The global warming debate - a personal perspective

• However this has to be a global effort. Australia on its own can do nothing. We should follow, not attempt to lead.

Scientists behaving badly

Certain scientists have behaved badly. Some have fudged their data. The shocking behaviour of some scientists does not alter the laws of physics. I hope readers will bear this truism in mind in what follows.

The physics explained - greenhouse effect in a nutshell

Incoming radiation from the sun

Energy from the sun reaches us in the form of electromagnetic (EM) radiation. 43% of the energy is in the form of visible light. About 8% is in the form of ultraviolet (short-wave) radiation. The rest is in the form of near-infrared (long wave) radiation.

97% of the ultraviolet (UV) radiation is blocked by the Earth's ozone layer.

All major atmospheric gases are transparent to visible light. On a clear day most of the visible light makes it through the atmosphere to the surface. Some of the light is reflected from the surface. Most is absorbed and serves to heat up the surface of the Earth. That is, mostly it heats up the surface of the oceans.

The picture for infrared (IR) is more complicated. The atmosphere is opaque to some wavelengths and partially transparent at others. For some IR wavelengths, the so-called atmospheric window, the atmosphere is completely transparent.

I can best summarise the situation as follows. If the atmosphere were completely clear and transparent at all wavelengths an average of 341 watts / square metre of EM energy would reach Earth surface from the sun. The actual amount would vary by time of day, season and latitude but 341 watts / square metre would be the average.

The actual average taking into account scattering by clouds and dust and absorption of same wavelengths by the atmosphere is 184 watts / square metre according to satellite measurements.

If that were all there was Earth surface would be frozen. Average temperatures at the surface would below freezing instead of around 15 degrees Celsius.

Upward radiation from Earth surface

Every body with a temperature above absolute zero radiates EM energy. Earth surface is no exception. The average upward radiation from Earth surface is around 396 watts / square metre. Most of this is absorbed by greenhouse gases which then heat the atmosphere.

Note that that the upward radiation from the surface is well above the direct incoming EM from the sun. How can that be?

Back radiation from the atmosphere

As the atmosphere heats up it too begins radiating EM energy. Some of this is radiated out into space and some back to Earth surface. Counter-intuitively the "back radiation" radiation from the atmosphere to Earth surface is almost twice as intense as the direct radiation from the sun. It is this back radiation that keeps average temperature at Earth surface above freezing.