|Energy balancing when no forcing|
There have been two or three people on the climate denial conversation on Twitter who cannot conceptualise global energy flows. Remember, almost all the deniers in this particular conversation are greenhouse effect deniers who don’t “believe” physics and chemistry. Nonetheless they’ve discovered a wonky diagram in the deniosphere somewhere and have asked how it works. The short answer is, it doesn’t. Not the way it’s portrayed in their diagram.
Dr Kevin Trenberth has kindly allowed me to publish this updated global energy flow schematic, which is about to be published. (I’ll post the doi when it is available.) Here it is, with an explanation below:
|Figure 1 | Global energy flows. Source: Kevin Trenberth (pre-publication)|
Energy coming in from the sun
Our source of energy is the sun. The sunlight travels as shortwave radiation, which we refer to as “light” (or visible light). It’s shown in yellow in the diagram above.
Some of this incoming energy is reflected by clouds and the atmosphere and doesn’t get to the surface.
Some of it is reflected from the surface. Ice is a good reflector. Oceans are not at all good and get heated up by the sun (they absorb the energy). Other parts of land vary in how much they reflect and how much they absorb. As you’d imagine, darker colours get hotter and lighter colours reflect more sunlight.
Energy coming up from the surface of the planet
The other side of the schematic (the brownish bits) shows what happens to the energy from the warmed surface. The surface emits longwave radiation, which we’d commonly term “heat” but it doesn’t have to be hot or even warm. This energy circulates within the earth system and some goes back out to space. (In a stable system, the amount of energy going out would equal the amount coming in.)
Some of this radiation coming off the surface goes straight back out to space and doesn’t stay in the system at all.
Some of it circulates within the system, as I’ve said. For example, some is absorbed by greenhouse gas molecules, such as water vapour and CO2. The molecules get more energy and can pass some of this energy onto other molecules. Within a few milliseconds they emit the energy back out and drop back to their normal state. That energy (a photon) can go in any direction, so statistically about half the photons head back to the surface (below a 180 degree plane, if you like). This goes on at all levels in the air, so there’s lots of opportunity for a photon to hit a greenhouse gas molecule and be absorbed. (I won’t go into the technical details here.) That part is shown in the brownish bit of the diagram labelled “downwelling radiation”.
Some energy from the surface is transferred to the atmosphere via thermals and evapotranspiration (as water vapour). The latter of course comes back again when the water condenses in clouds.
Stability when energy in = energy out
When the amount of greenhouse gases is stable (not increasing and not decreasing), the whole energy flow stabilises and the amount of radiation coming in from the sun (short wave) is the same as the amount going back out to space (short wave and longwave). However, this doesn’t happen immediately because the greenhouse gases slow down the radiation escaping. It takes a while for the system to get into balance. The surface warms up and eventually gets to a steady temperature that is higher than if there were no greenhouse gases. That is, energy is circulating within the system and, while some of the energy from the surface finds its way out, it is being topped up, if you like, by the sun every day.
Increasing greenhouse gases => warming planet
When greenhouse gases are increasing as they are now, then more energy remains in the system than goes out. As the energy system tries to equalise, it finds there are more greenhouse gas molecules than there were the day before, so there’s a bigger barrier in the way with every passing day and less energy can escape to space. That’s why we see global surface temperatures rising, ocean heat increasing, ice melting, seas rising, and a more energetic water cycle. When the greenhouse gases stop increasing, the system will balance and, once again, energy in will equal energy out, but the system will only cool down as greenhouse gases come out of the system (by photosynthesis, weathering etc.)
The shonky diagram, and why.
A denier put up a shonky diagram and asked for it to be explained. Well I can’t explain why anyone would draw it, but I can point out why it’s wrong. It’s incomplete. (Gilles exhibits strange, indeed disturbing behaviour at times. He keeps saying how he wants to crush people, and that altruism is evil.)
Here is the diagram Gilles posted.
The top left of the diagram shows net sunlight coming in (239 Wm-2). That is, the amount coming in minus the amount reflected back from the atmosphere and the surface. The bottom middle of the diagram shows the longwave radiation that’s been absorbed from the energy radiating up from the surface.
All the bits in between are missing.
The diagram doesn’t show sunlight hitting the planet or that reflected back to space. Nor does it show the the amount of longwave radiation being emitted from the surface or the energy radiated from the surface that goes back to space. Nor does it show any of the internal flows such as the water cycle. It’s only part of the global energy flow and so one bit doesn’t match the other. It’s not matching in the type of radiation, one’s short wave incoming the other is long wave greenhouse gas received from the surface and emitted back down (not the up bit).
The left hand side is energy from outside coming in. The right hand side is energy circulating within the system. Because the planet is warmer than it would be without greenhouse gases, there’s plenty of energy available to circulate within the system. It doesn’t all go straight back out to space.
The notations “cold to hot” are a story for another time. (I’ll give you a hint. This particular brand of denier doesn’t believe that all substances above absolute freezing emit radiation. They think photons are sentient and know when there’s a hot or cold object in their path, and decide to emit accordingly. They don’t understand physics.)
More energetic nonsense from deniers
Did I mention deniers are conspiracy theorists? This is one of the comments from “JoePublic”, who reverts to primitive vulgarity, cursing and other inanities when he figures he needs more attention. He or she is one of the deniers who’s pretending to want to learn about the energy flows on earth.
This was after he asked some “not even wrong” questions – like this and this. Joe is fairly typical of the crowd in that conversation, so you can understand why I say there’s little to no hope of deniers learning any climate science.
That’s it for now
My explanation above was deliberately kept as simple as I figured was needed so that deniers could understand it. (Not that they will, in part because they’ve indicated they don’t want to understand it.) There is more to global energy flows, of course. You can read more in the references below.
If there’s anyone who can’t understand all this, or anyone who thinks I got something wrong, let me know in the comments.
References and further reading
Kiehl, J. T., and Kevin E. Trenberth. “Earth’s annual global mean energy budget.” Bulletin of the American Meteorological Society 78, no. 2 (1997): 197-208.
Loeb, Norman G., Bruce A. Wielicki, David R. Doelling, G. Louis Smith, Dennis F. Keyes, Seiji Kato, Natividad Manalo-Smith, Takmeng Wong, 2009: Toward Optimal Closure of the Earth’s Top-of-Atmosphere Radiation Budget. J. Climate, 22, 748–766. doi: http://dx.doi.org/10.1175/2008JCLI2637.1
Trenberth, Kevin E., John T. Fasullo, and Jeffrey Kiehl. “Earth’s global energy budget.” Bulletin of the American Meteorological Society 90, no. 3 (2009): 311-323.
Wild, Martin, Doris Folini, Christoph Schär, Norman Loeb, Ellsworth G. Dutton, and Gert König-Langlo. “The global energy balance from a surface perspective.” Climate Dynamics (2012): 1-28.
Patrick T. Brown, Wenhong Li, Jonathan H. Jiang, and Hui Su, 2016: “Unforced Surface Air Temperature Variability and Its Contrasting Relationship with the Anomalous TOA Energy Flux at Local and Global Spatial Scales.” J. Climate, 29, 925–940.
doi: http://dx.doi.org/10.1175/JCLI-D-15-0384.1 (pdf here)
From the hotwhopper archives: