphere which means less heat released to the stratosphere, per #2, while the additional CO2 in the stratosphere will cause heat to leak into the layer above, per #1, the net effect being that the stratosphere will be losing more heat than it retains. It's emissivity vs. absorptivity ratios played out on a global atmospheric scale, and those ratios are determined by the different properties of the atmospheric layers.

    You ask: "How can CO2 increase emission of radiation to space if it is absorbing less radiation from below?"

    Per above, collisional deexcitation. As 'Anonymous' noted, when density and temperature are higher, there is greater opportunity for transfer of KE via collisions. The CO2 molecules deexcite, emitting heat energy through the thin atmosphere and out into space.

    You also make heavy weather (pun intended) of the graph by Clough and Iacono, JGR, 1995. However, you seem to misunderstand the graph by claiming it should depict something it was never meant to depict in the first place. The graph is meant to measure temperature as function of altitude and wavenumber, not altitude and *latitude* (which would be necessary if you're trying to measure the "hot spot" in the tropics). Outside of the tropics, we expect a positive lapse rate as we climb toward the stratosphere, but since the graph in question doesn't capture latitude, the point is moot.

    If you want to see CO2's influence on the troposphere, it's best to look at time series data. For this we can look at the radiosonde and satellite record courtesy of NOAA, UAH, RSS, etc. who have sampled ex situ measurements for the last few decades. All records show a pronounced warming signal over length of the record.

    - Daniel Bastian

    1. Daniel Bastian: "Due to the extremely different properties of these layers, changes in CO2 concentration produce inverse effects on temperature"

      I'm curious if you also believe that the differences in the location of CO2 molecules may cause cooling vs. warming in the Antarctic vs. Arctic. The warming in the Arctic since the mid-1990s has been attributed to increased CO2, of course. In contrast, for Antarctica, it was recently determined that increases in CO2 concentration cause cooling:
      For this region [central Antarctica], the emission to space is higher than the surface emission; and the greenhouse effect of CO2 is around zero or even negative, which has not been discussed so far. We investigated this in detail and show that for central Antarctica an increase in CO2 concentration leads to an increased long-wave energy loss to space, which cools the Earth-atmosphere system.
      So is it not only true that CO2 functions differently (causes warming or cooling) depending on how high it is located above the Earth, but also whether it's located in the Arctic vs. Antarctic on the Earth's surface?

      Furthermore, is it possible that CO2 causes warming or cooling depending on the decade (or century) the concentration increase occurs? In other words, is it true that in some decades CO2 causes warming and other decades CO2 causes cooling? I ask because there was a significant cooling in the Arctic from the 1940s/1950s to the early 1990s, just as anthropogenic CO2 emissions began their rapid ascent (human emissions were ~1 GtC/year in 1945 and over 6 GtC/year in 1990). Was this cooling in the Arctic caused by the dramatic increase in anthropogenic CO2 emission during those decades? If so, did this cooling caused by increased CO2 switch to warming caused by increased CO2 in the 1990s? What are the physics associated with this heating sign change based upon the decade of CO2 emission?
      “Absence of evidence for greenhouse warming over the Arctic Ocean in the past 40 years”
      In particular, we do not observe the large surface warming trends predicted by models; indeed, we detect significant surface cooling trends over the western Arctic Ocean during winter and autumn.
      Since 1940 ... the Greenland coastal stations data have undergone predominantly a cooling trend. At the summit of the Greenland ice sheet the summer average temperature has decreased at the rate of 2.2 °C per decade since the beginning of the measurements in 1987.
      Analysis of new data for eight stations in coastal southern Greenland, 1958–2001, shows a significant cooling (trend-line change −1.29°C for the 44 years), as do sea-surface temperatures in the adjacent part of the Labrador Sea, in contrast to global warming (+0.53°C over the same period).
      Trends over the 1901–2000 century in southern Greenland indicate statistically significant spring and summer cooling. General periods of warming occurred from 1885 to 1947 and 1984 to 2001, and cooling occurred from 1955 to 1984. The standard period 1961–90 was marked by 1–2°C statistically significant cooling.
      From the graph summaries on page 270 (3rd page down).
      “The CO [Climate Optimum] is 2.5 K warmer than the present temperature, and at 5 [thousand years ago] the temperature slowly cools toward the cold temperatures found around 2 [thousand years ago]. The medieval warming (1000 A.D.) is 1 K warmer than the present temperature, and the LIA is seen to have two minimums at 1500 and 1850 A.D. The LIA is followed by a temperature rise culminating around 1930 A.D. Temperature cools between 1940 and 1995.”