2011-02-03 21:10:41Flux vs energy balance
Paul D


Something has been puzzling me for months (I was going to say ages, but I only really started to try and understand climate science when climategate hit the fan). Physicists and climate scientists refer to 'flux' (actually I remember learning some basics about fluxes as a graduate and I don't think I really understood it then) and that 'less flux' radiated at the TOA means more warming.
Yet at the same time (and this makes more sense) the planet is in constant energy balance/budget, eg. what comes in, must eventually go out, otherwise we would spiral into something that goes beyond run-away warming.

Now this puzzles other people as well, including a retired teacher friend. To me, it doesn't make sense that less flux out would only mean a little warming, to me it would mean accelerated warming because the output is not balancing the input. I know I must have this concept totally wrong!

A typical example is presented by SoD:



"In essence radiative forcing is the change in TOA flux. When less flux escapes this is considered a positive radiative forcing. The reason is this: less flux radiated from the climate system means that less energy is leaving, which means the climate will heat (all other things being equal)."

Energy Budget:

"As the climate warms, if the lapse rate (note 3) stays the same, eventually the radiation to space – from this higher altitude – will match the absorbed solar radiation. This is how increases in radiatively active gases (aka “greenhouse” gases) affect the surface temperature (see note 4)."

(My emphasis in the energy budget quote.)

Can someone throw some light (not to technical) on the terms/differences. Energy budget makes sense to me, flux I find confusing.

2011-02-04 02:51:04
Mark Richardson

Let me know whether I helped or hindered here :P (also, flux is actually the flow of something through a unit area, but we don't need to know that to follow the concept!)


Flux is related to flow. In a week I might earn £100 and spend £100 with a bank balance of £1,000. Flux in equals flux out, so I'm at money balance. (it doesn't have to be the same pounds going in and out, it's just the total amount that matters!) If I started saving £2/week off my bus ticket I'd have a net flux of £2 into my account and it would start growing.


In the climate when flux in equals flux out you are at equilibrium or 'energy balance'. Greenhouse gases reduce flux out, so flux in is bigger and we warm. Warmer surfaces emit more radiation, so it pumps out more flux until once again equals flux in and you are back at energy balance but at a higher temperature.

So you have a net flux soon after the CO2 is added, but the Earth warms up and this warming up eventually cancels it out so there is no longer a net flux, but balance. The difference between transient and equilibrium climate change takes a lot of thinking about to follow and it's led to a lot of confusion. On WUWT they just assume they're right and scientists are wrong then write an article filled with their own ignorance...



water analogy:

Think of a bucket with lots of holes poked in it all the way up (e.g. every centimetre up the side there is a small hole). I pour water into the bucket 'flux in' at a rate that equals the water leaking out of the holes so that the amount of water (our analogue for 'temperature') is constant.

If I blocked 2 holes I've caused a 'flux imbalance', the water level will rise. But once it's found 2 other holes (ignoring pressure :P ) it will cancel out that imbalance and there'll be no net flux again but a 'water balance', just at a higher water level.


Flux is power through an area, and for something with constant area (like the Earth) then you can use it interchangably with power.


2011-02-04 03:14:05
Paul D


Actually I remember the flow through a unit area thing from my undergraduate days (I graduated in 1981!).
Seem to remember something about magnetic fields, transformers, induction etc.

So really then, the flux quoted by SoD (in this case) is a temporary situation until the in and out eventually balance.
Really though the net flux measured should be positive or negative, not just less or more.

Ha. That's what my energy flow meter shows on my Warmcast simulator.
I guess I knew what it was all the time.

The trouble is you can read these things and you begin to wonder if there is something else you hadn't taken into account.
Thanks Mark.

2011-02-04 04:06:54The Ville & MarkR
John Hartz
John Hartz

Thank you both for a very enlightening discussion. My undergraduate days were in the 1960s when I received a BS in Civil Engineering. My carrer was in transportation planning and program administration, not science. Needless, to say, my memory banks about basic physics and chemistry are full of cobwebs. Slowly but surely, I'm sweeping those cobwebs away.

MarkR: You post about flux and the bucket metahpor is a very well written explanation of a complex topic. If you haven't already done so, I recommend that you buff it up and post it as a general information piece on SkS. 

2011-02-04 04:35:30
Paul D


Ah Badgersouth, I had wondered where you get the time to spend so much effort on tackling skeptics on blogs etc!
It is clearer now. I actually thought you might be a teenager or student?!!

2011-02-04 05:51:34The Ville
John Hartz
John Hartz

Naw, I'm a retired "old fart" who is deeply concerned about what we are bequeathing to our children and grandchildren. 

I believe that John Cook invited me to particpate in the boiler room with you all in order to fill the role of "dummy-in-residence."

2011-02-04 05:51:35
Rob Painting
I agree with you Badger, the bucket analogy is always a "goodie".