Sunday, January 10, 2010

A student is asking ....

A student has sent me five questions on the issue of man-made climate change. As they may be seen as typical, I answer them here on the Klimazwiebel. This may be useful – for the student, who will be able to read the comments of the readers of the blog, – for the bloggers to better understand the issues and concerns among lay people, – for me, who will have a critical assessment of my response to the student.

The idea with this post is that the student will read it plus the comments - so that the different contributions should not represent too much piecework. Therefore, commenters, deal just with the questions raised, and try to make only one statement so that the material, which eventually gathers, is compact!

1. Human activities contribute to global warming – Yes, the major human influence on global warming is through the emission of so-called greenhouse gases (GHGs), in particular carbon dioxide, which accumulate in the atmosphere und remain there for several decades. The air temperature (near Earth surface) has risen since pre-industrial times (ca. 1850) by about 0.7 oC; this warming can not be explained by internal climate variability alone, but can only be understood as a result of contributing external factors, among them elevated GHG levels in the atmosphere. It is thought that most of the warming, in particular the strong warming since about 1970, can be explained only by the increased concentration of GHGs.

2. There are no practical solutions available to stop the current warming (man-made or not). – In the climate system there is some "inertia": developments "persist" for a while, so that any efforts to reduce the GHG-related warming (either the ongoing multi-decadal increase of temperature, or the level of temperature) will need at least two, three or even more decades of years to take effect. Thus a short term "stopping of the warming" or an "ending of the elevated temperatures and a return to preindustrial conditions" is not conceivable. – One issue, related to your question, is that of "geoengineering", in particular man-made modifications of the geophysical properties of the Earth surface or of the atmosphere, which would change the "radiative balance" (e.g., reflecting substances in the lower stratosphere). Research to this end is underway, but at this time, the public opposition to such efforts is massive, it seems. – If the current climate protection policy would have been successful in initiating a policy, which would really limit the change of global mean temperature to 2oC (relative to pre-industrial conditions; of which 0.7oC have already taken place), then a significant stress on societies and eco-systems would emerge, which would need broad efforts to manage the adaptation of societies and ecosystems to these changed conditions.

3. When a critical level of the temperature is passed, the warming of Earth can not longer be stopped. – You are referring to the "runaway effect", which is thought to have taken place of Venus, where temperature are very high now. I know little about this issue, but I would believe that in principle there may be such a critical level, but our climate models describe all futures with elevated GHG levels without such a runaway effect.

4. Earth has no mechanisms to counteract the current warming. – Again, this depends on the time horizon you are looking at. When dealing with horizons of, say 100 years, there is none; the effect of GHGs on the radiative balance is simply too strong. However, most (not all) of the additional GHGs in the atmosphere will disappear in the long run (of many hundreds of years) by sedimentation in the deep ocean and other mechanisms, so that on the long term Earth will return to its variations enforced by the configuration of its orbit relative to the sun.

5. The warming dramatically affects ecosystems, humans and their activities. – This depends on the intensity and the rate of warming. The warming, we have seen so far, had little effect (even if interested parties try to relate all kind of extremes, e.g., Katrina to the warming). The slower the warming, the easier the autonomous adaptation will be. – Locally there can be dramatic effects: if, for instance, a glacier is melting in the Alps, the ecosystem in that region will change; the water supply will change; tourism will be affected. Rising sea level will in general have various adverse effects; increasing the risk of inundation; forcing more efforts in coastal defence; problem with groundwater and salinity, coastal erosion. On the other hand, humans have always been ingenious when confronted with new challenges, and if enough time is available, one may expect this also in this century. (We may confidently predict the emergence of unexpected, entirely new knowledge and options in the course of this century.) – Also keep in mind that climate is just one changing condition of our life; many other things change at the same time: technology, social organisation, economic wealth and options, social values. Which of these changes will be the most important in 2050, for instance?


Dipl.-Ing. P Gosselin said...

Here are my answers, having followed the debate for years. Respectfully, I don't completely agree with Prof von Storch on some points. Please note that I'm paid by neither side.

No. 1
Temperatures have been going up since the low peak of the Little Ice Age, i.e. around 1700, long before human GHG emissions. It cannot be claimed that GHG are the main cause of the continued warming trend over the last 150 years.
It most likely has made a contribution, maybe of a couple on tenths of a °C. Strong solar correlations have been shown. Let's also not forget the urban heat island effect contaminating the temp. record.

2. Man cannot regulate the global temperature by a couple of degrees Celsius - maybe we can by a tenth or two, over decades, which is statistically unverifiable.
Anyone who claims he can regulate global temps is either God, or a charlatan.

3. The hypothesis of a tipping point is a dubious one. The earth, in its 4.5 billion year history, was warmer than it is today 85% of the time. It's now actually cold. The earth never had an irreversible tipping point in one direction or the other. Not even when CO2 concentrations were 20 times higher than today's level.

4. This is also a dubious claim. Clouds and solar factors have been severely neglected by attempts to model the climate. In fact there's a chance that the added CO2 fertilisation could lead to more moisture, which would lead to more clouds, and thus cooling. Just a hypothesis.

5. Climate change has always occurred, sometimes so severely that species have been challenged or even wiped out. The rate of climate change occurring today is completely within the normal boundaries. Nothing unusual is happening.

P Gosselin said...

The student should also read the following link. It's just another view - a different perspective. I don't necessarilly agree with it.

P Gosselin said...
This comment has been removed by a blog administrator.
plazamoyua said...

I find the very beginning somehow problematic:

The air temperature (near Earth surface) has risen since pre-industrial times (ca. 1850) by about 0.7 oC; this warming can not be explained by internal climate variability alone, but can only be understood as a result of contributing external factors, among them elevated GHG levels in the atmosphere. It is thought that most of the warming, in particular the strong warming since about 1970, can be explained only by the increased concentration of GHGs.

This implies internal variability and external factors are well known and understood. If so, I should be easy to get the temperature trend for the next five or ten years -or having get it right for the last ten.

This graph from Eduardo [-->] does tell us a non warming trend for a decade does not invalidate the model. But it tells us also that the probability for a single decade to be a non warming one is very low, if I am not wrong.

So, or AGW has been really unlucky, or something is very wrong with the model's idea about internal variability or external factors.

So, what the sensible layman answer? For me, waiting ten more years, when there should be a better answer.

Where am I getting it wrong?

Hans von Storch said...

plazamoyua, no. 5 - this issue has been dealt with under the headline "detection and attribution". Including the caveats. I do not intend to repeat arguments once made. But, of course, you do not need to accept my arguments, and you can assume that the variability is larger and has longer memory. We have, however, no evidence for that.
But, waiting a few more years or decades will lead to a more robust assessment, true.

Hans von Storch said...

Comment no. 3 - this comment labels a scientist asa a "charlatan", and his work as "rubbish". This terminology does not help to establish a constructive dialog, and I ask for understanding if I delete that comment.

The claim "One problem in climate science is that the system greatly rewards those who make the most dramatic and outrageous claims." is certainly interesting, and an analysis of this sort would be of interest. In the Bray-surveys there was one question to this end. But note that the dramatic claimsmaking takes place also among certain quarters of skeptics.

P Gosselin said...

Dear Prof von Storch,
I can understand your dislike of my comment number 3, a personal feeling - sorry again.
Please note that the scientists within his own circle labelled his scenario, let us call it, as "incredibly improbable". The assessment of his methodology was equally dismissive.
Yet, such "scenarios" get adopted by a supposively respectable IPCC, while those of the renown Nils-Axel Morner get simply ignored!
Something for your student to ponder.

Not wishing to get off the subject, the scientist in discussion here would never place a bet on his scenario of 1.7 meters in 90 years, i.e 18+ cm per decade. Never!
18 cm in the next decade? Good luck getting him to bet on that. I have yet to find a single so-called alarmist to even bet on 5 cm in the next 10 years (normally I'm very unlucky at gambling).

MY ADVICE TO THE STUDENT here is that he/she not restrict the focus of analysis on the last 150 years, instead examine over thousands and millions of years. If you do so, you will see that the AGW hypothesis falls to pieces. It is sad that so many resources and money are being wasted studying this non-problem.
Yet in the end, it's the Professor who gives you the final grade.
Good luck in this field!
(In the time it took me to write this, 60 children died of malnutrition worldwide).

P Gosselin said...

I would never put much stock in these attempts to model the climate, which are then used to attempt projections. That's what they are attempting to do. They are trying to try to make a projection. That's where their science is at at this stage. The models really are that bad.

Henk said...

H Hak

Slightly OT maybe but relevant to the reliability of the climate models. I have always wondered if you could run the GCMs backward and find some indications of the LIA or even the MWP. Let me guess: error margins larger than the Eiffel tower?
But shoudn't you be able to find at least a trend?
Some would counter that the LIA and MWP
were local or at least only NH phenomena.
My second question would then be:
Are there any models that would give us a breakdown between NH and SH and find the above trends in the NH if you run them backwards?

Tom said...

Henk suggests running the climate models back in time to simulate the Little Ice Age (LIA), as a means of validation. This may have been done but is, in my view, pointless. The problem is that the best models have a spatial grid resolution of 25 km or better, and data storage timestep of usually every 6 hours. Reliable observations for validation at such resolutions only exist for about the last 50 years, at best. So, it would be impossible to calculate meaningful error margins for the LIA. Moreover, to experience changing climate, models require some sort of forcing parameter, like rising CO2 levels, to drive the change - just like the real climate. So far as I know, the forcing for the LIA is not known with any precision, largely because of the lack of good climate data 100s of years ago.


Capt. said...

Herr VOn Storch,

Re the 0,7 degrees rise in temperature, how much do you estimate can be contributed to UHI and how much to natural causes. And how much are the error bars used in these calcualtions?

Knowing that most of the temperature rise is based on CRU data, which are now under fire, can we trust these figures?


Hans von Storch said...

Capt, 13: Urban Heat Islaneffect (UHI) contributes likely not to the warming (this has been taken care of); the CRU thermometer-based temp data are not really compromised (see previous contribution on this blog; also nature on-line: von Storch, H. and M. Allen, 2009: Reaffirming climate science, nature online 18 December 2009 doi:10.1038/news.2009.1155
Most of the recent warming since 1970 can be explained only by GHGs (given present knowledge); in total since 1850 about 2/3s or so.
Error bars on temp data, see CRU or any other source; error bars on human effect: can not be given.

My assessment becomes wrong - if we have missed a significant, so far unknown influence factor; if climatologists at various institutions in different countries have colluded to counterfeit the data. The first is unavoidable and always possible (but no indications so far); the latter is unprobable.

Werner Krauss said...

Dear student, here are my answers to your questions.

1.Human activities contribute to global warming:

Everybody knows how climate scientists will answer this question, quite split among: yes / no (or maybe just a tiny bit) / we will see. They are not the ones to ask. Quite the contrary, you as a layperson have to explain to them why we don't need their answers to this question anymore. They have done their duty; climate is already a political affair. All politics in the future will be climate politics. Global warming is already a global experiment, and we are all part of it. Instead of starting another round in this endless debate between alarmists / skeptics / honest brokers et., climate scientists should intensify their efforts to better understand the climate and all the open questions related to it. Meanwhile, we can reduce the emissions, and within the span of some decades, we may well see some effects. At that time, we may also be able to see the answer to your question, assuming, of course, that climate scientists will at that time be able to separate anthropogenic neatly from other effects.

Werner Krauss said...

2, There are no practical solutions available to stop the current warming (man-made or not).

There are many reasonable things to do, for many different reasons. Trying to stop current warming trends sounds to me like a proposal from some people a little too big for their boots. Modesty is a virtue, and we should do what we can. Aiming at doing the impossible is at least a heroic gesture.

3. When a critical level of the temperature is passed, the warming of the Earth can no longer be stopped.

We have always been scared that the sky is falling (as Chicken Little worried)....just like our forefathers or so-called primitive peoples also feared. The mythical tipping point argument embedded in this question is a deeply religious metaphor. Anthropologists sometimes discuss science as the religion of modernity, given its reliance on psychological arguments: the situation is scary; some time, some day, it is too late - for everything.

4, Earth has no mechanism to counteract the current warming.

Obviously, by the phrasing of this question, you must be a follower of the Gaia hypothesis? That is, you seem to think that the earth is a living mechanism, or a living being, with abilities, a will of its own and so on? Interesting. It is difficult to argue about world views (or earth views, in this case), but we should respect each others' beliefs. Personally, I think that the earth is pretty indifferent - warm or cold, earth doesn't care. But that's a belief, too.

5. The warming dramatically affects ecosystems, humans and their activities.

Global warming definitively does affect the world we live in. Climate always has done so. Has there ever been a time when we could trust the climate? And now, with six billion people, climate has become an even greater threat, even independent of global warming. Monsoons, hurricanes, flooding, droughts, et., accompanied by human mismanagement, exploitation and what have you - life in the capitalistic greenhouse isn't easy.
We don't need a consensus about global warming and the role of human activities; we already are not able to protect millions of people from diseases, hunger, exploitation, and the effects of natural disasters. To do so, we need a sense of humanity and responsibility. We should start immediately. it is the best protection against the effects of global warming, as well.

Rafa said...

Just a question:
It is OK talk about natural variability, but what is the specific mechanism that you suggested to explain the cooling of the last 10 years? Do you have any idea? Where is the heat going?

Anonymous said...

1. True but the question then is - how much?
2. True. We don't even know what has 'caused' the warming and much of it is random or chaotic fluctuation.
3. False. Arises only from a naive simple feedback model.
4. False. A warmer earth will emit more heat. Even if you believe the AGW story, oil is running out soon and the CO2 will be absorbed.
5. False. Warming has been only about 0.7 degrees over 100 years. If today was 0.7 degrees warmer than yesterday, would you even notice? Cold weather kills more people than warm weather. This aspect has been ridiculously over-exaggereated.

Capt. said...

S.g.Herr Von Storch #14:
Vielen Dank! Re "been taken care of", there has been an interesting discussion re UHI here:

Interesting question (amongst others) to be answered; has there been taken any consideration for making a difference between growing and stagnating UHI's? And what about windspeed measurements?

Re CRU temp data; I believe the raw data has been deleted, so it's impossible to reproduce the homogenized data?

"Most of the recent warming since 1970 can be explained only by GHGs (given present knowledge); in total since 1850 about 2/3s or so." Isn't this like "der Wunsch der Vater des Gedanken"?


Werner Krauss said...

Climate experts are like birds: once together, they endlessly chatter in their own language and forget completely the outside world. Was there a layperson asking something? Uh? There were five questions? Blue birds, green birds, black birds....endlessly discussing group building, mating practices, nest building, and not to forget cold and warm periods coming up...oh, another bird, what does this one think about AGW, GHG, CRU, UHI, LIA, MWA, and the CIA? How nice they sing! Sssssh, don't disturb!

MikeR said...

Not being a climate scientist, I don't really get to present a point of view. But I would have thought that the "layman's default" point of view is something like:
1) Presumably CO2 will and does contribute significantly to global temperature.
2) There are no practical solutions today, but probably will be in the next fifty years.
3) Given the history of the planet, runaway scenarios seem quite unlikely.
4) No idea, too complex to know.
5) My first assumption would surely have been that a few degrees will have numerous effects, but probably none too difficult to deal with if it happens slowly. This does not seem to be the consensus, but this layman needs convincing. I don't understand why anyone would consider gutting the world economy (which IMHO will kill zillions of people) to prevent this - unless you convince me the layman that I'm wrong and these changes would kill yet more people than trying to prevent them.

6) It makes Bayesian sense to spend most of our time and effort right now working these things out better, rather than doing things that may not help, may not be needed and probably won't work.

Werner Krauss said...

Bayesian inference is statistical inference in which evidence or observations are used to update or to newly infer the probability that a hypothesis may be true. The name "Bayesian" comes from the frequent use of Bayes' theorem in the inference process. Bayes' theorem was derived from the work of the Reverend Thomas Bayes.[1]

Reiner Grundmann said...

Werner - 15

You say, the scientists "are not the ones to ask... we don't need their answers to this question anymore. They have done their duty; climate is already a political affair. All politics in the future will be climate politics."

It is not quite so easy. The science debate will not go away as long as there are disputes about the legitimacy to spend money on mitigation. One major argument made by people who are against regulation of GHGs is that the natural variability is higher than observed modern temp. rises which result from GHGs.

That's why it is perceived to be important (for proponents of GHG regulations) to show that "the science is settled". And this is the reason why also on the Klimazwiebel scientists argue about observations that would falsify either side's theory (very much simplified ;-))

Werner Krauss said...

Reiner- 21

(don't want to break with the 'one statement' rule for this posting; we keep this for later, Reiner).

TCO said...

My one statement:

I think this is a situation where you really need to be careful about what questions you ask, about not over or improperly taking a direct answer to a limited quesiton as meaning more, and about (almost forcefully) constraining people to answer the questions posed rather than trying to argue larger or different issues or "guess what you wanted to know".

Hans Erren said...

ad 1: I would like to bring to your attention that according Roger Pielke Sr. the "cartell" carefully kept the following adverse results out of the IPCC reviews summarised in:

Pielke Sr., R., K. Beven, G. Brasseur, J. Calvert, M. Chahine, R. Dickerson, D. Entekhabi, E. Foufoula-Georgiou, H. Gupta, V. Gupta, W. Krajewski, E. Philip Krider, W. K.M. Lau, J. McDonnell, W. Rossow, J. Schaake, J. Smith, S. Sorooshian, and E. Wood, 2009: Climate change: The need to consider human forcings besides greenhouse gases. Eos, Vol. 90, No. 45, 10 November 2009, 413. Copyright (2009) American Geophysical Union.

Also please take note that the increase of CO2 correlates 99% with the increase of global population and therefore statistically is indistinguishable on a global average level. We need falsifiable criteria, not "is consistent with" publications.

Anonymous said...

For once, I agree with TCO about the questions being asked. Are they the right questions even? Or are they leading questions revealing an underlying belief system?

Anyhow, FWIW, here are my responses.

1. Human activities contribute to AGW. But which? There are probably many human activities that affect local and regional climate (desertification for example) and which could aggregate as 'global' warming. The real answer is that we don't know as much as we would like. This is a complex question. Can we trust the temperature record fed to us? Is CO2 really a problem? What about the logarithmic decay issue (like adding more curtains to keep out the light) which says that perhaps most of the CO2 related warming has already happened?

2. There are no practical solutions to stop the current warming. Depends on the cause. If CO2, unlikely. Hugely disruptive to change it. However, CO2 is likely not the problem, and in some senses (enhanced vegetative growth) may be part of a solution. If land-use factors as RP Sr argues, then there are specific responses re each situation. Re-hydration of the landscape is possible using approaches similar to those used by Permaculture, Peter Andrews and others.

Anonymous said...


3. When a critical level of temperature is passed, the warming of Earth can not longer be stopped. We don't know. Depends on whether there is warming or not? Whether it is natural or not? If anthropogenic, what is the cause?

4. Earth has no mechanism to counteract the warming. Seems unlikely. Earth is a very complex system, and there are self moderating/self healing influences. One is that higher temps cause more evaporation, increase moisture in the air, more clouds, more albedo, less sun heat to earth surface.

5. The warming dramatically affects ecosystems, humans and their activities. Perhaps. But it is highly likely that adverse events experienced locally (like droughts, floods, fires etc) are more to do with local situations - lack of precipitation, perhaps due to man's interference in natural hydrological cycles.

Complex issues. And too many people are oversimplifying.

Anonymous said...

@Henk and Tom , #9-10

It is easy to find the requested information of back-validated climate models: in the supplementary material to Chapter 8 of the working group I (The physical science base) of IPCC's AR4 (fourth assessment report), it is published on page 5 how climate models compare to the CRU temperature data for the late 20th century.

If I read the graphs correctly (I am a physicist, but not a climate scientist), climate models can reproduce temperatures in mid-latitudes quite well but fail to do so spectacularly over ice, hence in the Antarctic, Greenland and the northern parts of Eurasia.

If this view is correct, Question 1 can NOT be answered with confidence based on current knowledge. To me, this does not come as a surprise: Climate models more often than not ignore past, let alone future, variability in the sun and in clouds. Looking for a carbon dioxide effect in such simulations smells like circular reasoning.

H Hak said...

re 10 - 27
Thank you Tom and anonymous.
Tom , I know little about how the models are set up and your points are helpful.I will try and read up some more on GCMs. I see the problem with the lack of data from > than 50 - 150 years ago.
Your point about the lack of understanding re what kind of forcing was involved in creating the LIA and therefore the inability to put that in the models raises the question: what are we lacking now in our understanding of climate change that could have major impact in the future, possibly more than the impact of an increase in CO2?

Anonymous, if I understand you correctly you are saying that climate models are set up to see if the recent increase in global temperatures can be explained by CO2/GHG forcing (which theoretically we know to cause such a rise); and when the outcome fits we see this as evidence that CO2 is the main cause for the warming.
I am not sure that that is circular reasoning. It fits more in the category of "argument out of ignorance", ie because we cannot find another compelling reason to explain the warming and CO2 fits the bill therefore it must be the CO2.
People have argued about this on various blogs
and from a logical point of view this is faulty reasoning. In practicality however we use this kind of reasoning all the time; life would be very problematic otherwise. As a physician I am aware how little we sometimes know for certain about various diseases/ treatments but nevertheless I have to apply this limited knowledge in order to have the best outcome.
Now I would be on the wrong track if I start thinking that if something works therefore my knowledge must be correct and alternative explanations aren't worth looking for. Amazing how the history of medicine is full of debunkings of "established facts". Not to long ago Dr Marshall had to infect himself with Helicobacter Pylori to prove that stomach ulcers are usually caused by this micro organism. ( Yours truly didn't believe it either initially. It had been "proved" that hyperacidity, stress and genetics was the cause. The literature - peer reviewed and all- on this was very extensive. And antacids/ H2 blockers /PPIs helped therefore case closed?)
Now your other point is that climate modelers haven't looked at sun activity and cloud cover as an alternative explanation. There are contradictory statements on the historical data of the activity of the sun/sunspots/sun magnetic field on various blogs.On cloud cover and precipitation : Roy Spencer sounds rather plausible , and has not been debated much as far as I can see, but Lindzen and Choi 09 has been heavily criticised by Trenberth et all but also by Spencer.

Anonymous said...

Bjorn says (=Anonymous #27)

@H Hak
You nailed it.

We all probably agree that the sun is THE driver of Earth's climate, and that the second most important factor is clouds. Sun and clouds, however, are set as constant in all climate models projecting into the future, while there are some climate models that factor in the effect of past solar variability in their modeling the 20th century's climate.

It makes a lot of sense to gauge climate models on past decades, most preferrably recent decades when drivers and resulting climate are known to a 'sufficient' extent (whatever that be). As soon as climate models can reproduce past climate sufficiently well, we may accept their predictions.

Now, for past solar activity, there are several independent proxies. Global cloud coverage, however, can be measured with confidence only since the introduction of satellites in the 1970ies. Unfortunately, it has been shown that global cloud coverage is far from constant, and that we do not quantitavely understand the drivers for cloud formation. I am not sure on data for water vapour concentration (the by far most important GHG), but CO2 concentrations are known quite well. Therefore, it makes sense to set the reference window for back-testing computer models to the period from 1980 to 1999.

Taking into account the effects of sun, clouds and water vapour, CO2 seems to be a rather minor impact factor for Earth's climate, but it is the only input variable that climate models are able to use, given the lack of scientific undestanding of solar variability and cloud formation. (Most climate models do simulate water vapour concentrations.) You are fully right to say that this lack of understanding may lead to wrong medication and is best described as circular reasoning.

There are more mathematical arguments, why the accuracy of climate models can not be controlled systematically. The Navier-Stokes equation that describes the thermodynamic behaviour of the atmosphere and which is the basis for all climate simulations is a non-linear, partial differential equation. It can be mathematically proved that computer simulations are structurally unable to reproduce a realistic picture of the true dynamic of a physical system desribed by non-linear differential equations. This does not mean that the results of such computer simulation MUST be unrealistic, only that you need to be very lucky to get the right answer and that there is no test to find out which one is correct.

I don't blame climate scientists for their approach, however. Physics, like medicine, is full of scientific legends that have been disproved only decades after every physicist had been convinced. Take the phlogiston theory of fire or the ether explanation of light progression through space. This is how science works: a constant competition for the best ideas and the best available tool for climate sciences currently is computer simulations.

Where I am getting nervous is, if we spend trillions on abolishing technologies that may, or may not cause problems in a century's time, without providing sound evidence. There are some climate scientists who have left the path of credibility by drastically overselling the CO2 topic. To re-iterate my initial statement, Question 1 can not be answered with confidence, based on current scientific knowledge and methods. Furthermore, the over-confident behaviour of some climate scientists in the public will inevitably lead to reduced reputation of sciences as a whole.

eduardo said...

@ 28,29
Your having and interesting discussion, but some assertions must be corrected, sorry:

'and that the second most important factor is clouds. Sun and clouds, however, are set as constant in all climate models projecting into the future, while there are some climate models that factor in the effect of past solar variability in their modeling the 20th century's climate'

Clouds are not set constant in climate simulations. All climate models included in the last IPCC report simulate cloud cover changes interactively, i.e. responding to temperature, wind and humidity changes, and clouds themselves modulating the radiation balance. Actually much of the differences in the simulated warming by different models is due to the difference in the simulation of clouds. See for instance this abstract,Trenberth

Future sun activity: as far as I know it is not possible to predict solar irradiance for time horizons longer than a few years, and even these short-term predictions diverge quite widely. To prescribe solar irradiance as not changing in the future seems to me a reasonable thing to do under these circumstances.

The same can be said about volcanic eruptions.

Stan said...

Dear student,

My advice -- Beware the hubris of so-called "experts".

You ought to focus some of your attention to how remarkably incompetent much of the work in this area is. Never accept the appeal to authority fallacy. Anyone can, at least to some extent, evaluate whether the scientific method has been followed. If someone cites a study to you, ask if it has been replicated by others. Replication is the essential aspect of science. Ask about transparency of data, code and methods.

If someone cites computer models, ask if they have been verified and validated. Find out what forecasting experts say about the use of models which have not. If someone cites temperature datasets, ask what percentage of the monitoring stations meet basic scientific standards. Ask if the scientists in charge have ever calibrated their instruments or even bothered to check if anyone else ever did.

If someone cites the IPCC, research all the many errors which have been identified in their assessments. Find out why so many scientists have refused to participate in the process any longer. Your research may not change your conclusions, but it should inform the degree of uncertainty with which you make judgments.

Whatever you choose to do, do not simply acquiesce to the opinion of the first scientist you ask. Be curious. Exercise your own intellect. You may not have a science background that will allow you to wade very far into the details of studies, but you can always ask questions about the process. You will often learn a great deal from the answers.

Anonymous said...

Bjorn says:

Thanks for correcting my statement with regards to clouds. My source of information is IPCC's TAR and the AR4. It is a pleasure to see that the cloud coverage problem is studied in more detail since AR4 publication in 2007.

For the impact of solar variability, it is exactly my point that there is no viable model of solar radiation, therefore it HAS to be taken as constant in climate models, although there is a pronounced and well-known effect of the sun on Earth's past climate. The approach of "everything being equal" where it is known that there is large natural variability in a highly non-linear environment (no simple superpositioning of independent effects!) may lead to a circular reasoning.

On another note: If you are a computer modeller of Earth's climate, maybe you could answer the following question. I am referring to the supplementary material to Chapter 8 of the working group I (The physical science base) of IPCC's AR4 (fourth assessment report), and there specifically to page 5. The 23 climate models that entered the IPCC forecast of 21st century's climate are backtested there with the 20 years from 1980 to 1999. On pages 5 to 7, each model's annual average temperature is compared with the CRU climate observations by simple subtraction of simulation by observation on a spatial grid covering the entire Earth.

If we take the first model "BCC-CM1", does it show that the model produced long-term temperature averages that were too warm by 5°C or too cold by 5°C in almost all regions? I would expect that 5°C is about the difference between the Ice Age and the Holocene. If this particular model got the results so flatly wrong in the time from 1980 - 1999, why was its climate forecast included with the same weighting into IPCC's 21st century forecast?

Is this a correct observation, supporting the view that Question 1 can not be answered with confidence based on current knowledge? Please correct me if I am wrong.

eduardo said...

@ 32

Solar variability: perhaps my last comment was confusing; solar variations are indeed considered for simulations covering past periods, although with different degrees of complexity depending on the model. Some models simulate the even stratospheric photochemistry , others represent only the bulk- integrated solar energy in the visible and uv part of the spectrum. Only for simulations of future climate is solar irradiance fixed since there is no information about its future behaviour

Model validation: you raised an important point in my opinion. Yes you are right. The bias for some models is very large. Some models are clearly better than others. If you have time, you can try to identify which models are in your opinion the best and which are the worst - and report here :-) (40 MB). The concept of 'average model' , also shown in the supp. info of chapter 8 of the 2007 IPCC is popular, but I do not advocate it. In a previous post about precipitation in Spain I argued that the average model did not reproduce the observed trend, probably because in that average a lot of bad models are included.

The bias for precipitation is usually more severe than for temperature, and it easily surpasses the simulated future precipitation changes.

One particular source of concern is that regional models, models nested in global models and that cover with higher resolution a particular region, still show large biases in the mean climate even when they are driven at their boundaries by (pseudo) observations.

I hope we can post about model validation soon

Anonymous said...

Dear Mr. Hans Von Storch,

Am I allowed to ask my question in English?

Ich versuche es einmal. Wenn nötig werde ich es auch gern mit meinem dilletantischen Englisch übersetzen. Entschuldigung im Voraus! ;-)

Seit Jahren verfolge ich die Kliamdebatte und ich habe nur sehr wenige nette Wissenschaftler kennen gelernt, die sich die Mühe gaben etwas zu erklären, ohne den (zweifelnden) Laien als "dumm" zu bezeichnen.

Irgendwann fühlt man sich selbst dumm und stellt nicht mehr so gerne Fragen (ausser einigen prinzipiellen Streitfragen).

Also, eine sehr dumme Frage hätte ich noch übrig und ich konnte bisher keine Erklärung finden, bzw. habe ich eventuell noch nicht richtig danach gesucht. ;-)

Wenn durch Co2 die Luft erwärmt wird kann sie mehr Feuchtigkeit aufnehmen und dadurch wird es noch wärmer. Zu dem Treibhauseffekt des Co2 gesellt sich der des Wasserdampfes.

Meine Frage gilt dieser Rückkoppelung: Wenn die Wasserdampfrückkoppelung theoretisch sich selbst verstärken kann, wieso hört eine Erwärmung (durch Co2 oder andere Ursachen) überhaupt irgenwann auf sich zu verstärken?

Zum Beispiel hat sich die Erde zu Beginn des Holozän in kurzer Zeit um mehrere Grad erwärmt. Wieso hat diese Erwärmubng keinen "runaway" Effekt verursacht?

Die Rückkoppelung durch Wassergas soll ja das doppelte der Erwärmung (allein) betragen? Wenn Co2 allein 1 Grad mehr bringt, dann kommen noch einmal 2 Grad durch Wasser hinzu. Müsste dieser Effekt sich nicht immer ins unendlicche fortsetzen? Es ist doch eigentlich egal ob die Erwärmung vom Co2 stammt oder vom Wasserdampf allein, bzw. von den Bahnparametern der Erde, der Albedo usw... ?

Sollte meine Überlegung stimmen, dann hätte ich noch die Zusatzfrage, welche Prozesse diesen "runaway" Effekt stoppen konnten (zu Beginn des Holozän z.B.)?

Einmal abgesehen davon, dass wir eventuell nicht genau wissen welche "tipping points" das Klima für uns bereit hält, ist es nicht trotzdem wahrscheinlich, dass es immer ein Feedback gibt das der Erwärmung entgegenwirkt?

Und wenn das der Fall sein "müsste", wieso forscht niemand nach einem solchen Effekt? Oder tun das schon einige?

So, in der Hoffbung nicht schon wieder als der Dümmste der Dummen aufgefallen zu sein, und in der Hoffnung eine Antwort zu bekommen;

sehr liebe Grüsse und meine Hochachtung und meinen Dank an Sie beide lieber Herr Hans Von Storch und Herr Eduardo Zorita,

Ihr Eddy

Anonymous said...

Ähm bin wohl doch der Dümmste... ;-))

"May I ask my question in German" sollte es wohl heissen ....


Anonymous said...

Bjorn says:

Dear Eduardo,

thanks for your post and the confirmation of what I had understood how solar variability was handled in back-testing and in forecasting. I have actually read AR4's Chapter 8 and its supplement, and tried to digest each line. My PhD was in statistical physics, time series analysis and computer modelling, so I feel somewhat familiar with the issues in climate modelling, although I never did one myself. I am well aware that the most dangerous knowledge is half knowledge, nevetheless...

I am not quite sure about your usage of the word 'bias', but my English is far from perfect. I would have used 'bias' as a systematic error ('systematic trend towards one OR the other side'), not as a statistical error. If you say the "bias for precipitation is usually more severe than for temperature, and it easily surpasses the simulated future precipitation changes", then in my understanding, this could translate to "the forecasted trend in precipitation is larger than the error and hence not statistically significant". If this is truly the case (and maybe even for temperatures), then it is once more a confirmation for the lacking scientific confidence for answering Question 1. Even more worrysome if the IPCC made clear political recommendations based on statistically insignificant average forecasts...

My favorite climate model, when comparing back-testing results between individual models on pp. 5-7 of said document, is ECHAM5/MPI-OM from the University of Mainz/Germany. I hope it is the one you are working on ... ;-)

I find it quite remarkable that no single model is able to reproduce well temperatures on Antarctica, but maybe CRU's data set is not quite as complete as we may wish?

eduardo said...


Hallo Eddy,

mein Deutsch ist sicherlich auch nicht perfekt, ich werde aber Ihre Frage auf Deutsch beantworten.

Im Klimasystem wirken mehrere Rückkopplungsmechanismen, die eine Temperaturstörung von Aussen verstärken oder abschwächen können. Dazu zählt, wie Sie angesprochen haben, die Zunahme vom Wasserdampf in der Atmosphäre, aber auch Änderung der Wolkenbedeckung Änderung des vertikalen Temperaturprofils der Atmosphäre (lapse-rate feedback) und andere sind weitere Rückkopplungen. Das Vorzeichen der Wolkenrückkopplung ist noch ungewiss, d.h. Änderung der Wolken könnten die ursprüngliche Erwärmung verstärken oder entgegenwirken, die lapse-rate Rückkopplung ist negativ, entgegen die Erwärmung, und die Zunahme vom Wasserdampf ist eine positive Rückkopplung. Die wichtigste Rückkopplung wird aber selten erwähnt, weil eigentlich kaum Unsicherheiten darüber zu verzeichnen sind: diese Rückkopplung ist die Schwarzkörperstrahlung . Wenn die Erde als ganzes wärmer wird, wird auch mehr Infrarotstrahlung ins All gestrahlt. Dabei wird Energie für das Klimasystem verloren, wirkt sozusagen abkühlend. Diese negative Rückkoppelung ist im heutigen Klimazustand stärker als die Beitrage aller anderen bekannten Rückkopplungsmechanismen. Insgesamt ist also die Rückkopplung nicht positiv.

eduardo said...

@ 36


By bias I mean the difference between simulated and observed mean precipitation. The figures in page 5 of the suppl. info of Chapter 8 you were referring to show the simulated temperature bias.

For precipitation, this bias can be much larger than the differences between the simulated precipitation for the present and, say, 2100. It may happen for temperature for certain regions as well.
However, you have to take one aspect into account when comparing the simulated and observed mean temperatures. The topography in the models is not well resolved (Alps, Andes, high plateaus.., etc). This effect may give rise a percieved bias if the temperatures are not 'corrected' to represent temperatures at sea level altitude.

The model we used is ECHO-G. It is a previous version of ECHAM5. One of the worst models is GISS, which I am sure will make some of our friends at realclimate squeal with joy.
(being Friday evening, I have allowed myself a little unpoliteness)

Anonymous said...

Lieber Eduardo ZORITA, @37

Vielen Dank für die nette Antwort! Ihr Deutsch ist PERFEKT. Mein Englisch ist dagegen ein Trauerspiel.

Einen Punkt habe ich immer noch nicht verstanden. Durch Co2 soll es 1 Grad wärmer werden bei Verdoppelung der Treibhausgase. Die Globaltemperatur soll aber ungefähr um 3 Grad ansteigen.

Nehmen wir einmal an, die Erwärmung von 1 Grad wäre natürlichen Ursprungs. Müsste dann nicht auch die Temperatur insgesamt um 3 Grad ansteigen.

Ich verstehe nicht, wie ein Rückkoppelungsmechanismus stärker sein kann als die Erwärmung selbst. Das würde ja nie aufhören. Denn immer wenn es wärmer wird, nimmt auch wieder der Wasserdampf zu, und es wird wieder wärmer und so weiter und so fort.

Jede Veränderung der Forcings zu einer höheren Temperatur müsste sich doch immer ins Unendliche fortsetzen.

Meine Fragen:

1) Ist obige Überlegung falsch? oder

2) Ist die Überlegung richtig und man kennt schon Rückkoppelungsprozesse, die die Erwärmung in Grenzen halten?

Vielen netten Dank noch einmal und bis bald vielleicht


Henk Hak said...

bjorn re 29
I agree with your concerns re spending trillions of dollars on CO2 reduction based on a science that is far from settled and seriously influenced by political motivations.
I used to think the global warming issue was a
win - win situation (and maybe some politicians believed the same):
-- if AGW is real, and we move away from fossil fuels : so much the better , less dependance on politically unstable regions.
-- if AGW is not true: no problem , nothing lost, still better to be more independant energy-wise.
Well, as you know things are quite different. I did not realise that in order to have a CO2 reduction that actually would reduce temperatures significantly (in theory) we basically have to go back to an industrial level of the pre-1940s as far as fossil fuel use. And that with a world population far greater than today's. So the cost of actually achieving a meaningful reduction is astronomical. Apart from that there is no way to enforce individual countries to comply. The present "solution" with carbon offsetts etc is a bad joke and a very corrupt process.
So there is no win - win situation; it is critical that we get the science right without interference from politics.

eduardo said...


Stell Dir vor, wir fahren ein Auto auf eine gerade ebene Landstraße. Die Geschwindigkeit wird von 2 Faktoren bestimmt: wie viel Benzin wir verbrauchen - sprich wie viel Gas wir gebe- und wie stark die Reibung und die Luftwiderstand ist. Es stellt sich eine Art Gleichgewicht zwischen Antrieb und Reibung ein. Nun erhöhen wir den Verbrauch: die Geschwindigkeit erhöht sich auch, bis ein neues Gleichgewicht erreicht wird, und zwar wenn der Antrieb und die Reibung sich auf einem höherem Niveau angeglichen haben.

In diesem Beispiel spielt der Verbrauch die Rolle eines externen Antriebs, z.B. der CO2 Konzentration oder aber auch der solaren Einstrahlung. Die Geschwindigkeit stellt die Temperatur dar. Wenn die CO2 Konzentration steigt, erhöht sich die Temperatur bis ein neues Gleichgewicht erreicht wird.

Nehmen wir nun an, dass unser Geschwindigkeit bei einem Verbrauch von 4 l/100km 50 Stundenkilometer ist. Nun geben wir mehr Gas, der Verbrauch steigt bis 8 l /100 Km und die Geschwindigkeit stell sich letztendlich bei 90 Stundenkilometer ein. Die 'Sensitivität' wäre dann 40 Studenkilometer (=90 - 50 ).

Die Erde wäre aber kein passives Auto, dessen Form und Aerodynamik unverändert bleibt, sondern ein Wunderauto. Die Form dieses Wunderauto würde sich mit der Geschwindigkeit auch ändern. Unser Wunderauto 'Made in Germany' würde vielleicht insgesamt flacher und schmaler, so dass die Aerodynamik sich verbessert. Wenn wir nun den Verbrauch bei diesem Wunderauto von 4 auf 8 l/100 km erhöhen, kann die Endgeschwindigkeit viel höher sein als bei unserem Referenzauto (90 Stundenkilometer), vielleicht sogar 200 Stundenkilometer.

Nicht alle Wunderautos werden aber in Deutschland hergestellt. Ein Wunderauto 'Made in Spain' würde sein Gestalt anders ändern: höher statt flacher, breiter statt schmaler, und dazu würden die Räder bei einer höheren Geschwindigkeit eiern statt perfekt drehen. Bei diesem Auto Gas zu geben, und den Verbrauch von 4 auf 8 l/100 Kilometer zu erhöhen, beutetet vielleicht eine Endgeschwindigkeit von nur 70 Stundenkilometer.

Das deutsche Wunderauto wäre ein Beispiel einer positiven Rückkopplung, das Spanische Auto eines einer negativen Rückkopplung. In Wirklichkeit würden bei einem Wunderauto Teile beider Hersteller vorhanden sein: z.B. bei einer höheren Geschwindigkeit würde es flacher aber auch breiter. Es wäre schwierig, die Endgeschwindigkeit theoretisch zu berechnen. Wir würden nur wissen, dass die Geschwindigkeit mit dem Verbrauch steigen würde, aber wir würden nicht genau berechnen können, wie viel. Aber unabhängig davon, welches Auto wir in Wirklichkeit fahren, es wird bei einem bestimmten verbrauch doch eine Endgeschwindigkeit erreicht. Sie kann nicht ins Unendlich steigen, denn die Reibungsverluste erhöhen sich immer viel rascher: Es sei dann das Auto sich in der Luft auflöst.

Anonymous said...

Lieber Eduardo Zorita,

Entschuldigen Sie bitte meine Verspätung. Ich wusste nicht wie ich anfangen sollte, habe aber jetzt gerade diese hilfreiche Darstellung gefunden:

DAS ist der Effekt, den ich meine. Wasserdampf in der Atmosphäre soll die Erwärmung durch Co2 noch einmal mindestens verdoppeln. Das heisst, auf 1 Grad Erwärmung durch Co2 kommen noch einmal 2 Grad durch Wasserdampfrückkoppelung.

In zitiertem Artikel wird erklärt dass der Effekt durch Wolkenbildung kontrolliert wird: "Dass sich diese Verstärkung ins Unendliche fortsetzt, wird aber dadurch verhindert, dass durch mehr Wasserdampf auch mehr Wolken entstehen".

Meine erste Frage bleibt also bestehen. Wie kann ein Rückkoppelungseffekt, der doppelt so gross ist wie die Originalerwärmung gestoppt werden?

1) Wenn ich hier lese, dass die Wolken den Effekt in Grenzen halten, frage ich mich, wieso man dann erklärt er würde die Erwärmung verdoppeln bis verdreifachen. Weiss man denn, wann diese Rückkoppelung einsetzt und wo sie aufhört?

2) Wenn der Effekt 2 - 4 Mal stärker ist als die Originalerwärmung, wie kann man dann überhaupt natürliche von menschgemachten Einflüssen unterscheiden. Jede natürliche Erwärmung, egal welchen Ausmasses, würde doch euch einen sich unendlich fortsetzenden Wasserdampffeedback auslösen, der nur rein zufällig (durch Wolken) wieder aufhört?

3) Die Übergänge von Warm und Kaltzeiten müssten doch für das Verständnis dieser Zusammenhänge eine ideale Gelegenheit bieten.

Wieso ist so wenig über diese Phänomene gewusst? Die Dansgaard-Oeschgerereignisse haben doch auch immer nach wenigen Jahrzehnten von selbst aufgehört.

Es ist also nicht so, dass ich den Wasserdampffeedback in Frage stelle. Mich interessiert bloss wie dieser Effekt gebremst wird und wieder ins Gegenteil gekehrt wird.

Ich kann mir beim besten Willen nicht vorstellen, wie man Klima verstehen kann, ohne diese Wetterphänomene zu verstehen. Die Jahrtausendsommer 2003 und 2006 waren sehr warm, aber auch die Wetterlage war aussergewöhnlich, wogegen dieser Winter sehr kalt ist und die Wetterlage ziemlich gewöhnlich.

Müsste dieser Winter z.B. nicht auch eine Rückkoppelung auslösen?

Die Nordhalbkugel soll ja klimabestimmend sein? Normale Sommer und kalte Winter könnten den Erwärmungstrend eventuell umkehren?

Leider kann ich es als Laie nicht besser ausdrücken und ich entschuldige mich noch einmal für die Verspätung und bedanke mich ganz herzlich für ihre sehr netten Erklärungen, die mir aber leider nicht weiter geholfen haben.

Sehr liebe Grüsse und ein riesiges Dankeschön

Ihr Eddy

PS : Ich heiss übrigens offiziell Edouard, werde aber Edy genannt. Wird sind also Namensvettern ;-)

Anonymous said...


a) Ich muss mich korrigieren:

Ich glaube nicht dass Dansgaard-Oeschgerereignisse immer nach wenigen Jahrzehnten aufhörten.

b) Ich muss mich genauer ausdrücken:

Wenn man sagt dass eine Erwärmung von 1 Grad eine Wasserdampfrückkoppelung von 2 Grad zusätzlich auslöst, dann ist die Rückkoppelung grösser als die Erwärmung selbst.

Die zusätzliche Erwärmung von 3 Grad insgesamt (1° durch Co2 und 2° durch H2O) müsste ja auch wieder mehr Wasserdampf entstehen lassen. Die zusätzliche Erwärmung durch Wasserdampfrückkoppelung wären dann insgesamt 3° (Co2 + H2O) + 6° (H2O) = 9°.

Dass dieses Problem prinzipiell besteht wird in dem Link aus meinem vorigen Beitrag deutlich.

Das Problem wird aber m.E. auch durch Wolken nicht aus der Welt geschafft, weil eine Verdoppelung der ursprünglichen Erwärmung von 2° durch Wasserdampfrückkoppelung m.E. IMMER zu einer unkontrollierten unendlichen Erwärmung führen müssten.
Das Problem würde erst dadurch gelöst, wenn das Feedback durch Wasserdampf kleiner wäre als die ursprüngliche Erwärmung selbst. In unserem Falle also weniger als 1° durch Co2.

Eine andere Alternative wäre ein negativer Rückkoppelungseffekt. das heisst, dass die galoppierende (theoretisch unendliche) Erwärmung durch Wasserdampfrückkoppelung durch Wolkenbildung gestoppt würde.

Das hiesse, dass der Effekt zwar in der Form existieren würde wie oben beschrieben, dass er aber "periodisch" durch irgend eine Art von Wolkenbildung gestoppt und umgekehrt würde (bei den Dansgaard-Oeschgerereignissen z.B., oder nach Beginn des Holozän):

Gingen wir davon aus, dass Co2 eine Erwärmung hervorruft, die durch Wasserdampf gesteigert würde und dass diese Erwärmung sich selbst potenziert und ad infinitum fortgesetzt würde ohne die Wolkenbildung hätten wir eventuell ein Modell das so ähnlich funktioniert wie die Klimamodelle.

Sollten die Wolken aber gleich zu Anfang den Einfluss der Wasserdampfrückkoppelung stoppen (und nicht erst durch einen noch unbekannten negativen Rückkoppelungseffekt der zu einem unbekannten Moment irgendwann einsetzt), dann frage ich mich wie man von einer Verdoppelung des ursprünglichen Effekts ausgehen kann.

DENN: Würde sich die Atmosphäre durch natürliche Prozesse (z.B. Wasserdampf oder Sonne) um 1° aufwärmen würde der Wasserdampfgehalt steigen und eine zusätzliche Erwärmung würde stattfinden. Dieser Effekt würde sich doch immer selbst verdoppeln bis ins Unendliche.

Würden Wolken sogleich zu Anfang den Effekt abmildern, dann könnte aber niemals eine Verdoppelung der Temperatur daraus resultieren.

Das Problem ist, dass der Rückkoppelungseffekt grösser ist als der ursprüngliche Effekt und es keine Erklärung dafür gibt, dass er sich nicht selbst ins Unendliche verstärkt.

Ich hoffe es wurde jetzt noch einmal deutlicher, was mein Problem ist?! ;-)



eduardo said...

Hallo Ed,

Sie haben recht, dass bei einem System wo die Summe aller Rückkopplungen positiv sein sollte, instabil wäre: jede kleine Störung würde ins Unendlich wachsen. Dabei muss man aber nicht ein einzelne Rückkopplung betrachten, sondern alle alle Rückkopplungen.
Im Klimasystem sind viele Rückkopplungen aktiv. Die stärkste Rückkopplung ist negativ, und auch grösser als die Summe aller anderen Rückkopplungen, so dass die Gesamtrückkopplung negativ ist. Das heisst, dass eine ursprüngliche Störung der Temperatur immer in Grenzen gehalten wird.
Diese negative Rückkopplung - siehe meinen früheren Kommentar - ist die Infrarot-Strahlung, die von jedem Körper abgegeben wird. Die Intensität dieser Strahlung steigt sehr schnell mit der Temperatur an, und zwar mit der vierten! Potenz der Temperatur. Selbst wenn keine Wolken in der Atmosphäre entstehen würden, würde die Temperatur nach einer Erhöhung der CO2 Konzentration nur bis zu einem gewissen Grenzwert steigen

Anonymous said...

Hallo lieber Eduardo,

Leider beantwortet das immer noch nicht meine Hauptfrage. Lassen wir das Co2 zuerst einmal ganz weg. Wenn Wasserdampf allein eine Erhöhung der Temperatur bewirkt, dann müsste auch diese Erhöhung der Temperatur die Fähigkeit der Atmosphäre, mehr Wasserdampf aufzunehmen, erhöhen. Dieser Prozess müsste sich also unendlich fortsetzen. Nehmen wir jetzt an dass durch IR-abstrahlung diese Erwärmung begrenzt ist. Die Erwärmung durch H2O wäre trotz allem immer noch das Doppelte als die Erwärmung durch Co2 allein.

Wenn also der Wasserdampf allein die Erwärmung durch Co2 verdoppeln können sollte, dann ergäbe das für mich keinen Sinn, denn die Originalerwärmung durch Co2 wäre nicht notwendig. Jede natürliche Erwärmung würde den gleichen Prozess auslösen.

Woher wissen wir so genau welche Ursache eine bestimmte Erwärmung hat?

Hätten sie einen Motor der bei 1 Liter Benzin allein durch die Bewegung des Autos noch einmal gratis die Energie von 2 zusätzlichen Litern Benzin liefern würde, dann würde die Geschwindigkeit immer weiter zunehmen, auch wenn sie das Auto einfach nur anschieben würden. Nehmen wir einmal an der Luftwiderstand wäre die negative Rückkoppelung. Dann würde das Auto immer weiter beschleunigen bis auch ein mehr an Energie keine höhere Geschwindigkeit mehr zulassen würde.

Trotzdem könnte man am Anfang der Rechnung den einen Liter Benzin einfach weglassen, indem man das Auto anschiebt.

So ist es doch auch bei der Wasserdampfrückkoppelung? Sie müsste die gleiche Erwärmung liefern auch ganz ohne Co2, weil der Wasserdampfeffekt stärker ist als der Co2effekt?

Mit freundlichen Grüssen und einer grossen Entschuldigung für die bohrenden Fragen ;-)


eduardo said...

Hallo Ed,

in Deinem Kommentar sind mehrere Aspekte miteinander vermischst. Versuchen wir es noch einmal..:-)

Die Wirkung von CO2 und Wasserdampf ist nicht direkt eine Temperaturerhöhung sondern zuerst eine Zunahme der Energie, in Form von Strahlung, die auf die Erdoberfläche einwirkt. Die darauf folgende Temperaturerhöhung hängt von dieser Energiemenge und von anderen Faktoren ab. Von daher ist es nicht korrekt zu sagen, dass 'eine Verdopplung der CO2 Konzentration allein eine Temperatur um 1 Grad bewirkt'. Diese Zahl, ein Grad, wäre das Ergebnis eines Zusammenspiels zwischen der erhöhten CO2-Konzentration und der auch erhöhten IR-Abstrahlung. Dabei muss man berücksichtigen, dass die Wirkung von CO2 ein Treiber ist, die IR-Abstrahlung dagegen entsteht als Reaktion zu der Temperaturerholung. Wenn Wirkung und Reaktion sich angeglichen haben, entsteht ein neues Gleichgewicht. Eine Verdopplung der CO2-Konzentration bewirkt eine Zuname der auf die Oberfläche eingehenden Strahlung um ca 3.8 W por Quadrat meter. Die IR-Abstrahlung ist aber proportional zu Temperaturerhöhung T, und zwar ca 3.5 watt pro quadrat meter pro Grad .
Wenn beide gleich sein sollten (im Gleichgewicht) ergibt sich 3.8 = 3.5 T, und daraus resultiert eine Temperaturerhöhung von T= 3.8/3.5

Wenn aufgrund der Temperaturerhöhung nicht nur die IR-Abstrahlung sich ändert, sondern auch der Wasserdampf, wird die Zahl 3.5 kleiner, da weniger IR-Strahlung abgestrahlt werden kann. Sagen wir mal, diese Zahl reduziert sich um 50%. Das heisst, die IR-Abstrahlung ist nun nur noch 1.75 watt pro quadrat meter pro Grad. Die Temperaturerhöhung wäre dann T = 3.8 / 1.75, also doppelt so viel wie mit der Wirkung von CO2 allein.

Natürlich können Änderungen des Wasserdampfes allein eine Temperaturerhöhung bewirken. Nehmen wir an, dass eine zufällige Erhöhung des Wasserdampfes tatsächlich stattfindet. Die Temperatur erhöht sich dann beispielweise um 1 Grad. Die IR-Abstrahlung ist dann 1.75 watt pro quadrat meter . Die Erde wäre aber dann nicht mehr im Gleichgewicht, und die Temperaturänderung würde wieder auf Null sinken. Der kritische Punkt dabei ist, dass die IR-Abstrahlung immer im positiven Bereich bleibt und immer in der Lage ist, netto Energie los zu werden. Wäre der Effekt von Wasserdampf so gross dass die Zahl 1.75 eher null oder negativ werden würde, dann könnte eine kleine anfängliche Erhöhung des Wasserdampfes weiter wachsen.