Proving or disproving a theory.

By Pat Hackett

A scientific theory can never ultimately be proven but it can be disproven. This is easily seen when we consider a single theory but is a bit more complex when we relate this to complex arguments that incorporates many separate interactions such as climate change.

A single theory.

Take for example Newton’s theories on gravity. Isaac Newton was aware he could not ultimately prove his theories but Albert Einstein eventually proved them to be inaccurate. According to Newton’s laws light should not be deviated by gravitational forces as was predicted by theories on relativity. When light was observed to bend on passing the sun then Newton’s Laws were seen to be ultimately flawed. This of course does not mean we throw them out and never use them again, for the simple fact that they are easy to use and in many cases give us the predictive power we need. Further we know where and where not the predictions will be good enough for the purpose.

Proving Climate theory.

There have recently been challenges given with financial rewards offered for anyone being able to prove that climate change today has been primarily caused by human activity. This of course is safe. It can never be ultimately proven no matter how useful the anthropogenic argument may be.

Disproving Anthropogenic Climate change.

 On the other hand to disprove is possible. However as the AGW theory is complex it can be difficult. The AGW theory includes many factors that can cause our climate to change and one could always argue that if it were not for the AGW then our climate would be very different than what it presently is.

It seems that both of these offers of rewards, for either proof or disproof, cannot be achieved. However if the physics underlying AGW theory could be disproved as in the example above with gravity then you would have a strong claim to have disproven the AGW theory. The whole argument would collapse.

Does back radiation of infra red radiationviolate the second law of dynamics? Many have made these claims. 

Violation of the second law of thermodynamics.

By Pat Hackett

Of course the 2^nd Law of thermodynamics cannot disprove greenhouse gas theory.

 It is true, that in macroscopic terms there is a net heat flow from the hotter object to the colder object. The colder object can radiate energy and the hotter object may absorb some of these photons.

We must bear in mind that all objects can radiate heat if their temperature is above 0K. The colder object will radiate heat in all directions and some of these photons will be absorbed by the hotter 
object. Superficially then it may seem that the 2nd law of thermodynamics has been violated.

More photons per second will be emitted from the hotter object. In fact the energy radiated depends on the temperature of the object and not on the temperature of any other object. The photons don’t know the temperature of any other object and thus they are emitted equally in all directions.

In contrast the net heat flow between two objects will depend on the temperature difference between the two objects. The smaller the difference between the temperatures between the two bodies then the smaller the net heat flow from the hotter to the colder object. Equilibrium can take considerable time to be achieved. With back radiation a higher equilibrium value of temperature can be achieved.

An analogy is useful here.

A gently heated container of water will reach an equilibrium value of temperature. This equilibrium value is achieved when the rate of heat loss from the hot container reaches the rate of energy into the container. The rate of energy into the container may be constant but the rate of heat loss increases with the temperature (in fact proportional to the 4^th power of the temperature ignoring other external heating). In the case of the container this may be an electrical heater placed inside the container. (In the case of the Earth this is from solar radiation that can pass easily through the atmosphere). Place a jacket around the container. The 2^nd law of thermodynamics tells us that if the jacket was at a lower temperature than the hot container then the jacket will not heat the container. True:- This is what the claims merely focus on. However it is clear that because the rate of heat loss is reduced the equilibrium value of the container can be considerably higher.

The Earth’s radiative budget as is proposed here clearly shows that the surface emits more IR radiation than it receives from back radiation. You may have some disagreement with these precise values but it does not violate the 2nd Law of thermodynamics. However it is clear that back radiation increases the equilibrium value of the surface temperature. The surface emits 390W/m2 of radiation, the back radiation is 324W/m2 and the net radiated heat flow is the difference….66W/m2. Heat flows from the hotter object to the colder. As long as there are an appreciable number of molecules involved this must be the case.

If you still believe that this is in violation of the 2^nd law of thermodynamics I would suggest that you will not need to wear a jacket the next time you go out on a freezing cold night.

The second law of thermodynamics being violated argument is based on the simplest of mistakes:- confusing radiation of photons with heat flow.

A separate discussion.

No longer focusing on the 2^nd law of thermodynamics this diagram seems to show more back IR radiation reaching the surface than radiation leaving the Earth. 

This chart shows a net flow and ignores vertical variation. The objection here is easily explained with heat loss increasing with temperature. At each level there is an equal flow of radiation in all directions. Further this diagram shows the total radiation at any level, in the assumed new equilibrium state, is in balance. If you care to take the jacket analogy further you will see that the same applies to that situation.