rhoda

No, it's not handwaving nonsense. It makes perfect sense and is totally supported by everything known about climate behaviour on all time-scales. Which is why instead of addressing the points I made, you are being shouty and dismissive.

"BTW I must apologise in advance for a further period of silence coming up." I'm off to the text books too, I think we've got a tiger by the tail here! -:)

OK, BBD let's try another tack. Atmospheric CO2 increases have been running at about 2 ppm/yr. The current value is about 400 ppm. So a doubling of CO2 with BAU would take about 200 years. This would increase global temperatures by about 1K. The next 1K would take another 400 years if we did nothing and so on. We know there are those who say the actual increases would be greater but their arguments require acceptance of the scale of H2O (cloud) feedbacks which it is generally acknowleged are so far poorly understood.

So what you worried about BBD?

"So what you worried about BBD?" I can't say, but BBD started out as a sceptic and has been persuaded by the evidence he's uneartherd to move to alarmism. Pigs, runway anyone?

I really shouldn't be taking part in these discussions because I still don't know the difference between a forcing (an agency's response to a situation) and a feedback (an agency's response to a situation).

For example when the beaver builds a dam, are the resultant inundations forcings (by the beaver) or feedbacks (to the beaver's behaviour)?

Or if a forest fire causes widespread devastation is it a forcing due to the alleged actions of an arsonist or just another feedback to an ordinary lightning strike?

Maybe someone can enlighten me with an explanation that defines the essential difference.

(Perhaps it's that only wretched humans are responsible for forcings).

Good question Simon, I used to know the difference and it's really quite simple in electrical engineering terms. There is a source of electrical energy, generator, cell etc. a system, electrical circuit and an output which feedsback into the input. If the feedback from the output amplifies the input its a positive feedback. If the feedback from the outpout lowers the input it's a negative feedback.

In climate science I've found this definition:

"Natural forcings are of two types.

External Forcings: These are essentially linked to changes in the orbital parameters of the earth that control the intensity and location of incident solar radiation, and fluctuations in solar energy.

Internal Forcings: These comprise all those changes that occur within the earth system itself, in particular volcanic activity, fluctuations in ocean circulations and large-scale changes in the marine and terrestrial biosphere or in the cryosphere.

So I'm guessing "feedback" is anything that amplifies/decreases the effects of these internal and external forcings. Indeed it seems that CO2 is a feedback which triggers more water vapour with the extra heat which in turn triggers more heat from the water vapour, which triggers more water vapour which triggers... you get the picture. I still don't understand how this cycle stops or what happens to atmospheric pressure and volume with this increasing heat, but that's my, probably flawed, understanding.

Still it looks pretty simple to model and make accurate forecasst 50 to 100 years out doesn't it?

I still don't understand how this cycle stops or what happens to atmospheric pressure and volume with this increasing heat

Conservation of energy. Energy radiates into space from the upper atmosphere. Unless you keep on turning up the sun, radiative balance is achieved.

Within the climate system, positive feedbacks amplify forcings but the increase in effect (warming/cooling) is logarithmic: it diminishes toward zero over time, preventing 'runaway' feedback. Even so, very extreme climate change is possible, eg end Permian event, PETM and various snowball earths in the deep geological past.

Re: Jul 13, 2012 at 9:05 AM | rhoda

"OK, I thought I was on to something when one of the CO2 bands appeared to be saturated, or at least have no significant increase in absorbtion over 25 years. So I wondered what effect that would have on the well-known 3.7 w/sqm per doubling. It cnnot remain the sme if CO2 is tapped out in prt of its range, right? So what part of the 3.7 is down to the unresponsive band? And I can't find the derivation of that number in plain english anywhere. It is supposed to be in Ramaswamy et al, but that turns out to be, well, disputed in terms of validity (it's grey lit) and soundness in reaching that conclusion other than by modelling. So, where is the justification for 3.7, and what contribution comes from the different bands?"

Interesting, Rhoda, according to IPCC :

"The simple formulae for RF of the LLGHG quoted in Ramaswamy et al. (2001) are still valid. These formulae are based on global RF calculations where clouds, stratospheric adjustment and solar absorption are included, and give an RF of +3.7 W m–2 for a doubling in the CO2 mixing ratio. "

Also -

"For the RF calculation, the data from Law Dome ice cap in the Antarctic are used because they show the highest age resolution (approximately 10 years) of any ice core record in existence."

http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2-3.html

Yet according to Steve McIntyre the Law Dome data remains unpublished -

"Oxygen isotope series are the backbone of deep-time paleoclimate. The canonical 800,000 year comparison of CO2 and temperature uses O18 values from Vostok, Antarctica to estimate temperature. In deep time, O18 values are a real success story: they clearly show changes from the LGM to the Holocene that cohere with glacial moraines.

On its face, Law Dome, which was screened out by Gergis and Karoly, is an extraordinarily important Holocene site as it is, to my knowledge, the highest-accumulation Holocene site yet known, with accumulation almost 10 times greater than the canonical Vostok site. (Accumulation is directly related to resolution: high accumulation enables high resolution.)...

Given the high reliance on O18 series in deep time, one would think that paleoclimatologists would be extremely interested in a publication of the Law Dome O18 data and be pressuring Tas van Ommen on this point....

But despite the apparent opportunity offered by Law Dome, there has been virtually no technical publication of a high-resolution O18 or delD isotope series....

As I’ve mentioned before, the Law Dome series was discussed by IPCC authors in the preparation of AR4. Their Southern Hemisphere graphic showed two proxies: Cook’s Tasmanian and Oroko Swamp NZ tree ring chronologies. As noted a few days ago, these two proxies are the only two proxies in the medieval portion of the Gergis et al network. So despite its claims to novelty, there is nothing new in its medieval portion...

On a personal level, I understand that people can’t do everything in the world. But nonetheless, the deep Law Dome hole was drilled between 1987 and 1992. It provides the highest resolution ice core for the two-millennium period. And remains unpublished. Amazing."

http://climateaudit.org/2012/06/12/an-unpublished-law-dome-series/

although as Steve updates bits have since been archived by some authors but one wonders at their general reluctance to do so.

rhoda

The 'middle' 15μm band isn't saturated. Nor does saturation matter anyway in the lower troposphere where the dominant mechanism for vertical heat transport is convection. It only matters at the tropopause. And 15μm certainly isn't saturated at altitude. Pressure (height of tropopause) and temperature are vital parts of the mechanism which determines efficiency of radiation at TOA and therefore *surface* forcing in W/m^2. I'm sure RB can point you at a good source for detail on this.

rhoda

It is my conjecture that the magnitude of this with evaporative and water vapour feedbacks in both senses completely blows away CO2.

Ah. No. There's a good explanation of why this is mistaken here. It becomes increasingly relevant from ~ ¼ of the way down the page - look out for this:

Now there is a popular misconception that more greenhouse gases warm the surface on the pure basis that they enhance the downward infrared emission. I want to examine what is going on in a bit more detail, because saying that the globe is warming simply because the downward IR has increased is not accurate. The below figure shows how a quick profile of the atmosphere.

And read on, noting:

But it would be misleading to say that the heat content change is due to re-radiated IR. The global mean heat content change is the result of changes in *net* radiation reaching the ocean surface, which includes downward re-radiated IR due to CO2, water vapor, clouds, etc., but also includes any increase in the *absorbed* solar radiation at the ocean surface due to any long-term decrease in clouds. But I should be more clear on what happens when you change the greenhouse composition of the atmosphere.

By making the lower levels more opaque to infrared radiation, you decrease Prad and so you are forced to extrapolate temperature in the vertical further along the adiabat to reach the surface. This is because the effective radiating level has now shifted to higher levels where the planet can emit the radiation back to space. Recall that temperature decreases with altitude, and radiation diminishes with temperature. This means that making the lower levels more opaque in the infrared, you decrease the rate by which the Earth can get rid of heat by forcing the the mean altitude from which infrared emitted upwards makes it to space to ever higher altitudes. These are colder layers, and so radiate more feebly. The net inlux of solar radiation remains constant, while the planet is now radiating at colder temperatures, and so less efficiently.

Part II is here. More on absorption and re-radiation by CO2, water vapour feedback, and the 'runaway greenhouse'.

I hope this helps.

rhoda

I am not Chris Colose! Surely you can tell from the difference in prose style? I'm sorry that you didn't see why the linked material might be useful in exploring your question. I was trying to be helpful, not introduce a tactical diversion. Please accept at least the intention at face value, if not the information.

...and further input on feedbacks -

"...the figure at the top of this post, if it turns about to be robust, raises fundamental issues with respect to the ability of global climate models to skillfully model the role of humans in altering the climate.

...Indeed, the Vonder Haar et al 2012 provides further support to the conclusion by De-Zheng Sun in the paper

Sun, D.-Z., Y. Yu, and T. Zhang, 2009: Tropical Water Vapor and Cloud Feedbacks in Climate Models: A Further Assessment Using Coupled Simulations. J. Climate, 22, 1287-1304

....As part of their conclusions, they wrote

“The extended calculation using coupled runs confirms the earlier inference from the AMIP runs that underestimating the negative feedback from cloud albedo and overestimating the positive feedback from the greenhouse effect of water vapor over the tropical Pacific during ENSO is a prevalent problem of climate models."

"While De-Zheng was reluctant to relate his findings to multi-decadal global climate model simulations of the role of humans in the climate system, the new Vonder Haar et al 2012 paper provides further support that the water vapor feedback is overstated by the IPCC models." "

http://pielkeclimatesci.wordpress.com/2012/07/16/new-paper-weather-and-climate-analyses-using-improved-global-water-vapor-observations-by-vonder-haar-et-al-2012/

rhoda, it's absorption. As any fule kno.