Thanks to No Tricks Zone for posting work (here) by Dr. Dai Davies of Canberra. In his writing I found a fine summary paradigm leading to the image above. This post presents a scientifically rigorous view of our planetary climate system, starting with an airless rocky surface and then conceptually adding the dynamic elements in layers. The text below with my bolds and images comes from Energy and Atmosphere by Dr. Dai Davies of University of Canberra, Website: http://brindabella.id.au/climarc/.
The Earth’s atmosphere in stages
This is an hypothetical scenario that allows us to build up a picture, step by step, of how having an atmosphere can influence a planet.
Baseline: Airless, Rocky Planet
As a starting point we consider how the Earth’s temperature might vary through the daily cycle if it was an airless, rocky planet much like the moon. During the day, the sun heats up a surface layer of the rock which cools through infrared radiation. The temperature follows the sun’s irradiation almost directly, rising and plunging over a range of hundreds of degrees.
Add: Radiatively Inert Atmosphere
If we add a radiatively inert atmosphere, its only means of gaining and losing heat would be thermal conduction through direct contact with the Earth’s surface. The heat capacity of a square meter column of the Earth’s atmosphere is equivalent to that of about 12 tonnes of granite, so far greater than a thin layer of rock heated by the sun. While the surface would still go through a temperature cycle, the atmosphere would achieve an equilibrium where the mean lower atmosphere matched the mean surface temperature – give-or-take geography and atmospheric circulation. It would act as a buffer that would stabilise surface temperatures – cooling the surface during the day and warming it at night. This is discussed further in note (a) with some simple calculations.
All molecules are radiatively active if the energy is high enough. A realistic atmosphere, such as a nitrogen and oxygen mix, absorbs some energy from the light and UV components of incoming solar radiation, but still can’t lose heat through infrared radiation.
Add: Water Vapour, Ignoring Condensation
We now add water vapour to the atmosphere at typical Earth levels of up to 4%, but ignore the effects of condensation. Water molecules are kicked into excited states by collisions with nitrogen or oxygen molecules which lose some kinetic energy in the collision. Most of this energy will return to kinetic in subsequent collisions. Otherwise, the energy is radiated in a random direction as an infrared photon, which creates a radiation flux that travels much faster and further than molecular movement. Their mean free path (mfp) is typically 50 metres in the surface atmosphere, increasing with altitude as the density of the air decreases and collisions are less frequent. A small part of this energy escapes to space, a smaller part is absorbed by the Earth’s surface, leading to a net transfer to space.
This radiative flux greatly increases the thermal coupling between the surface and near-surface atmosphere, adding to the transfer via direct thermal conduction and reducing the daily temperature cycle of the surface, tying it closer to the temperature of the lower atmosphere. Due to the highly nonlinear nature of radiant emission, this will have a net heating effect on the surface as described in note (a).
The increase in mfp with altitude means there is a small upward bias in photon transmission through the atmosphere’s photon sea created by molecular collisions. This net upward transfer of energy largely substitutes the direct infrared radiation from surface to space, adding a slight delay in the order of milliseconds. Heat is not ‘trapped’, as is commonly claimed, just slowed a little. It’s a rapid conduit, not a reservoir.
Add: Liquid Water Covering 70% of Surface
For the next stage in the transition towards our current atmosphere we add our present distribution of liquid water over 70% of the rocky surface. This changes things dramatically. First, rather than just heating a thin surface layer of rock that can radiate heat rapidly, the sun’s rays penetrate deep into the oceans, heating water that retains its heat until physical mixing brings it to the surface. In the upper ‘mixing layer’ this happens in days to months. Some is mixed deeper and can travel for centuries in deep ocean currents before surfacing.
At the surface of the oceans and wet land we now have evaporative cooling which extracts heat of vaporisation and cools the surface just as sweat cools our skin. Water vapour is lighter than air and reduces the air density. The lighter air rises, creating convection. As it rises it eventually cools to the point where liquid water condenses out to form clouds and dumps the heat of vaporisation into the upper atmosphere. The main impact of clouds is to reduce incoming solar radiation by reflecting it back out to space.
Most of the heating is in equatorial regions. The rising air creates the major Hadley circulation cells that carry heat polewards in the upper troposphere. The radiating upper air cools and becomes more dense as it travels, eventually sinking back to surface level and returning to equatorial regions.
Water isn’t the only radiative gas in our atmosphere, but it dominates. The next in significance is carbon dioxide. It’s main impact is in the upper atmosphere where most of the water vapour has condensed out. This impact is cooling. Its influence in the lower atmosphere is discussed later.
Finally, we add Life.
Early on, it added the oxygen to our atmosphere. Now, its plants have changed the surface albedo – the amount of the sun’s energy reflected back to space. Through transpiration they also add to evaporation in increasing the input of water vapour to the atmosphere. Some plants and algae produce aerosols that seed clouds – terrestrial plants increasing their chances of rain – marine biota reducing the incidence of destructive UV.
There is much more to be learned from this thorough, well written article, but I will conclude with Davies’ summation:
The most fundamental of the many fatal mathematical flaws in the IPCC related modelling of atmospheric energy dynamics is to start with the impact of CO2 and assume water vapour as a dependent ‘forcing’ (note e). This has the tail trying to wag the dog. The impact of CO2 should be treated as a perturbation of the water cycle. When this is done, its effect is negligible.
Extensive analysis of radiosonde data over time, and an associated theoretical analysis, by Miskolczi (6) has shown that the water cycle adapts to maintain saturation – maximum impact – in the combined effects of water vapour and any other radiative gasses.
The sudden increase in evaporative cooling of warm water creating an upper bound for wet surface temperatures, along with the freezing point of water limiting ocean temperatures at the poles, anchor the overall surface temperature of the Earth. The Earth’s orbit, variations in solar activity, and long term transport of heat in ocean currents, provide cyclic variations. The lapse rate just determines the height of the tropopause. The net effect of CO2 is to help cool the upper troposphere where water vapour levels are low.
The current small peak in temperatures is partly the result of heat returning from past millennial cycles – the historians’ climate optima of the Medieval, Roman and earlier warm periods. As then, solar activity is now at low levels.
Davies provides a concise synopsis of several posts touching on key elements of earth’s climate.
My own discussion of climate layers is in Climate Reductionism
The effect of an inert atmosphere is shown empirically in Planetary Warming: Back to Basics
The reference above to Dr. Miskolczi is elaborated in The Curious Case of Dr. Miskolczi
The role of oceans in storing and distributing heat is described in Climate Water Wheel
The passage of energy through the atmosphere is explained at On Climate Theories
“The Earth, a rocky sphere at a distance from the Sun of ~149.6 million kilometers, where the Solar irradiance comes in at 1361.7 W/m2, with a mean global albedo, mostly from clouds, of 0.3 and with an atmosphere surrounding it containing a gaseous mass held in place by the planet’s gravity, producing a surface pressure of ~1013 mb, with an ocean of H2O covering 71% of its surface and with a rotation time around its own axis of ~24h, boasts an average global surface temperature of +15°C (288K).
Why this specific temperature? Because, with an atmosphere weighing down upon us with the particular pressure that ours exerts, this is the temperature level the surface has to reach and stay at for the global convectional engine to be able to pull enough heat away fast enough from it to be able to balance the particular averaged out energy input from the Sun that we experience.
It’s that simple.” E. M. Smith