Dear Jennifer,
A couple of weeks ago I became quite agitated after reading an article in The Australian’s Higher Education section by Roger Jones of CSIRO. Jones questioned the sceptics drawing attention to flaws in the computer models and then went on to explain what the models were supposed to do, not what they actually do!
I responded to The Australian with the following submission:
Global Warming: Solving an Environmental Problem or Creating a Social Crisis?
Prevention of dangerous climate change, particularly through implementation of a national carbon pollution reduction scheme, has emerged as a primary policy objective of the Rudd government. The rationale for the policy is the scientific assessment of the Intergovernmental Panel on Climate Change (IPCC) and its computer-based projections of global warming. We are told by the IPCC ‘consensus of scientists’ that continued burning of fossil fuels, and a range of other industry activities that increase the concentration of ‘greenhouse gases’ in the atmosphere, will lead to dangerous climate change, possibly passing a ‘tipping point’ causing ‘runaway global warming’.
What does this all mean, really?
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.
How then do we explain to people who are going to be affected by reactionary government policies what are the greenhouse effect and its enhancement by additional carbon dioxide?
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 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.
Additional warming of the surface will come about when the greenhouse effect is enhanced. The fundamental question is how much warming will additional greenhouse gas concentrations cause and will it be dangerous?
An increase in the atmospheric carbon dioxide concentration reduces the emission of longwave radiation to space and increases the back radiation at the surface. An increase in back radiation adds energy to the surface, which will further warm the surface. However there is a constraint on the surface temperature rise because of the commensurate increase in rate of energy loss from the surface: both the rate of infrared emission and the rate of evaporation of latent heat increase with temperature.
The increase in radiation emission from the surface can be calculated from the well-known Boltzmann equation and is 5.4 units/oC at 15oC. The earth’s surface is mainly ocean or freely transpiring vegetation and evaporation will increase near exponentially with temperature according to the Claussius-Clapeyron relationship and is 6.0 units/oC at 15oC. According to the IPCC, the radiative forcing from doubling of carbon dioxide concentration is 3.7 units.
The actual surface temperature increase is derived from the ratio of the radiation forcing (3.7) to the natural rate of increase in surface energy loss with temperature (5.4 + 6.0). The direct surface temperature rise from a doubling of carbon dioxide is therefore 3.7/(5.4 + 6.0) = 0.3oC.
A 0.3oC global temperature increase towards the end of the 21st century from a doubling of current carbon dioxide concentration is not obviously dangerous. However, what also needs to be taken into account is the positive feedback. A warming of the surface temperature will cause a warming of the overlying atmosphere, an increase in the water vapour concentration (another naturally occurring greenhouse gas), a further increase in back radiation, and an incremental increase in surface temperature. Each successive incremental surface temperature increase will cause another incremental temperature increase through the positive feedback amplification.
The amplification follows standard mathematical treatment and, as long as the ratio r is less than unity, the gain is given by [1 / (1 – r)]. Here r is the ratio of natural increase in back radiation with temperature (4.8 units/oC – estimated from a standard radiation transfer model) to the natural increase of surface energy loss with temperature (as previously, 11.4 units/oC). The natural gain is 1.7 and increases the surface temperature rise from a doubling of carbon dioxide concentration from 0.3oC to 0.5oC.
A 0.5oC increase in global temperature over the coming century is within recent short-term temperature variability and is less than the apparent global temperature rise of the past century. Moreover, both the direct forcing of surface temperature and the amplification gain are tightly constrained by the magnitude of the natural increase of surface energy loss with temperature increase. It is not immediately apparent how ‘runaway global warming’ could come about with such a constraint.
A fundamental question arises as to why the IPCC global temperature projections for doubling carbon dioxide concentration, based on computer models of the climate system, lead to estimates of about 3oC, or about six times the above estimate.
A clue to the conundrum can be found in published descriptions of the performance of the computer models used in the IPCC fourth assessment. Isaac Held and Brian Soden, writing in the Journal of Climate (2006) note that the rate of increase of evaporation in the computer models, on average, only increases at about one-third of the rate expected from the Claussius Clapeyron relationship. Additionally, Frank Wentz and colleagues, writing in the journal Science (2007), have confirmed the under-specification of evaporation increase with temperature and, from satellite based observations, have determined that global evaporation does indeed comply with the Claussius Clapeyron relationship.
It is clear from the above formulation of the surface temperature rise and the associated amplification gain that each is sensitive to the specification of evaporation increase with temperature. Substitution of the average evaporation specification of computer models into the formulation will boost the projected temperature rise from the above expected value of 0.5oC to 1.5oC, the lower end of IPCC projections. When the specification of evaporation increase with temperature is very low, as in the more extreme models, then the feedback amplification gain increases to a value of about ten; the temperature sensitivity of the computer model becomes highly exaggerated and model would likely simulate the behaviour of runaway global warming. The behaviour, of course, is false and arises only because of the significant under-specification of evaporation.
Despite the many claims that the IPCC projections of human-caused global warming are sound, the consensus of climate scientists and that the science is settled, there are disturbing shortcomings to both the essential explanations and to the computer modelling. The shortcomings are disturbing because the projections and their associated predictions of diabolical impacts on environmental systems are the only rational justification given for wholesale government restructuring of our industrial base and lifestyles.
This is the first time in human history that there has been a conscious move at the national level to discard the tools that have underpinned security, wellbeing and comfort. We are deliberately abrogating energy usage from proven and widely available sources on the basis of a perceived environmental threat which is poorly articulated and substantiated only by recourse to obviously deficient computer modelling.
Why am I reminded of Charles MacKay’s 1841 tome, “Extraordinary popular delusions and the madness of crowds’?
William Kininmonth
Melbourne, Australia.
William Kininmonth is a former head of Australia’s National Climate Centre; a consultant to the World Meteorological Organization; and author of Climate Change: A Natural Hazard (2004, Multi-Science Publishing)
P.S. The four important papers underpinning my analysis are:
Riehl, H and J. Malkus, 1958. On the heat balance of the equatorial trough zone. Geophysica, v6, Nos 3-4 pp503-538 (This paper describes how heat and moisture from the tropical boundary layer is distributed through the troposphere by way of deep buoyant convection, thus offsetting net radiation loss of energy of the troposphere. Buoyant convection requires a decrease of temperature with altitude, thus the surface must be warmer than the effective emission temperature of the troposphere – the greenhouse effect!)
Priestley, C.H.B., 1966. The limitation of temperature by evaporation in hot climates. Agricultural Meteorology, 3 pp241-246 (This paper explains, supported by data, why deserts are hotter than vegetated lands. Essentially, the earth’s surface loses energy by way of conduction, evaporation and emission of infrared radiation; for dry surfaces there is a shift in energy loss to conduction and radiation at higher temperatures whereas for wet surfaces there is a shift to evaporation of latent heat at a lower temperature. This analysis clearly makes a nonsense of the IPCC claim of a linear relationship between surface temperature increase ΔTs and radiation forcing ΔF, that is, (ΔTs/ΔF = λ). From surface energy balance (or conservation of energy), ΔTs = ΔF*[4*σ*Ts4 + A*L*(dqs/dT)]. Here (dqs/dT) is the rate of increase of water vapour saturation specific humidity with temperature (the Claussius Clapeyron relationship); the first term in the brackets on the right hand side is the rate of increase of surface infrared emission with temperature; and the second term is the rate of increase of latent heat exchange with temperature. For a dry surface, the rate of increase of infrared emission with temperature is approximately linear over short temperature ranges – earth’s surface happens to be approximately 70 percent water and a large part of the remainder is transpiring vegetation.)
Held, I.M. and B.J. Soden, 2006. Robust response of the hydrological cycle to global warming. J of Climate, v19 pp5686-5699 (The paper identifies that, in the GCM used in the IPCC fourth assessment, the rate of increase of surface evaporation is on average only one third the Claussius Clapeyron relationship (dqs/dT). The authors use this deficiency to explain why the rate of convective overturning of the models decreases as temperature increases. The important point is that the GCM apparently significantly under-estimate surface evaporation and latent heat exchange with temperature increase.)
Wentz, F.J., L. Ricciardulli, K. Hilburn and C. Mears, 2007 How much more rain will global warming bring? ScienceExpress 31 May (published later in Science, 13 July 2007). (This paper confirms, from satellite data over recent decades, that global precipitation (and hence evaporation and latent heat exchange) increases with temperature according to the Claussius Clapeyron relationship. Thus the under-estimation of evaporation in GCM also implies an underestimation of precipitation increase with warming. The authors do not recognise that under-estimation of evaporation and latent heat exchange will also lead to overestimation of surface temperature rise! I have quantified the over-estimation of global temperature rise in the analysis that follows.)
Jennifer Marohasy BSc PhD has worked in industry and government. She is currently researching a novel technique for long-range weather forecasting funded by the B. Macfie Family Foundation.