July 16, 2008 C02Skeptics Stephen Wilde has been a Fellow of the Royal Meteorological Society since 1968. The first eight articles from Mr Wilde were received with a great deal of interest throughout the Co2 Sceptic community. In Stephen Wilde's ninth and exclusive article for CO2Sceptics.Com called "Greenhouse Confusion Resolved" he answers the questions that have been raised as a result of his previous work "The Hot Water Bottle Effect".
GREENHOUSE CONFUSION RESOLVED - by Stephen Wilde
A short while ago I published an article on this site attempting to explain why the so called atmospheric greenhouse effect was insignificant as a planetary heat store in comparison to the oceans. The Hot Water Bottle Effect
I received interesting comments from AGW proponents and sceptics alike which showed an astonishing range of differing interpretations and understandings of the greenhouse effect none of which bore much relation to the actuality.
Perhaps those who made no comment were free of such confusion but somehow I doubt it.
The fact is that unless one can properly appreciate the nature and scale of the effect that an atmosphere has on planetary surface temperature then the significance of my article and indeed the entire underlying debate is impossible to assess meaningfully.
This article will attempt to resolve that confusion.
1) Planets with atmospheres are seen to be warmer at the surface than they otherwise would be. The Earth and the Moon are on average equidistant from the sun but have very different surface temperatures. Mars and Venus follow the same principle in that their huge surface temperature differences are caused primarily by their different atmospheres and not by their different distances from the sun. The atmosphere of Venus is very dense so the surface is much hotter than it otherwise would be. That of Mars is very thin so the surface is only a little hotter than it otherwise would be. The Earth is a special case because I would argue that the oceans should be regarded as a form of atmosphere in much the same way as the air because both air and oceans have heat storing properties. In effect Earth's ‘atmosphere' is in two parts for heat storing purposes and water is the primary player in both components.
2) The only significant heat source for the purpose of this article is solar energy. When solar energy reaches the Earth it is in the form of radiant energy which travels at the speed of light. When that energy hits molecules in the atmosphere the energy is absorbed by the molecules in the atmosphere which then vibrate more quickly. The heat contained in a molecule is expressed by the speed of vibration. First the molecules in the atmosphere warm up followed by those on the surface whether it be land or sea. Part of the total radiant energy is absorbed by the atmosphere, part by the oceans and part by the land.
3) It is important to distinguish between the effect of solar energy falling into the air, onto the land and that falling onto and into the sea. In the case of land the energy hardly penetrates the ground at all hence the consistent coolness of caves worldwide. In the case of oceans the energy does penetrate the surface layers and is often carried away for eventual release elsewhere, depending on the ocean currents.
4) Once the radiant energy has arrived in the air, on the land and in the oceans the question arises as to how it then exits Earth back out to space. According to satellite observations there is always a net balance between radiant energy coming in and radiant energy going out. That must be so because the Earth quickly arrives at a thermal equilibrium by virtue of the fact that radiant energy coming in and radiant energy going out both travel at the speed of light.
5) A warming effect in the atmosphere arises because between coming in and going out the radiant energy is ‘processed' by the molecules in the atmosphere into heat energy and then back again, often many times for a single parcel of radiant energy, the number of times being directly proportionate to the density of the atmosphere. It is the density, not the composition which gives more or less opportunities for such collisions between radiant energy and molecules whilst the incoming and outgoing radiant energy is negotiating the atmosphere. When an atmospheric molecule absorbs radiant energy it vibrates faster thereby becoming warmer. It is momentarily warmer than the surrounding molecules so it releases the radiant energy again almost immediately. The speed of release is again dictated by overall atmospheric density because greater density renders it less likely that the neighbouring molecules are cool enough for a release of radiant energy to occur. However the time scales remain miniscule on the level of an individual molecule BUT on a planetary scale they become highly significant and build up to a measurable delay between arrival of solar radiant energy and it's release to space.
It is that interruption in the flow of radiant energy in and out which gives rise to a warming effect. The warming effect is a single persistent phenomenon linked to the density of the atmosphere and not the composition. Once the appropriate planetary temperature increase has been set by the delay in transmission through the atmosphere then equilibrium is restored between radiant energy in and radiant energy out.
There is much confusion over the issue of ‘re-radiation.' An environmental activist told me that re-radiation occurs repeatedly from greenhouse gas molecules with a consequent runaway warming effect. If that were so then only a handful of greenhouse gas molecules at the creation of the Earth would have destroyed it by now. I think that misconception is at the heart of the public's AGW fears even though some scientists know better.
There is a kernel of truth in that when a molecule in the atmosphere re -radiates the radiant energy previously absorbed then it does so in all directions i.e. half of it goes back down towards the surface again. However one cannot create heat or energy from nothing so there is no net heat gain merely a delay until the part sent down is radiated back up again and has another attempt at leaving the planet. Even if it hits another molecule on the way up then that second molecule sends only half of the initial half back down again so repeated re- radiations decline in size geometrically.
The fundamental point is that the total atmospheric warming arising as a result of the density of the atmosphere is a once and for all netting out of all the truly astronomic number of radiant energy/molecule encounters throughout the atmosphere. The only things that can change that resultant point of temperature equilibrium are changes in solar radiance coming in or changes in overall atmospheric density which affect the radiant energy going out. In the real world the most obvious and most common reason for a change in atmospheric density occurs naturally when the oceans are in warming mode and solar irradiation is high as during the period 1975 to 1998. The increased warmth allows the atmosphere to hold more water vapour so that total atmospheric density increases and the atmospheric greenhouse effect strengthens. This effect is far greater than any CO2 effect. When the atmosphere cools again water vapour content declines and the atmospheric greenhouse effect weakens. CO2 and other trace gases are far too small a proportion of the atmosphere to have any significant effect in comparison to the water vapour effect. Even the water vapour effect has never provoked any tipping point in the face of the primary solar/oceanic driver so CO2 could never do so.
6) Nevertheless a legitimate question is as to whether an increase in one or more allegedly potent greenhouse gases such as CO2 or methane can cause a significant difference on a planetary scale.
The fact is that every molecule in an atmosphere contributes to the greenhouse effect of the entire atmosphere. Some constituents such as CO2 and methane have a stronger effect than average but their quantities are so small that even large proportionate increases have no significant effect on overall atmospheric DENSITY. If as I suggest one includes the much denser oceans as a component of atmosphere then increases in CO2 become irredeemably trivial in terms of their power to alter overall density and thus the global heat retaining process.
Furthermore each constituent of an atmosphere reacts slightly differently to incoming radiant energy. As a result each constituent can only operate as a greenhouse gas with certain limited bandwidths of incoming energy. If there is not enough energy of the right bandwidth coming in then the greenhouse effect of a particular constituent stops. That is why it is often said that the greenhouse effect of CO2 declines logarithmically as the available bandwidth gets used up. Some say that at the current level of 380 parts per million we are close to saturation as regards more warming effect from extra CO2.
That mechanism is quite separate from the matter of density which overrides the matter of absorption characteristics anyway. The atmosphere of Venus is mostly CO2 but the atmospheric heat arises as a result of the density of the Venusian atmosphere (apparently more than 60 times that of the Earth) not just the absorption characteristics of CO2. On Earth the proportion of CO2 is so small that it cannot affect overall atmospheric density even if it increases by many multiples of the current level.
Much of the warming feared by the alarmists relies upon a positive feedback involving increased water vapour exaggerating any CO2 warming effect. However that process is unconvincing to my mind because it ignores the water vapour reducing processes of evaporation, convection, condensation and rainfall which are all substantial, but so far unquantified, moderating effects as far as atmospheric warming from water vapour is concerned. In the past no tipping point has ever been known to have occurred as a result of runaway warming from extra water vapour so how have we been persuaded to fear it so much?
I see no scientific grounds for a speculation that increasing CO2 will have a significant effect on the temperature of Earth when we have the far more important, long lasting and frankly overwhelming Hot Water Bottle Effect to consider and here I will go on briefly to link the contents of this article to my previous one.
7) When land receives radiant energy the surface layer of molecules becomes warm quickly but penetration is insignificant. The heat is quickly radiated back into the atmosphere and joins the rest of the radiant energy in the atmosphere in the process of release to space. Despite any atmospheric greenhouse effect land gets cold very quickly at night and in winter. This suggests that if the planet were entirely land then the speed of heat loss to space would soon make Earth more like Mars or the Moon than Venus. Without the humidity from the oceans there would never be enough density from all the other gases in the atmosphere to achieve a density that could save us from rapid freezing.
8) Now the important bit.
When solar energy reaches the ocean it penetrates the surface. Some is reflected into the atmosphere but compared to land, very little. Ocean currents tuck it away for use another day. Huge amounts of past solar energy are locked in the oceans and only released to the atmosphere when solar driven oscillations deign to release it to us.
The average near surface temperature of Earth's atmosphere is much the same as the average surface temperature of the oceans. That will always be so for as long as we have big enough oceans. Consequently to be able to affect us any extra atmospheric warming effect of CO2 would need to be able to warm up the oceans in order to make any difference to global atmospheric temperature. Due to the huge volume of sea water and the density differentials between air and ocean that would be impossible or would require such huge amounts of atmospheric heating and such huge lengths of time that for practical purposes it should be ignored. To be convinced of that one only needs to consider the impracticality of heating the air in a bathroom in order to raise cold tap water to the temperature of a warm bath. It just doesn't happen. Where air and water are involved the air temperature is always dictated by the water and never vice versa. Stored solar energy built up in the oceans over past millennia dictates the temperature of the oceans which then dictate the temperature of the atmosphere. The atmospheric greenhouse effect is an irrelevance in the face of The Hot Water Bottle Effect. Any extra warmth generated in the atmosphere by CO2 or any other trace gas will quickly be neutralised by the hugely greater effect of the oceans in so far as it has not already been dispersed by increased radiation to space, evaporation, convection, condensation and rainfall.
Warming activists have tried to deal with this problem for their theory by asserting that over time a warmer atmosphere will have a warming effect on the oceans. However they suggest merely a couple of decades. They are ignoring the issue of scale and erroneously believe that the greenhouse effect and not the oceans sets the global atmospheric temperature. Before any measurable warming effect on the oceans can occur the following problems must be overcome:
i) CO2 and other trace gases are too small a proportion of the atmosphere to make a significant difference to overall atmospheric density even if their volumes were to be multiplied many times over. This problem for warmists is greatly enhanced if one considers the much more dense oceans as part of the planetary atmosphere for heat storage purposes.
ii) The respective absorption bands for each trace gas will be exhausted long before the volumes of those gases in the atmosphere become big enough to make a measurable difference to the overall density of the atmosphere and the size of the greenhouse effect which is density dependent.
iii) Any increase in temperature differential between atmosphere and space will increase the outward flow of radiant energy and reduce the overall temperature change if any
iv) Any increase in temperature differential between the surface of the Earth and the top of the atmosphere will increase evaporation, convection, cloud formation and rainfall and so further enhance the flow of radiant energy to space thereby further reducing any temperature change
v) After all that, only a residual greenhouse warming effect (and it may be zero) will be left to have any effect on the oceans. In the unlikely event that it is still large enough to have any effect at all it may well take millennia for any warming of the oceans to become apparent by which time it would be dwarfed by natural changes anyway. Without a warming of the oceans we cannot see a warming of the atmosphere, both are fixed in lockstep with the oceans as the leader.
The Greenhouse Effect is only a tiny part of the global temperature control mechanism. In addition there is The Hot Water Bottle Effect whereby the oceans release stored heat intermittently at variable rates depending on the average state of the various oceanic oscillations at any particular time. The current assumption that the oceanic oscillations are ‘just' a mechanism for redistributing heat already available to the atmosphere must be wrong. The oceanic heat store should be regarded as an additional heat source that adds or subtracts the effect of earlier solar irradiance (or lack of it) to or from the present day effect of current solar irradiance.
The total heat store available in the oceans is so large that it is capable of rendering changes in any Greenhouse Effect an irrelevance for all practical purposes.
Oceanic oscillations are sufficient to cancel out or enhance the effects of natural variations in solar irradiance or other forms of solar input to the heat budget of the Earth for variable periods of time. A range of a mere 4 Watts per square metre or less in Total Solar Irradiance is sufficient to explain changes in Earth's atmospheric temperature for the past 400 years. Outside that narrow band of apparent solar normality we would have more to worry about than any Greenhouse Effect.
The global temperature switches from cooling to warming mode frequently as a result of the ever changing interplay between variations in solar influence and intermittent heat flows from the oceanic Hot Water Bottle. The mechanism by which the oceanic effect is transferred to the atmosphere involves evaporation, convection, clouds and rainfall the significance of which has to date been almost entirely ignored due to the absence of any relevant figures.
The atmospheric Greenhouse Effect merely sets a theoretical background atmospheric temperature level that is continually overridden as a result of the size of the constant interlinked changes in both the solar and oceanic heat inputs. It is wholly swamped by the far more powerful oceanic Hot Water Bottle Effect.
The atmospheric greenhouse effect is a flea on the back of an oceanic elephant and the influence of CO2 but a microbe on the back of the flea and the influence of anthropogenic CO2 but a molecule on the back of the microbe.
By Stephen wilde,
U.K. Private Client Solicitor and lifelong Weather and Climate enthusiast.