My thanks to Ben Wouters, who posts as Ben AW here at the talkshop. He has been patient and easygoing throughout the N&Z debate, injecting his own perspective in various comments, some of which I’ve pulled together here to form a loose narrative of his line of thought. To my own way of thinking, his ideas don’t actually conflict with N&Z’s theory. I’ll explain why in comments.
Looking from space system earth is a sphere that receives ~1364 W/m^2 on a disk with the same radius as system earth and radiates away to space from all sides.
Just draw a sphere (circle in 2D) and show incoming from one side, and outgoing everywhere.
If anywhere in this system radiation is 100% reflected, it doesn’t influence the energy of system earth, and may as well not be there.
So in my opinion albedo is the same as throttling down the sun, or placing a partly reflecting mirror outside system earth.
Assuming 30% reflected radiation incoming solar is 955 W/m^2 on the mentioned disk, distributed over the whole sphere makes ~239 W/m^2. If the averaged outgoing is also ~239 W/m^2, sytem earth is radiatively in balance with incoming solar, and the total energy (and temperature) doesn’t change over time.
What happens inside system earth and what the temperature is at some places is what everybody is arguing about. I have a very simple model in mind, that explains to me all kinds of processes, without going into much details initially. Everything that happens INSIDE system earth is just redistribution of energy, having no influence on the total energy.
Incoming solar is either:
- absorbed somewhere and transported or re-emittted and thus part of the energy budget of system earth
- or it is reflected without doing anything and may as well not exist for system earth.
I’m not interested in black, gray or purple bodies in whatever flux field you can imagine. It’s not relevant for my system earth.
It seems 239 W/m^2 IS the average outgoing radiation, so incoming HAS to be reflected partly to match this number.
Can we continue and use 70% of incoming solar after albedo as realistic and have a balanced radiation budget?
Next step in the creation of a simple model for system earth.
Initially system earth was a sphere of molten material, radiating away like crazy and thus cooling down, not much the sun could do to stop this.
A very thin solid layer formed on the outside, and by outgassing an atmosphere formed, containing ao water vapour. Raining out ( and perhaps some help from the occasional meteor) formed the oceans, initially very hot.
New phase for system earth, hot mantle “sealed” by a thin layer of rock, covered by a hot ocean.
Lets say 350K or so, way above what the sun seems capable of doing and more or less evenly distributed over the surface and into the deep of the oceans.
(will add the continents later, they mostly just create weather)
So in this phase we have a hot mantle covered with a solid crust keeping the heat inside, and still very hot oceans. Since there is no more heat coming from the hot mantle, the oceans cool down.
Next phase for system earth. It rotates, receives 70% of solar at the surface and has no tilted axis yet.
By conduction, evaporation, radiation the oceans lose heat to the atmosphere.
Lets assume convection hasn’t been invented yet.
By conduction only the atmosphere will develop a nice lapse rate towards space. May take a couple of million years but earths is not in a hurry.
We need some components of the atmosphere to radiate away to space, otherwise system earth can’t cool down at all.
I think that water vapour will do the trick, but anything that works is fine to me.
So the oceans are cooling through the atmosphere, and the sun is shining over the equator during daytime. Most of the cooling will be near the poles, less near the equator since the sun slows the cooling there.
Since before climate science came along cold water went down, and warmer water came up, I’ll assume this still to be true, so eventually all the warm water from the bottom came up and the deep of the oceans get colder and colder.
Earth is still radiating away more than it receives from the sun, and is thus still cooling.
Simple model, present time.
eg. the Pacific profile.
Most of the oceans have cooled down to just above freezing, lets say 275K or 277K on average.
Only a small surface layer, where all the warm water from below has ended up, is still above this temp.
Reason being that incoming solar and cooling through the atmosphere cancel each other out.
So we have radiative balance with the sun, and a temperature at the surface that is at least 275K in the polar regions, and higher at the equator (~300K)
(to keep the temp near the poles ~275K, we need to begin adding ocean currents, warm at the surface, cooler down below.)
This “band” of warm water that spans the earth is all that is required to prevent the deep oceans from cooling down.
This warm band is about 750m deep at the equator, and reduces to 0m around the polar circles.
So this simple model explains imo why we have a temperature that is above the GHE 255K greybody temperature without the use of backradiation or similar constructs.
Let’s start adding some complexity.
Axis tilt. The warm band moves north and south, following the sun with a delay of about one month.
This allows the polar seas to freeze over during winter, and the sun melts the ice again during summer.
Everything that changes the amount of incoming solar, changes the volume of the warm band.
eg. change in TSI, Milankovitch cycles, volcanic eruptions etc. etc.
Less solar, the depth and width of the band decreases, more solar the opposite.
Ocean currents transport warm water from the equator towards the poles. Warm water at the equator expands, so this water will probably flow “downhill” towards the poles, turning east due to the corriolis effect. Backflow will be in the deeper oceans probably.
Continents. They will disrupt the simple ocean currents from equ. to poles.
They will create “weather”, since they heat up easily, and cool down rapidly without sun.
I have hardly mentioned the atmosphere, since it’s heat capacity is equal to about 3,2 m of ocean water, so rather a minor player. They’re basically a gaseous extension of the oceans.
But a lot of the weather (and thus climate) can easily be explained using this simple model as base.
Some loose ends.
- The incredible stability of the oceans surface temps. during day and night surprised me.
Explanation is here: http://www.terrapub.co.jp/journals/JO/pdf/6305/63050721.pdf
Less than 1K variation between day and night, except in very calm weather.
- The very small influence that the hot inner parts of the earth are supposed to have.
(< 1 W/m^2 if I remember correctly)
We may be in for a surprise here. Apart from ocean vents, under water vulcanic eruptions etc.
we also seem to have places where the crust is totally gone, exposing the oceans to the hot mantle.
http://www.livescience.com/1317-mission-study-earth-gaping-open-wound.html and http://dro.dur.ac.uk/8919/
Should have some influence on the earth’s temperature, since the heated water will show up at the surface sooner or later.