Is the Faint Young Sun Problem Solved by Increased Greenhouse Gases?

[Bill Illis]

Bill;

Here's a paper on albedo during the last glacial maximum.
Haven't had time to study it, but hopefully its useful although it is in watts/m^2

http://kiwi.atmos.colostate.edu/pubs/Burt_Randall_Otto-Bliesner_submitted.pdf

BTW, some of the figures in your post are not coming thru.
They look like just small boxes with a red x.

Thanks Xnn, this is the only paper which goes through it in understandable detail that I have seen.

"As expected, the global ice albedo feedback is positive from LGM to PI; the change in the clear-sky absorbed shortwave at the surface is 11.68 W m-2 ..."​

... which would translate into an Albedo number of about 0.331 (I will have to go through the paper in more detail because clear-sky is not quite the full picture because of the cloud factor again.)

But if anyone else is having problems with the charts showing up, here are direct links to the charts in the order I posted them which might work.

http://img51.imageshack.us/img51/2127/last3iceages.png

http://img109.imageshack.us/img109/9195/milkanvsiceages.png

http://img27.imageshack.us/img27/3616/dustandiceages.png

http://img187.imageshack.us/img187/6840/sbEarth'surfacetemp.png

http://img189.imageshack.us/img189/2608/sbtempcperwatt.png

 

[sylas]

Thanks sylas, I guess I will have to give up this effort.

I've tried similar kinds of effort myself, and ironing out the bugs can be a great way to learn.

But I still have a problem with the inconsistency in all these numbers.

240 watts/metre^2 of solar energy results in 255.0K or 1.06K/watt/metre^2

That's the effective radiating temperature of the planet. Basically, Earth radiates the same amount of thermal energy as an equally sized blackbody at 255 K. However, you can't give a simple linear relation of 255/240 to mean anything. The relation is Stefan-Boltzman, given by

Q = \sigma T^4​

with Q = 240, T = 255, and σ = 5.67*10^-8 as the constant.

3.7 watts/metre^2 of 2XCO2 forcing results in 3.0K or 0.8K/watt/metre^2

That's our best guess, but there are significant uncertainties. This forcing is the difference in energy at the top of the atmosphere. This response to a forcing includes feedbacks.

1.0 watt/metre^2 of extra energy in the SB equation results in 0.3K/watt/metre^2

Right; except that is using the surface temperature, not the effective radiating temperature. You can get a rough approximation by introducing an effective emissivity, so that the radiation to space is related to the surface temperature as follows:

Q = \epsilon \sigma T^4​

In this case, T is a mean surface temperature; taking a mean temperature over the Earth so as to give the right energy flux into the atmosphere from the surface. The effective emissivity basically relates the energy radiated from the surface to the energy radiated into space.

The full energy details are more subtle than this, of course. You have energy flowing up from the surface by convenction as well, with the balance made by by a backradiation from the atmosphere. However, the equation with ε gets into the ball park.

With this approximation, we have

\frac{dQ}{dT} = 4 \epsilon \sigma T^3 = \frac{4Q}{T}​

Thus the change in energy out the top of the atmosphere per unit temperature is 4Q/T = 4*240/288 = 0.3. This is called the no-feedback response, or Plank response, of the planet.

It is the same temperature response you would have for a grey body with a constant emissivity.

288K at the surface is the equivalent of 390 watts/metre^2 in the SB equation (or 0.74K/watt/metre^2)

adding 1.0 extra watt/metre^2 to 390 watts/metre^2 only results in an extra 0.18K/watt/metre^2

You are just doing a simple division here; which doesn't work. You can use the Stefan-Boltzman law to get about the right magnitudes, as shown above.

I think there has been too much averaging in all these estimates and in the climate models and the incremental differentials are not being used (the equations should be logarithmic).

Well, climate models do the best we possibly can with as much physics as they can handle. Without a climate model, we can use the simple averaging methods described above to get approximate answers, but a climate model looks at the whole distribution of temperature around the planet and all the energy flows. They are not complete by any means, but they do use physically sensible equations for the energy flows that they do represent.

One of the things we haven't looked at is the effect of feedbacks. Climate models can represent various other processes; for example they calculate humidity, using equations like the Clausius–Clapeyron relation and others.

Water, as you may know, is the major greenhouse gas on Earth... but you can't increase humidity by just emitting water into the atmosphere. The lifetime of water in the atmosphere is very short, and so the humidity is determined largely by temperature.

Here's a really simple thought experiment.

Suppose that adding a greenhouse gas gives a forcing, and the non-feedback temperature response is given by 0.3 degrees per unit forcing, as estimated above. But suppose also that any rise in temperature gives additional humidity, with a greenhouse forcing of 2 W/m² per degree. This is feedback.

What happens to temperature ΔT when we add a forcing F? The total additional forcing is going to be 2 ΔT + F. The equation becomes

\begin{array}{lll}<br /> &amp; \Delta T &amp; = 0.3(2 \Delta T + F) = 0.6 \Delta T + 0.3 F \\<br /> \Rightarrow &amp; \Delta T &amp; = 0.75 F<br /> \end{array}​

The number 2 there is not far off, in fact, as far as we can tell... and there are all sorts of other feedback processes as well which give an additional secondary forcing (either positive or negative) in response to temperature change. If f is the feedback in forcing per degree, and λ₀ is the no-feedback response, then the real response turns out to be

\frac{\lambda_0}{1 - f \lambda_0}​

This is the way I look at it and I will delete this post (and probably move on to other issues) if people have a problem with it.

I don't think you need to delete it; but that's up to you.

You can extend this chart all the way out to 63,250,000 watts/metre^2 for the surface of the Sun and the temperature of 5,779K will be correct.

The incremental each extra watt/metre^2 at the surface is only 0.18K. The Sun needs to add 50,000 watts/metre^2 to add 1.0K to its surface temperature.

Actually, the Sun is very close to a blackbody, so it is much simpler. The proper equation from differentiating Stefan-Boltzman gives

\frac{dQ}{dT} = 4 \sigma T^3 = 43,800​

Try taking the difference between σT⁴ for 5779 and 5780 degrees.

Cheers -- sylas

 

[Bill Illis]

You can get a rough approximation by introducing an effective emissivity, so that the radiation to space is related to the surface temperature as follows:

Q = \epsilon \sigma T^4​

In this case, T is a mean surface temperature; taking a mean temperature over the Earth so as to give the right energy flux into the atmosphere from the surface. The effective emissivity basically relates the energy radiated from the surface to the energy radiated into space.

The full energy details are more subtle than this, of course. You have energy flowing up from the surface by convenction as well, with the balance made by by a backradiation from the atmosphere. However, the equation with ε gets into the ball park.

With this approximation, we have

\frac{dQ}{dT} = 4 \epsilon \sigma T^3 = \frac{4Q}{T}​

Thus the change in energy out the top of the atmosphere per unit temperature is 4Q/T = 4*240/288 = 0.3. This is called the no-feedback response, or Plank response, of the planet.

It is the same temperature response you would have for a grey body with a constant emissivity.

Water, as you may know, is the major greenhouse gas on Earth... but you can't increase humidity by just emitting water into the atmosphere. The lifetime of water in the atmosphere is very short, and so the humidity is determined largely by temperature.

Here's a really simple thought experiment.

Suppose that adding a greenhouse gas gives a forcing, and the non-feedback temperature response is given by 0.3 degrees per unit forcing, as estimated above. But suppose also that any rise in temperature gives additional humidity, with a greenhouse forcing of 2 W/m² per degree. This is feedback.

What happens to temperature ΔT when we add a forcing F? The total additional forcing is going to be 2 ΔT + F. The equation becomes

\begin{array}{lll}<br /> &amp; \Delta T &amp; = 0.3(2 \Delta T + F) = 0.6 \Delta T + 0.3 F \\<br /> \Rightarrow &amp; \Delta T &amp; = 0.75 F<br /> \end{array}​

Cheers -- sylas

Thanks for continuing to indulge me (because I do want to figure this out).

In your formulae above, can we just substitute the different Q's and T's between the surface and the tropopause emission level.

Surface Q = 390 W/m2
Surface T = 288K

Tropopause Emission Q = 240 W/m2
Tropopause Emission T = 255K


4 Q/T Surface = 4*390/288 = 5.4W/m2/K = 0.18K/W/m2

I can certainly see an increased greenhouse forcing can be doubled through increased humidity but that only results then in 0.36K / W/m2.

---

If one just sticks to the tropopause emission level and assume all the 2XCO2 forcings estimates are calculated from that perspective (and are not meant to apply to the surface):

4 Q/T = 4*240/255 = 3.76 W/m2/K = 0.265K/W/m2 or 0.53K/W/m2 (assuming doubled humidity forcing).

Do we have to make the assumption then that the surface will respond according to the Plank response - that the Wet Adiabatic Lapse Rate will remain stable and the surface will warm at the same rate as the tropopause emission level. I think the Stefan Boltzmann equations imply that the Lapse rate will in fact change by some amount.

 

[sylas]

In your formulae above, can we just substitute the different Q's and T's between the surface and the tropopause emission level.

Surface Q = 390 W/m2
Surface T = 288K

Tropopause Emission Q = 240 W/m2
Tropopause Emission T = 255K4 Q/T Surface = 4*390/288 = 5.4W/m2/K = 0.18K/W/m2

This is correct, but it is not the change in radiation into space. At the surface you have a lot more than merely the radiant energy flows to consider. There's also a thermal radiant flux downwards from the atmosphere (backradiation), and convection moves a significant amount of additional energy up from the surface into the atmosphere. A recent estimate of all the various energy flows is in this diagram:

Figure 1 from Trenberth et. al. (2009) http://ams.allenpress.com/archive/1520-0477/90/3/pdf/i1520-0477-90-3-311.pdf , in Bulletin of the AMS, Vol 90, pp 311-323.​

Indulge me... I'll try a crude back of the envelope estimate.

Simplifying those flows, and balancing up a bit to look at an equilibrium state with no heating of the ocean, suppose we have the following averaged flows between space and the planet:

• 342 from space to the Earth (SW).
• 102 reflected back (SW) for an albedo of 0.298
• 240 thermal emission out the top of the atmosphere (LW)

Flows at the surface, excluding the backradiation:

• 162 solar absorbed at the surface (SW)
• 390 thermal up from the surface (LW)
• 97 by convection up from the surface (including latent heat of evaporation)

Assuming an equilibirum energy balance we can derive from these numbers:

• 78 solar absorbed in the atmosphere (SW)
• 335 = 97+78+390-240 thermal backradiation from the atmosphere down to the surface.

Sticking with integers, consider what happens when you get a forcing from a greenhouse effect of 4, but with no feedbacks. This is little more than what you get with doubling CO₂. All the shortwave fluxes remain unchanged. The convection should be about the same as well. What happens is that the thermal fluxes at the surface increase.

Now to a first approximation we can simply say that the forcing means 4 less out the top of the atmosphere, and delivered to the surface, before the equilibrium is restored. In the no-feedback response, the surface and the atmosphere all heat up until you get balance again.

The lapse rate remains the same, given no feedbacks, and the top and the bottom of the atmosphere will heat up by about equal amounts. The greenhouse effect basically works because the atmosphere radiates into space from the upper regions where it is cold, thus reducing the efficiency of Earth as a thermal radiator.

Assuming that all the radiation into space is from the atmosphere (which isn't really true; there's about 40 getting through the infrared window when cloud cover permits) we have presumed that the thermal radiation out the atmosphere dropped from 240 to 236.

Using Stefan-Boltzman Q = σT⁴ to estimate the effective radiating temperatures:

• 240 is an effective radiating temperature of about 255.
• 236 is an effective radiating temperature of about 254.

Now the backradiation out the bottom of the atmosphere is 335, with an effective radiating temperature of about 277. This is cooler than the surface, of course; we can say that we are getting thermal radiation mostly from the lower troposphere.

Raise that by a degree, and you get about 340, so the surface needs to heat up to emit 395, which has an effective temperature of about 289; not quite another degree.

The numbers here are not precise. The key point is that a forcing at the top of the atmosphere results in a larger forcing at the bottom. Your calculation of 0.18 K per W/m² is about right. Combined with 0.3 K per W/m² as the non-feedback response to the top of the atmosphere forcing, you can derive about 5 W/m² at the surface boundary for every 3 W/m² at the top of the atmosphere. That makes sense given the higher temperatures at the surface.

Do we have to make the assumption then that the surface will respond according to the Plank response - that the Wet Adiabatic Lapse Rate will remain stable and the surface will warm at the same rate as the tropopause emission level. I think the Stefan Boltzmann equations imply that the Lapse rate will in fact change by some amount.

The lapse rate is not based on radiation transfers, so Stefan-Boltzman is not used. Rather, the lapse rate largely depends on the adiabatic movement of air. The major feedback effect is that with increased humidity, the lapse rate falls, as the moist adiabat is less than the dry adiabat. This works as a negative feedback, since it effectively raises the temperature of the upper atmosphere by comparison with the surface, making the Earth a more effective radiator. This moderates the larger positive feedback from the strong greenhouse effect of the additional water in the atmosphere. But I was doing a non-feedback estimate above.

Cheers -- sylas

PS. Let me repeat my suggestion from [post=2498277]msg #32[/post]. Get hold of a free copy of "Principles of Planetary Climate". Given how much you like calculating things for yourself, this book will be right up your alley!

 

[Winzer]

I think the general consensus by the scientific community is:
The Earth's average temperature is rising.

However, it is not so clear(conclusive) why(i.e. man made, natural causes, etc, or combinations).

Sound about right?

 

[Bill Illis]

Thanks a bunch sylas.

I think I'm starting to see now.

I've gone through parts of Pierrehumbert's book before but it is a heavy read. I will come back when I've gone through it all this time.

 

[sylas]

I think the general consensus by the scientific community is:
The Earth's average temperature is rising.

However, it is not so clear(conclusive) why(i.e. man made, natural causes, etc, or combinations).

Sound about right?

Yes, although I'd put it more strongly. The rising temperature is a measurement, and the amount of rise is well within measurement accuracies. This is data.

Full details of all the causes is not known, and the sensitivity of climate to different forcings is known only approximately. But the primary cause is almost certainly anthropogenic; not natural. There's still plenty of sorting out details, but the major warming contribution is anthropogenic, with most of the natural forcings since the mid twentieth century likely to be a net cooling effect. That is, over recent decades, natural causes seem to have reduced the anthropogenic warming impact a little bit, rather than contribute to the observed warming.

Cheers -- sylas

 

[Xnn]

I like to download data and check the numbers against the assertions made.

I was finally able to view the graphs; it may have been security on the other system that prevented their display.

Anyhow, I also like to download data and check it out.
Do you know where the data for the time series charts can be found?
Solar irradiance, CO2 and ice dust levels for the last 400,000 years.

 

[Xnn]

I think the general consensus by the scientific community is:
The Earth's average temperature is rising.

However, it is not so clear(conclusive) why(i.e. man made, natural causes, etc, or combinations).

Sound about right?

No; the scientific consensus is that man made causes have also dominated over natural causes for the last 60 years of warming.

If it weren't for all of us humans, the world would be icing up.

 

[Bill Illis]

I was finally able to view the graphs; it may have been security on the other system that prevented their display.

Anyhow, I also like to download data and check it out.
Do you know where the data for the time series charts can be found?
Solar irradiance, CO2 and ice dust levels for the last 400,000 years.

Most of the material I've accumulated comes from the NOAA paleoclimatology website. There is a lot of data there.

http://www.ncdc.noaa.gov/paleo/data.html

If you want to spend some time looking through subdirectories, the FTP site has lots of little surprises.

ftp://ftp.ncdc.noaa.gov/pub/data/paleo/

I've also put up most of the data I'm using in easy-to-use Excel spreadsheets together with direct links to the datasources used at this Mediafire link. (a few of the direct links don't work anymore and there is some newer data from the last month or so, particularly with respect to CO2 in the last 20 million years from Tripati and Pagani which are not included, but one could just add to the spreadsheets as newer info becomes available).

http://www.mediafire.com/?sharekey=cc80321597b8ea7b4c17ca8801618ef794bf8b95c230d06a947708e37b913e74

Newer CO2 data could be added from these two papers.

http://www.seas.harvard.edu/climate/seminars/pdfs/tripati.etal.sci.2009.pdf

http://www.nature.com/ngeo/journal/v3/n1/abs/ngeo724.html

http://www.nature.com/ngeo/journal/v3/n1/extref/ngeo724-s1.pdf

 

[sylas]

If it weren't for all of us humans, the world would be icing up.

I think that is going much too far. The cooling contribution of natural forcings since the middle of the twentieth century has been tiny. If you go back further, natural forcings certainly contributed to the heating in the first part of the century. If you look on the scale of millenia, the Holocene is usually believed to have a long time yet to run, even if humanity was out of the picture entirely.

But we risk topic drift here.

Cheers -- sylas

 

[Xnn]

There is a relevant paper on the subject of an early Anthropocene.

http://earth.geology.yale.edu/~avf5/teaching/Files_pdf/Ruddiman2003.pdf

 

[sylas]

There is a relevant paper on the subject of an early Anthropocene.

http://earth.geology.yale.edu/~avf5/teaching/Files_pdf/Ruddiman2003.pdf

Yes; I am familiar with this notion. The major proponent is William Ruddiman, who is famous for his "early anthropocene", meaning that he believes the human impact on climate began with agriculture, thousands of years ago, and it has prevented the onset of the next ice age.

This is a minority few at present; and the weight of evidence is running against it. The debate goes on, and Ruddiman's stature ensures that it continues to be taken seriously.

Basically, Ruddiman proposed that the Holocene would be coming to an end by now, and the start of a new ice would have begun, if not for the climatic effects of widespread agriculture.

The alternative view, proposed by Loutre and Berger and others, is that Holocene should be expected to be a long interglacial due to low eccentricity, and that absent any human impact the next ice age is still some 30 thousand years or more in the future. A similarly long interglacial occurred in stage 11, some 400 thousand years ago, when eccentricity was also low.

Pre-industrial human impact on climate is mostly regional, rather than global, according to other research.

The nice thing about the IPCC reports is that they give a pretty comprehensive survey of the literature on competing ideas like this. Chapter 6, in paleoclimate, is the relevant part. The more common view at present is for a long integlacial, discussed in section 6.4.1.8 (When will the current interglacial end). Ruddiman's early anthropocene idea, and criticisms, are discussed in section 6.5.1.2 (Why Did Holocene Atmospheric Greenhouse Gas Concentrations Vary Before the Industrial Period?).

The evidence seems to be running against Ruddiman's proposal, though it is still open. The paper you have cited was followed shortly by a "comment" paper by other researchers indicating that Ruddiman's proposal was flawed.

References (starting from the paper cited by Xnn and looking at the subsequent exchange of contrasting views.)

• Berger, A. and Loutre, M.F. (2002) "An Exceptionally Long Interglacial Ahead?" in Science, v297 (23 Aug 2002), pp 1287-1288.
• Ruddiman, W.F. (2003) "The Anthropocene Greenhouse Era began Thousands of Years Ago", in Climatic Change v 61 pp 261–293.
• Claussen, M. et. al. (2005) "Did Humankind Prevent a Holocene Glaciation?" (comment on Ruddiman 2003) in Climatic Change v 69, pp 409-417. (The author's answer is "no".)
• Ruddiman, W.F. (2007), "The early anthropogenic hypothesis: Challenges and responses", in Rev. Geophys., 45, RG4001, doi:10.1029/2006RG000207. (Acknowledges widespread criticisms and proposes answers to them.)

There are more papers by both Claussen and Ruddiman and their respective colleagues that continue to debate this matter. Ruddiman appears to acknowledge that he has not so far managed to convince the rest of the paleoclimate community, and also that there is still not a conclusive case. By and large, the long interglacial hypothesis seems to have more support, and pre-industrial human impact on climate is not considered to have prevented an ice age.

Cheers -- sylas

 

[Xnn]

Sylas;

Appreciate your feedback and understand that Ruddiman's original hypothesis should not be completely accepted. However, my impression it is accepted that there was a pre-industrial age human contribution of roughly 10 ppm CO2 and 100 ppb CH4 to the atmosphere. In addition, we know that over the last 5000 years orbital changes have lead to a gradual cooling of the arctic that is expected to continue for several thousand years. So, absent human activities, we could have expected an expansion of glacial coverage in the northern hemisphere. This doesn't mean that there should have been a rapid expansion of ice conditions, but rather a continuation of what is known as the little ice age. That is, there would have been an gradual icing of the earth, especially in the northern hemisphere.

Unfortunately, I haven't been able to locate copies of the papers criticizing Ruddiman's work to study. However, I notice that a integrated analysis of solar insolation such as that performed by Huyber (figure 2E) appears to distinguish between recent solar forcing and that of 420 Kyrs ago.

http://www.sciencemag.org/cgi/reprint/313/5786/508.pdf

 

[eachus]

sylas said: "Engineering is, of course, rather different to science. "Validation" is a normal part of working for designed or engineered constructions; but it does not have quite so central a position in empirical science.

For example... what would it mean to "validate" a climate model? We already know that they are not complete and only give a partial picture of climate. To quote a common phrase: climate models are always wrong but often useful."

Sorry, I can't accept that. If you want to say that it is against my religion, fine. But in this case my religion is what I learned from professors and colleagues that it takes to do statistics right. The difference can be summed up in two books: Lies, Damned Lies and Statistics by Michael Wheeler, and The Visual Display of Quantitative Information by Edward Tufte. Go read both books, then go look at the original hockey stick again and decide which author describes it...

Terry Oldberg said: "According to Gray, he urged description by the IPCC of how the IPCC's models could be statistically validated. He says that the IPCC blew him off on this issue and implies that the IPCC's models are neither validated nor susceptible to validation. If Gray is correct, then the IPCC's models are not "scientific" models under Karl Popper's criterion of falsifiability."

Amen Terry! For me this sums up perfectly why I count myself an anthropogenic global warming skeptic even though I think there are good reasons for reducing CO2 emissions.

Although much of my work has been in the area of programming languages and algorithms, I have a MS in Statistics. I recently made a post on a completely different topic in which I said: "Beware of EDA (exploratory data analysis) without validation. There are times when you must split the sample available to you in half, one part for EDA, the other for validation. Anything else is junk science, or at least junk statistical analysis." (Since I am quoting myself here, I felt I could make some minor edits without adding brackets. ;-)

So the problems I have with climate science as a whole, are the incestuous sharing and editing of data, which makes anything like an independent test almost impossible, and the attitude that even when falsified, climate models should be kept the parameters juggled, new data added etc. No one should be surprised that climate models have no predictive power given the culture in which they have been created.

Will there be a real climate science at some point in the future? Probably. But I can't see it evolving from the current climate experts. They are not real scientists, although they do claim that on TV.

Am I being too harsh? I don't think I am being harsh enough. As a statistician who finds EDA to be fun, I often ask for the data behind papers in in areas such as cosmology, superconductivity, and the solar neutrino problem to mention a few. (I have also asked for such data in fields where I am known, but I am ignoring that.) In every area except climate science, the only problem I have is that the scientists are so glad to have someone interested who is a statistician and programmer who can help with validation, that my validation (or falsification) is not independent.* But in climate science the story is much different.

Yes, I have looked at the data which is now publicly available, and I am regularly shocked at how poor it is. What use is data from sites where measurements were only taken when it wasn't too cold, snowing, or raining? Or where normal and unavailable are represented by the same symbol (0). Climate researchers have often further processed these data to substitute proxies where original data is missing, but now any validation is impossible. At best, attempts to duplicate results will end up either accepting the researcher's assumptions, or with a much different data set. This is the "one tree in Siberia" problem.** If you have access to the original data you can run tests to determine the possible degree of measurement error and the amount of (unbiased) random error present. But when the only data available have been merged, outliers removed, and otherwise "cleaned up," you have to either accept it on religious grounds or reject it as unverifiable.

The other way, of course, to test models is to use them for prediction. Yes, I have seen models which did predict colder temperatures in 2008 and 2009--but they are based on sunspots, and cosmic rays. They are definitely not part of any IPCC consensus.

Finally, Bill Illis has linked to some (decent) NOAA data showing CO2 levels over 6000 ppm, or 20 times current levels millions of years ago. The simple application of the Stefan-Boltzman law would call for about 16 degrees C of ratiative forcing, which was clearly not the case. I certainly understand why the simple thermodynamics doesn't work. There are windows in the CO2 absorption spectrum which remain open no matter how many doublings of CO2 partial pressures occur. It doesn't take much data analysis either to realize that the answer is that water vapor and clouds have a complex response to temperature. But the shouting down by "climate scientists" of weathermen who use statistics to develop and validate complex models of how water vapor actually works is pretty shameful. (They probably watch the predictions of those models every night on TV to see what to wear in the morning, while shouting the models down during the day.)

I'd love to share some of those weather models with you, but there is an entirely different problem involved. The weather data itself is available from NOAA to anybody, in more detail than most desktop computers can handle. But there is a tremendous competition, part of it commercial, part of it military, to come up with better long-term weather prediction models. (And when long-term is long enough, it becomes climate.) Most of this work is done within a few miles of Bedford, MA, either at commercial weather forcasting companies, or by government agencies headquartered at Hanscom AFB.

I worked at MITRE Bedford for over a decade, and as I said at the beginning, my work involvement in these projects usually involved such things as programming languages support, distributed systems development, or (complexity) analysis of algorithms. So the data and models were not mine to distribute. However, the development effort in house was approximately three times as much effort on validating models as on creating new ones. When the models were turned over to the Air Force, the additional validation costs were huge. The additional work created by running multiple models side-by-side for a year or so is appalling. Back then it was basically one model run per supercomputer with multiple runs of the same model necessary every day. Part of the pain is that the data used in the run are usually twelve to twenty-four hours stale by the time the run finishes--and it often took two supercomputers to produce one result every twelve hours. If you read the forcasts from the National Hurricane Center you will find that today (well this year) they usually run four different models against the data from each hurricane every few hours.

The big prediction problem incidently is still the rain/snow line in three dimensions. It is easy to see how snow vs. rain on the ground results in a different albedo once the storm is over, but the same line is very important in heat transport within summer thunderstorms. And validation there is just a bit harder. I've seen pictures of aircraft that came back with (fortunately only slightly)) bent wings. And with lots of dents from flying into hail.


*I remember one case where I suggested non-parametric statistics as a way to tease a signal out of the background. The Wilcoxon rank sum test pulled out a very clear and statistically significant result--which after a few more days of data turned out to be from the heating system in the building. Sigh! At least I helped him track down what would have been an embarrassing systematic error, even if it did mean he had to start data collection all over again.

** Yes, I know that the tree ring data from Siberia was not based on data from just one tree. The problem is that the processed data wipes out the normal random variations that can be used to test for significance.

 

[sylas]

Appreciate your feedback and understand that Ruddiman's original hypothesis should not be completely accepted. However, my impression it is accepted that there was a pre-industrial age human contribution of roughly 10 ppm CO2 and 100 ppb CH4 to the atmosphere. In addition, we know that over the last 5000 years orbital changes have lead to a gradual cooling of the arctic that is expected to continue for several thousand years. So, absent human activities, we could have expected an expansion of glacial coverage in the northern hemisphere. This doesn't mean that there should have been a rapid expansion of ice conditions, but rather a continuation of what is known as the little ice age. That is, there would have been an gradual icing of the earth, especially in the northern hemisphere.

Fair enough. 10 ppm CO2 is a forcing of about 0.2 W/m², and 100 ppb CH₄ is a forcing of about 0.06 W/m², using approximation formulae for estimating forcings from a change in greenhouse gas concentrations. (Formulae are in the http://www.grida.no/publications/other/ipcc_tar/?src=/climate/ipcc_tar/wg1/222.htm .) If climate sensitivity is sufficiently high, this could make a significant difference. Climate sensitivity is about 0.8 +/- 0.4 degrees per W/m², so this anthropogenic pre-industrial forcing could drive as much as 0.3 degrees... not much more, I think.

I was reacting to the phrase "the world would be icing up". If you mean a little bit of additional glaciation, then yes; but it could easily be taken as something much more than this; a new ice age. I think that is unlikely. The Holocene would more likely continue mild, with small variations and perhaps a very slow cooling trend of the order of fractions of a degree per century.

An example of Holocene cooling trend estimation is

• Kullman, L (1993) http://www.jstor.org/pss/2997659, in Global Ecology and Biogeography Letters 2, pp 181-188.

I've only read the abstract. It derives a cooling trend of 0.12 degrees per millenum, a bit less than one hundredth of the current warming trend. The abstract indicates this value is consistent with the work of Berger on a long interglacial, cited previously. This trend is over some 8000 years, and corresponds to a drop in temperatures of about a degree, which seems about right. It would mean current temperatures are not quite as high as at the Holocene thermal maximum as yet, which makes sense to me. So 0.3 degrees off set from that helps.

We came out of the little ice age mainly because of natural variations, I think; it was not part of a longer trend but more of a dip... and mostly regional rather than global.

Unfortunately, I haven't been able to locate copies of the papers criticizing Ruddiman's work to study. However, I notice that a integrated analysis of solar insolation such as that performed by Huyber (figure 2E) appears to distinguish between recent solar forcing and that of 420 Kyrs ago.

http://www.sciencemag.org/cgi/reprint/313/5786/508.pdf

Found a freely available preprint of that:

• Huybers, P.J. (2006) Early Pleistocene glacial cycles and the integrated summer insolation forcing in Science 313(5786): pp 508-511.

I'll have a look at it. It appears to look at the Early Pleistocene, rather than the current Late Pleistocene. The final sentence of the paper is:

However, the 100-ky glacial cycles of the late Pleistocene have a more complicated relationship with the forcing, and their explanation will require a better understanding of ice sheet–climate interactions.[/color]​

420,000 years ago is still part of the late Pleistocene. The paper seems to divide early and late at about 1 million years ago, according to figure 2E, which is all labeled as part of the late Pleistocene.

There's another source you might find interesting. Ruddiman has a guest post available at the realclimate blog, which is a deliberate attempt to communicate issues in climate science to a wider general audience. He discusses the contrasts between his ideas and those of Berger and indicates what it would take (in his view) to distinguish them. It is a nice informal and open ended discussion.

Cheers -- sylas

 

[sylas]

Hi eachus. I don't mind if we disagree on general matters such as the quality of climate science generally, or the role of "validation" in science, and so on. I'm content with my perspective as stated previously, particularly in [post=2507536]msg #80[/post] which you have quoted, and don't see much value in expanding on it.

So I'll just comment on a two simpler points that can be resolved more easily.

The other way, of course, to test models is to use them for prediction. Yes, I have seen models which did predict colder temperatures in 2008 and 2009--but they are based on sunspots, and cosmic rays. They are definitely not part of any IPCC consensus.

If you have an actual citation for such predictions, then this could be the basis for an interesting new thread. It would be better as a new thread, it's a bit off topic here. To my knowledge the proposals for sunspots and cosmic rays are nowhere near able to give clear predictions like that, and certainly don't explain the large short term variations. Colder temperatures in 2008 is quite unconventionally recognized as part of the short term ENSO cycle. 2009 is heating up again, and appears to be the fifth hottest year on record. So if anyone was predicting colder temperatures, they've been falsified.

Finally, Bill Illis has linked to some (decent) NOAA data showing CO2 levels over 6000 ppm, or 20 times current levels millions of years ago. The simple application of the Stefan-Boltzman law would call for about 16 degrees C of ratiative forcing, which was clearly not the case.

I think you are mistaken. Bill's links go back some 20 million years, and CO₂ levels have remained below 600ppm over that period. Is 6000 a typo?

In any case, the forcing for 600ppm over pre-industrial levels would be around 4 W/m², and given current best estimates for sensitivity this would give a temperature rise of around 3 degrees, plus or minus 1.5; it is close to double to pre-industrial level.

But even assuming 6000 there still seems to be an error. Using 3*Log₂(C/C₀) for climate sensitivity of 3 degrees per doubling, this works out to a bit over 13 degrees gain over the pre-industrial levels of 280ppm. Note that this is presuming positive feedbacks to get climate sensitivity of about 3. If you simply ignore feedbacks and use radiative transfers alone, which seems to be what you mean by "Stefan-Boltzman", the temperature effect is less than half this.

I don't know how you got 16, but I think there is an error somewhere in your calculation as well.

Also... the highest CO₂ levels in the Cenozoic were during the "Paleocene-Eocene Thermal Maximum" (PETM) about 55 million years ago. This was a short period of greatly elevated temperatures. CO₂ levels beyond a million years or so reply on estimates from carbon models and proxies, as we don't have ice cores to give direct readings. Estimates are as high as 3000ppm. You don't get higher than that until you go back more than 400 million years.

Cheers -- sylas

 

[JohnMurphy]

The allegations of M&M have been evaluated by two commissions/panels, a ad hoc commision Wegman and the NAS panel of North. Both confirmed the crtique of M&M , despite all attempts to cover that

.This is not correct and I have often seen these Committees mixed up. Wegman was indeed chair of the National Academy of Sciences (NAS) Committee on Applied and Theoretical Statistics, but he produced the non peer-reviewed 'Wegman Report' for the US House Committee on Energy & Commerce.A peer-reviewed 'Committee on Surface Temperature Reconstructions for the Past 2,000 Years' was assembled by the National Research Council (NRC) of the National Academies (Board on Atmospheric Sciences and Climate) under Gerald North, and their report acknowledged that there were statistical shortcomings in the MBH analysis, but concluded that they were small in effect.
http://books.nap.edu/openbook.php?record_id=11676&page=R1"Additionally, the American Statistical Association (ASA), in a session at the Joint Statistical Meetings, 2006 - which included Wegman - came to the same conclusion as the NRC.
http://www.amstat-online.org/sections/envr/ssenews/ENVR_9_1.pdf"

 

[Andre]

.


This is not correct and I have often seen these Committees mixed up.

and yet another attempt to discredit wegman.

see here

 

[Bill Illis]

I think you are mistaken. Bill's links go back some 20 million years, and CO₂ levels have remained below 600ppm over that period. Is 6000 a typo?

Cheers -- sylas

The data I linked to sylas goes back 570 million years with the highest CO2 level being 7,069 ppm at 520 million years ago (GeoCarbIII from Berner). There are estimates going farther back with the last solid calculated ones being 12,000 ppm at the end of the last Snowball Earth period 635 million years ago (this wouldn't have been high enough to end the Snowball so it had to be super-continents Rhodinia/Pannotia breaking-up and moving off the south pole) and 4,200 ppm at 770 million years ago. It is inferred that CO2/GHG levels were increasingly higher as we go back farther in time or the Earth would have been a frozen iceball in all earlier time periods due to the Faint Young Sun.

 

[sylas]

The data I linked to sylas goes back 570 million years with the highest CO2 level being 7,069 ppm at 520 million years ago (GeoCarbIII from Berner). There are estimates going farther back with the last solid calculated ones being 12,000 ppm at the end of the last Snowball Earth period 635 million years ago (this wouldn't have been high enough to end the Snowball so it had to be super-continents Rhodinia/Pannotia breaking-up and moving off the south pole) and 4,200 ppm at 770 million years ago. It is inferred that CO2/GHG levels were increasingly higher as we go back farther in time or the Earth would have been a frozen iceball in all earlier time periods due to the Faint Young Sun.

Thanks for the correction. I missed that.

These estimates are based on models of the geological carbon cycle (GeoCarbIII), and they do involve very large concentrations many hundreds of millions of years ago, which I did refer to in my post, though I failed to find them in your links. After hunting around, I found the location within the NCDC ftp site: ftp://ftp.ncdc.noaa.gov/pub/data/paleo/climate_forcing/trace_gases/phanerozoic_co2.txt. Values are for RCO₂, which is the ratio to present levels (pre-industrial). The dataset reference suggests RCO₂ = 1 corresponds roughly to 300ppm.

Of course, going back hundreds of millions of years means we also need to consider changes in the solar output. As you say, the Sun was dimmer but the elevated CO₂ levels still meant Earth was warmer than today.

The major reference for this data set proposes the following formulae:

• Temperature impact of RCO₂ is 4*Ln(RCO₂).
• Temperature impact of faint Sun t million years ago is 7.4*t/570

At 520 Mya, with RCO₂ = 26.2, we have 13 degree gain from the greenhouse effect, and 6.75 degree loss from the faint Sun. These are very rough estimates, but they are in the ball park for a Cambrian that is about 6 degrees warmer than now, which is about right.

Going back to the snowball/slushball is very interesting; and I know you have done some work on this. Alas, we are going of topic.

Thanks for setting me straight on this.

Cheers -- sylas

 

[Bill Illis]

[*]Temperature impact of faint Sun t million years ago is 7.4*t/570
[/list]


Cheers -- sylas

I think it is better to think of it as the Solar Irradiance reaching the Earth was 30% lower 4.55 billion years ago and it has increased in very close to a straight line over time.

So, Solar Irradiance 520 million years ago was = 1366 (0.7*520/4550) = 1319 = 252.8K

or -2.2K change 520 million years ago from lower solar irradiance.

Go back to 4.55 billion years ago and the Te was 233K.

This comes from D. Gough 1981, Kasting 1988 and outlined a little better in a more recent paper by Kasting.

http://geosc.psu.edu/~kasting/PersonalPage/Pdf/annurev_03.pdf

 

[Trakar]

I think it is better to think of it as the Solar Irradiance reaching the Earth was 30% lower 4.55 billion years ago and it has increased in very close to a straight line over time.

So, Solar Irradiance 520 million years ago was = 1366 (0.7*520/4550) = 1319 = 252.8K

or -2.2K change 520 million years ago from lower solar irradiance.

Go back to 4.55 billion years ago and the Te was 233K.

This comes from D. Gough 1981, Kasting 1988 and outlined a little better in a more recent paper by Kasting.

http://geosc.psu.edu/~kasting/PersonalPage/Pdf/annurev_03.pdf

Ahhh! Thanks for the link, I had a copy of this about 2 years ago and lost it, memory wasn't good enough to pull it up in a search.

 

[sylas]

I think it is better to think of it as the Solar Irradiance reaching the Earth was 30% lower 4.55 billion years ago and it has increased in very close to a straight line over time.

So, Solar Irradiance 520 million years ago was = 1366 (0.7*520/4550) = 1319 = 252.8K

or -2.2K change 520 million years ago from lower solar irradiance.

Go back to 4.55 billion years ago and the Te was 233K.

This comes from D. Gough 1981, Kasting 1988 and outlined a little better in a more recent paper by Kasting.

http://geosc.psu.edu/~kasting/PersonalPage/Pdf/annurev_03.pdf

Thanks for the link. The calculation you present is better founded on the power law relating temperature to energy; but over the time scales of GeoCarb, this is not actually going to make much difference. A linear approximation works okay.

The real problem is that this calculation ignores all feedback effects, which are actually pretty crucial to the final temperature. Going back 520 Mya, the fractional decrease in insolation is 0.3*520/4550 = 0.0343. Insolation, after allowing for albedo, now about 240 W/m². The reduction is 0.0343*240 = 8.3 W/m². Assuming a climate sensitivity of about 0.75 K per W/m² you get a temperature change at the surface of 6.2K.

This is about what we get also from the numbers in the reference for the GeoCARB III reference, which is

• Berner, R.A. and Z. Kothavala(2001) GEOCARB III: A Revised Model of Atmospheric CO2 over Phanerozoic Time, American Journal of Science, v.301, pp.182-204, February 2001.

The two papers are consistent with each other, and the factors used for temperature difference over time due to the dimmer Sun take into account both the numbers you have presented for how solar radiance changes, and also the climate feedbacks that affect how the planet responds to that change, which is not simply given by Stefan-Boltzman.

Your latest reference spells this out explicitly. You have cited

• Kasting, J.F. and Catling D. (2003) Evolution of a Habitable Planet, in Annual Review of Astronomy and Astrophysics, Vol. 41, No. 1. pp. 429-463.

On page 442 (my bolding)

If one reduces the value of S by 30% in (1), holding A and ΔT_g constant for simplicity, one finds that T_e drops to 233 K and T_s = 266 K, well below the freezing point of water. If the calculation is repeated with a climate model that includes the positive feedback loop involving water vapor, the problem becomes even more severe. The dashed curves in Figure 4 show T_e and T_s calculated using a one-dimensional, radiative-convective climate model, assuming constant CO₂ concentrations and fixed relative humidity (Kasting, Toon & Pollack 1988). The results are remarkably similar to those predicted earlier by Sagan & Mullen: T_s drops below the freezing point of water prior to ~2 Ga. Combined with the snow/ice-albedo feedback loop, this temperature drop would almost certainly lead to a globally glaciated Earth. However, geologic evidence tells us that liquid water and life were both present as far back as 3.5 Ga and maybe longer. The oldest zircons, zirconium silicate minerals that must have formed in liquid water, are dated at more than 4.3 Ga and may indicate the presence of an ocean at that time (Catling & Kasting 2002, Mojzsis, Harrison & Pidgeon 2001, Wilde et al. 2001).

How can the faint young Sun problem be solved? A large decrease in cloudiness would do it (Rossow et al. 1982), but this seems unlikely for reasons mentioned in Section 3.1. Instead, the answer probably lies in increased concentrations of greenhouse gases. Both CO₂ and CH₄ are plausible candidates. ...[/color]​

The numbers used in the GeoCARB III reference, which give a temperature difference of about 6 degrees 520 Mya, correspond to estimates that take water vapour and other factors into account, just as Kasting and Catling describe here.

Cheers -- sylas