I was looking at a Hansen article from the 1980s, and think I am starting to understand where his bloated theories about climate sensitivity come from.
You may want to click on the above image to see it larger.
Look at his calculations for radiative and convective equilibrium temperature on Venus. The convective equilibrium numbers make sense – it is a simple calculation of lapse rate times height of the atmosphere – and yields the correct value for the surface temperature. As the atmosphere convects, falling air compresses and heats – while rising air expands and cools. He shows the lapse rate of Venus (7) not much different from Earth (5.5.) (This in itself should be enough information to convince someone that the idea of a runaway greenhouse effect is nonsensical.)
But the problem lies with the radiative equilibrium calculation (1.) He starts with a WAG (Wild Ass Guess) of atmospheric infrared opacity – 100 times greater than Earth.
The statement below is unpalatable, because it assumes no convection.
A quantitative estimate of the greenhouse effect can be obtained under the assumption that only radiation contributes significantly to vertical energy transfer.
Then he assumes that he can calculate the surface temperature based on the total atmospheric opacity? That is ridiculous. The atmosphere of Venus is very thick and is covered with a layer of thick opaque clouds. The total opacity tells us little or nothing about the temperature profile or surface temperature, particularly since he assumes that Venus atmosphere is not convecting – which obviously it is.
Equation 2 is adequate and correct. His usage of equation 1 looks useless to me and apparently is the basis of his theories about climate sensitivity.
Having checked the paper, it turns out that the estimates of atmospheric infrared opacity are not a “Wild Ass Guess”; the paper explains how they are CALCULATED, see text around equation (2.5).
As for the usage of equation 1, if you think it “looks incorrect to me”, then there are a couple of possibilities, (a) the NASA scientists are wrong and (b) you don’t understand it. I think (b) is rather more likely for two reasons: They are well trained scientists with their professional reputations on the line (if it was wrong, their rivals would be only too happy to point it out), and secondly rather than identify the error and give the correct usage, you just say “it looks incorrect to me” – a rather criticism given it is too vague to address.
The fact that the lapse rate is nearly identical to Earth should give you a clue that composition of the atmosphere has very little to do with the temperature at the surface. If Venus thick atmosphere had an identical composition to earth, it would still be very hot.
100 is obviously a WAG.
What would be a more realistic estimate for the lapse rate on Venus?
I think you are fogetting that the trophosphere of Venus’ atmosphere is 62km thick, whereas for the Earth it is only about 17km thick. So with a lapse rate of 7C per km it will loose 434 degrees C, for the Earth, with a lapse rate of 5.5 deg C per km it will loose about 93.5. Sounds about right to me. Lets try the sums:
Since Hansen published his article, the thermal profile of the upper atmosphere on Venus has been measured by a probe sent there (Venus Explorer), from which we can easily calculate the lapse rate. According to M. Pätzold (et al.) Nature 2007 (http:/dx.doi.org/10.1038/nature06239), the temperature at the top of the trophosphere is about 215K (-58 degrees C) [Figure 1]. So assuming the surface is at 462 degrees and the depth of the trophosphere is about 62 Km [again Figure 1], then the lapse rate is approximately (462 – -58)/62, which is about 8.4. So while Hansens’ at least in the ball park.
As for the “100 is obviously a WAG.”, I’ve already pointed out how it was calculated, just asserting it is a WAG a second time doesn’t make it so.
Where did you get the idea that the lapse rate is incorrect?
I misread your post is the simple answer. However as it turns out the lapse rate on Earth is 5.5 deg C per km and on Venus it is 8.4 deg. C per km, which is hardly “nearly identical”.
NASA shows less than 10% difference in the lapse rates.
http://mc-computing.com/qs/Global_Warming/Venus.html
You think a 10% difference is “nearly identical”?
BTW, if you are going to quote NASA, then give a link to something written by NASA.
Interesting that figure 2-1 has the RWP and MWP both warmer than today, along with the the past 1000 years having a natural variability of 1c. So are we really supposed to think current warming is outside normal variability?
No–but we still have to come up with an explanation for it. There hasn’t been much change in insolation, there haven’t been any megavolcanoes, the Earth’s orbit and axial tilt haven’t changed, the continents have’t drifted. So what’s causing the warming? The only thing that’s really changed is the composition of the atmosphere.
The amount of change in the Earth’s atmosphere since 1850 has been a whopping 0.00011 (110 ppm.)
Have you measured all other variables to that same precision?
110 ppm, or otherwise written as an increase from 280 ppm to 390 ppm.
That’s a 39% increase and now is at a higher level than for the past 800,000 years.
ChrisD, you are still a cretin, still a virgin and still posting shite. So what’s the atmosphere changed from? 1200 ppm as it has been before? So we’re dangerously low? Anyone who thinks carbon dioxide drives anything other than sweet fa, is a complete twat. You’re on the government payroll aren’t you?
A 0.000110 change is a 0.01% change in atmospheric composition.
The obsession with CO2 is bizarre.
“The only thing that’s really changed is the composition of the atmosphere.’
OK let’s examine that. I’ll use CH4 as the example.
CH4 + 2O2-> CO2 + 2H2O
So for our example of burning a fossil fuel we get more water molecules than carbon dioxide by a 2:1 ratio.
Water in vapor form has a specific heat of about 2.8 and CO2 has a specific heat of about .87. So we should be changing the specific heat of the atmosphere (air) from 1.004 to something higher. Like maybe 1.006 or 1.010.
I have read nothing about the specific heat of air being changed.
If it was changing it would mean the atmosphere would take longer to heat up or take more input to get it to heat at the same rate as before. I have seen nothing about more input from the sun lately.
So I must conclude on this rough estimate that given the same input from Sol we are not heating the atmosphere as high as we should if CO2 was having the major impact.
The additional water vapour resulting from combustion (or indeed any other source) stays in the atmosphere only a matter of days before it precipitates out again, which is why it has no real effect on climate (unlike long term increases in humidity from a warming trophosphere). The additional carbon dioxide stays in the atmosphere for hundreds to thousands of years (yes I know the residence time is only about 5 years, but it is athe adjustment time that matters, which is much longer). CO2 is a long lived GHG, which is why emissions are important, unlike excess water vapour it is going to stay with us for a long time.
While your at it, come up with the explanation for MWP, RWP, LIA, etc. And are you 100% sure that the only thing that has changed is the composition of the atmosphere? 90%, 50%?
That’s an old trick called “inappropriate denominator.” The ratio of CO2 to the total weight of all sumo wrestlers would be just as meaningful in this context.
99.96% of the dry atmosphere is non-GHGs and has very little to do with keeping the Earth warm enough for us to live on. If you want a meaningful percentage, divide the CO2 increase by total GHGs, not total atmosphere. CO2 is something like 95% of that number, so a 40% increase is very significant.
LOL – The whole global warming story is based on water vapour feedback. If it disappears in a matter of a few days, then Hansen’s story goes down the toilet.
ChrisD,
2% of the Earth’s atmosphere is the primary greenhouse gas H20.
Your claim”99.96% of the dry atmosphere is non-GHGs” is beyond ridiculous. Do you have any idea what you are talking about?
Steve wrote: “LOL – The whole global warming story is based on water vapour feedback. If it disappears in a matter of a few days, then Hansen’s story goes down the toilet.”
You should have read my post in a bit more detail as I specifically excluded the water vapour involved in feedback “(unlike long term increases in humidity from a warming trophosphere).”
The amount of water vapour the atmosphere can hold depends primarily on temperature, warm air can hold more water vapour than cold air. So if the atmosphere warms due to increased CO2, then that warming allows the atmosphere to contain more water vapour, which is itself a GHG, and so you get some additional warming – which is the feedback.
Now if you don’t warm the atmosphere and chuck water vapour into it, it just falls back out again as rain a couple of days later. CO2 doesn’t, if you chuck CO2 into the atmosphere it takes a very long time for CO2 levels to fall back to “normal” again (hundreds to thousands of years).
Scoff all you like, but you ought to have known that.
More water vapour means higher temperatures means more water vapour means higher temperatures means more water vapour means higher temperatures means more water vapour means higher temperatures ………
How is the patient Doctor?
Well Sister, we’ve performed a very successful operation on the patient, very successful indeed.
Unfortunately the patient died.
CO2 is not the culprit
The earth’s atmosphere can put up with a lot more but a little CO2.
So the best thing for Hanson to is to stop behaving like an ass, act like a scientist, get back to the drawing board until he gets it right and stop the “death train” activism.
The US taxpayer, NASA and the rest of civilization would be grateful for such a gesture.