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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@richard Verney
You have to take into account both heat sources and heat sinks. The earth’s surface is primarily warmed by the sun during the day and cooled by the deep cold of the empty cosmos which is only 3 degrees K above absolute zero. There is very little daytime warming at the top of Mt.Everest because it is covered in snow which reflects better than 90% of incident sunlight and has little atmosphere between it and the cold of outer space to buffer it. If the top of Mt. Everest could somehow be made dark it would be hot enough to boil water by mid-day much like the surface of the moon which heats up quite rapidly to black-body equilibrium temperature of about 120C not long after sunrise.
The moon is a natural laboratory for comparison to earth. It is made up of the same basic material as the earth but it has no hot mantle and no atmosphere. You can learn a lot about it by following links I’ve left in comments:
http://www.google.com/search?hl=&q=springer+regolith+site%3Awattsupwiththat.com&sourceid=navclient-ff&rlz=1B3GGGL_enUS290US290&ie=UTF-8
@ur momisugly Dave Springer
Thanks, indeed as Lichanos commented Darwin was taken aback by Kelvin’s calculation; however he stuck to his guns and was eventually proved right.
It makes you wonder if current climate science will look a century from now similarly naive, lacking one or more key insights without which real understanding and analysis are impossible. From what direction will these insights come?
@Dave Springer says:July 24, 2011 at 4:04 am
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Dave, whillst I appreciate your comments, you completely fail to grasp the point that I am trying to consider.
I am trying to ascertain what would be the poistion if for one moment the sun was switched off, the oceans sucked dry, the atmoshphere removed and Earth was a barren planet much like Mars but with a hot active core as possessed by the Earth. Leaving aside the obvious consequences of not having the solar input, would the temperature of the rock at the top of Everest be as hot as the rock which at the deepest valley of the oceans? In other words, is the hot core trying to heat the deep oceans.
SteveE provided an interesting paper in which the survey found the average sea bottom sediment to be 4.2degC. The average deep ocean temperature is about 2deg C (may be a little more). If the average sea sediment temperature all over the planet is truly 4.2degC, it would appear that that the ocean crust is constantly trying to heat the deep ocean. This constant heating be additional to heat via hydrothermic venting.
Dave
I don’t think that much can be learnt from the moon.
You cannot compare a water world with a barren rock. The oceans, and the three phases of water are the key to climate on Earth. It is the oceans and water that drives the Earth’s climate.
richard verney says:
July 25, 2011 at 7:28 am
Just a quick follow up, the temperature of the water at the bottom of the Mariana Trench was measured at 2.455C (figure 4) @ur momisugly 11197db, however the temperature minimum was reached at 4700db with a temperature of 1.455C. The reason for the increase in temperature with depth is the result of adiabatic compression, where by a fluid increases in temperature is it is compressed. I think this demonstrates that the temperature of the mantle is not really contributing to the heating of the deep oceans as you suggest.
The local tectonics would have an effect such as on a hotspot or rift, however pure depth wouldn’t, as there are some many more factors that have a much greater influence.
http://www.terrapub.co.jp/journals/JO/pdf/6103/61030447.pdf