Thank you missouriboy.
Fatjohn, a couple of questions…
1)You indicate that 6.81 watts per square meter will cause 1.25C of direct warming or just under 0.2C per watt per square meter based on a blackbody calculation. I thought the number for the earth was about 0.3C instead of 0.2C. Are you confident of the 0.2C value for the earth (not a blackbody)?
2)You haven’t mentioned feedbacks in your discussion. When the oceans warm they release CO2 which adds to the greenhouse gas levels. Warmer atmospheres can hold more water which is a greenhouse gas. Is there a feedback effect from these added greenhouse gases which should be considered? How large is it in your view?
I have not taken any feedbacks into my discussion so yes this is only a critique on the initial forcing calculation that was made on this blog.
I am not in a place to really debate the size of the feedback effects since I have not looked deeply into them yet. My intuition would say that the earth's climate is a fairly stable system since we had volcanic eruptions or solar minima in near history that knocked a few degrees of the thermometer without pushing the Earth in a spinning snowball state. So it would suprise me that an upward move would all of a sudden cause a large instability.
I do think that the Earth, given it's location of continents and thus given a certain albedo when certain continents and islands get or lose an icesheet, does have certain levels of temperature where the climate is stable at and some levels where it is unstable at. Additionally, when one looks to the temperature data over the last million years or so one can see that the downward movements were down whilst upward movements happened more gradually.
At this point I do believe in anthropogenic warming but I think it probably contributed less than half to the rise of the past 200 years. Other large factors that in my opinion have compounded the warming is the almost complete lack of stratospheric volcanic eruptions during the past century (quite unusual and in stark contrast with the activity that took place in the century before) and the global solar maximum.
Going back to the blog that I originally linked to, here is another part of the series that tries to explain the greenhouse effect (and does so quite well in my opinion)
scienceofdoom.com/2010/02/19/co2-an-insignificant-trace-gas-part-seven-the-boring-numbers/Interestingly here it uses an example of CO2 doubling (not the rise to 1000 ppm in my previous example) and comes up with a value of radiative forcing of 3.7 W/m^2, this is a value that the IPCC uses as well.
Instead of using the blackbody calculator, the author here uses the Stefan Boltzmann law to calculate the increase in temperature.
This is where I think he gets it wrong. He adds only solar with the new extra radiative forcing and calculates the difference. Completely letting out the radiative forcing that all greenhouse gasses already do. If you do it like that, you are just basically wondering how much a blackbody's temperature would rise if said blackbody gets light shed upon at 239 w/m^2, has no protective cover of greenhouse gases and has an equilibrium temp of 288K and suddenly gets a small jacket of CO2 that causes a radiative forcing of 3.7 W.The correct calculation should obviously be.
So there you have at least that. This is the only way I have so far have seen someone derive the 1-1.2 degrees no feedback climate sensitivity figure and it seems to me it has a glaring error in it and should only be 0.67 degrees.
Astoundingly, this seems to be propagated through a lot of literature and just stated as fact, without a clear reference to the calculation.
See for example here:
www.pik-potsdam.de/~stefan/Publications/Book_chapters/Rahmstorf_Zedillo_2008.pdf on page 38 which links to the third IPCC report (where I did not manage to find the 1 degree reference) to back its claim and was in turn referenced by wikipedia for the climate sensitivity article:
en.wikipedia.org/wiki/Climate_sensitivityAn MIT course that states that 4 W/m^2 leads to 1 degree warming, no calculation there:
ocw.mit.edu/courses/earth-atmospheric-and-planetary-sciences/12-340-global-warming-science-spring-2012/lecture-notes/MIT12_340S12_lec15.pdfAlso SkepticalScience comes up with the 1.2 degree figure. No explanation necessary off course, physics just tells us.
skepticalscience.com/climate-sensitivity-feedbacks-anyone.htmlAnother blog, 1 degree:
theness.com/neurologicablog/index.php/the-climate-tipping-point/A report of the royal society, 1 degree:
royalsociety.org/~/media/Royal_Society_Content/policy/publications/2010/4294972962.pdfOn Clivebest we get the following quote:
See:
clivebest.com/blog/?p=4923So here we get back to the 0.3 value that dwuyane cited and the question is it fair to assume the earth is a blackbody?
Well I have not much to go by, but it seems that the greenhouse gas theory in itself relies on the globe is a blackbody for its theory.
Here you have a denier trying to deny the fact that Earth is a blackbody:
jennifermarohasy.com/2011/03/total-emissivity-of-the-earth-and-atmospheric-carbon-dioxide/And here you have a believer trying to prove Earth is almost a blackbody:
scienceofdoom.com/2010/04/07/the-dull-case-of-emissivity-and-average-temperatures/Note that in clive best there was an allusion made to the stefan boltzmann law, which only works for blackbodies.
When we go here we find a formula that is supposedly used by the IPCC to find that 0.3 figure for climate forcing:
web.ma.utexas.edu/mp_arc/c/11/11-16.pdfIt's the first formula in the link.
Note that this formula is entirely valid for blackbodies.
Also note that they use a temperature value of 255K to come to the climate sensitivity value of 0.3.
Also note that this value of 255K is completely in line with a blackbody that radiates 239 watts.
This is wrong in my opinion. They act as if the 239 watts is the only thing that heats the blackbody to 288K and that the radiative forcing of 157 watt already in the system doesnt have an effect.
It basically assumes the 1st watt of forcing has the same effect as watt number 987.
If you ask me the equation in that paper should have Ts and Te being both equal to 288K (or 289 probably) and then it does simplify to... the equation given in the clive best blog! But if one calculates that with an emissivity of 1 we get a forcing of 0.1846, thus to get it up to the 0.3 value the emissivity of the Earth should be as low as 0.615.
From wikipedia we have:
Ugh now it's getting close to 0.3 indeed.
However I am not certain yet that you can really take clouds into account like that.
I'll have to think about this for a little while...
Sad.
sigurdur, Very interesting, will have to look into this.