Santer says

Santer et al have a new paper out on trends in the tropospheric temperature.

Because of the pronounced effect of interannual noise on decadal trends, a multi-model ensemble of anthropogenically-forced simulations displays many 10-year periods with little warming. A single decade of observational TLT data is therefore inadequate for identifying a slowly evolving anthropogenic warming signal. Our results show that temperature records of at least 17 years in length are required for identifying human effects on global-mean tropospheric temperature.

Please keep comments to the subject matter of the paper.

Comments

[geronimo]

Richard, you have inadvertenly stumbled on the issue that will cause a great red mist to rise in sceptical eyes. Models.

Your point about irradiance in the early part of the 20th century came as a surprise to me, because I remember seeing a chart of rising irradiance throughout the 20th century which was in lock-step with the temperature rise, can't remember where now, might have been NASA. I was reliably informed by 400,000 hectoring realclimate habituees that solar irradiance was a denier red herring. I am not a climate scientist but have grave reservations about statements that tell me the sun has little effect on our temperature, so I'm please that Dr Bradley et al feel, or felt, because the paper was written before the denier community started trumpeting the increase in solar irradiance as a possible cause, that it does have an effect on the temperature.

[HaroldW]

Dr Betts-
Thanks for providing the reference to Lean et al. 1995 above. As this is the first time I've seen this paper, it will take a bit for me to absorb its contents, but even at first glance I'm rather surprised by their Figure 2(a), which shows the reconstructed solar irradiance (TSI). It certainly shows a significant increase in the early 20th century as you say, thereby providing the basis for the claim that the warming observed then is directly attributable to TSI.

However, the figure also shows that the TSI during the Maunder Minimum was a full 3 W/m^2 less than the 20th century value. Using a climate sensitivity value of 0.75 K/ (W/m^2) [e.g. from Hansen&Sato 2011], this would imply that the mean global temperature was lower then by greater than 2 K. None of the historical temperature reconstructions that I have seen, show anywhere near this amount of variability -- the anomaly given for that period is in the range of -0.5 to -1.0 K (rounding off). On the surface, this would seem to be evidence that sensitivity is in the range of 0.2 to 0.3 K/(W/m^2).

Can you please help me resolve this apparent contradiction? Thanks.

[ScientistForTruth]

BBD "I'm not 'waving it away'. I'm saying that despite the best efforts and modern instruments, there is no evidence for any forcing sufficient to explain most of the recent warming except CO2."

There is no evidence for CO2 either, so this simply reduces to an argument from ignorance.

The later twentieth century warming was remarkably similar to the early twentieth century warming. Now, physics and measurement instruments were pretty good in the early to mid-twentieth century, yet no satisfactory cause (other than a natural one, not understood) has been attributable to the earlier warming. We all know that G.S. Callendar attributed it to CO2 in 1938, but no-one believes that today. As Weart points out:

"Callendar seemed to be picking only the data that supported his case.

Most damaging of all, Callendar’s calculations of the greenhouse effect temperature rise ignored much of the real world’s physics.

…he argued for conclusions that mingled the true with the false"

Sounds shockingly familiar to me.

"The scientists who brushed aside Callendar’s claims were reasoning well enough. Subsequent work has shown that the temperature rise up to 1940 was, as his critics thought, mainly caused by some kind of natural cyclical effect, not by the still relatively low CO2 emissions."

Some kind of natural cyclical effect, not properly understood, then, but not some kind of natural effect today?

[Shevva]

BBD

'I'm not 'waving it away'. I'm saying that despite the best efforts and modern instruments, there is no evidence for any forcing sufficient to explain most of the recent warming except CO2.'

I'm confused I thought there had been no warming for 15 years? how do you explain this? Chinese coal? CO2s still going up, wheres the heat? It's a travesty?

You use the word 'Most', most implys a fraction, what is the fraction? 8/9 due to CO2?

[sunderland steve]

@ Mike Haseler

Not quite what I mean't, just didn't leave enough space . :)

[HaroldW]

As a postscript to my 5:32 PM, I realise that I erred in using the entire change in TSI; as approximately 30% of TSI is immediately reflected. Hence the top-of-atmosphere forcing is only 70% as large, or 2.1 W/m^2. This changes the naive estimate of climate sensitivity to 0.3 to 0.4 K/(W/m^2), which is still about a factor of 2 from the value given in Hansen & Sato.

[Athelstan]

@"That's what climate science is trying to do in informing (but not prescribing) policy - on adaptation as well as mitigation."
Sep 5, 2011 at 4:36 PM | Richard Betts

"Informing on adaptation, as well as mitigation"

Mankind has done that [adapted] quite nicely himself for millennia, without the help of a - bunch of climate computer generated simulations, that's why we're still here.
The innovation, the adaptability and tenacious spirit of mankind throughout history, he has so far overcome tremendous though not insurmountable odds.
AGW if we are to believe the scenarios [and I do not] gives us tens/scores of years....... an eruption of a super volcano would make things very interesting and very quickly:>( ?!

However, what I do find baffling is the idea [implanted by the doom sayers - is that: AGW will be the death of us all - the warming of decades since the LIA has been beneficial to mankind - has it not Mr. Betts?].

Furthermore, you probably didn't notice, frankly though: I am aghast at the expansive presumption of the above statement.
A statement, not atypical of a certain clique.

[Peter Whale]

When a kid I made a lot of models, they looked like the real thing but never acted like them. Isn't it time that climate scientists who play with models grow up?

[ZT]

@Gareth - thanks!

I had forgotten that:

'“what if” projections of future climate that correspond to certain emissions scenarios' aren't predictions!

please just substitute the approved climatological phrase:

'“what if” projections of future climate that correspond to certain emissions scenarios' where I used the single word 'predictions'. (this may make my comment easier to follow, for climatologists).

@Richard

Assuming that we're not talking about the number of leeches applied to foreheads, a difference between medicine and climatology (apart from the complex phraseologies of both fields) is at least an attempt at statistically demonstrating that a treatment produces a beneficial effect in medicine.

Here the words 'statistically' and 'demonstrating' would have their normally ascribed meanings as understood by scientists, the Oxford English dictionary, etc...

[Phillip Bratby]

Athelstan:

Indeed. If the Dutch could adapt to rising sea levels in the Middle Ages (before the industrial revolution), adaptation has to be a doddle these days. In this country we could easily adapt to a sea level rise of a foot and a few degrees of warming without any trouble.

[Richard Betts]

Athelstan

Mankind has also very often come a cropper of extreme weather and climate events (naturally caused) because it didn't see them coming, or wasn't appropriately prepared. I don't see why there is a problem with trying to use science to try to foresee them, or how they might (or might not) change due to human influence or other factors, or see how bad they might be in order to reduce vulnerability.

But anyway the motivation of climate scientists is considerably O/T and BH specifically asked that we remain focussed!

[Breathe of Fresh Air]

Richard, I am getting confused, the 2 warming periods each of 30 years were both of equal increase rate, the models say the first one was because of the Sun (first I had heard of this but nice to hear anyway that the sun does have an effect after all) and the second is due to CO2. Forgetting about the idea that a model run is proof (see Dr Kelly's thoughts as part of the Russell Muir Enquiry as a good reason to say a model is not proof) we are also told that AGW is true because we are having 'Unprecedented Warming' in the later half of the 20C which is not matched by any other period. But if the models say that without CO2 you can still have this rate of warming what is so 'Unprecedented' about the 2nd warming period.

[Messenger]

@Richard Betts

The medical analogy doesn't really work. The patient usually has an accurate diagnosis. Medicines being given are at least rigorously tested before being implemented, - and even then there are some errors and previously unrecognised side-effects.

The (C)AGW "cure" is previously untested, crashingly expensive, we've no idea if it will work, but we know it will produce horrendous and harmful side effects, and it's being implemented for a "disease" we're not even sure that we have got, as the diagnosis has not been confirmed..

[PaulM]

Harold, greensand et al, it's important to be aware that the Lean et al paper is a 'reconstruction' (as in the infamous MBH98 'reconstruction', and with a common author) based on a sequence of assumptions explained not very clearly at the top of p 3197.
We only really know about solar irradiance since about 1980.

Climate scientists like this reconstruction because it fits with their theories. They tend to be less keen on other ones that don't fit so well such as Hoyt & Schatten that show an increase in the early and late 20th C. If you look at the numbers in the IPCC report, table 2.10, the numbers are all over the place.

[Messenger]

Bishop- apologies for the OT, but I was responding to something RB said earlier.

[Philip]

Richard Betts (3:17 PM)

More recent studies than Lean's suggest that TSI remained approximately constant during early 20th C. For example, slide 16 in http://www.leif.org/research/Does%20The%20Sun%20Vary%20Enough.pdf.

[Phillip Bratby]

Richard:

You say the models take months to run. This leaves me somewhat concerned. Firstly, why have 20+ models if they are all so computer-intensive? Why not have 2 or 3 at the maximum?

Secondly, I spent years involved in validating complex thermal-hydraulics models. To do a proper job of validation we had to do maybe a hundred runs on each model. How can these climate models have any validity?

[Philip]

Furthermore, the standard explanation for mid 20th C temperature variations is also problematic. See for example, http://judithcurry.com/2011/02/16/mid-20th-century-global-warming-part-ii/ and figure 3 of http://www.atmos-chem-phys.net/11/1101/2011/acp-11-1101-2011.pdf (also linked by Curry). The natural conclusion is that the IPCC has no more idea of the mechanisms for change in the 20th C than the rest of us. Nonetheless, the conclusion of Santer sounds very plausible: "temperature records of at least 17 years in length are required for identifying human effects on global-mean tropospheric temperature".

[KnR]

Rule Two Climate science
The length of a valid time line is proportional to the way in which it can be used to support AGW.

Rule one is the ever popular , if the value of the model and reality differ , it is reality which is in error .

[BBD]

Thinkingscientist

There is no evidence for CO2 either, so this simply reduces to an argument from ignorance.

I am astonished. Why then does the average temperature not drop to well below freezing at night?

The later twentieth century warming was remarkably similar to the early twentieth century warming.

You would be the first to tell me that correlation is not causation. So similar slope and duration for these warming events implies absolutely nothing about their respective causes. RB has made this clear upthread, but it bears repeating.

Some kind of natural cyclical effect, not properly understood, then, but not some kind of natural effect today?

You are going too far here. There is no evidence for a 60-year sinusoidal variation going back earlier than the beginning of the C20th. This being so, there's no evidence that recent warming is all or even partially natural in origin (although it may be partially natural; I'm not claiming as some do that all the warming since the mid-70s is purely anthropogenic. Just most of it).

[BBD]

Shevva

I'm confused I thought there had been no warming for 15 years? how do you explain this? Chinese coal? CO2s still going up, wheres the heat? It's a travesty?

This thread is about a paper by Santer et al. which attempts to answer your question. The short answer is natural variability offsetting CO2 forcing on timescales under a decade. At this point it's worth noting that many sceptics, including ThinkingScientist, seem to argue that recent warming is of natural origin.

Now let's look at the temperature data for the lower troposphere over the last 15 years.

GISTEMP, HADCRUT, UAH, RSS. 1996 – present; common 1981 – 2010 baseline; trend.

It is warming, although as we both know, there's been no trend for the last decade. But the context is what matters; longer time-series reveal much more than short ones about climate change.

First, here's the full satellite record 1979 - present:

UAH and RSS. Common 1981 – 2010 baseline.

Now, look at the 10 year mean over the full record:

UAH and RSS. Common 1981 – 2010 baseline; 10 year mean.

The exaggerated slope shows the decade-on-decade warming very clearly. In the current absence of any known alternative explanation, that is generally assumed to be mostly the result of CO2 forcing.

[MikeN]

So what is the current tropospheric temperature trend? When does the 17 year window expire?

[MikeN]

BBD why did you use a ten year mean? That shuts off quite a bit of recent data.

The 5 year mean shows a different picture.
http://woodfortrees.org/plot/uah/mean:60/plot/rss/offset:-0.1/mean:60

[Philip]

BBD, "I'm not claiming as some do that all the warming since the mid-70s is purely anthropogenic. Just most of it"

You may easily be right, I don't know. One aspect I've unsure of, is why surface SW increased during the 90s. The direct reason presumably is changes in cloud cover. But what caused those changes? Furthermore, what caused the temperature rise in the first half of the 20th C if it wasn't TSI?

[BBD]

ThinkingScientist

Conversely, claims for significant positive feedback due to CO2 are incompatible with the ice core data. The 800 year lag between T and CO2 is the same whether in a warming from ice age or cooling into ice age. That is physically impossible if the RC CO2 model for exapl,ing ice ages is followed (which is what you seem to be doing) - starter event from Milankovich cycle, warming enhanced by large positive feedback casued by CO2. So how do you get back to an ice age? If the Milankovich effect is too small to get you warming and you need to invoke CO2, then Milankovich effects could never reverse the CO2 effect to get you back to an ice age. Follow the CO2 model and you get only 1 ice age, not repeated cycles. Logically, CO2 effect must therefore be very small and I suspect probably negligible.

How do you get back to an ice age? Time. Once peak Milankovitch forcing has passed, the temperature gradually falls as reduced DSW eventually begins to have more impact on the net RF at the surface (GHGs elevate DLW, but the climate gets its energy from the sun, so the reduced DSW always becomes dominant on long enough timescales). Hence the long, slow cooling until the NH ice sheet begins to expand enough to start a very strong positive ice-albedo feedback which triggers a full glacial.

The 'Vostok lag' is a tired old non-argument. Of course CO2 lags T. Milankovitch forcing begins to warm the oceans, which being to outgass CO2, which slightly forces T and gives Milankovitch a boost in further warming the oceans... etc.

[BBD]

MikeN

The argument in Santer et al. is that longer timescales give a clearer indication of trends in T. Decade for decade, the increase in T is substantial. That's why the ten year mean has a steeper slope than the five year mean. If you are implying that I cooked the graph, I'm not amused.

[geronimo]

Back at the crease BBD the indefatigable defender of the faith. I hesitate to get into all this, but I've had a modicum of experience with chaotic systems and believe that the earth's climate is just such a system. While applauding the work being carried out to to try to understand it better and bring more accuracy to forecasting events, I have to say that I doubt it's going to be tamed. One thing for sure you can say about a chaotic system, you can forecast what can come out with reasonable experience e.g winter will follow autumn, but you cannot forecast the numbers. The seem to me to be an improbable amount of variables acting stochastically on the climate, and as I've said before, while accepting CO2 is a GHG the historical records appear to show that temperature and CO2 density in the atmosphere live different lives. It could well be that CO2 has caused most of the recent warming, but I believe it's a reasonable position to wait until we can quantify in an old fashioned scientific sum the relationship between CO2 density in the atmosphere and temperature. We must have been trying for the last 20-30 years, all the best brains we have, yet nothing remotely likely to move the hypothesis to observable forecast has come out. Why is that? We produced an atom bomb in pretty short order, got a man to the moon in pretty short order in both cases by throwing money at the problem, why can't we tie down the relationship and then move the argument on?

[Lord Beaverbrook]

'The continuing rapid increase in carbon
dioxide concentrations during the past 10-15 years has
apparently been unable to overrule the flattening of the
temperature trend as a result of the Sun settling at a
high, but no longer increasing, level of magnetic activity.'

Reply to Lockwood and Fröhlich – The persistent role of the Sun in climate forcing
Svensmark, H. and Friis-Christensen, E.
Danish National Space Center
Scientific Report 3/2007
http://icecap.us/images/uploads/SvensmarkPaper.pdf

[BBD]

geronimo

The climate system's chaotic nature may well cause it to do unpredictable things when forced. What is known with reasonable certainty is that increasing the fraction of a GHG like CO2 in the atmosphere will increase the RF at the surface and so T. I'm pretty sure Richard Betts would agree that there are considerable uncertainties about how this will play out on a regional scale.

But energy will accumulate in the climate system, and it will get warmer. The potential negative effects on global agriculture are of great concern, especially looking forward to a global population of around 9 billion by mid-century. It frightens me how readily most here just dismiss this as nonsense or 'warmist propaganda' etc.

[Richard Betts]

BBD

The climate system's chaotic nature may well cause it to do unpredictable things when forced. What is known with reasonable certainty is that increasing the fraction of a GHG like CO2 in the atmosphere will increase the RF at the surface and so T. I'm pretty sure Richard Betts would agree that there are considerable uncertainties about how this will play out on a regional scale.

Yes I agree with that.

I think there's other posts above that I've not caught up on yet - need to check back...

[kuhnkat]

""Our results show that temperature records of at least 17 years in length are required for identifying human effects on global-mean tropospheric temperature.""

So, in 1988 when James Hansen was screaming doom he had nothing?? The IPCC was formed for NOTHING??

Of course, we aren't looking at human effects. How long does it take to determine NATURAL effects. Oh, y'all haven't studied those yet huh?

[BBD]

Philip

One aspect I've unsure of, is why surface SW increased during the 90s. The direct reason presumably is changes in cloud cover. But what caused those changes? Furthermore, what caused the temperature rise in the first half of the 20th C if it wasn't TSI?

Take a look at Wild (2009) (full text).

Changes in atmospheric transparency may have as much or more to do with variation in DSW at the surface. From the abstract, (emphasis added):

There is increasing evidence that the amount of solar radiation incident at the Earth’s surface is not stable over the years but undergoes significant decadal variations. Here I review the evidence for these changes, their magnitude, their possible causes, their representation in climate models, and their potential implications for climate change. The various studies analyzing long-term records of surface radiation measurements suggest a widespread decrease in surface solar radiation between the 1950s and 1980s (‘‘global dimming’’), with a partial recovery more recently at many locations (‘‘brightening’’). There are also some indications for an ‘‘early brightening’’ in the first part of the 20th century. These variations are in line with independent long-term observations of sunshine duration, diurnal temperature range, pan evaporation, and, more recently, satellite-derived estimates, which add credibility to the existence of these changes and their larger-scale
significance. Current climate models, in general, tend to simulate these decadal variations to a much lesser degree. The origins of these variations are internal to the Earth’s atmosphere and not externally forced by the Sun. Variations are not only found under cloudy but also under cloud-free atmospheres, indicative of an anthropogenic contribution through changes in aerosol emissions governed by economic developments and air pollution regulations. The relative importance of aerosols, clouds, and aerosol-cloud interactions may differ depending on region and pollution level. Highlighted are further potential implications of dimming and brightening for climate change, which may affect global warming, the components and intensity of the hydrological cycle, the carbon cycle, and the cryosphere among other climate elements.

Also, be careful not to confuse TSI (the total solar output) with insolation (DSW at the Earth's surface).

[ManicBeancounter]

This is quite a change of direction. Look back 3-5 years and every new paper seemed to say something more extreme than the last, with the usual conclusion "it is worse than we thought".
Now a team of 17 has got together to bombard a large array of supercomputers to run the numbers in every way they can think of to extract an AGW signal in the troposhere. The conclusion is pretty inconclusive.

[Philip]

BBD:

Thank you, I'm aware of Wild's paper. In the context of this posting, the reason for raising the issue of surface radiation and cloud cover was that the effect mentioned persisted for less than 17 years. On the other hand, the change in temperature during the first half of the 20th C lasted for more than 17 years and recent studies suggest was not due to changes in TSI (as suggested by Richard). So does this mean that the former change was natural and the latter human-caused? Presumably not. But the arguments I've referred to above do suggest that the AR4 explanation of 20th C temperature change is as incoherent as skeptic arguments against the GHE.

BTW, I'm a little curious why everyone is arguing about a scientific detail like the one in Santer's paper? It's fairly plausible, seemingly a dig at those who claim flat-lining during the 00s, and just as pointless. I think that science is again being used as a proxy for arguments over politics. Why? Because development and environment are falsely characterized as incompatible both by the greens and by their opponents on the right.

[Mike Jackson]

BBD

There is no evidence for a 60-year sinusoidal variation going back earlier than the beginning of the C20th.

Would this be relevant?
"A. Mazzarella and N. Scafetta, "Evidences for a quasi 60-year North Atlantic Oscillation since 1700 and its meaning for global climate change", Theor. Appl. Climatol. (2011) DOI 10.1007/s00704-011-0499-4"
They appear to be arguing that

These findings suggest that INAO can be used as a good proxy for global climate change, and that a ~60-year cycle exists in the global climate since at least 1700.

[BBD]

Philip

I agree with the question over the AR4 solar attribution. Just to check, are you thinking along the same lines as Bob Tisdale?

I also agree with your second paragraph.

[BBD]

Mike Jackson

Thank you for the reference. If M & S are correct, then the question is why has global temperature trended up since about 1910?

I'm not by any means disagreeing with M & S (which I haven't read), but can the INAO explain the overall rise in T? If so, how does it do it?

[TomRude]

You've got to love the ad hoc results they came up with. They always come up with THE desired answer but the annoying thing is that they never anticipate the problem: had they laid that egg back in 2001 they would have looked brilliant. Instead they simply add a peer reviewed paper to cover their failed predictions.

[John Whitman]

Santer et al 2011;

Key Points

- Models run with human forcing can produce 10-year periods with little warming

- S/N ratios for tropospheric temp. are ~1 for 10-yr trends, ~4 for 32-yr trends

- Trends >17 yrs are required for identifying human effects on tropospheric temp.

------------------

All the TLT data available must simply be used without delimiting the analysis in anyway. Otherwise it is cherry picking. So, I sense here that Santer et al 2011 have an intention of blurring past anthropogenic-forced conclusions into the future; ensuring a place marker in the AR5 in order to attempt extending the AR4 alarmism. Santer et al 2011 might have significant impact on AR5 given that Santer’s climategate associate T. Osborn is an IPCC AR5 Lead Author.

John

[Mike Jackson]

BBD
Having just bumped into the link, immediately after I had read your comment, I haven't read it either. I simply thought that since it appears to present a challenge to something you had said you would want to know about it.
Surely the 20th century trend is up from 1910 to 1940, down from 1940 to 1970, up from 1970 to 2000. At least that is what I have learnt. It may well be that the trend from 1910 to 2000 is up but there are a number of ways of interpreting that depending on the result you want and the information you want to convey, are there not?
It's called "lies, damned lies and statistics".
The warmist argument is, as you say, that the 20th century trend is up to which the alarmist adds that this trend will result in [insert scare of choice here] though usually without ever specifying when. The sceptical view is that there are two distinct warming periods and one distinct cooling period in the 20th century and if we follow that pattern we are due for a 30-year cooling period.
I'll know more when I've read the paper.

[Athelstan]

@Sep 5, 2011 at 5:58 PM |Richard Betts

HUA.

[tutut]

the thing with this evil CO2 is that it is plant food.
If it were someting like ozon depleting OK, we shld do something.

but with CO2, in worst case you stop dramatically producing CO2 and the ocean and land sinks will deplete the amount back to normal levels in about the same timespans (or maybe double the timespan but not like 10 times the timespan).

this is reversible and when torium or fusion come online without leftwingers sorry paperpushers corrupting the industry, we WILL see the ppm go down from where they are now.

If all problems were reversible..

The day we see the CO2 ppm go down, there will be lots of whining , this time substantiated, that this will lead to desertification and less food.

[Richard Betts]

Sep 5, 2011 at 5:45 PM | HaroldW

Only just found your excellent question.

You are right to take off 30% for albedo, but to get from total irradiance to radiative forcing you further need to divide by 4 because the energy received over the cross section of the Earth (pi times radius squared) is distributed over the Earth's surface area (4 pi times radius squared).

[HaroldW]

Richard Betts --
Thanks...When I "do the math" from scratch I make that conversion correctly, but obviously wrote too quickly. Oh well, not the first time I've made a stupid mistake, and (sadly) not the last either.

Thanks for putting me straight.

[Ibrahim]

Don't forget this:
"We will see that the greenhouse effect, itself, presents little cause for alarm from increasing levels of CO2since the effect is modest. Concern is associated with the matter of feedbacks that, in models, lead to amplified responses to CO2. Considerations of basic physics (as opposed to simply intercomparing models) suggests that current concerns are likely to be exaggerated."

http://noconsensus.files.wordpress.com/2011/08/acs-2011-lindzen1.pdf
http://www-eaps.mit.edu/faculty/lindzen/236-Lindzen-Choi-2011.pdf

[AusieDan]

We are dealing with a chaotic system.
We must first sort out noise from signal.
We can then determine what is natural variation.
Then we can begin to estimate the impact of human CO2 emissions.

That would require many centuries of accurate data, collected and compiled in exactly the same manner.
Why not just wait until we have collected this data?
Then it will be time to consider:
(1) can we take any steps to alter the temperature?
(2) would that be desirable, taking into account that there would be favourable and unfavourable effects of such action?

[geronimo]

BBD: I don`t believe anyone is arguing that it isn't warming. 2000 was warmer than 1900, on the other hand 1900 was warmer than 1800, which itself was warmer than 1700. So we have to decide if, and at what cost to humanity, we can turn down the dial on CO2 emissions.. The first question we need to answer is whether CO2 is the major driver of climate, in my opinion, in the absence of any quantifiable relationship other than "It`s not A so it must be B." we have failed to do that. You asked what kept the earth from freezing when the sun went down, well from my experience it isn't CO2, at least to any extent thats noticeable. I have liived in hot humid climates and, briefly, in hot arid climates. In the latter temperature drops between night and day can be in the region of 30C, sometimes more. While in the former the night following the day is at the same, or near the same temperaure as the day. This suggests to me, and for once I agree with AR4 that it is water vapor that`s keeping the world warm not CO2. Perhaps you know of a paper tha refutes these observations.

As for the effects on agriculture, as I understand it, the effects of a warming world will be for the poles to warm more than the equator reducing the temperature gradient (which in the physics I read at school suggests fewer extreme weather events not more), This means that the temperate areas will have a an increase in temperature, while the tropics will remain around the same temperature, as happened in the Eocene, when the CO2 in the atmosphere was at 1000ppm. The increased precipitation, an increase in food available for plants, the increased warmth over a land mass probably twice or more the size we have available today suggest an agricultural problem to the climate science community. There have to be massive benefits to humans from a warming earth, and more precipitation surely?

[lapogus]

BBD - "It is warming, although as we both know, there's been no trend for the last decade. But the context is what matters; longer time-series reveal much more than short ones about climate change.

First, here's the full satellite record 1979 - present:

UAH and RSS. Common 1981 – 2010 baseline.

Now, look at the 10 year mean over the full record:

UAH and RSS. Common 1981 – 2010 baseline; 10 year mean.

The exaggerated slope shows the decade-on-decade warming very clearly. In the current absence of any known alternative explanation, that is generally assumed to be mostly the result of CO2 forcing."

Are you seriously suggesting that data from 1981 is long term? 1981 isn't even a nanosecond ago in geological time. 30 year climate baselines are a joke. 300 year periods would help pick out the 60 year cycles. But there are very likely to be 2000 year cycles also. As I have said to you before raw data from these 8 historical weather stations do not suggest there is anything to worry about:

http://oi49.tinypic.com/rc93fa.jpg

looking back a little further at this interglacial:

http://www.foresight.org/nanodot/wp-content/uploads/2009/12/histo2.png

and for some real context:

http://www.foresight.org/nanodot/wp-content/uploads/2009/12/vostok.png

Wake me up when the ice sheets start forming over the Scottish Highlands again, until then I will so my best to enjoy this so called warm period.

[lapogus]

Geronimo - agree with your hot humid and hot arid observations. I have my own for a not so warm country; early in the winter of 2009-10, I observed the following night-time minimum temps as the high pressure system took hold of Scotland's climate:

1st night -11C Aviemore -14C
2nd night -12C Aviemore -15C
3rd night -13C Aviemore -16C
4th night - 8C Aviemore -15C

My residence is situated about as far from the sea as you can get in the Highlands, and Aviemore is about 40 miles to the north as the crow flies (if it is not hit by any wind turbines). The conditions were identical, 100% covering of low and high level snow (very dry powder), no wind and and clear skies for the first 3 nights. On the 4th night there was a some thin cloud cover here (but not Aviemore). My conclusion? CO2's effect is negligible compared with what a little H20 can do, and the CO2 AGW thesis is bollocks.

[Philip]

BBD

Yes, I think so - thank you for pointing out the Tisdale post. I'm also pleased you agree with my second point above. I wonder if it is worth asking the others here how they respond to the following questions:

o Is ongoing development and growth desirable?
o Is prevention of environmental degradation desirable?

I think it is perfectly reasonable to answer "yes" to both.