Dr. Roger Pielke Sr. writes:
News Article On The Earth’s Heat From Radioactive Decay
An intriguing news article has appeared by Charles Q. Choi titled
Radioactive decay fuels Earth’s inner fires
The article includes the text
“Extraordinary amount of heat remains from primordial days, scientists say
The researchers found the decay of radioactive isotopes uranium-238 and thorium-232 together contributed 20 trillion watts to the amount of heat Earth radiates into space, about six times as much power as the United States consumes. U.S. power consumption in 2005 averaged about 3.34 trillion watts.
As huge as this value is, it only represents about half of the total heat leaving the planet. The researchers suggest the remainder of the heat comes from the cooling of the Earth since its birth.”
To convert the estimate in the MSNBC news article to watts per meter squared, 20 trillion watts must be divided by the area of the Earth [5.1 x 10^14 meter squared] which yields a heat source of 0.039 watts per meter squared.
This is well less than the significant radiative forcings as estimated in figure SPM.2 in the 2007 IPCC WG1 report and, except for local effects where lava flows and volcanic eruptions are occuring , this heat is of minor climatic importance [the outgassing of sulphur dioxide and other chemicals and of ash, of course, are a different issue]. The heating of the interior and resulting effect on currents in the Earth’s mantle, however, are important in climate on very long time scales as this helps drive plate tectonics, such as continental drift.
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John:
Unlike fresh water, sea water (3.5% salts) does not have a temperature of maximum density above its freezing point. Its coefficient of thermal expansion is almost zero at these near-freezing temperatures, but never goes negative, as fresh water does below about 4C.
A while back I suggested that taking the crustal temperature around the world with 50′ boreholes would be a much better way to measure how warm the Earth is.
I will use this opportunity to put in a shameless plug for geothermal heating. We have had a closed loop system for about ten years and it is one of the best decisions we ever made. We have missed the rise in nat gas and fuel oil prices. They make a lot of sense if your electricity is relatively cheap…..say under 12 cents per kwH.
2 trillion sounds like a big number but it is 192 thousand trillion times less than the Sun puts out.
Without the Sun and the gravitational energy of the atmosphere, the 0.03 watts/m2 would translate into a temperature of -258C.
Paul Irwin says:
July 21, 2011 at 3:11 pm
Paul, you lost me with the “at night when there is no incoming solar energy”. For the earth there is always incoming solar energy 24 hours a day. This energy is going to be redistributed by the atmosphere and the oceans. Convection by air and water has a far greater effect than conduction from the ground into the air or water.
Drill a borehole 2 km deep and it will equilibrate rapidly to the ground temperature – no chance for convection. Sink a mine shaft and eventually it too will equilibrate without ventilation. That is why the Chilean miners got hot. But so what? Expose that ground to the air or water, circulate it and the wall rock will equilibrate to the air or water temperature very quickly. So absorbed thermal radiation from the sun is much greater than thermal gradient energy from the earth.
Geothermal energy is great but the amount of energy it produces is pretty small – yes enough to heat or cool a house but not enough to meet the energy needs of a nation.
These gravitational flexing(s) would certainly affect the crack crevice expulsion and draw. It would also introduce rhythmic patterns to thermal convection waves. Isn’t it wonderful, to “hear” stimulating discussion. GK
prjindigo says: J uly 21, 2011 at 2:29 pm
I think the heat in the Earth comes more from the gravitational dough-hooking the Moon and Sun provide than anything to do with radioactive decay. The lack of general understanding of physics most scientists expose is quite astounding.
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In principle, the gravitational pull of the moon is likely to cause warming, it is just a question of scale.
Coniser IO, which is the most geological active body in the solar system This is due to tidal heating caused by gravitaional pull. Of course, IO is subject to significant gravitaional force from Jupiter on the one hand, and the other Galilean moons on the other hand. The Earth is not being so squeezed but the fact that the moon can distort the oceans gives an indication of what it is doing/trying to do the core. This obviously must generate some heat.
Baa Humbug says:
July 21, 2011 at 11:25 am
Why doesn’t the deep ocean freeze up? My understanding was that the enormous amounts of pressure applied to non-compressable water keeps that water from freezing.
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No, surely you’ve heard… it hasn’t frozen because the ‘globe’ has been ‘warming’. Keep up!
The atmosphere ain’t nothing but an insulation blanket – keeping heat both out and in – the AGW folks like to push the wild-eyed hypothesis that the atmosphere governs all, but it is just ‘there’ and moves heat from the oceans inland… last to the relatively extreme heart of the continents.
If you get really bored you can dive into the geotechnical whiplash curve and find that the earth’s subsurface energy gradient is primary, the polar axis seasonal tilt secondary, and atmospherics tertiary.
The solar activity and cosmic ray crowd may bump the atmospherics to forth or fifth place though.
AGW is driven by atmospheric proponents alone… basic thermo would push that factor out as trivial as temp change in a hydro plant and they do not like it.
I think the point is that the interior of the earth is still not well understood. It seems that most of the guess at the sources of the heat and the amount of heat are still quite immature. It is acknowledged that there are four sources of heat inside the planet:
– heat from the initial planetary formation
– heat from internal friction as heavy elements sink into the core
– radioactive decay (and remember that recent idea that cosmic rays affected that rate?)
– friction from the tidal effects of the moon and sun working on the fabric of the planet
None of these have been precisely quantified and this recent article is part of that ongoing science I guess. I would guess that all of these create time varying heat fluxes at the surface but who knows what the timescales or amplitutudes of variations are? It is immature science still.
It has always seemed strange to me that the heat budget diagrams either don’t show this source or show it as being trivial when it is poorly measured and poorly understood.
What I have wondered for years is how much of the Earth’s interior heat is not from radioactive decay, but from nuclear fission.
This one talks about Natural Fission Reactors at 17 locations in a rich ore deposit in Gabon.
http://www.scientificamerican.com/blog/post.cfm?id=natures-nuclear-reactors-the-two-bi-2011-07-13
I remember reading about in is Sci Am almost 20 years ago (though I thought it was South Africa).
The Gabon reactors were concentrated by aquias solution, then moderated by ground water the influx of which was balanced by evaporation when the reactor reached a critical assembly.
I’ve grown up hearing the Earth has an iron core, or an iron-nickel core to explain the Earth Magnetic fields. I don’t doubt iron and nickel are present, but I think over the course of 4 billion years, a great many highly dense metals have migrated toward the core, including uranium.
Is it possible that in the inner and lower part of the outer core, the conditions are ripe for a low energy, barely critical, breeder reactor? It would be kept in balance by changes in temperature; it wouldn’t take much delta-T with an assembly several hundred miles in diameter.
What about reactor poisons? These might prevent the whole thing from working. Lead would sink too, but is slightly less dense than U. Would it stratify with a richer U preferentially under a lead rich layer?
I had hopes from the referenced articles that talked about neutrino flux that some discussion about fission as different from decay would be brought forth. But the 07-18 link from Dan seems quite confused about this point “Over the billions of years of Earth’s existence, the radioactive isotopes have been splitting, releasing energy as well as these antineutrinos—just like in a man-made nuclear reactor. …. how much of Earth’s heat results from this radioactive decay.
The large proportion of radioactive decay IS nuclear fission. Those Gabon locations date from an era when the constant apparently varied, not by the voodoo you read about.
The issue I have with your theory, Rasey, is simply that there is no gravity at the center of the effective Earth-Moon mass, heavy objects could NOT be forced into a tiny little space and compressed there. The null gravity location is off-center from the Earth’s rotational axis.
There is no radioactive material which would survive several billion years of active half-life in a heated (accelerated) environment.
richard verney says:
July 21, 2011 at 6:57 pm
prjindigo says: J uly 21, 2011 at 2:29 pm
I think the heat in the Earth comes more from the gravitational dough-hooking the Moon and Sun provide than anything to do with radioactive decay. The lack of general understanding of physics most scientists expose is quite astounding.
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In principle, the gravitational pull of the moon is likely to cause warming, it is just a question of scale.
Con[sider] IO, which is the most geological active body in the solar system This is due to tidal heating caused by gravitational pull. Of course, IO is subject to significant gravitational force from Jupiter on the one hand, and the other Galilean moons on the other hand. The Earth is not being so squeezed but the fact that the moon can distort the oceans gives an indication of what it is doing/trying to do the core. This obviously must generate some heat.
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Sorry for the long quote. So you agree that the agitation should generate heat; especially considering the inverse event horizon which occurs at the center-of-gravitational-mass of the Earth-Moon system. (Io is a bad example since you can actually induction heat sulfur once above a threshold temperature, much like using microwaves to continue melting already heated glass.) It simply becomes a question of how much heat combined with induction heating by magnetic systems and how much remission of heat loss the added solar energy adds to the total environment act as an insulating system to maintain the temperatures necessary for the orbital mechanics to continue generating heat. Such a concept begs the question of whether vulcanism is caused by plate tectonics or by stored up heat within the system requiring release. Does the earth crack open and spew magma and lava simply because the system must equalize? Has anyone actually ASKED these questions before?
Curt says:
July 21, 2011 at 4:08 pm
“Unlike fresh water, sea water (3.5% salts) does not have a temperature of maximum density above its freezing point.”
Thanks Curt, I guess I missed that chapter. And, I’ve never worked with salt water. This just adds to my belief that water is a very odd substance.
Tim Folkerts says:
July 21, 2011 at 3:25 pm
prjindigo says: J uly 21, 2011 at 2:29 pm
I think the heat in the Earth comes more from the gravitational dough-hooking the Moon and Sun provide than anything to do with radioactive decay. The lack of general understanding of physics most scientists expose is quite astounding.
An interesting hypothesis. Please provide calculations of the magnitude of this heating effect. Or a link to textbooks or scientific articles that quantify the tidal heating of the earth. Enlighten us on the proper physics.
Or enlighten us as to the mistakes in the article attributing half the heating to radioactive decay as evidenced by detection of neutrinos.
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When I bend #12 copper wire it gets hot. I can thaw steaks with compression and flexing.
Hot reactors generate more fission, is the fission driving the heat or is the heat driving the fission?
I think you’ll find that adding several thousand degrees to any random mass of heavy metals will generate a great deal more fission than would otherwise normally occur if they were laying around the lab. I don’t appreciate soapbox trolling and I was discussing the discussion.
Using neutrino detection in the article’s way sounds much like trying to determine which fans in a full stadium are Ford owners based only on the sounds they make. It strikes me as an attempt to generate a data set simply to meld into whatever shape is wanted to support a pre-determined hypothesis. Politicians change the data to support hypothesis, scientists just raise their hands and say “its just a lot of noise”.
My posting on this site could easily statistically lead you to conclude to which I am more akin.
I think that this confirms what we have already discussed about geothermal activity that it is a small part of the energy buget of the earth .It has been mentioned that as we get closer to the molten part of the mantle then the temperature rises also the molten part of the mantle can rise closer to the surface and the surface will get warmer.The local warming caused by volcanic activity could cause pressure changes in the atmosphere which determine the direction winds flow the wind direction is important in things like the ENSO,AO and NAO and other weather patterns.
20 million watts is an awful lot of blog posts, I’ll never be off the damn computer….! 🙁
Follow Up…
If you get really bored you can dive into the “geotechnical whiplash curve ”
Sorry to say, if you were really really bored and ‘binged’ that, you unfortunately had few relevant hits,
the first hit being from our very own .gov “DRAFT Conceptual Engineering/Socioeconomic Impact Study”, first of just seven references being Anderson & Ladanyi 1994, “An Introduction to Frozen Ground Engineering”. I do not have that on my shelf but do have a precursor by Andersland and Anders (1978) and have had numerous papers in journals by all three. Have ready access to cite #4, have on the shelf #5, and sold #7(but should not have).
The whiplash curve has already been referenced. It is verifiable everywhere on earth. If you want to really really believe that a big ball of fire millions of miles over your head has more impact on the temperature of your feet than a big ball of molten rock a few miles below, well, everybody needs to believe in a little bit of magic.
@prjindigo – You are correct that at the exact center of the earth, there is no gravitational pull. But if you do the math, for a sphere of uniform density, gravitational acceleration falls off linearly with r as you descend into the sphere. (Mass falls off with r^3, but Gravitational acceleration increases with 1/r^2)
But the earth is not of uniform density. The core is higher density than the mantle. So at a radius of 2000 mi (1/2 Earth’s radius) you probably have 0.55 G. Gravity still works in the outer core.
As for the plate tectonics question, Yes, people have asked it. John Fredrick Dewey is a structural geologist who is/was a leader in tectonic geophysics. When everyone was saying late 80’s?) mantle convection drove the plates, he believed the viscosity of the mantle was a couple of orders too high for this to be the driver. His observation was that oceanic crust and the mafic roots of sialic crust were more dense than the upper mantle, creating an unstable system where the crust wants to overturn. The overturning of solid plates on a lava lake is the same physics, but a trillion times faster.
Part of his proof/argument was how the Indian plate subducted under the asian plate. The Tethian oceanic leading edge of the Indian plate dove under the Asian, pulling the rest of the indian plate North as the tongue sank. A few million years ago, that diving tongue broke off. Freed from that descending weight, the rest of the crust, including the southern portion of the asian plate, rebounded creating the Himalayan chain. Dewey sad this was a good argument explaining how the Himalayas are higher than they should be isostatically if they had a typical mafic root system.
@H.R. RE: amount of error in the calculation.
Always good to bring up uncertainty.
There is another assumption they have made: the neutrino flux they are measuring today is related to the heat flow we are measuring today. The problem? Neutrinos will be detected almost instantly after they were created. But the heat flow out of the core will take a ?million? years.
One of my favorite bargain book finds was “End in Fire” about the SN1987A supernova. Toward the end of the book they described what that Supernova would look like view from within its solar system. First of all, any planet inside the orbit of Saturn would have been destroyed earlier phases the star’s death. But suppose an intelligent race survived on a planet at Neptune’s distance. At the instant of the SN collapse and detonation, a cloud of neutrinos is generated. Unhindered by the mass of the star, they escape immediatly. As inactive as neutrinos are, there are so many of them that those poor souls on Neptune, 2 billion miles away, will get a lethal dose of ionizing radiation and be quite “incapacitated” when the SN photons rip through the star’s surface eight hours later.
(Sorry for the off track)
Baa Humbug:
How could water pressure be increased if water was not compressible?
Actually it is about four times as compressible, or elastic if you like, as steel.
SteveP says:
July 21, 2011 at 10:55 am
So if I read that article correctly, of the energy leaving the earth, 0.039 W/m^2 is due to radioactive decay and a similar amount is from residual heat from the earth’s formation. For a total of 0.078 W/m^2 (?), but as Roy Spencer points out, this is insignificant compared to the 240 W/m^2 that has to be radiated away to balance out energy from incoming sunlight. I don’t think I’ve ever seen internal heat from the earth shown on any of those spiffy “Earth’s Energy Budget” diagrams. So, interesting for Geology; for Climatology, not so much.
When that heat is radiated away, it leaves as long-wave IR. Consequently, if CO2 impedes reradiated solar energy from immediately radiating into space, it also would trap this energy as well. What I am really astonished at is the “newly discovered” bit. In geology back before plate tectonics was even taught, it was well known that granite contained enough radioactive material, decaying in sufficient quantities, and granite was a poor enough conductor, that over time masses of deeply buried granite could heat themselves to the point of melting. Physical geology classes were occasionally required to calculate this for themselves.
But here’s a question, and forgive me if this is naive but I am curious so if anyone can enlighten me I’ll do my best to be appreciative. Neither of these heat sources – radioactive decay and cooling from a molten state – are constant over time. Nor have they changed linearly over time (half-life is exponential by definition, the exponent being 1/2, correct?). So, over geologic time, might they have been significant in the past? Maybe even in the ballpark of contributing to the Early Faint Sun paradox?
They were indeed more significant in the past than now. See:
http://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor
IIRC, the difference is not nearly enough to overcome a 20% short fall from the sun. In fact, if you look into Snowball Earth:
http://en.wikipedia.org/wiki/Snowball_Earth
it would appear that during the Proterozoic there seem to have been several episodes of planet-wide or near-planet-wide “ice-ball” states, possibly with ice clear to the equator. The sun would indeed have been cooler, but radioactivity clearly wasn’t picking up the slack.
Just how weird a coincidence would that be, the sun picking up the slack at just the rate needed to balance out the Earth’s reduction in internal heating? …
See previous.
And right you were.
I’ve always wondered about something. Would it make sense to place on the moon (the side always facing us), a sensor (or perhaps 3 to eliminate any error between them) that measures whatever can be measured from 200,000+ miles away in a constant orbit (albeit receding a few mm a year). Whereas satellites require altitude adjustments (among other problems), lunar observation would effectively be measuring the same exact line around the Earth forever. Changes would have to show up here and this would be as good as a planetary average as might be possible.
Tim Folkerts says:
July 21, 2011 at 11:56 am
Barry Day says: July 21, 2011 at 10:34 am
?????this heat is of minor climatic importance???Yeah!!! Only,If you ignore the 3 million +++ SUBMARINE Volcanic and black smokers that warm the Ocean
If you check the numbers, the area of the ocean is about 300 million km^2. so there is one smoker for every 10 km^2 = 10 million m^2. Even if the smokers average a megawatt of heat, then that is still only 0.1 W/m^2. Compared to 240 W/m^2 from the sun, this 0.1 W/m^2 of thermal energy is indeed “minor”.
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Tim, What happens when the Ocean current travels same direction as the plate boundaries and the heated water gets continually reheated time and time again.Wouldn’t that make your equations meaning less?There would be a localized strip of heated water alongside a landmass which would most certainly NOT be “minor”.!!!
@ur momisugly Steve from Rockwood
“Geothermal energy is great but the amount of energy it produces is pretty small – yes enough to heat or cool a house but not enough to meet the energy needs of a nation.”
Wouldn’t it depend on the nation? According to the Wikipedia article below Iceland gets about 70% of its electricity from hydropower and the rest from geothermal energy. However, since it has large untapped reserves of both it would presumably be feasible for Iceland to rely entirely on geothermal energy for electricity production, not that there would be any point in abandoning hydroelectric power.
http://en.wikipedia.org/wiki/Renewable_energy_in_Iceland
Roy