How Water Vapour Dominates Energy Transfer Between Earth and Space

In the debate regarding climate the second law of thermodynamics is often quoted but rarely explained. For a starter lesson watch Flanders and Swan sing the basics. But these are rules. Not the understanding of them. The problem is understanding the nature of energy which is in reality a flux over a time.  Energy only exists as a static quantity when stored in some indirect primary form, in a battery, fuel tank, rubber band, hydroelectric dam, chemical molecule or nucleus, etc,  and is only able to do work when released to create an energy flux that must do work, which may be to store itself in another form, as heat, chemical energy, etc. To do this a flow of electromagnetic energy must occur, from a more energetic source to a less energetic sink. Crucially, energy cannot flow uphill.

So the fundamental truth is that energy will always flow from a place where the energy density is higher to one where it is lower, to balance the Universe. This is the universal entropy heat death theory. Not coming any time soon, as there is lot of localised energy hot spots around the Universe with very intense energy left to redistribute. This also means  energy must flow from a hotter to a colder place, because temperature is an indication of the energy intensity/density of a substance, energy per unit mass. In an ideal gas or vacuum the majority of the energy flow is a radiative flux, pure energy propagating to another place, which is always unattenuated in a vacuum, also in some atmospheres, to a location where it might be stored in another form to that which it was stored in before, perhaps doing work on the way, or simply lost in space as low grade heat, far, far, away.

This is both poorly explained and poorly understood. It is because pure energy is a flux, it does not exist in a static form, it must be used to do work as produced, or be stored as potential energy, in a battery, pumping water uphill, winding up a rubber motor, whatever. Otherwise, when radiated from a planet it is lost in space (Microwave background is such an energy field throughout the Universe). Generally this involves the energy becoming much less dense or intense, so more physical matter is required to store it in its new form, it becomes less structured than before.

Energy stored for use elsewhere must be in some other form than electromagnetic radiation. For example, in molecular or atomic structures, made in stars,  the most energy intense structural forms of molecular binding energy or nuclear binding energy, released by chemical reactions or nuclear fission & fusion. These two are the main power sources of developed economy, because the higher the energy intensity, the more efficient and lower cost per unit is the energy extraction from its source. The more extreme the intensity, the more difficult to achieve, with the bonus that the higher the temperature difference, the higher the efficiency of conversion/energy transfer.

From there we can go down to the relatively weak gravitational potential energy, for example water collected behind a dam, to form a lake that can energise a hydro energy scheme, where the water loses gravitational potential energy on its way from higher up to lower down. Other weak forms of energy flux are wind and water flow in tides.

Water is of interest to this account of the way solar energy flows through the Earth’s surface systems. In hydro power it gives up the energy it gained by being converted from a liquid to a gas, water vapour, lifted into the atmosphere by convection in air warmed by the ocean surface, all powered by the solar radiative flux, gaining in gravitational potential energy as it is lifted higher into the troposphere. The energy stored in the latent heat of vapourisation of water is also transported towards space by this convection in the warm, so less dense, atmosphere rising from the surface. When it gets high enough, so cold enough, the change from liquid to vapour structure of water vapour is reversed and the water vapour condenses. The energy of latent heat is released as radiation to space, where it is colder, as discussed later. The now liquid droplets of colder so denser condensate fall back to earth as rain to be aggregated in river system to fill the lake and increase the store of gravitational potential energy. This store of gravitational potential energy, originally provided by solar energy that uplifted it,  can now create hydro power when converted to the kinetic energy of water flow, in a flux of water in this case, the kinetic energy is usually harvested from the water in a turbine located below the lakes surface water level where it becomes an electrical flux of pure enrgy. The water then returns to the ocean to repeat the water cycle, energised by the Solar radiation from the nuclear fusion generator 93 Million miles away. A cycle that we have exploited to extract a small part of the solar energy that drives it.

But where does the energy stored in the water vapour go when it condenses?

As with a chemical or atomic reaction, the pure energy produced by the condensation process has to go somewhere. In a solid, liquid or gas this may be by conduction and convection – thermal excitation of colliding molecules, in a vacuum only electromagnetic radiation can transport energy. In an atmosphere both radiation and convection can be powerful contributors to energy transport. As the atmosphere thins, it is in ever reducing contact with itself, so energy transfer will increasingly be by radiation, which is measured as a flux of electromagnetic energy. This happens at the top pf the lower atmosphere, at 0.1Bar, in the tropopause. This energy flux can be described as radiative or photonic, per the duality of energy and matter at quantum levels. It’s the same thing, pure energy realised in different ways by the physics because physics needs two ways to best describe what happens, as we measure it.

 This flux can only flow to a place where energy levels are lower, so to colder matter it interacts with and excites, until an equilibrium between the source and sink is reached and flow stops as the two systems come into thermal equlilibrium, as in a cooling curve…

….OR to space itself from the warmer body to the near absolute zero of surrounding space.  Because space naturally needs to be of a uniform energy level, energy will always tend to flow from points of high energy to areas of lower energy, to try to flatten the overall energy level of the universe, in the same way that a water mountain in the ocean is not sustainable.  The more different they are the higher the flow. Wherever the energy levels equalise the flow of energy ceases. This does not happen in this case the case of space as there is a lot of emptiness to fill.

To be very clear, energy cannot flow from a less intense energy source to a more intense one, the flowing uphill of the first paragraph. This requires a reduction in entropy, which cannot happen in a Universe where every conversion of energy into work increases entropy, creating more disorder that is measured by the resulting entropy, a form of energy that is unrecoverable to do useful work.  This requires some maths to fully grasp, and a read of Maxwells theories, but is just as well qualified in words. I hope this helps understand the second law of thermodynamics.

brian.catt@phsyics.org / brian.catt@deconfused.com

Why does this matter now? I am involved in a debate around the way that energy released in the atmosphere from condensing oceanic evaporation must be lost to space, and cannot return its latent heat as warming energy to the lower and hotter atmosphere as frequenty claimed by climate scientists.

Because, as already explained above, when that radiative energy is released in the colder Troposphere, it can only flow one way, down the energy intensity hill to space, where its colder. Much colder. Not towards the warmer surface. Not uphill.

This, hopefully, also explains why the atmosphere cannot heat the oceans, the atmosphere is mainly heated by the dominant heat sink of the oceans, directly warmed by the Sun which absorbs and stores roughly over 96% of all the energy absorbed by the earth’s surface, and is the only source of atmospheric warming for half the day. The oceans can do this because they have 1,000 time greater thermal capacity than the thin atmosphere above. They are greater in both mass and specific heat. I leave that simple maths to you to check. Any smart speaker will give you the numbers to determine the total mass and specific heat of air and water.

When the structural store of latent heat energy in condensing water vapour is released as radiative energy flux in the Troposphere it is no longer contained by the water vapour, and must immediately leave for somewhere colder. That is to the Universe, and beyond, travelling perhaps for human ever, at the end of its interrupted journey into space, from the heart of our Sun, through the Earth’s energy balance system, down the inevitable thermal gradient to deep space, still energy as a flux seeking interaction to do work in space.

In particular,  this transfer by latent heat is measured to provides one third of all Earth’s radiative heat loss to  space. So the strongest planetary cooling of Earth’s surface is by latent heat alone. That varies with the quantity of water vapour, which is measured to change at close to 7% per degree Kelvin across most of the oceans, over a wide range of temperature humidity. As tabulated and illustrated below.

Once free of its structural bonds, the latent heat energy of oceanic evaporation must leave Earth as electromagnetic radiation and won’t come back, because Earth, heated continuously by the Sun, will stay warmer than wherever that radiation went, for now.

This matters because it’s claimed by some Climate Scientists, as regards evaporation from the oceans, that when the water vapour condenses in the Troposphere “it returns the heat to the atmosphere and surface”,  in “warm rain” and other fictions that are denied by the measurement of the whole system energy balance, as well as the 2^nd Law of Thermodynamics, as explained above .

To summarise, this  is simple nonsense because the water already lost its latent heat energy as it condensed, as the radiative flux that immediately flowed to much colder space, as seen in Earth’s energy balance, measured by satellites to be departing this Earth.

We also observe that the condensate, as it accumulates to a drop size large enough to fall under gravity in the warmer rising atmosphere from the hotter surface below, often starts off as ice in the troposphere, and is in fact warmed by more warm and humid rising air from the mainly ocean surface on its way down through the warming lapse rate of the atmosphere. This is well described in school as the water cycle.

The idea that the latent heat energy in evaporation can return to the surface in rain is wrong, because it directly denies the well observed laws of physics at work. And the reality we measure. The latent heat component of the energy in water vapour must leave for colder space as the radiative flux it creates during condensation. It won’t be back. The atmosphere now returns to the surface, cold and dense in its convective circulation, to be uplifted again, energised by the solar energy warming the surface and transporting more of the latent heat of evaporated water vapour to the Troposphere, to repeat the transfer of solar energy by this natural escalator of latent heat energy to space. I hope I have explained why it works like that. And is not reversible, as some activist climate scientists claim. Without any scientific basis for their claims. Going down the up escalator in natural thermodynamics is not difficult, it’s impossible.

nb: Possible by adding energy in a heat pump that does work using another energy, but that’s another story.

Earth’s Radiative Energy Balance – Summary

	Source		NASA 2010 10y Avg		Trenberth 2009 4y Avg		Sensitivity % K-1
			Wm-2		Wm-2
	Solar Energy Insolation (24h average)		340.4		341.3
	Of which:
	Energy reflected by Atmosphere		-77.0		-79
	Energy absorbed by atmosphere		77.2		78
	Energy reflected by surface		-22.9		-23
	Energy absorbed by surface		163.3		161
	Solar energy absorbed by Ocean & Atmosphere:		240.4		239
	Energy radiated to space from Ground unscattered		40.1		40		1.4
	Energy radiated to Space from surface scattered by GHE		17.8		23		1.5
	Energy radiated from the atmosphere to space		77.2*		78.5*		1.5
	Latent energy of evaporated water vapour radiated to space after condensation		86.4		80		7
	Atmospheric thermal energy convected to troposphere radiated to space		18.4		17		0.3
	Total Outgoing LWIR radiated to space		239.9		238.5
	Net imbalance on Earth		0.6		0.9
	Nb: 4 π Internal GHE scattered radiation, including upwelling and downwelling, is identical in magnitude and does not leave the system, so cancels in the balance. GHE is an internal state variable with a small net effect.		340.3		333

Nb: Values are derived from diagrams. Imbalance is temporary & unimportant within overall scale and balance, which the system must converge upon.

Brian RL Catt 2024

NASA ENERGY BALANCE 2010

https://www.dropbox.com/scl/fi/783mijobopn46s163kmhx/NASA-Earth-s-Energy-Budget-Annotated-BRLC.png

TRENBERTH ENERGY BALANCE 2009

https://www.dropbox.com/scl/fi/k8ny3s9ckbjz79fa1bz49/Trenberth-2009.png

ENDS