quote:

The earth is not a perfect black body, so climate models need to be used to estimate sensitivity to forcings.

Agreed, my calculation assumes an unchanged luminescence and is not assuming a black body.

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As I understand it, the expected sensitivity to a doubling of CO2

I assume you mean anthropogenic CO2.

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There are however feedbacks, such as increases in water vapour that add additional radiative forcing, and when all these are assessed you get into the range of the rise expected by IPCC.

I thought the juty was still out on whether water vapour forcing vs cloud negative forcing will dominate.

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The above refers to a doubling of CO2. At the current rate of 2ppm per year, we would reach this in 90 years, but some of Heretic's scenarios concern a potential acceleration in the increase of CO2 (unrelated to accelerations in anthropogenic emissions). Others relate to increases in methane which adds an additional forcing.

But the others only happen if there is a significant (several degrees) temperature rise and temperature looks pretty bounded given Infrared increases to the power 4 while CO2 effectiveness only increases logrithmically.

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I assume you mean anthropogenic CO2.

No, I mean total CO2 (including anthropogenic) - preindustrial levels were 280ppm. They are now 380ppm and rising at about 2ppm per year.

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I thought the juty was still out on whether water vapour forcing vs cloud negative forcing will dominate.

No I don't believe so. There are uncertainties in the forcings caused by the fact that aerosols make clouds brighter (so reflect more light) - was that what you were thinking about?

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But the others only happen if there is a significant (several degrees) temperature rise and temperature looks pretty bounded given Infrared increases to the power 4 while CO2 effectiveness only increases logrithmically.

Even at our current temperature we above the scale of the last many thousands of years. Even the Holocene optimum doesn't appear to compare if you check the temperature reconstructions from then, because that was not a global warming phenomenon. Look where the 2004 arrow points in the following graph:

en.wikipedia.org/wiki/Image:Holocene_Temperature_Variations.png

And we still expect 1.5-4.5C more rise in the next 100 years. So I would say we don't yet have a good idea of what nasty feedbacks are hiding in the woodwork.

quote:

Originally posted by Son of Mulder:
But the others only happen if there is a significant (several degrees) temperature rise

Bear in mind that temperature changes will not be uniform. Changes in the arctic have been greater than elsewhere so feedbacks like melting Siberian permafrost may happen at a relatively low global temperature rise.

Steve_M

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There are however feedbacks, such as increases in water vapour that add additional radiative forcing, and when all these are assessed you get into the range of the rise expected by IPCC.

Yes but this would also increase the rate of transport of latent heat from the surface to the higher atmosphere another cooling addition.

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No I don't believe so. There are uncertainties in the forcings caused by the fact that aerosols make clouds brighter (so reflect more light) - was that what you were thinking about?

No simply that more water vapour will create more cloud as well as a faster transfer of latent heat of evapouration from the surface. Isn't this where currently the models are parameterized because the science can't be modelled (yet)?

quote:

Even the Holocene optimum doesn't appear to compare if you check the temperature reconstructions from then, because that was not a global warming phenomenon. Look where the 2004 arrow points in the following graph:

en.wikipedia.org/wiki/Image:Holocene_Temperature_Variations.png

But that shows an average of a whole load of different proxies. Some (most) of which show very dramatic swings as you can see. Hence I'm not surprised that the average is a lot smoother (quieter). But there was only one real average temperature. Why should faith be put in the average. Maybe one of the wild swings is more realistic? If some of the proxies are considered as unrealistic then why are they included in the reconstruction of temperature process?

Mindcrime

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Bear in mind that temperature changes will not be uniform. Changes in the arctic have been greater than elsewhere so feedbacks like melting Siberian permafrost may happen at a relatively low global temperature rise

Do you know what th necessary rise for siberia is for melting to occur?

quote:

Originally posted by Son of Mulder:
Do you know what th necessary rise for siberia is for melting to occur?

Some melting has already happened. I don't know (but I don't think anyone knows) the quantitative relationship between temperature and amount of methane released, which is what you really want.

This would, of course, release more land for those displaced by rising sea levels elsewhere in the world.

quote:

This would, of course, release more land for those displaced by rising sea levels elsewhere in the world.

Hmmm...not sure the Bangladeshis will be too keen on being relocated to Siberia. Suspect the Turkish won't go there either and will just relocate to other parts of the EU when the droughts start to impact in the next couple of decades and assuming they're not busily at war with Syria over Euphrates water rights.

quote:

Originally posted by Steve_M:

quote:

This would, of course, release more land for those displaced by rising sea levels elsewhere in the world.

Hmmm...not sure the Bangladeshis will be too keen on being relocated to Siberia. Suspect the Turkish won't go there either and will just relocate to other parts of the EU when the droughts start to impact in the next couple of decades and assuming they're not busily at war with Syria over Euphrates water rights.

They might or might not be keen. All life forms have had to adapt to nature over the course of millions of years. Homo sapiens will need to as well.

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They might or might not be keen. All life forms have had to adapt to nature over the course of millions of years. Homo sapiens will need to as well.

How about adapting to needing to burn a lot less fossil fuel, can Homo Sapiens manage that?

quote:

Originally posted by Steve_M:
How about adapting to needing to burn a lot less fossil fuel, can Homo Sapiens manage that?

They may but I'm going to burn as much of it as I can in my Cadillac while I still can.

en.wikipedia.org/wiki/Image:Holocene_Temperature_Variations.png

quote:

But that shows an average of a whole load of different proxies. Some (most) of which show very dramatic swings as you can see. Hence I'm not surprised that the average is a lot smoother (quieter). But there was only one real average temperature. Why should faith be put in the average. Maybe one of the wild swings is more realistic? If some of the proxies are considered as unrealistic then why are they included in the reconstruction of temperature process?

The different results of the different proxies are because the Holocene optimum was not a global phenomenon, not because of errors of reconstruction. So while it was apparently very warm in Greenland, the Antarctica was cold.

So the average doesn't have the same meaning as now because then it reflected a warmer northern hemisphere and a colder southern hemisphere, whereas the average now reflects global warming. Furthermore, their are fewer proxies, so the computed average may be inaccurate.

Nevertheless, we have a situation now where even the conservative predictions of the IPCC (1.5C) predict a warming such that by 2100 all parts of the globe, including Greenland, could be warmer than they ever were for the last 12000 years.

quote:

The different results of the different proxies are because the Holocene optimum was not a global phenomenon, not because of errors of reconstruction. So while it was apparently very warm in Greenland, the Antarctica was cold.

So what - while it's been very warm in winters in the UK recently it's been very cold relatively in Bangladesh?

The Wikipedia article says it may have been warmer in Northern vs southern hemisphere you seem more definite - why?

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So the average doesn't have the same meaning as now because then it reflected a warmer northern hemisphere and a colder southern hemisphere, whereas the average now reflects global warming. Furthermore, their are fewer proxies, so the computed average may be inaccurate.

So what caused the warmer northern hemisphere and colder southern hemisphere?

The major thrust of my comments concerns the significant increase that one would expect in Infrared radiation if average temperature rises by 1 deg C. Completely wiping out the forcing due to GH Gasses.

No one has even attempted to scientifically criticise this assertion. Why? The AGW brigade have had nearly a week to muster some semblance of an intellectually rigorous argument.

quote:

The major thrust of my comments concerns the significant increase that one would expect in Infrared radiation if average temperature rises by 1 deg C. Completely wiping out the forcing due to GH Gasses.

No one has even attempted to scientifically criticise this assertion. Why? The AGW brigade have had nearly a week to muster some semblance of an intellectually rigorous argument.

I thought we agreed that a 1C rise would approximately balance out the expected 4W/m^2 forcing of doubling CO2. Beyond that, I think the "AGW brigade" here lack direct access to some of the details.

Checking the 3rd assessment report of the IPCC it appears that there are a number of papers stating that water vapour feedbacks alone will double other forcings, and also saying that within models, water vapour feedbacks amplify cloud feedbacks to possibly increase warming by a factor of 3.5:

www.grida.no/climate/ipcc_tar/wg1/268.htm

I've always based my understanding of the greenhouse theory using a model as simple as yours (radiative forcing balanced by black-body radiation), but I've just checked realclimate, and their latest article goes into greenhouse gas theory in a bit more detail.

www.realclimate.org/index.php/archives/2007/04/learning-from-a-simple-model/

Their calculation is a little bit more complicated than yours and temperature in their model is a little bit more sensitive than in your model, but the two are quite close. I will try to more fully digest the article and the comments (in particular comment number 1) later.

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The Wikipedia article says it may have been warmer in Northern vs southern hemisphere you seem more definite - why?

I think the article is saying it was definitely a lot warmer in the northern hemisphere and it may not have warmed so much (or at the same time) in the southern hemisphere. The "wild swings" of the Greenland ice sheet seem to be particularly exceptional. The main reason why I brought this up was that it is evidence that we may be within unknown territory with respect to temperatures experienced for 100 thousand years, and temperatures are still going up.

quote:

Originally posted by Steve_M:
..The main reason why I brought this up was that it is evidence that we may be within unknown territory with respect to temperatures experienced for 100 thousand years, and temperatures are still going up.

This is a very highly suspect, hugely speculative statement. It is much in line with notorious goofball Al Gore's statement that the sea level will rise 25 feet in the next 100 years.

quote:

This is a very highly suspect, hugely speculative statement. It is much in line with notorious goofball Al Gore's statement that the sea level will rise 25 feet in the next 100 years.

No, it's evidence. On the other hand your comment is made up.

I don't really care about Al Gore as he is a US politician and I haven't seen his film, but having read an alleged transcript of the film I asked in another thread whether Al Gore really did say that the sea would rise 20 feet in 100 years, and got a resounding silence. I've now found confirmation from the New York Times review it says:

quote:

citing no particular time frame, envisions rises of up to 20 feet and depicts parts of New York, Florida and other heavily populated areas as sinking beneath the waves, implying, at least visually, that inundation is imminent.

So it seems that the science in the film is sound, though some of the things that were implied by the imagery were arguably alarmist. Great job Al.

Steve_B

Thanks for the ref to the RealClimate article.
Because my calculation is based on existing combined radiation from the surface I'm comfortable it's consistent with the calcs used in the article.

Between 1750 and now there has been a forcing of 2.5 Watts per Sq Metre due to CO2/CH4/NO2/Other Hydrocarbons.

There has been a 0.6 deg C temperature rise which I estimate at approx 3 watts per sq Meter negative forcing due to increased Bolzmann related radiation.

Ok so approx balance but with a slight cooling excess.

Now you stated that if CO2 doubles vs 1750 level then the CO2 forcing will rise to 4 watts per Sq metre (currently it's about 1.5 Watts / sq Metre so 2.5 extra CO2 watts / sq metre forcing.

But an additional 1 deg C temperature rise by the end of the century vs today (which is what I understand to be the lower end estimate of temperature rise by the IPCC) will generate a further 5.4 watts per square metre according to my calculation. This means there is another (5.4 - 2.5 = 2.9) watts per square metre of negative forcing available to balance other increased positive forcings which I assume is water vapour.

Now interestingly I note that water vapour is missing from the radiative forcing chart which I'd referenced in my earlier post (below).

http://www.st-edmunds.cam.ac.uk/cis/houghton/images/fig6.jpg

So what is the predicted forcing of water vapour in 2100 vs now and now vs 1750 in watts per sq metre? It's not clear from the site you posted (below).

http://www.grida.no/climate/ipcc_tar/wg1/268.htm

But I trust you see why I've so little belief that there will be accelerated GW. But any uncertainty looks like it's tied up with water vapour forcing.

Son of Mulder.

I checked out the scenarios used by the IPCC. I picked out a mid-range one (the A1B scenario) and found the predicted forcings for 2100 (as compared with 2000, rather than the 1750 that they use as the comparison for current forcings). In the chart, forcings from GHGs comes to around 4.1W/sq metre with CO2 at 3.48W/sq metre and lots of other gases providing small additional contributions. So the basic calculation implies a further 1C or so rise.

The models, though, predict a range of 1.8-4.2 for this scenario, so I've posed the question to realclimate about where the feedbacks come from - not got a very satisfactory answer so far. In the meantime I had a quick look at one of the references from the IPCC (Try google scholar on "Hall and Manabe, 1999") where they ran a model with and without water vapour feedback, finding that with the feedback warming went up from 1.05C to 3.38C.

I can't find figures on the "forcing" that the extra water vapour provides. The paper I referenced suggests that the distribution of the vapour in the atmosphere is relevant (whereas gases such as CO2 is distributed evenly) so maybe it's a bit more complex.

Steve_M
Son of Mulder


Thank you both for some intelligent and informative postings

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The vertical stratification, with warmer layers above and cooler layers below, makes the stratosphere dynamically stable: there is no regular convection and associated turbulence in this part of the atmosphere. The heating is caused by an ozone layer that absorbs solar ultraviolet radiation, heating the upper layers of the stratosphere.

This is a segment of the wiki article on the stratosphere. It is clear that the comment by the author of this thread that colder weather affects the recovery of the ozone layer is incorrect. The ozone layer is independently heated by UV radiation from the sun, and because of the lack of convection will not be affected adversely or proactively by the troposphere.
Another point

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If it were true, Venus should be a great deal cooler. Venus has highest planetary surface temperature in the solar system at around 500°C. Being much further away from the sun, Venus only receives about 25% of the solar energy that warms Mercury -- but Venus is still much hotter, because of to the CO2 greenhouse effect.

This is not necessarily true. CO2 is an invisible gas which most notably is a by product of combustion.
The atmosphere of Venus is profoundly opaque. This can't be due to CO2 content. Since there is another component to Venus' atmosphere it is possible that this other component (Acid clouds) is the mechanism of the runaway greenhouse effect and the CO2 is merely the by product.

Scratch that last comment.

It has come to my attention that Venus doesn't revolve or more precisely it revolves once a year with a certain portion of its surface facing the sun for years at a time,only gradually turning, over the coarse of decades, so that the whole planet takes a turn in the sunshine.
Thus there is no need for a *solar forcing* mechanism to explain the stifling heat on Venus. CO2 is just the effect of the intense heat as everything that could possibly burn did so, caused by the neverending daylight on the stationary non spinning planet.
This GH gas effect is a hoax even on Venus.

quote:

Originally posted by papertiger0:

This GH gas effect is a hoax even on Venus.

Here’s something else to bring to your attention. Your last remark was rubbish.

Here’s snippits from RealClimate

The basic physical principles upon which the Theory of Global Warming is based include the notion of interconvertibility amongst forms of energy (introduced by Fourier in his formulation of planetary energy balance), thermodynamics (air cools when it rises), thermodynamics of phase change (cold air holds less water), quantum theory (absorption and emission of infrared by CO2 and other greenhouse gases), blackbody radiation, and Newton's laws of motion. Each of these components has passed literally thousands of tests in the laboratory. There is essentially zero uncertainty in the validity of such things, which form the basic physical underpinning of the Theory of Global Warming. If any of these parts of the theory didn't work, neither would microwave ovens, computers, steam engines, infrared remote controls, and any number of other everyday devices.

And Venus…

“the atmosphere of Venus has as much mass as about 100 Earth atmospheres, and it is almost pure CO2.”

“the upper atmosphere is whizzing along at a rate of about one rotation every four Earth days.”

Taken from:-

http://www.realclimate.org/index.php/archives/2006/04/l...from-venus/#more-287