Regional Greenhouse Effect – Based on Observational Evidence
Written by Hans R. Jelbring
Any solar system planet or satellite with a thick atmosphere shows a positive Greenhouse Effect (GE) according to NASA. The average planetary surface temperature and the average longwave radiation flux seen from space has both been measured extensively. This information provides a basis to calculate the planetary (global) GE. Hence, the NASA planetary GE values for Venus, Earth, Mars and Titan are 510, 34, 0 and 10 degrees Kelvin (NASA 2016). It can and should be questioned why the GE differs so much on different planets. A way to come closer to an answer is to calculate a number of regional GEs (RGE) on earth and study their variations.
This is possible since the outgoing longwave radiation (OLR) has been measured carefully during many years by several space crafts. It is possible to calculate an average emission temperature for any specific region on earth. Gridded monthly data of both OLR and surface temperature for selected regions averaged over many years were provided by www.cdc.noaa.gov (2009), data which have been used in this study. It turns out that the RGE values on earth varies between about minus 10 to plus 52 Kelvin depending on a number of physical factors. The RGE value was highest in Amazonas and lowest at the South Pole. The RGE values were above the average of 34K over the oceans and in equatorial regions strongly suggesting an impact of water vapor concentration as an important factor. Which physical mechanism that probably is dominating the GE value on earth and any planet with a dense atmosphere is discussed.
It is a physical fact that the surface of either Venus, earth and Titan is warmer than the atmosphere at an elevation where the bulk (in the troposphere) of the absorbed solar radiation is leaving the planet as longwave electromagnetic radiation. This temperature difference constitutes the true definition of the Greenhouse Effect. Such a definition is solely based on observations and do not indicate the cause of why a GE on Venus is 510K, why it is 34K on earth and 10K on Titan. Hence, the name Greenhouse Effect is a misnomer as long as it is interpreted that “greenhouse gases” solely are responsible for the observed planetary GE.
The solar energy flux reaching earth is 1361 W/m² according to NASA planetary fact sheets (2016). 30.6% if that flux is directly reflected back to space. The incoming absorbed energy flux is hitting a circular surface of as seen from Sun where R is the radius of Earth. If the atmosphere succeeds in distributing the incoming absorbed solar energy evenly around all the surface of earth the energy emission area will be . Hence, an averaged assumed constant OLR (over any long time period) would then be 236 (W/m²). All regions of Earth certainly doesn´t send a constant amount of longwave energy flux back to space from everywhere which is clearly shown by space craft data and table 1. This simple model has produced rather crude planetary GE values. Still, this NASA model does not lack merits.
To calculate RGEs over all areas of earth would thus be an improvement relative the calculation of a global GE. This is not done in this work but the maximum and minimum monthly OLR values at 15 specific regions have been collected. These regions should be seen as representative samples where different physical conditions are producing RGE values that substantially differ from the crude 34K global value. These RGE values certainly indicate a number of physical factors that are important for the variability of RGE values on earth and it follows that these factors also have to influence the global GE. Each RGE value calculated in this work way is more accurate than the global one calculated by NASA as described above. The NASA global planetary values rest on the assumption that the received solar energy can be equally distributed to all part of the surface of earth. An atmosphere has to be relatively thick if this should be a fair approximation. This condition is not met in the Martian atmosphere but is well met in the Venusian and in Titan´s atmospheres.
Approximately the same solar energy flux that each planet receives have to leave the planet over a longer time period. Daily and yearly variations can be filtered out by choosing to investigate a time period which is long relative to a day and short relative to a year. The choice here is to select a month as a suitable time period for investigating the variability of the RGE values. The chosen regions span the most extreme regions of earth as well as sea, continental and high altitude regions and are found in table 1. There was an option in the cdc.noaa (2009) data to select any area of earth to get the monthly OLR for the selected region (averaged over several years) and also the monthly temperature for the same region. For each region, a summer month and a winter month were chosen showing the highest and lowest OLR values. These were mostly found in January and July and are listed in table 1.
The RGE values are calculated by 1) using the OLR value to calculate the regional average longwave emission temperature by the aid of Stefan Bolzmann law just as NASA does for planets and 2) to subtract the average regional surface temperature given by the gridded cdc.noaa data (2009).
The observed range of flux is surprisingly “narrow” and vary from about 160 W/m² (North Pole during mid-winter) to 350 W/m² (summer in Sahara). This lends support to the way NASA calculates global GE values on planets. The energy flux to space during the winter darkness in the Arctic region is thus an amazing 160 W/m² while the average global long wave emission flux to space is 236 W/m².
The selected regions are ranked by the highest RGE value during summer. To get an impression of seasonal impact a ratio called OLR ratio has also been calculated. It is simply the maximum monthly summer OLR divided by the minimum monthly winter OLR.
Table 1. Regional Greenhouse Effect, averaged monthly values over several years (Kelvin)
The high spread of RGE values from 52.1K to -10K is quite remarkable. These values can and should be treated in detail but such a treatment will be left out in this short presentation. Some remarks are made below about the RGE variability. The following statements seem to be supported by the RGE values in table 1.
The RGE values are highest during summer months indicating a dependence on solar irradiation.
The RGE values are high along the equator.
The RGE values are high over oceans.
The seasonal variation of RGE values over oceans is small.
The seasonal variation of RGE values is large over big land masses such as Siberia, US Plain, Tibet and Barents Sea. The latter one should be regarded as land since it is ice covered much of the year.
The lowest RGE values are found at the poles and on Greenland.
High altitude seems to diminish the RGE value.
The physical mechanisms influencing RGE valus will only be discussed for Vostok which has a negative RGE value. This value depends on a combination of several physical factors. 1) The atmospheric mass per area unit is low, 2) there is little moisture in the atmosphere preventing longwave radiation to quickly reach space, 3) the high altitude makes it easier for infrared radiation to reach space, 4) the great inversion (several km thick) makes the air above the surface warmer than the surface itself and 5) the cold air moving downslope creates an adiabatic heating when air is subsiding towards to the polar surface. South Polar region is unique. A complex combination of physical mechanisms is at work preventing a normal positive RGE at the South Pole.
Jelbring has claimed that the major reason for the development of a planetary GE is the atmospheric mass. This work and earlier result (Jelbring 2003) has not changed the opinion of the author. The major reason why Venus has a GE of 510K is strongly suggested to depend on the fact that its atmospheric mass is 90 times the one on earth. The reason why Mars has a GE of zero K is that its atmosphere is less 1/100 of earth´s atmosphere. Its thin atmosphere lacks the ability to transfer solar energy around the planet to any large extent making the NASA model very inaccurate for Mars. The chemical composition of any atmosphere is suggesting to be much less important than the its mass per surface area as a cause for a GE.
Without doubt water vapor and high temperature affect the RGE values. It is hard to find a more humid area on earth than Amazonas which has the highest RGE value. A high moisture content over oceans are also increasing and stabilizing RGE values over the season as can be seen in table 1. Another important mechanism is the global atmospheric circulation making air to rise at the equatorial area (Intertropical Convergence Zone, ITCZ) and to release condensation energy in high altitude clouds.
It is also obvious that RGE values are higher than 20K in most regions except in the polar ones. This should be the case since in a hypothetical insulated static atmosphere gravity will induce an adiabatic temperature lapse rate in the troposphere according to first principle physics (Jelbring 2003). The only region outside polar areas that has a RGE value below 20K is Tibet during winter. Then the atmosphere is thin and cold carrying little water vapor, factors that are diminishing the RGE values.
RGE values do vary because of a number of physical reasons also meaning that the temperature lapse rate on earth deviates from the theoretical (a static atmosphere) value of -9.8 K/km. The observed value according to the 1976 U.S. Standard Atmosphere is -6.5K/km. On Venus, on the other hand the temperature lapse rate is following the theoretical one almost exactly from the surface to an altitude around 40 km.
The result from this work and Jelbring (2003) strongly supports the opinion that the dominating physical process causing GE on planets is the energetic equilibrium state that an atmosphere would tend to reach if it would be totally insulated from its surroundings. This situation is close to persist in Venus´ troposphere. Very little solar irradiation is reaching the surface of Venus. If earth´s atmosphere were 90 times as massive it would also have a GE around 400-500 K. Water vapor has an influence on earth in a similar way as methane has on Titan since both these gases condense and produce clouds which affect the energy fluxes and consequently also the RGE values.
Acknowledgment: The author thanks the few scientists that have reacted in a proper way to my 2003 paper instead of ignoring it for 13 years. No scientist has yet proven its conclusions to be wrong and the author is looking forward to discuss the paper in a serious way also with established climatologists.
Gridded climate data bank, www.cdc.noaa, 2009.
Jelbring H. R., The Greenhouse Effect as a Function of Atmospheric Mass, Energy & Environment, Vol. 14, Nos. 2 & 3, 2003.
NASA planetary fact sheets, http://nssdc.gsfc.nasa.gov/planetary/factsheet/(planet)fact.html, 2016.
US Standard Atmosphere, http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19770009539.pdf, 1976
Editor’s note: the above analysis is not necessarily supported by scientists and researchers of Principia Scientific International.