Could ‘the greenhouse effect’ be one of those things that everybody claims to understand because it is apparently so important, but in reality it is not supported by a credible scientific literature?
That’s the view of Bill Kininmonth, meteorologist and head of Australia’s National Climate Centre from 1986 to 1998.
Furthermore, Mr Kininmonth is of the view that, “the role of greenhouse gases is to cool the atmosphere and this, with the surface warming from solar radiation, generates convective instability. It is the temperature lapse rate required for deep convection that leads to the ‘greenhouse effect’”
Well in the following note, Mr Kininmonth explains in more detail:
The closest you will come to an explanation of carbon dioxide and the green house effect is in the ‘Frequently Asked Questions’ of the on-line IPCC Fourth Assessment Report.
My critique on them follows.
“The IPCC’s most recent assessment attempts to be helpful to the casual enquirer by having a series of explanations for ‘frequently asked questions’, or FAQs. The first FAQ is ‘What factors determine earth’s climate’? We are informed that, on average, the earth emits 240 w m-2 of radiation to space and that this equates to an emission temperature of -19oC. The earth’s temperature, however, is about 14oC and the -19oC temperature is found at a height of about 5 km above the surface. To quote the IPCC: “The reason the earth’s surface is this warm is the presence of greenhouse gases, which act as a partial blanket for the longwave radiation coming from the earth’s surface. This blanketing is known as the natural greenhouse effect”.
This explanation by the IPCC is clearly misleading, if not wrong. The inference that the greenhouse gases are acting like a blanket suggests that they are increasing the insulating properties of the atmosphere. However, the main gases of the atmosphere are oxygen and nitrogen, non-greenhouse gases, and they are also excellent insulators against the conduction of heat (like a blanket); adding additional trace amounts of carbon dioxide will have no appreciable impact on the insulating properties of the atmosphere.
In its third FAQ, ‘What is the greenhouse effect?’ the IPCC comes to the nub of the issue but provides a different and equally misleading explanation. “Much of the thermal radiation emitted by the land and the ocean is absorbed by the atmosphere, including clouds, and reradiated back to earth. This is called the greenhouse effect”. According to the IPCC’s global energy budget, the surface emits 390 W m-2 of radiation and the energy radiated back to the surface is 324 W m-2. It is difficult to see how an ongoing net loss of longwave radiation energy from the surface of 66 W m-2 can lead to warming! Indeed, we are all aware that between dusk and dawn the earth’s surface cools.
The IPCC has not explained in a scientifically sound and coherent way, how the ‘greenhouse effect’ is maintained. The greenhouse gases do not increase the insulating properties of the atmosphere and the back radiation does not warm the surface. The IPCC explanation of the greenhouse effect is obfuscation and, even to the mildly scientific literate, reflects ignorance of basic processes of the climate system.”
I am of the view that ‘the greenhouse effect’ is one of those things that is accepted because it is there, everybody claims to understand it because it is so important, but in reality few know how it comes about. My explanation follows (and you will not find this in IPCC publications):
“A credible explanation has no need for smoke and mirrors. The energy flow through the climate system is predominantly by way of four stages: 1) absorption of solar radiation at the surface; 2) conduction of heat and evaporation of latent energy from the surface to the atmospheric boundary layer; 3) convective overturning that distributes heat and latent energy through the troposphere; and 4) radiation of energy from the atmosphere to space. We will see that it is the characteristics of convective overturning that keep the surface warmer than it would otherwise be.
The Kiehl and Trenberth (1997) global average energy budget of the earth (see figure, where the units are W m-2) is used by the IPCC and is a useful starting point for explanation of the establishment and maintenance of the greenhouse effect.
Of the 340 units of solar radiation entering the earth’s atmosphere, 67 are absorbed by the atmosphere and 168 are absorbed at the surface. There is thus an ongoing source of solar energy available to the atmosphere and the surface.
At the surface there is a net accumulation of radiation energy because the incoming solar radiation (168 units) exceeds the net loss of longwave radiation (66 units).
In the atmospheric layer there is absorption of 417 units (390 of emission from the surface, less 40 that go directly to space, plus absorption of 67 of solar radiation) and an emission of 519 units (324 back to the surface and 195 direct emission to space). The net effect of the interaction between the greenhouse gases and radiation is a tendency to cool the atmosphere because it is continually losing energy.
Overall there is a dichotomy, with radiation processes firstly tending to warm the earth’s surface and secondly tending to cool the atmosphere. Air is an excellent insulator against conduction of heat and will not transfer heat through the atmosphere, as is necessary for energy balance. Also, the thermodynamic properties of air (potential temperature increases with height) ensure that turbulent motions of the atmosphere will mix energy downward, not upward as required.
The process for transferring energy from the surface to the atmosphere, necessary to achieve overall energy balance of the climate system, was explained by Herbert Riehl and Joanne Malkus (the latter better known as Joanne Simpson) in a 1958 paper, On the heat balance of the equatorial trough zone (Geophysica). Riehl and Malkus noted that boundary layer air, rising buoyantly in the protected updraughts of deep tropical convection clouds, converts heat and latent energy to potential energy. Away from the convection, compensating subsidence converts potential energy to heat.
What is implied in the Riehl and Malkus model is that deep tropical convection, and the transfer of energy from the surface to the atmosphere, will not take place without buoyant updraughts within deep convection clouds. That is, there is a need for the temperature of the atmosphere to decrease with altitude and that the rate of decrease of temperature must be sufficient to allow buoyancy of the air ascending in the updraughts. From well-known thermodynamic laws, the rate of decrease of temperature must be at least 6.5oC/km to allow the buoyancy forces of convection to overcome the natural stratification of the atmosphere.
The climate system will come into energy equilibrium when temperatures are such that the net solar radiation absorbed is balanced by the longwave radiation to space. At equilibrium, the greenhouse effect (ie, that the average surface temperature of 14oC is greater than the -19oC blackbody emission temperature of earth) is an outcome from the need for convective overturning of the atmosphere.”
Essentially, the role of greenhouse gases is to cool the atmosphere and this, with the surface warming from solar radiation, generates convective instability. It is the temperature lapse rate required for deep convection that leads to the ‘greenhouse effect’. But this takes the wind from the sails of the AGW folk.
Mr Kininmonth is the author of Climate Change: A Natural Hazard available from Amazons.