Our Saviour – The Hydrological Cycle
Extra CO2 in the air from human sources is supposed to put us on a route to catastrophe but the message is a bit garbled.
Some say the extra CO2 heats the air and that is enough to do the trick. Others accept (correctly) that that is unlikely due to the thermal inertia of our oceans and their cooling effect on the air so they propose an ‘ocean skin’ theory whereby warming of the topmost molecules on the ocean surface from extra downwelling infra red radiation from extra human CO2 in the air is supposed to reduce the natural energy flow from sea to air so that the oceans get warmer and then heat the air and kill us off that way.
The term ‘ocean skin’ is rather a misnomer because in reality the area of interaction between air and water is a haze of mixed water and air molecules in constant dynamic interaction.
Interestingly, and importantly, the power of downwelling infra red radiation is insufficient to get past the region involved in evaporation. In that respect it is unlike soar radiation which penetrates the ocean to hundreds of metres depending on wavelength.
Is either proposition realistic?
If water is cooler than air (as a result,say, of more greenhouse gases warming the air) then it cools the air (sea fog, anyone ? ). The energy taken from the air by the water is trivial compared to the amount of energy required to warm a volume of water as much as the same volume of much less dense air. One could barely measure the increase in water temperature if ALL the energy were transferred to the water from the same volume of air. I think the ratio is something like 800 to 1. In practice only a transfer of a tiny proportion of the energy in the air occurs. Just enough to reduce the air to the same temperature as the water. Thus the warming of the water is too small to measure.
On that basis alone the cooling effect of the oceans would dictate that it would take many millennia for any warming effect in the air from extra CO2 to become measurable let alone dangerous.
As regards a warming of the ocean skin, evaporation is a continuous process caused by temperaure, density and pressure (not just temperature) differentials between water and air so that the rate of evaporation accelerates when a water surface is warmed such as from the warming effect of extra greenhouse gases (especially if the air is dry).
As long as the air remains unsaturated (nearly always, due to wind and convection) the air is capable of holding more water in vapour form so itdraws more energy from the water by converting more water molecules to vapour. Note that hot dry air above water will increase the rate of evaporation but so also does cold dry air above water. That is important for the rest of this article.
Water vapour is a gas whereas water is a liquid and to achieve that change of state a very large quantity of energy gets tied up in the molecules of vapour in latent form which means that it’s presence is not reflected in the actual temperature ot the air which carries it.
Now, consider what happens when extra downwelling infra red radiation from extra human CO2 reaches the ocean surface.
Note that any extra energy taken by evaporation from warm air above cooler water or from warm water below cooler air will be used to bring forward the timing of the change of state of those molecules already on the cusp of changing state (there are always many such molecules because evaporation is a constant process when the air above the water is not saturated which is nearly all the time).
In relation to those molecules which do change state earlier than they otherwise would have done the energy required to provoke the change of state is always less than the latent heat taken from the surrounding environment of water AND air when the change of state occurs. The latent heat of evaporation is a big number.
As a result of the consequent cascade effect bringing forward the timing of the change of state of multitudes of water molecules, the increased evaporation results in an increased net flow of energy from water to air . The rate of evaporation always increases in proportion to the supply of extra energy to water molecules at the surface or to molecules of air that are in contact with the water surface so that no warming of the ocean by the air can occur.
When the air is cooler than the water, evaporation can slow down (especially if the air is humid) because the transfer of energy from water to air could be inhibited by the reduced capacity of the air to carry it as water vapour with it’s attendant latent energy but evaporation still occurs continuously (in the absence of saturation) because of the density and pressure differentials between ocean and air and also because of the processes of wind and convection which make the reduced vapour carrying capacity of cooler air less significant than it’s continuing ability to accept evaporating water molecules.
Crucially it does not matter whether the water or the air is the warmer because the latent heat required can be taken from either. The evaporative process will always draw it’s latent heat from the most readily available source whether it be water or air. The size of the temperature differential between air and water combined with the rate of movement of both air and water within the region of interaction dictates the rate of evaporation and the density and pressure differential dictates the direction of energy flow which on Earth is always continuous at variable rates from water to air.
Thus direct solar heating of the air will cause increased evaporation as will warming of the water surface by increased downwelling infra red radiation onto the water surface from, say, extra human CO2. The so called ocean skin theory therefore fails because despite any warming of the ocean skin the evaporation rate increases to compensate for it and there is no net reduction in the ‘normal’ energy flow from ocean to air.
The transfer of energy from water to air is always in that one direction whether water or air is the warmer. It is part of the one way transmission of solar energy through the Earth system, sun to oceans to air to space (at variable speeds dependant primarily on internal oceanic behaviour, not the composition of the air). The sun provides variability in the energy flow over centuries but the oceans provide much larger variability in the energy flow over decades.
The air circulation systems move latitudinally poleward or equatorward depending on whether there is net cooling or warming of the air at a gradual if variable rate all the time and climate shifts in any given location depend mainly on the changing position of that location in relation to the latitudinal position of the major air circulation systems.
Throughout all this the oceans are in control because internal oceanic circulations in each ocean combine to vary the rate of energy emission to the air (The Hot Water Bottle Effect).
Weather on a day to day basis is simply a level of chaotic variability imposed on the combined effects of all the above.
The oceans control the background rate of energy flow from ocean to air via The Hot Water Bottle Effect and it is the energy flow from ocean to air (supplemented to a miniscule extent by the greenhouse effect) that drives the rate of evaporation by creating varying temperature differentials between sea surface and air at the surface. In turn, the rate of evaporation drives the entire hydrological cycle by altering the size and latitudinal positions of the air circulation systems and thus the rate of energy transfer from surface to space.
All weather and climate follows, in a plethora of observed phenomena, from that underlying process. Extra GHGs merely cause an additional miniscule adjustment in the size or position of the alr circulation systems and no measurable effect on air temperatures.
Warm air cannot cause warming of the ocean bulk because the rate of evaporation increases proportionately to the extra energy available and the latent heat of evaporation is taken mostly from the air. It is then no longer available to warm the water.
If the warm air is saturated so that the rate of evaporation cannot increase then condensation occurs and the extra energy in the air is released into the air and radiated away upwards and not into the water. The droplets of condensation are always at the temperaure of the water below. Again the extra energy is no longer available to warm the ocean bulk.
Warmer water surfaces from extra downwelling infra red cannot cause warming of the ocean bulk because the rate of evaporation increases proportionately to the extra energy available and the latent heat of evaporation is then taken mostly from the water.It is then no longer available to warm the ocean bulk.
If the cool air is saturated so that the rate of evaporation cannot increase then the water surface releases steam instead and the extra energy is still released into the air and radiated away upwards and not into the water below. Again the extra energy is no longer available to warm the ocean bulk.
It is the ability of the evaporation process to choose which medium (water or air) to extract the necessary energy from that ultimately stabilises the Earth’s equilibrium temperature, maintains the ‘normal’ energy flow from water to air and thus enables the Earth to retain it’s oceans.
“In every situation any extra energy from any source in the air alone fails to get transported into the ocean bulk. All energy removed from either the water or from the air by evaporation becomes latent energy in the air which does not raise the air temperature of the air (it being latent) so that the temperatures of the air and of the topmost molecules in the so called ocean skin always move towards equilibrium The flow of latent energy (held by water vapour) from surface to space is further enhanced via wind, convection and ultimately condensation out at a much higher level above the surface where that energy is more readily radiated to space.”
Thus extra energy in the air from extra GHGs increases the evaporation rate which increases the speed of the hydrological cycle which prevents the extra energy in the air from warming the oceans whether via the ocean skin theory or otherwise.
AGW is thus falsified because the air cannot warm the oceans and the air circulation systems always adjust to bring surface air temperatures back towards sea surface temperatures.
Climate models do not reflect this obvious truth and the ideas of Tyndall et al whilst correct if taking the air in isolation cannot affect the global equilibrium temperature set by the constantly varying interplay of sun air and oceans.
Common misconceptions :
1)“This assertion probably needs some qualification. It is falsified by the simple fact that ice water (and cold beer) does get warmer when exposed to warmer air. A similar mechanism certainly does transfer energy from the atmosphere to the ocean.”
In that situation the ice water or cold beer warms by conduction from the surroundings through the container. There is no direct net energy transfer from air to liquid.
Evaporation from the open surface of the container continues throughout and removes more energy from the liquid than is added from contact with the air.
The liquid nevertheless warms up because the energy from conduction exceeds the energy lost by evaporation. That cannot happen with a huge ocean overlain by a thin layer of air exposed to space. In that situation the energy flow is always continuous and one way only. However the rate of flow does vary and it is that variability in the rate of flow that ultimately falsifies the idea of human induced climate change. Any extra energy in the air or on the ocean skin simply accelerates the flow of energy from water to air to compensate for any extra energy input caused by characteristics of the air alone.
Extra energy from the sun or changes in the rate of emission of energy by the oceans are not cancelled out so readily by changes in the rate of evaporatrion and over time will change the Earth’s equilibrium temperature. The air alone cannot do it.
2)” I’ll stop storing my ice cubes in the freezer then, and put them in the larder.”
Ice does not evaporate as freely as water because it is a solid although over time even in a freezer it does evaporate away in the process known as ‘sublimation’ though the temperature remains below freezing.
In a larder the cooling effect of the evaporation of any melted ice will always exceed the warming effect of direct contact of the water with air but melting has to occur first. Overall the warming effect of conduction would exceed the energy lost by evaporation hence the melting.
Note that in the larder the surface of the ice has to melt first before evaporation can increase to full speed. The initial melting does take more energy from the air than is lost in evaporation but that energy then becomes latent energy in the water and so the air is cooled but the remaining ice is not cooled. The dominance of conduction is what melts the rest of the ice.
3)Surely mixing of ocean surface waters with water below will transport energy downwards?
If the surface waters are disturbed so that some mixing can occur then that is more than offset by the surface area of the water increasing due to the development of waves. That is one reason why increased windiness will also increase the rate of evaporation. Again, the extra energy is not available to the ocean bulk.
However, changes in the internal circulations of the oceans (not mere ocean currents) will alter the rate of energy emission from water to air and thus over time change the equilibrium temperature of the Earth but that is part of the sun/oceanic interaction and nothing to do with changes in the composition of the air alone. Changes in the air alone cannot get energy into the oceans past the evaporative process.Published by Stephen Wilde July 17, 2009