The CSIRO’s Version

The Greenhouse Effect According to the CSIRO [3]

1.Sunlight passes through the atmosphere, warming the earth’s surface.
2.In turn, the land and oceans release heat, or infrared radiation, into the atmosphere, thus balancing the incoming energy.
3.Water vapour, carbon dioxide and some of the other trace gases absorb part of this radiation, allowing it to warm the lower atmosphere, while the remainder is emitted to space.
4.This absorption of heat, which keeps the surface of our planet warm enough to sustain us, is called the greenhouse effect.
5.Without heat-trapping greenhouse gases the surface would have an average temperature of –18°C rather than our current average of 15°C.

I will investigate these 5 points by reference to the energy budget as proposed by Kiehl and Trenberth below:-

The Earth’s Energy Budget
Figure 3: The Earths Energy Budget [4]
1.Sunlight passes through the atmosphere, warming the earth’s surface.
This is a bit misleading. The implication is that Sunlight passes through the atmosphere un-impeded. This is obviously not true.
Of the 342 units of Sunlight reaching the Earth, 77 (or 22.5%) is reflected by the atmosphere – mainly by clouds. Clouds are – yes – H2o – which has a major contribution to the Greenhouse effect. Also 67 units (or about 20%) is absorbed by the atmosphere (once again – mainly by clouds – this energy does not reach the surface of the Earth). 30 units or about 9% is reflected at the surface. Of the original 342 units only 168 warm the Earth’s surface….
2.In turn, the land and oceans release heat, or infrared radiation, into the atmosphere, thus balancing the incoming energy.
NO – once again this is misleading. The incoming 168 units of energy is balanced by outgoing convection and radiation. According to Kiehl and Trenberth’s model, 102 units of energy are released from the surface due to convection (air flow and latent heat), and 66 units by radiation. (This is obfuscated in the diagram – there is 350 + 40 upwards and 324 downwards = 66 upwards)
3.Water vapour, carbon dioxide and some of the other trace gases absorb part of this radiation, allowing it to warm the lower atmosphere, while the remainder is emitted to space.
‘Part of this radiation’ means part of the 66 units (see above). It is incorrect to say that absorbed radiation in the cold atmosphere will  warm the warmer Earth. It may restrict heat flow to space – thus warming the planet.
However, what happens to the 102 units of energy absorbed by the atmosphere due to convection  and the 67 units absorbed from the direct sunlight. How is this energy emitted to space? All up 235 units are emitted to space – by Greenhouse Gases in the atmosphere. If these gases were not present this energy could not be emitted. Why is this not considered in CSIRO’s explanation?
4.This absorption of heat, which keeps the surface of our planet warm enough to sustain us, is called the greenhouse effect.
There is no need for this effect!
5.Without heat-trapping greenhouse gases the surface would have an average temperature of –18°C rather than our current average of 15°C.
NO – the temperature of the Earth when calculated correctly is 6°C. Where does this calculation come from? Why is the CSIRO re-hashing this flawed calculation.  The value of –18°C comes from incorrectly assuming the Earth to have an absorptivity of 0.7 for incoming radiation and then treating the Earth as a ‘black-body’ for out going radiation! This is a fundamental error. It would be more useful to equate absorptivity with emissivity (both = 0.7). When this value is used the average temperature of the Earth is about 6°C. This sounds about right when you include the atmosphere when estimating the average temperature.

[4] Kiehl, J. T. and Trenberth, K. E., 1997 Bull. Amer. Meteor. Soc., 78, 197-208.
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