Uncertain Sensitivity

October 27, 2007 · 159 Comments

There are numerous feedbacks in the climate system, and the feedbacks which affect global temperature are overwhelmingly positive. One example is water vapor feedback: increased temperature leads to greater absolute humidity in the atmosphere, and water vapor is a potent greenhouse gas, so this further increases warming. Another is ice albedo feedback: warmer conditions reduce snow and ice cover, which are highly reflective of incoming sunlight; when snow and ice are replaced with open land and ocean (which are far less reflective), earth’s albedo decreases, so the planet absorbs a greater fraction of incoming sunlight and again we experience further warming.

Suppose warming of amount 1 deg.C leads to a further warming of $f$ deg.C; we can call $f$ the feedback factor. Then we expect this additional warming of $f$ also to trigger the feedback mechanism, so we’ll see yet more warming, in the amount $f \times f = f^2$ . This additional warming also triggers the feedback mechanism, causing yet more warming in the amount $f \times f \times f = f^3$ , and so on and so on, etc., etc. The total warming is therefore

$\Delta T = 1 + f + f^2 + f^3 + ... = 1/(1-f)$ .

Thus if the basic feedback factor is $f$ , then the total increase due to feedback will be different. We can call this the gain due to feedback, so

$G = 1/(1-f)$ .

If there were no feedbacks in the climate, then we can estimate climate sensitivity with considerable precision: each increase in climate forcing of 1 W/m^2 (watt per square meter) would lead to temperature increase of between 0.3 and 0.31 deg.C. Another way to state climate sensitivity is that doubling CO2 concentration leads to an increase in climate forcing of about 4 W/m^2, so would lead to about 1.2 deg.C temperature increase. We can call this the no-feedback climate sensitivity to doubling CO2, or we can just call it $S_0$ . With feedbacks, this change will be multiplied by the gain factor $G$ , so the actual climate sensitivity to doubling CO2 will be $S = GS_0$ .

A recent post on RealClimate discusses a new paper by Roe and Baker about why estimates of the probability distribution for climate sensitivity are so asymmetric; they have a long “tail” at the high end with small but not insignificant probabilities for very high values, but almost no probability of very low values. The fundamental reason is that we don’t really estimate the total feedback, i.e., the gain, $G$ , what we really estimate is the feedback factor $f$ .

Suppose we know the probability distribution for the feedback factor $f$ . This is a function $P_f(f)$ such that the probability that $f$ lies in a small interval of width $df$ , centered on the value $f$ , is

$Prob. = P_f(f) ~df$ .

What will be the probability distribution for the gain factor? It’s straightforward to compute that if we know the probability distribution $P_f(f)$ for one variable (in this case, $f$ ), we can compute the probability distribution $P_G(G)$ for another variable (in this case, $G$ ) which is simply a transform of the original variable:

$P_G(G) = P_f(f) / [dG/df]$ ,

where $dG/df$ is the derivative of $G$ with respect to $f$ . Since we know that in this case $G=1/(1-f)$ , we get

$P_G = P_f(f) / (1-f)^2 = G^2 P_f$ .

There are two important consequences of this. One is that if the probability distribution for $f$ is symmetric, like for example the normal distribution, then the probability distribution for $G$ will not be. In fact it will have a long tail on the high end, with small but not insignificant probability of very high values, but almost no chance of very low values. Another is that if the probable accuracty of our estimated feedback factor $f$ is $\sigma_f$ , then the probable accuracy of our estimated gain factor $G$ will be greatly magnified, approximately given by

$\sigma_G = G^2 \sigma_f$ .

An example may clarify. Suppose the probability distribution for $f$ is approximately the normal distribution, with mean value $\bar f=0.7$ and standard deviation $\sigma_f=0.14$ . Then the probability distribution for $G$ looks like this:

It follows that the probability distribution for climate sensitivity looks just like it (after all, $S$ is just a multiple of $G)$ :

In this graph I’ve added dashed lines indicating the usual range of likely values quoted in the press, from about 2 to 5 deg.C per doubling CO2. There’s a striking difference between the tails of this distribution; the high end shows nontrivial likelihood extending even to very high values, while on the low end the probability quickly drops to near zero. There’s another difference too: the “spread” of the probability distribution, which is the basic uncertainty in our estimate of $G$ , is much greater than the spread in our distribution of $f$ . For this case, the uncertainty 0.14 in $f$ translates to uncertainty of approximately 1.6 in $G$ , and that translates to uncertainty of about 1.9 deg.C in climate sentivity $S$ .

It’s in the nature of things that methods of estimating feedback actually amount to estimating the feedback factor $f$ . The gain $G$ and sensitivity $S$ are then derived from this. It’s also in the nature of things that probability distributions which emerge from our estimates of $f$ are roughly normal. Hence the probability distributions for $G$ and $S$ will always have a bigger, longer tail at the high end, and much more uncertainty, than the distribution for $f$ . Even if we can estimate the feedback factor $f$ with reasonably good precision so $\sigma_f$ is low, the precision in $S$ will be not so good.

Roe and Baker’s analysis has implications for policy choices, above and beyond its scientific interest. It has been suggested that it’s not really a good idea to set a “hard target” for limiting CO2 concentration (such as the sometimes-suggested 450 ppmv), because if sensitivity turns out to be substantially greater than 3 deg.C (an oft-quoted average value) then that goal won’t be good enough to avoid extremely dangerous climate change. Instead targets should be flexible, so that if sensitivity turns out to be higher than expected we can adjust the target to keep climate change in the less-dangerous range. However, we’re rapidly approaching the point at which it will be no longer realistic to aim for such targets. CO2 levels currently are about 382 ppmv, and rising at about 2.1 ppmv/yr, which if sustained will bring us to the 450 ppmv level right around the year 2040 (perhaps in my lifetime). And since CO2 emissions are increasing, and there are signs that the ability of oceans and biosphere to absorb part of the increased CO2 from human emissions, this would seem to be an optimistic forecast.

It also should be taken as a stern warning. It really is possible, even if unlikely, that climate sensitivity is on the high end of estimated ranges, or higher. If that’s true then we’re headed for real trouble. For me, this emphasizes the urgency of the problem. It’s not something to leave for the next generation, or even the next decade. We need strong action to limit tampering with the climate, and we need it now.

Categories: Global Warming · climate change

159 responses so far ↓

NeuvoLiberal // October 27, 2007 at 4:53 pm

Interesting observation, Tamino.

From my non-expert point of view, it seems to me that the presence of water on earth makes our system less sensitive than say Venus. Increased temperature seems to make for greater precipitation and that’s a negative feedback.

However, the net feedback appears to be positive and that seems to be the nature of the system at the current state.

Case in point being, I found it interesting that while Arctic sea ice is setting records for minimum extent (and maybe area as well. Is it?), Antarctic sea ice seems to have set record for maximum area, but with the net sea ice area dropping fairly rapidly and especially so since circa 2000 AD.

It’s like we are rapidly melting out ice and snow in NH and sending that partly to the sea as water, partly to become new ice in SH, and some into the atmosphere as water vapor. That’s the big picture I am seeing in terms of water cycle modulation underway.

Regarding your formulation here, the question is, of course, what the value f approximately is. If f is say 0.1, then the asymptotic sensitivity ΔT = 1/0.9 ≅ 0.111. Another question here is the what the time-constant for this temperature auto-sensitivity could be estimated to be.

[Response: Actually 1/0.9 = 1.111..., and that's the gain, not the sentivity; you multiply that by the no-feedback sensitivity 1.2 to get about 1.3.

I'm not sure, but I think the announcement of a new record maximum in southern hemisphere sea ice was preliminary, and has since been retracted. Even if not, the announced new record was only 0.9% above the previous record, whereas the northern hemisphere minimum broke the old record by 27%.

Different feedbacks have different timescales. Water vapor feedback is practically instantenous. Ice-albedo feedback is both short and long; it's fast for reduction in snow cover but it's slower for ice wasting. CO2 feedback is slow because of the long mixing time for the deep ocean, but might end up being faster than that if melting permafrost releases significant CO2.]
Hank Roberts // October 27, 2007 at 7:14 pm

The important consequence that I haven’t seen documented yet is that the winter sea ice accumulates algae that drops into the ocean when the ice melts.

The rate at which food becomes available is going to change as melting happens faster. The total amount of food will change if the total amount of ice surface (at least) starts to decline.
Leif Svalgaard // October 27, 2007 at 7:18 pm

tamino: “We need strong action to limit tampering with the climate, and we need it now.”

Isn’t cutting CO2 tampering with the climate?

[Response: Is this an attempt to be provocative? Do you disagree that putting an end to fossil-fuel CO2 *emission* represents *stopping* interference with climate?]
Leif Svalgaard // October 27, 2007 at 7:48 pm

“Is this an attempt to be provocative? Do you disagree that putting an end to fossil-fuel CO2 *emission* represents *stopping* interference with climate?”

if we found a method to take CO2 OUT of the atmosphere [iron seeding, algae blooms, what not - who knows what future capabilities we'll have] there might people or groups that would like to induce global cooling or undo the warming that has happened [which was "bad" in some people's eyes]. So, putting an end to CO2 emissions does not represent stopping interference, only that particular kind of interference. I never intend to be provocative.

[Response: Such efforts fall under the umbrella-term "geoengineering." I'm highly skeptical of our ability to anticipate the consequences; it could lead to very unpleasant unexpected side effects. For the health of the planet, I think it's a better idea to "quit smoking."

But many have explored geoengineering strategies. The method "du jour" seems to be injecting sulfate aerosols into the stratosphere; there's a post about that on RealClimate.]
cody // October 27, 2007 at 8:46 pm

Isn’t the non-feedback CO2 relationship complicated by what levels the doubling starts at?

I thought that the effect of increased CO2 is not linear, but decays logarithmically. So if we double from present levels, it will not have the same effect as doubling from an hypothetical 191ppm to get to present levels? Or put it another way, the next 10 ppm will be less effective in warming than the previous 10.

Somewhere I’ve seen charts of the decreasing efficacy of rising CO2 levels but don’t any longer recall where.
NU // October 27, 2007 at 8:52 pm

“It’s also in the nature of things that probability distributions which emerge from our estimates of f are roughly normal.”

What is the justification for that statement?

We don’t measure f directly; we infer it from observations of temperature and other physical quantities. I might buy that temperature measurements have normal errors, but if the feedback factor is not related linearly to observed temperature (and I don’t think it is), it will have a non-normal error. (Things are more complicated when you consider multiple observational constraints.)

The Roe and Baker analysis just seems to beg the question, shifting the question of the long tail of climate sensitivity onto the normality of the feedback factor.

I will agree that any transient observations over a period much less than the equilibration time will make it hard to rule out large climate sensitivities, since over a sufficiently small time they will have an observational signature similar to more mainstream sensitivity values.

But the devil is in the details: the real question is even if there is some kind of asymmetric tail, how much can we shrink the tail by including more kinds of data, and how much benefit will we get from that? Annan and Hargreaves have already argued that we can shrink it enough to be policy relevant. I don’t see R&B’s qualitative analysis as really addressing that question.

[Response: Feedback factors can be estimated from theoretical physics, and from climate model simulations. Water vapor feedback, for instance, can be computed from physical principles based on the assumption that with rising temperatures, *relative* humidity remains roughly constant (an assumption with a solid physical basis and observational support). Ice albedo feedback can be computed if we know the changes in ice and snow, which we can estimate from both observations and model simulations (we've only recently become aware that estimates of the rate of ice loss are too low, which bodes ill for the climate). We can then compute the climate *forcing* from these changes in water vapor, snow/ice, etc., in W/m^2, and use that to compute the feedback factor f. The feedback factors of all the various feedback mechanisms are additive, to give the total feedback factor.

Model simulations end up doing the same thing. Multiple runs amount to a large number of experiments, usually with a variety of parameter values (to explore parameter space), and the multiplicity of parameter choices and physical processes amount to a large number of factors which *accumulate* to determine the feedback factor f, because *the physics is in the feedback factor, not the final sensitivity*. That's why, as Roe and Baker show, the probability distribution functions estimated from ensemble runs of model simulations are reasonably well approximated by a normal distribution for f -- but definitely NOT for S.

Because the feedback factor is the *accumulation* of many physical mechanisms (both for theoretical and model-based estimates), we can apply the *central limit theorem* -- that its probability distribution will be assymptotically normal. It's not perfectly normal, only approximately so; but the distribution for sensitivity is nowhere near normal.

Annan and Hargreaves make a strong case that sensitivity lies in the IPCC range, from 2 to 4.5 deg.C.]
Heretic // October 27, 2007 at 9:08 pm

I find your reflexion a little puzzling, Dr. Svalgaard. Extracting carbon that has been stored in the crust for tens or hundreds of millions of years and injecting it in the atmosphere is, so far, the largest direct climate interference ever realized.

Perhaps you’d argue that land use/characteristics (the only comparable magnitude change coming to mind) are as much of an interference, which is debatable.

In any case, you may not agree that the consequences of the current uncontrolled carbon experiment are “bad” but you can not show either that they are “good.”

Another point: “who knows what future capabilitites we’ll have?”
Indeed, nobody really knows, but some are nevertheless intent on betting that these yet unknown capabilities could be apt at solving planetary scale problems. I remain skeptical.
NU // October 27, 2007 at 11:00 pm

Tamino,

As I alluded to earlier, I could equally well apply the central limit theorem to temperature observations, claim that they have a normal distribution, and demonstrate that the feedback parameter can’t (since the two are related nonlinearly).

In fact, you can’t apply the CLT to prove that the feedback factor should be normally distributed. The CLT applies to the sum of identically distributed random variables. If I say that the total feedback is the sum of many different feedbacks, f = f1 + f2 + f3 + …, then I can only apply the CLT if the means of f1, f2, f3, … are the same. (Also their variances, and in general they have to come from identical distributions.) That is, we need to f1 = f2 = f3 = … (or rather E(f1) = E(f2) = E(f3) = …) in order to conclude that f is normally distributed. But of course this is not true, since the fi are different feedbacks, not merely multiple estimates of the same feedback.

Look at it this way: we know what happens to the temperature response in an ideal CO2-doubling experiment: it rises at some rate determined by the transient dynamics, and after a long time asymptotes to a value equal to the equilibrium climate sensitivity. If the ECS equals, say, 3 degrees, we can certainly rule out, say, 10 degrees with high probability if we wait long enough: just keep measuring temperatures until they visibly approach an asymptotic value.

This requires making observations after a period of time comparable to the equilibration time, but it’s possible in principle, and is a counterexample to the idea that ECS will always have a long tail.

The reason why it does still have a long tail now is because we haven’t been able to make measurements for such a long time.

However, by combining extended observation periods (instrumental + paleoclimate), or by combining shorter-term but complementary observations (e.g., surface temperature + ocean heat uptake), we can hope to effectively reproduce such a long period of measurement, and cut off the tail.

As you note, Annan and Hargreaves make a case that paleoclimate can exclude a lot of the ECS > 4.5 C probability mass; others have shown that ocean heat uptake as an additional constraint can cut off a chunk of the tail too (Tomassini et al. this year in J. Climate is the most recent example I can think of).

In summary, the extent to which you can cut off the long tail of ECS is still an open question, Roe and Baker’s analysis notwithstanding.

[Response: Only the most crude formulation of the central limit theorem applies exclusively to identically distributed variables. I have shown this myself in the peer-reviewed literature. As long as the variance is not dominated by a small number of variables with far greater variance than the others, it still applies. And the fact that the variables have different mean values is completely irrelevant.

And you *cannot* apply the central limit theorem to sensitivity (which is the real issue), because sensitivities are nowhere near additive. Feedback factors, and the physical processes which determine them, are at least approximately so.]
peterhearnden // October 28, 2007 at 8:04 am

Dr Leif Svalgaad said

“Isn’t cutting CO2 tampering with the climate?”

What about adding CO2 to the atmosphere? Is that tampering?

Surely reducing Co2 back to where it was before we started adding it (and started tampering with the atmosphere) is to simply do that - to remove our tampering.

Dr Svalgaard, I’ve seen versions of your argument before - I simply don’t get where you are coming from.
cody // October 28, 2007 at 8:40 am

tamino, is it true that 75% of any possible temperature increase from CO2 doubling has already taken place, because of the decreasing sensitivity of the atmosphere to each extra increment of CO2? I finally tracked down a source of this assertion, and it was attributed to a paper by Pielke which is no longer available online.

But is this right? And if it is, then why is there all the emphasis on stopping further rises, which would seem not to be capable of having very grave effects?
Leif Svalgaard // October 28, 2007 at 2:14 pm

peterhearnden: “Surely reducing Co2 back to where it was before we started adding it (and started tampering with the atmosphere) is to simply do that - to remove our tampering.”

Tampering is a negative word, as if we were doing something wrong. Now, if we could all the CO2 we have produced since the little ice age [LIA] back in the ground, we would presumably return to LIA conditions and miserable climate. This does not seem to be something desirable [just ask wheat growers in Canada and Russia]. So rather than ‘tampering’ it would seem to me that what we have been doing is ‘ameliorating’ the climate. And a far as I’m concerned, we could use some more of that. I would consider returning to the LIA as tampering. So, now we seem to have two camps: A) the return-to-LIA fanatics and B) the bring-on-the-warmth fanatics. I’m in camp B and perhaps you are in camp A. Maybe there is a camp C: I-don’t-want-any-change. Camp C is not realistic because climate changes all the time, some natural, some not, and the question [to me, at least] is how we and our political institutions best deal with such change.
S2 // October 28, 2007 at 3:36 pm

Thanks, Tamino, for another instructive post - I certainly understand more than I did before I read it.
ks // October 28, 2007 at 6:30 pm

“They stated that cold can be just as dangerous as heat, if not more so. While that is true in an abstract sense, it is hardly a reason to be complacent about climate change. Furthermore, it illustrates a fundamental lack of understanding of the problem.

Climate change is more than global warming. Seeing it in that way is an unfortunate consequence of being hobbled by one-dimensional thinking (hot vs. cold). If the temperature would merely change, up or down, with all other parameters remaining the same, we could deal with that. But dealing with increased climate variability is a much more difficult problem. Gerberding and Boxer pointed this out. Unfortunately, people who have one-dimensional thought processes don’t grasp this concept. “
Hank Roberts // October 28, 2007 at 8:10 pm

http://www.pnas.org/cgi/content/abstract/104/37/14580
http://adsabs.harvard.edu/abs/2007GeoRL..3405607C
http://www.pacificscience.org/tfoceanacidification.html
http://co2.cms.udel.edu/Ocean_Acidification.htm

Warm hell.
William Connolley // October 28, 2007 at 9:31 pm

Did you notice that the R+B formulation gives a finite probability of f > 1?
Leif Svalgaard // October 29, 2007 at 12:30 am

ks: “But dealing with increased climate variability is a much more difficult problem.”

I’m not sure if you mean “weather” variability. Climate being defined as average over decades (used to be 30 years) would not vary much on top of the change due to a steady increase of CO2. So I’ll assume “weather”, like hurricanes, storms, etc. The atmosphere is a heat engine. The work you can get out of a heat engine does not depend on the mean temperature, but on the temperature difference. Since the high and mid-latitudes seem to heat up more than the tropics [the latter being good at shedding the heat by shoving it to higher latitudes.

global warming might mean a smaller latitude gradient of temperature and thus a smaller difference and less work out of the engine, thus less weather variability. I’m sure this is well-trodden ground and that y’all heard all this before and that it does not matter what I say, but do allow this old 1D person to present his views. But do tell me were I go wrong, when and if. And do try to keep it civil.
cce // October 29, 2007 at 5:22 am

Eyeballing a chart from AR4, CO2 in the LIA (270 ppm) and the MWP (280 ppm) was separated by about 10 ppm, and we are currently about 100 ppm higher than during the MWP. Assuming we could put the CO2 back, the idea that it would result in “LIA conditions” is a bit of a stretch. Instead, why don’t we try to limit warming to 2 degrees, thus keeping the climate within a range relevent to human beings.
CraigM // October 29, 2007 at 12:58 pm

leif/dr svalgaard

“So, now we seem to have two camps: A) the return-to-LIA fanatics and B) the bring-on-the-warmth fanatics. I’m in camp B and perhaps you are in camp A. Maybe there is a camp C: I-don’t-want-any-change. “

Well, i might be in another camp; maybe camp D. Im like, lets not go back to another major ice age or a LIA (wasnt that caused more by a reduction in solar ouput?). And we might have discovered a way of doing that: simply add c02 to the atmosphere.

And if we are to warm this sucker up, lets like, maybe, have a go slow policy in place and figure out what might actually happen before we rush gun-ho into a possible 5 oC warming in just the next 100 years. Yknow, maybe stretch things out over a few 100 to 100o years. Just so we can get our adaptation policies in place. That way us Australians and Africans might have more time to get sorted out. And Denmark and Norway, or whoever owns greenland, will be happy also (its a shame the polar bear is gunna get shafted though. Such a beautiful animal). So, i guess, Im in the ‘lets have slow change rather than quick change’ camp.
Leif Svalgaard // October 29, 2007 at 1:57 pm

A: “LIA (270 ppm) and the MWP (280 ppm) was separated by about 10 ppm, and we are currently about 100 ppm higher than during the MWP”

B: “LIA (wasnt that caused more by a reduction in solar ouput?).”

re A: this is like having your cake and eating it. It is hard to blame MWP (and the millions of other warmings through geological time - say one every 1000 years) on CO2, but you do blame the current warming solely (or mainly) on that, because they are “not alike”.

Re B: solar output whether in terms of TSI, magnetic field, and EUV does not seem to have changed significantly in the last 400 years, so we should not attribute the LIA to the sun (however convenient it might be).

“figure out what might actually happen”
This is good advice, but if we are in panic mode we won’t accomplish much.
ks // October 29, 2007 at 2:16 pm

Dr. S

the words were not my own, hence the ” “. I fail to see how it was not a civil comment. You are trying to treat a problem as a single variable when it has been predicted to be multi-variable.

For example, http://www.usaid.gov/our_work/environment/water/climate_change.html

and no, I don’t think the author of the quote meant “weather variability.” Last I checked, drought was not considered weather.
EliRabett // October 29, 2007 at 2:46 pm

Just to be clear Svalgaard is convinced that there has been no significant change in solar insolation in the past 400 years. There are not many in his field or who study climate who agree and there are multiple lines of evidence against it.

However, that being the case you have the problem of what did cause the variations in climate that were observed. You could chalk it up to natural variability, but that stretches the envelope quite far.
cce // October 29, 2007 at 3:16 pm

1) There is no way that the CO2 concentration is going to fall 100 ppm anytime soon.
2) If it did it wouldn’t mean LIA conditions any more than it would mean MWP conditions
3) The concentrations of many GHGs, among them CO2, N2O and Methane have been significantly thrown out of whack by human activities. Current conditions and the recent past are not “alike” because they are not “alike.” They are not alike in their causes, and they are not alike in the amount and speed of the temperature change.
4) No one is advocating another LIA.
5) You, however, are advocating increasingly warmer conditions, arrived at with unusual speed, on top of already warm conditions.
Leif Svalgaard // October 29, 2007 at 4:59 pm

Eli: “just to be clear Svalgaard is convinced that there has been no significant change in solar insolation in the past 400 years. There are not many in his field or who study climate who agree and there are multiple lines of evidence against it.”

There very careful phrase “solar insolation” calls for a clarification: as we don’t know what variation there has been in the Earth’s albedo over the last 385 years, I’ll discuss the solar output:

There are two issues:
1: does the solar output vary [other than by a trivial amount]?
2: could and do these variations cause climatic changes?

If the answer to 1 is “no”, then we don’t need to consider 2.

A very authoritative review was published a few years ago:

Solar radiative output and its variability: evidence and mechanisms, by
Fröhlich, Claus; Lean, Judith,
The Astronomy and Astrophysics Review, Volume 12, Issue 4, pp.273-320, 2004. DOI:10.1007/s00159-004-0024-1

They summarize thus:
“The historical irradiance reconstructions shown in Fig 30 b) all assume the existence of a longer term source of irradiance variability, in addition to the 11-year cycle. [...] Which of the time series in Figure 30 [can be found on my website http://www.leif.org/research click on CAWSES - IMF, EUV, TSI.pdf ( CAWSES Newsletter: vol 4, issue 2, new2007)] better represents actual irradiance variability is unknown. The primary uncertainty is whether the secular changes that the models assume actually occur (Willson and Mordvinov, 2003), or not (Foukal and Milano, 2001; Lean et al., 2002). Nor is the extant contemporary database of sufficient duration to adequately judge the various approaches. The comparisons in Figure 31 show that the historical reconstructions deviate from each other prior to 1980, which is when actual observations were just commencing. Lack of a clear physical relationship between the 14C and 10Be cosmogenic isotopes and irradiance variability is a critical impediment to improved understanding of long-term irradiance variability. Whereas the sources of irradiance variability are magnetic active regions near the surface of the sun, cosmogenic isotopes variations occur because the extended solar atmosphere in interplanetary space modulates the flux of galactic cosmic rays that reaches the Earth’s atmosphere (Bard et al., 2000; Webber and Higbie, 2003). The recent simulations of magnetic flux transport on the sun, suggesting the lack of a linear relationship between total and open flux (and hence irradiance and the interplanetary magnetic field) are preliminary, and raise additional questions about the role or meridional transport and the extrapolation of surface magnetic fields to the corona and heliosphere that require further study.”

Such further studies are now becoming available. And they seem to indicate that the variation of both TSI and solar magnetic output are much smaller that thought in 2004. I can mention two:

Shortwave forcing of the Earth’s climate: Modern and historical variations in the Sun’s irradiance and the Earth’s reflectance, Journal of Atmospheric and Solar-Terrestrial Physics, Volume 69, Issue 13, September 2007, Pages 1556-1568, by P.R. Goode and E. Pallé.

They conclude:
“From the helioseismic data, we now have an internally consistent picture of the origin of frequency changes that implies a Sun that is coolest at activity maximum when it is most irradiant. [...] We conclude that the Sun cannot have been any dimmer, on the time steps of solar evolution, than it is now at activity minimum.”

A Floor in the Solar Wind Magnetic Field, by Svalgaard, L.; Cliver, E. W., The Astrophysical Journal, Volume 661, Issue 2, pp. L203-L206., 2007, DOI:10.1086/518786.

They conclude:
Various lines of evidence indicate that the solar wind magnetic field has a “floor” or baseline state to which it falls when the sunspot number goes to zero for extended intervals (several rotations). During such periods, the IMF in the ecliptic plane at 1 AU is ~4.6 nT, and the radial component of the polar IMF at 1 AU is ~3 nT, independent of the solar polar field strength. The floor appears to have been stable since ~1500. We identify the floor with a constant solar open magnetic flux of ~4×1014 Wb and a constant corresponding strength (~1011 A) of the current in the HCS. Solar cycle variations of the IMF ride atop the floor. The existence of a floor in the solar wind has a bearing on
such topics as the solar dynamo, space weather, and cosmic ray modulation. Specific implications of the floor for solar grand minima, solar wind models, [...] were discussed in § 3. The basic question of how the Sun maintains a constant baseline open flux in the face of variable polar field strength remains unanswered. The strength of the solar polar fields does not determine the IMF strength.”

The evidence is pointing to a lack of a secular variation of any “background” solar irradiance [possibly caused by solar magnetic fields], and that leaves the variation [as Goode and Palle delicately note] “climatologically small”.
Leif Svalgaard // October 29, 2007 at 5:20 pm

In case my long post didn’t hit home, it can be summarized thus:
‘The solar output during the Maunder Minimum was what it is right now, today.’ Both for TSI and for the magnetic field.

If there was no lower output to explain the LIA, there must be other natural causes, that are not considered by deniers.
CraigM // October 29, 2007 at 11:26 pm

dr. leif

“… if we are in panic mode we won’t accomplish much.”

well, we cant turn everything off. I cant image walking into a hospital and turning every heart monitor off, sheesh. It would be utter disaster. We have to encourage new technology and become more efficient with our energy usage. We have to do that but at the same time not damage our economy so much thats things go pear shaped there.

The thing is, we havent been in panic mode for 15 years. In fact we have done very little. Panic mode is more likely to come about if we sit on our hands and wait. I mean, if we wait and wait and things dont turn out the way we like in terms of climate then you are likely to see panic on a scale you aint seen before. So we dont want panic, no doubt.

Right now is a good time to start implemeting a few simple strategies to encourge new technology: carbon taxes, cap and trades, targets for emission reduction….whatever. The sooner we do that the less damage we will do to our economy because things can be spread out over numerous years. Do that now and we can slow this climate change thing down a bit. We are locked in to some warming now it seems. And there we will have to work on our adaptive strategies too. But im all for slowing things down and acting early, yknow, with a bit of fore-thought and not leaving everything to the last minute.

So i guess, in summary:

Im all for slowing down climate change. So we have plenty of time to adapt and figure out whats going on…

To do the above means acting early in terms of adjusting our economy, so we dont suffer too much of an economic shock.

thats my 2c
Leif Svalgaard // October 30, 2007 at 1:47 am

Craig,
Reducing emissions is good in itself as it leads to a cleaner air. When I worked in L.A. in the early seventies, you couldn’t see across the street on most days, that is much better today. In China they have severe problems with foul air and they need to do something about that. London’s smog is mostly gone now because of not burning sulphuric coal . A cleaner environment is something to desire in itself.
I don’t think we disagree there.

About ‘panic’. The ‘planet in peril’ and ’save the planet’ things look like panic to me, or at least an attempt to create panic. In a panic some people are always been taken advantage of and swindled. This we don’t need. A measured approach as you (and I, actually) advocate is very hard to emerge from the vitriolic ‘debate’ that is taking place. The improvement in climate that may have resulted from burning fossil fuels
may come to an unfortunate end as oil climbs above $100 a barrel (it was near $94 today), as conservation may come simply because it is becoming too expensive to burn the stuff.

In my previous post and in others I have tried [albeit with little success] to point out that all the previous millions of warming [assuming that the last 3000 years are typical - I even take away from that number the last two decades] were not caused by humans injecting 14C from burning fossil fuels. There are indications that variations in solar output are “climatologically small”, so I think we are neglecting or not understanding some other natural fluctuations.
Dano // October 30, 2007 at 2:26 am

I can actually find a point of agreement with Leif - I don’t like the ’save the planet’ stuff either. The planet will carry on long after we destroy ourselves. It’s arrogant to think otherwise.

Nonetheless, Leif, the last 650k years are the key record length, as this recent time period covers most of the adaptations made by plants (albeit not the grasses, the most-advanced of the plants) and most of the adaptations by animals to recent planet-wide ecosystem swings (and CO2 ppmv has never been higher in this time period than now.

We learn little about earth systems wrt adaptation by looking 55MYA.

Best,

D
dhogaza // October 30, 2007 at 3:20 am

In my previous post and in others I have tried [albeit with little success] to point out that all the previous millions of warming [assuming that the last 3000 years are typical - I even take away from that number the last two decades] were not caused by humans injecting 14C from burning fossil fuels.

Sure, but humans weren’t around to be driven to extinction by such events millions of years ago (if I interpret “millions of warming” correctly).

You do understand the basic selfishness of our concern, right? As Dano points out, we’re not really talking about “saving the planet”, we’re about saving OUR SPECIES.

OK, even that’s perhaps more extreme than necessary. We’re talking about “minimizing the number of humans killed”.
Leif Svalgaard // October 30, 2007 at 3:50 am

re number of warmings: there seems to be warming about every 1000 years; none of these except perhaps the last can be attributed to humans ‘tampering’ with the climate by releasing CO2. For the sun to be the culprit, the climate sensitivity to the minuscule solar variations must be much, much higher than we thought it was [cf. Goode and Palle] and if so, maybe the current warming is mainly due to the sun. There are [respected] solar physicists that argue that the sun now is more active that in the last 11,000 years. [Unusual activity of the Sun during recent decades compared to the previous 11,000 years, S. K. Solanki, I. G. Usoskin, B. Kromer, M. Schuessler, J. Beer,
Nature 431, 1084 - 1087 (28 Oct 2004) Letter]. That combined with the Goode&Palle hypersensitivity might mean that most of the current warming is due to the sun. I mention this as a possibility, although I personally do not believe so [that the sun is so unusual now].
Whether or not we consider the last 650,000 years or billions of years does not alter the arguments that has been MANY warmings even under close to current conditions.

“saving our species”: there seems to me to be a much larger chance that we do ourselves in by warfare than by climate change. And talking about ’saving our species’ is the kind of alarmist cry that leads into panic if enough people go for it. I can just see the headlines: “Maybe we need to bomb them chinks into reducing their carbon footprint”.
Hank Roberts // October 30, 2007 at 4:03 am

Bribes, not bombs.

The smart move would have been to develop the “no regrets” technology over the past 20 years and had it ready to sell as the Chinese reach the point of really nasty air pollution and developing environmental activism.

Instead — if we’re lucky — they shut down enough vehicles and factories to have a breathable Olympic Games, doing the great experiment no other country has done (with the exception of the USA shutdown of aircraft operations for 3 days after 9-11).

Those experiments are the ones that are convincing, they make very clear what the effects of human activity are.

China really wants an Olympic Games where the athletes don’t have breathing problems.

So they’re going to do the experiment there with cars and factories.

Let’s hope they also instrument the heck out of the area and get good science out of it, convincing science, knowing that they are positioned to profit from doing so.

With luck, they do that, and we get the chance at best to design along with them and see them manufacture the next generation technology that allows controlling the pollutants better than our 1960s-1970s technology.

They leapfrog us. So it goes. Maybe.
nanny_govt_sucks // October 30, 2007 at 6:23 am

… this recent time period covers most of the adaptations made by plants

Dano, can you explain why most plants thrive best at around 1000-1200ppm CO2?
Dano // October 30, 2007 at 1:43 pm

Define ‘thrive’ and where this ‘thrive’ occurs, plz.

Best,

D
Dano // October 30, 2007 at 1:48 pm

And talking about ’saving our species’ is the kind of alarmist cry that leads into panic if enough people go for it. I can just see the headlines: “Maybe we need to bomb them chinks into reducing their carbon footprint”.

Fellow Pompeiians! Fear not the rumblings beneath your feet!

Anyway,

If I may, Leif, you either know nothing about terrestrial ecosystems and their responses, or you know something but don’t share it with others. Our Western societies are entirely dependent upon ecosystems. Perturb them beyond their tipping points and we’re living in systems for which we have no precedent for living, for economy, for growing crops.

You may want a hard landing for societies, but I don’t. Hard landings are, well, hard. Sounds cruel to me.

Best,

D
John Cross // October 30, 2007 at 3:30 pm

Nanny: I think you took your argument from the first paragraph without reading the rest.

So please back up your assertion.

Regards,
John
Hank Roberts // October 30, 2007 at 3:35 pm

http://pediatrics.aappublications.org/cgi/content/abstract/peds.2007-2645v1?ct
luminous beauty // October 30, 2007 at 4:00 pm

Leif,

I would say we have a pretty good theoretical understanding of natural climate variation, i.e. GCMs. How well they correlate to what real-world mapping we have, low resolution as it may be, is compelling if not absolutely probative.

You are absolutely right on that solar variability does not appear to be much of a factor. What is telling to me is that until we began observing the sun from space, for all we knew, TSI was a constant. I also suspect that hyper-climate sensitivity would hold for the IR rebound of greenhouse gasses as well. Even more so, as the sun only shines on half the planet at any given moment.

I do appreciate your big picture deep time astronomical perspective, but we do have to live on this planet.
Leif Svalgaard // October 30, 2007 at 4:29 pm

luminous beauty:

to quote myself: “TSI during the Maunder Minimum [and other Grand Minima] was not any lower than what it is today, right now, this minute”.

This means that *unless* climate sensitivity to solar forcing is an order of magnitude higher than commonly thought [and 'understood'], the LIA was not caused by the sun, the MWP, the ‘Roman’ warming [e.g. grapes grown in England during Roman times] was not caused by the sun, and all the other warmings and coolings were not caused by the sun either. And they were not caused by man-released CO2 either, so there is enough natural terrestrial variability present to account for those, leading to the question how much of the present warming is due to those natural causes and how much is due to human activity. Simply to say that the current warming is mainly man-made, is akin to the argument for why Uri Geller’s current spoon-pending trick is genuine given that in the past he was shown to be a fraud.

[Response: As an aside, there is at least one researcher (William Ruddiman) who argues that anthropogenic CO2 has been an important climate forcing for a very long time (6000 years or more), not due to fossil-fuel burning but because of land-use changes associated with agriculture. He argues that if not for human activity, we'd be well into the next ice age. I think most in the climate science community would reserve judgement, neither affirming nor denying its correctness.]
Leif Svalgaard // October 30, 2007 at 5:45 pm

Yes, I’m aware of Ruddiman and there might be something to it. My point is that both his mechanism and the current CO2 injection probably have some effect, but those are on top of the natural causes and we don’t know how much is really due to either. But he and I apparently agree that human activity has been for the better. When fossil CO2 runs out [don't know when], the CO2 that we put into the atmosphere begins slowly to settle out and after some time [centuries?] will be back to the pre-industrial value, and maybe we cannot stave the ice age off anymore.

on a different note: the current hurricane season has turned out to be flop (like the last one). This is, of course, a disappointment to the alarmists, but there is always NEXT year…

[Response: It's my opinion that computer model simulations of the 20th century (see the IPCC report for more details) argue strongly that we *do* have a pretty good idea "how much is really due to either." If you want an opinion from leading researchers, you could inquire at RealClimate.

I was under the impression that the 2006 hurricane season in the Atlantic was average, not a "flop," and that the season in the Pacific was quite active. In any case, the lack of destructive storms striking the U.S. over the past two years is not a disappointment to me, it's a relief. But I don't consider myself an "alarmist"; I'm hoping to avert disaster rather than celebrate it. Perhaps that's a line of demarkation between the concerned and the genuinely alarmist.]
Dano // October 30, 2007 at 6:17 pm

This is, of course, a disappointment to the alarmists, but there is always NEXT year…

I’d like to know who these straw-people are. Can anyone name these mythical hair-shirt wearers who profess (loudly, surely for Leif to know what they want) their disappointment over a lack of destruction (presumably so we can go back to feudal times)?

Best,

D
tamino // October 30, 2007 at 6:33 pm

I reiterate: if something is said which angers you, please exercise exceptional restraint in responding.

At the same time, I’ll agree with Dano that the comment “This is, of course, a disappointment to the alarmists” strikes me as an unnecessary straw-man.
Leif Svalgaard // October 30, 2007 at 6:53 pm

tamino: It’s my opinion that computer model simulations of the 20th century (see the IPCC report for more details) argue strongly that we *do* have a pretty good idea “how much is really due to either.”

In that case one should be able to quantify that, so, let’s try. Consider the sequence of events:
RW (Roman warming)
MC (Early medieval cooling)
MW (medieval warming)
LIA (little ice age)
CW (current warming)

put three numbers (e.g. degrees change) on each event. The first number is solar forcing, the second one is “natural variability” and the last one is that due to human influence [I'm not including Ruddiman here]. If you can do that and show why EACH of the numbers is as you put them, I’ll agree that we have a ‘pretty good idea “how much is really due to either”‘. If not, I’ll say that we do not have such a good understanding of these things.

hurricanes 2007: I live in Houston, so I follow the tropical activity closely. Evacuated during Rita. It is almost impossible to get real information nowadays, but if what I see matches my own experience, it registers positively with me. Here is my source:
http://www.coaps.fsu.edu/~maue/tropical/
By: Ryan N. Maue, Florida State University
Cross Post at Climate Audit (h/t) Steve McIntyre
“Unless a dramatic and historical flurry of activity occurs in the next 9 weeks, 2007 will rank as a historically inactive TC year for the Northern Hemisphere as a whole. During the past 30 years, only 1977, 1981, and 1983 have had less activity to date (IMAGE: January-TODAY, Accumulated Cyclone Energy ). For the period of June 1 - TODAY, only 1977 has experienced LESS tropical cyclone activity than 2007. For the North Atlantic basin, Tropical Storm Noel is currently too weak to impact any of these results. However, one should always be prepared for late-season developments since hurricane season ends on November 30.”

2007 lowest September activity on record since 1977
2006 and 2007 lowest October activity on record since 1976 and 1977

You are clearly not one those you want to exclude from posting because of foul language etc [kind of the opposite of G. Marx: I don't want to belong to a club that would accept me as a member :-)] so perhaps one mark of a concerned person is civility. If so, one has a handy way of determining on which side of the line of demarcation someone is.
Leif Svalgaard // October 30, 2007 at 7:18 pm

“disappointment to the alarmists”

how can there be ANY doubt that I did not mean that some people want destruction? What do you take me for? What I clearly meant was if 2006 and 2007 HAD have many severe and destructive hurricanes, that some people would have said: “see, do you now understand how important it is that we stop tampering with the climate” using the many hurricanes as support for their viewpoints without taking the few hurricanes as weakening their argument.

[Response: I have no doubt that you did NOT really mean that some people would delight in destruction. But can you see how it might be misinterpreted that way? Certainly Dano thought so. And we have actually heard pretty much exactly the same words before, from people who *did* intend that reprehensible meaning.]
Dano // October 30, 2007 at 8:19 pm

Hmmm…mild sarcasm discouraged. Understood.

(you can delete if you wish, sir).

Best,

D

[Response: I actually enjoy mild sarcasm. My comment was more a warning than a criticism. And please bear in mind I'm being extra cautious, in order to establish a new order of things. Generally, it's going pretty well, people seem to be doing a fine job abiding by the new practice, the tone of commentary is *much* better, and the commentary itself seems much more to the point and productive.

I really do hope to loosen up soon. One difficulty is that traffic -- both hits and comments -- have actually increased since the new policy, contrary to my expectation.]
JesusChristHimself // October 30, 2007 at 8:48 pm

On named hurricanes, Houston recently had 5 billion in property damages and lost 22 human beings. The storm had a name, but it wasn’t Rita.

Several years ago hurricane experts recommended Galveston build a seawall. The good folks decided they had better things on which to spend their money. They revisited the arguments, and built an especially expensive seawall.
nanny_govt_sucks // October 30, 2007 at 9:04 pm

Define ‘thrive’ and where this ‘thrive’ occurs, plz.

For more info:

Please see the first full paragraph on the page here:
http://tinyurl.com/32jfek

Also, there’s http://ars.usda.gov/is/AR/archive/jul97/gcc0797.htm which experimented with a doubling of CO2 concentrations (still far above what we see in the ice cores record).

It would seem that plants “remember” a time when CO2 concentrations were much higher, does it not? Or is there some other interpretation?
Heretic // October 30, 2007 at 9:08 pm

“One difficulty is that traffic — both hits and comments — have actually increased since the new policy, contrary to my expectation.”

Bloggers are like children, they need boundaries…
tamino // October 30, 2007 at 9:27 pm

Leif:

one should be able to quantify that

Others far more capable than I have already done so, although estimates of climate forcings generally don’t extend much beyond the last thousand years. Series of estimated forcings usually include solar, volcanic aerosols, and greenhouse gases. Examples are Bard et al. 2000 (Tellus B, 52, 985-992); Mann et al. 2005 (Journal of Climate, 18, 417-456); Crowley 2000 (Science, 289, 270-277). Quite a few forcings are estimated for the last 400 years in Robertson et al. 2001 (J. Geophys. Res., 106, 14783-14803). NASA GISS has forcing estimates since 1880 for well-mixed greenhouse gases, ozone, stratospheric water vapor, land use, snow albedo, stratospheric aerosols, black carbon, and the aerosol indirect effect.

There’s a great deal that isn’t known about climate forcings and climate dynamics. But we’re not just taking potshots in the dark; an immense amount of work has gone into understanding, and quantifying, these things.
Dano // October 30, 2007 at 9:50 pm

I appreciate the fact that, na_gs, you can’t find anything older than 1997, despite the plethora of research since then, including the research I included in the 44 other times I’ve responded to your assertions.

Likely this time issue is because many of the actual FACE results disagree with your assertion, but as to your impaired memory restricting your assimilation of the provided material…what could the reason be?

Best,

D
Leif Svalgaard // October 30, 2007 at 10:00 pm

“one should be able to quantify that …
Others far more capable than I have already done so”.

I do understand that an immense amount of work has been done. In my own field, if people asked me a similar kind of question I would be able off the top of my head to quote at least orders of magnitude for the contents of my little table. F.ex.: in degrees C [solar, natural, human]
RW [0, 3, 0]
MC [0, -2, 0]
MW [0, 3, 0]
LIA [0, -2, 0]
CW [0, 2, 1]

or some such numbers. I would take a certain pride in being able to do that without having to ask the questioner to go look it up among that “immense amount of work”.

Other people here who KNOW at lot more than I might prefer a different table, e.g.:
RW [0, 0, 0] denying that it was there
MC [0, 0, 0] denying that it was there
MW [0, 0, 0] denying that it was there
LIA [-2, 0, 0] the sun did it
CW [0, 0, 3] we did all of it
With such a table, the discussion gets onto a firm foundation, because each particular number can now be referred back to the precise papers that deal with that particular time or the precise formula or model that allows that particular number to be derived.

Without such SPECIFIC numbers, I’ll maintain [at least to my satisfaction] that we do not have a “pretty good understanding”. Now, it’s perfectly OK that different people have vastly different tables in mind. That is regular science: we have SPECIFIC disagreements and they can be resolved by further research [and might even show what need to be looked at]. So, I would issue a challenge: let every participant here state what his/hers table looks like. It is OK to use question marks, e.g. the table
RW [?, ?, ?]
MC [?, ?, ?]
MW [?, ?, ?]
LIA [?, ?, ?]
CW [?, ?, ?]
is perfectly valid [albeit a bit uninformative].
jonathan // October 30, 2007 at 10:25 pm

Somehow nature is absorbing 55% of our CO2 emissions. So cutting CO2 emissions by 45% will stop the rise of CO2 in the atmosphere. Thats about what burning coal contributes. So lets replace every coal power plant by a nuclear one and put out those HUGE coal seam fires in China!
tamino // October 30, 2007 at 11:13 pm

I’ve never claimed that climate science is my field, let alone paleoclimate, and I don’t have estimates off the top of my head. But I do have enough data on my computer to make very rough guesstimates:

RW [?, ?, ?]
MC [?, ?, ?]
MW [+0.2, 0, 0]
LIA [-0.2, -0.2, 0]
CW [+0.1, -0.1, +0.8]

These are not pronouncements, I’m just “taking a stab” at it. If you want real expert opinion, look in the literature.

As for this:

I would take a certain pride in being able to do that without having to ask the questioner to go look it up among that “immense amount of work”.

I tried to point you to far better estimates of paleoclimate influences than I’m able to supply. To be perfectly candid, I think you would greatly benefit from looking up some of that immense amount of work.
Leif Svalgaard // October 30, 2007 at 11:47 pm

tamino
in your your table, what are the numbers? degrees C? I see numbers like several degrees floating around.
does it mean that you think there was no MW except the measly +0.2 due to solar forcing?
And RW and MC are hardly paleoclimate. These events are recent enough to be within the range of conditions similar to now and their causes are of immediate interest. Since you discount MW maybe you also discount RW ad MC? in which case, of course, it is moot what their causes were. I’ll maintain that without firm numbers (rather than “stabs”) there can be no serious discussion. Suppose I in a week came back to say that I’ve scoured the literature and that I found CW [+0.1, +2.1, +0.8], would you accept that? I don’t think so. You must [should] have a specific reason for CW [+0.1, -0.1, +0.8] rather than CW [+0.1, +2.1, +0.8]. As I said, EACH number can be and should be accounted for. Just telling to RTFM is not enough.
nanny_govt_sucks // October 30, 2007 at 11:49 pm

I’m not referring to soil fertility, Dano. That’s 2 evasions. Is this a difficult question?
Hank Roberts // October 31, 2007 at 12:29 am

A happens.
Yes, if you also have B.
EliRabett // October 31, 2007 at 1:20 am

Of course the possibility that shall not be named is simply that Svalgaard is wrong. Which seems a reasonable POV. I would also not get sucked into the Rome warming bit, because frankly no one has more than a guess what the Italian temperatures were, let alone the global temperatures\let alone the forcings. That little side track seems to be a red herring in a red herring barrel.
tamino // October 31, 2007 at 1:34 am

in your your table, what are the numbers? degrees C?

Yes. That’s what you asked for.

I see numbers like several degrees floating around.

Where? From what I’ve seen, several degrees is absolutely not credible.

does it mean that you think there was no MW except the measly +0.2 due to solar forcing?

Why do you call it “measly”? Do you have solid evidence that it is otherwise, or are you basing this on numbers “floating around”?

I based my estimate of the size of the MWP and LIA on the Moberg reconstruction (smoothed with a low-pass filter), adjusting for the fact that it’s only hemispheric, not global. I based the fraction attributable to different causes on the forcing estimates of Crowley, except for the modern era which is based on forcing estimates from NASA GISS.

And RW and MC are hardly paleoclimate.

The National Academy of Sciences report on the reliability of climate reconstructions for the last 2,000 years refers to it as paleoclimate.

The NAS report expresses high confidence in paleoclimate reconstructions for the last 400 years, less confidence in reconstructions back to the year 900, and low confidence in reconstructions before that. I have yet to see a reconstruction of sufficient precision to address the question, which extends before the year 0, and those I’ve seen which go back that far are only hemispheric. So to posit RW and MC as though they were established facts seems not credible.

Statements like this one of yours, your earlier questioning whether CO2 increase is primarily anthropogenic, and some of your comments on the IPCC report, are why I suggest that you would greatly benefit from a lot more study of the literature.

I’ll maintain that without firm numbers (rather than “stabs”) there can be no serious discussion… Just telling to RTFM is not enough.

I’ll maintain that if you want a serious discussion, RTFM is what you most need to do.
Dano // October 31, 2007 at 1:55 am

I’m not referring to soil fertility, Dano. That’s 2 evasions. Is this a difficult question? /i>

na_gs, if you can’t understand that there are conditional propositions for ‘thrive’, then you are being used.

And you may want to mouseover more than one link before you choose a rhetorical tactic with me.

Conditionality and multiple factors are why I asked for the definition of ‘thrive’ and where this ‘thrive’ occurs, as it doesn’t occur in ag because of what I alluded to earlier, and it doesn’t occur in forests due to N and HOH limitations (and some O3). So that eliminates ‘most plants’.

So, I give you another opportunity to, instead of old news, you should answer in your own words if you wish to eliminate past precedent and appear credible, rather than appearing to cut-paste sans comprehension.

Second, rhetorically, if you also must hand-wave and can’t address the fact that I gave more recent research that sheds new, bright light on your old news, then you aren’t playing in a very fun way at all.

You’ll want to address why your 1000-1200ppm CO2? statement isn’t true, not distract away from the fact that you wrote something that isn’t true.

Please explain why 1000-1200ppm CO2 ‘thriving’ isn’t ‘thriving’ at all.

Thank you in advance for not straying off topic.

Best,

D
luminous beauty // October 31, 2007 at 1:59 am

Leif,

Paleoclimate is roughly definable as that which precedes the instrumental record. That would include RW and MC.

Just about everything before the 20th century that can be resolved on a global scale.
Dano // October 31, 2007 at 2:33 am

Preview good.

I can’t always see when I haven’t closed a tag, esp. after a Bushmill’s after a loooong day.

Best,

D
Leif Svalgaard // October 31, 2007 at 2:48 am

“I’ll maintain that if you want a serious discussion, RTFM is what you most need to do.”

When I do, I see things like this:

Science 29 November 1996:
Vol. 274. no. 5292, pp. 1503 - 1508
DOI: 10.1126/science.274.5292.1503

The Little Ice Age and Medieval Warm Period in the Sargasso Sea

Lloyd D. Keigwin

Sea surface temperature (SST), salinity, and flux of terrigenous material oscillated on millennial time scales in the Pleistocene North Atlantic, but there are few records of Holocene variability. Because of high rates of sediment accumulation, Holocene oscillations are well documented in the northern Sargasso Sea. Results from a radiocarbon-dated box core show that SST was ~1°C cooler than today, 400 years ago (the Little Ice Age) and 1700 years ago, and ~1°C warmer than today 1000 years ago (the Medieval Warm Period). Thus, at least some of the warming since the Little Ice Age appears to be part of a natural oscillation.

The range here is 2 degrees. It seems that one can cherry pick one’s numbers from the immense amount of work out there. You see, I’m here to learn, but the signals I get don’t match.

My good friend [the late] Gerard Bond [http://lasp.colorado.edu/sorce/news/sns/2003/sns_dec_2003.pdf] looked at sediments deposited on the ocean floor by the melting of icebergs from eastern Canada. He found that a cycle of warming climates released the icebergs every 1000-1500 years or so, leading to a periodic cooling of the ocean by several degrees. He could follow these events 100,000 years back [published in Nature, 1993].

Now, the standard argument against stuff like this is that the cycles were just regional, etc., and I don’t know how valid that is. It may be that climate changes e.g. in the polar regions are large, but when averaged over the whole globe they diminish by an order of magnitude. So maybe what is important is just the relative size of the numbers.

Your numbers:
MW [+0.2, 0, 0]
LIA [-0.2, -0.2, 0]
CW [+0.1, -0.1, +0.8]
ascribe significant effect to solar forcing and that is something I do not think is justified. You can, however, find many papers in the literature that claim a significantly large solar effect, but just toting up papers on both sides of the argument and comparing the number of papers found is not fruitful.

If you move the solar part for the LIA over in the “natural causes” column you are getting close to my view that there are significant natural variation.
Leif Svalgaard // October 31, 2007 at 3:35 am

with the solar forcing = 0, your table looks like this:
MW [0, +0.2, 0]
LIA [0, -0.4, 0]
CW [0, 0, +0.8]

so the natural causes [NC] for LIA seem to be half of human causes [HC] for CW, What is the basis for saying that NC for CW is zero? since we don’t know what NC are nor model NC, how can we say that there are no NC for CW?
Leif Svalgaard // October 31, 2007 at 3:48 am

I have a small confession to make. I have an ulterior motive for beating this dead horse, namely that I’m giving a paper in the ‘Global Climate Change’ session at the Fall meeting in December of the American Geophysical Union:

GC31B-0351: (No?) Century-scale Secular Variation in HMF, EUV, or TSI, Leif Svalgaard.

Since it is almost dogma that (”of course”) the sun influences the climate, it is hard to get people to listen when you say that the sun does not vary on longer timescales so this blog here is a good training exercise for me on how to deal with a hostile crowd :-)
ks // October 31, 2007 at 4:29 am

“since we don’t know what NC are nor model NC, how can we say that there are no NC for CW?”

you should probably read the IPCC AR4 before prematurerly jumping to this conclusion. figure 22 of the Technical Summary (page 61 of the report) consists of a comparison of observed changes to modeled anthropogenic and natural forcings. You should probably also look at FAQ 9.2 (page 702) “Can the warming of the 20th century be explained by natural variability?” I’ll go one step further and recommend the full chapter 9, “Understanding and Attributing Climate Change” with the relevant section “Understanding Pre-Industrial Climate Change”

My own advice would be to not claim something has not been done in another field without first looking to see if that is indeed true.
nanny_govt_sucks // October 31, 2007 at 4:38 am

na_gs, if you can’t understand that there are conditional propositions for ‘thrive’, then you are being used.

Is this something about the definition of “is”?

It’s not a complicated question, Dano. It seems that optimal CO2 concentrations for plants are somehwere above 1000ppm, yet we don’t see concentrations that high in the ice cores record. Why do you think that is?
Hank Roberts // October 31, 2007 at 7:16 am

Because it requires excesses of nitrogen and minerals, beyond what’s available in natural environments. Because nature doesn’t do ‘optimal’ —

“optimization requires processes that are more complex than those needed to merely satisfice” [satisfying the minimum requirements]
wordnet.princeton.edu/perl/webwn

Success in nature is measured by fitness, loosely defined as number of grandchildren. Success in gardening is defined as maximum yield with all necessary effort to supplement everything to achieve that, far beyond what a plant’s got to do to get viable seed into the next generation.
Dano // October 31, 2007 at 12:02 pm

It seems that optimal CO2 concentrations for plants are somehwere above 1000ppm,

na_gs, recent findings dispute this statement, despite your concerted attempts to ignore this fact. You can’t hand-wave away from this.

Thank you for playing, but I’m bored with the level of argumentation presented.

Best,

D
nanny_govt_sucks // October 31, 2007 at 4:45 pm

Dano, the recent findings you pointed to included study of soil fertility limitations to growth, and the introduction of ozone which is “toxic to plants”. I’m sorry, but this is not what I am referring to. I am specifically talking about optimal CO2 concentrations for plants. But I’m sure you know that.
tamino // October 31, 2007 at 5:15 pm

Leif:

It looks like you’re going to try to sell no-solar-variation to the AGU climate science community. It won’t be easy, but it may not be as hard as you expect. Here’s my advice, for what it’s worth, take it with a grain of salt.

Be cautious making statements outside your field. Frankly, you have made some statements here that would be very embarrassing.

It helps to be familiar with the IPCC AR4. For an audience of climate scientists, this is the conservative concensus. And don’t be too critical of it; a lot of your audience will be the people who wrote it. But don’t worry too much about learning the whole field of climate change; you’re there to talk about the sun.

Regarding climate of the last two thousand years, it may be to your advantage that the estimated global temperature changes are actually quite small by comparison to modern temperature change. Yes, there are lots of studies showing things like swings of several degrees in SST in the Sargasso Sea, but SST isn’t global surface temperature and the Sargasso Sea isn’t the globe. When it comes to explaining global temperature variations over the last few millenia, the concensus view is there really isn’t much to explain.

But what little does exist, seems to need some explanation. I think simply calling it natural variation will be a hard sell. Pure internal variability looks like a stationary process, small at that, and seems to be able to bring about significant local variations with little affect on global temperature. The audience will want to understand things like MWP and LIA, however small they may be thought to be, in terms of physically explicable changes to the planetary energy balance (solar, volcanic activity, albedo changes, land use, greenhouse gases, etc.). Solar is an appealing hypothesis because it obviously impacts energy balance, and its effect is global.

You may well be asked why, if the sun isn’t a factor, do solar reconstructions correlate reasonably with estimated climate changes. Lots of people think the LIA is at least partly due to reduced solar activity, and the coincidence with the Maunder minimum may be brought up. But the LIA appears to start before the sunspot record begins, and I have the impression that solar reconstructions before the telescope era are mainly based on abundances of cosmogenic isotopes (I’ll bet you know a lot more about it than I do). That has always struck me as sketchy evidence. As I understand it, cosmogenesis is a proxy for the interplanetary magnetic field, which itself is a proxy for solar output, so we’re dealing with a “proxy of a proxy” and you could emphasize its uncertainties. For estimates from the telescopic era, the Lean reconstruction is very popular, be prepared to address the question why it should not be relied upon.

A very big source of skepticism in your audience will be the 20th century. Computer models do an excellent job reproducing 20th-century temperature change, and they include solar variations to do so. Again, you could emphasize uncertainties in some of the other factors (without disparaging them). And don’t forget that you don’t have to explain any discrepancies; give them good cause to doubt solar variations, they’ll go looking for an explanation themselves.

Play to your strength. You’re a solar physicist, they are not — this is AGU, not AAS. Focus on the sun and your evidence that its variability is negligible; don’t worry too much about explaining climate, that’s their job.

Finally, don’t assume they’ll be hostile. They’re not solar physicists, and AGU is not the blogosphere. The solar advocates who arouse suspicion among climate scientists are trying to establish more solar influence on climate, and you seem to be moving in the other direction.

For the love of God, don’t breathe a word about your belief that global warming will be good for us unless you want to ignite a firestorm.
Dennis Wingo // October 31, 2007 at 6:47 pm

Tamino

For CO2 these feedbacks are well quantified. They are identified in Loudon’s “The Quantum Theory of Light” page 83-104.

Guess what, you need the QM equations to get the exact value of the CO2 feedback.

[Response: I think you misunderstand completely. I also get the distinct impression you're trying to insist that quantum mechanics is essential to any quantitative treatment of its greenhouse-gas effect, and I disagree.

CO2 feedback refers to the fact that temperature increase can trigger processes which release more CO2 into the atmosphere. This includes reduced solubility of CO2 in ocean water, melting of permafrost, and wasting of ice sheets. I seriously doubt these are identified in Loudon's "Quantum Theory of Light."]
Dano // October 31, 2007 at 6:57 pm

I am specifically talking about optimal CO2 concentrations for plants.

The references you provided to back your assertion were outdated, BTW. I provided updated findings which refuted your assertions, as I have the previous 47 times we’ve been thru this (albeit not at this site).

Now I grow bored at the same tactics as the last 47 times, as I’ve corrected the incorrect assertion yet again & move on.

Best,

D
Eli Rabett // October 31, 2007 at 7:20 pm

It’s not dogma that the sun varies on a centuries time scale, it’s what the solar physicists, et al. have been saying since the year dot. So if we are going to assign responsibility for this, it does not rest with the climate science community but with the guys and girls in the solar physics community (SPC). That being said, the most recent “dogma” pronouncements from the SPC decreases the amount of variation and this is reflected in the AR4. Still zero is the bottom of the range.
nanny_govt_sucks // October 31, 2007 at 8:18 pm

Dano, as I pointed out in my previous post, your links were referring to different subjects.
Hank Roberts // October 31, 2007 at 10:25 pm

Nan, you’re talking about gardening — optimization, by intelligently designing the conditions for maximum yield of just the one plant of interest. Right?

If so, no argument, people can do that.

Nature doesn’t. Any argument there?
Dennis Wingo // October 31, 2007 at 11:08 pm

CO2 feedback refers to the fact that temperature increase can trigger processes which release more CO2 into the atmosphere. This includes reduced solubility of CO2 in ocean water, melting of permafrost, and wasting of ice sheets. I seriously doubt these are identified in Loudon’s “Quantum Theory of Light.”]

I see. What is in Loudon is the qualitative effect on absorption and emission of infrared energy from increased CO2 concentrations. I would appreciate if you could point me toward any treatment of this subject that is better than what is at realclimate.
Hank Roberts // October 31, 2007 at 11:42 pm

Dennis, feedback is going to change amounts of CO2, water vapor, and stratospheric chemistry.

When you ask for an answer that’s “qualitative” you’re asking for the kind of information that is used to explain in simple terms, but that comes _after_ the math is done or else it’s just speculation.
George // November 1, 2007 at 5:47 pm

Leif Svalgaard said:

“solar output whether in terms of TSI, magnetic field, and EUV does not seem to have changed significantly in the last 400 years, so we should not attribute the LIA to the sun (however convenient it might be).’

‘The solar output during the Maunder Minimum was what it is right now, today.’ Both for TSI and for the magnetic field.’”

I am curious about those statements.

First, specifically, what does “significantly” mean? (To within what fraction of a percent?)

It seems that while a very small upward trend in TSI (eg. 0.05%) might not be climatologically significant if it occurred for just a single decade (ie, if the total change were just 0.05%), it would nonetheless be climatologically significant if it continued for something on the order of a century or more (ie, if the overall change were 0.5%, for example)

and directly related to #1)

2) Can one be confident that TSI has remained constant to within 0.5% over the last several centuries?

If so, what is the basis for such confidence?
Leif Svalgaard // November 3, 2007 at 2:30 am

George: There are five lines of evidence forming the argument that the sun has not been any dimmer in the past. And by ’past’ I mean ’recent past’ [thousands, not billions of years - when the Earth was formed, the sun was 25% dimmer; it has slowly increased in brightness and will continue to do so over billions of years].
Line 1;
The Total solar Irradiance (TSI) does have several sources. The first and most important is simply the temperature in the photosphere. The hotter the sun, the higher the TSI. Some spectral lines are VERY sensitive to even minute changes in temperature. Livingston et al. has very carefully measured the line depth of such temperature-sensitive lines over more than 30 years spanning three solar cycles [Sun-as-a-Star Spectrum Variations 1974-2006, W. Livingston, L. Wallace, O. R. White, M. S. Giampapa, The Astrophysical Journal, Volume 657, Issue 2, pp. 1137-1149, 2007, DOI; 10.1086/511127]. They report [and I apologize for the somewhat technical turn my argument is taking, but if you really want to know, there is no avoiding this], “that both Ca II K and C I 5380A intensities are constant, indicating that the basal quiet atmosphere is unaffected by cycle magnetism within our observational error. A lower limit to the Ca II K central intensity atmosphere is 0.040. This possibly represents conditions as they were during the Maunder Minimum [their words, remember]. Within our capability to measure it using the C I 5380A line the global (Full Disk) and basal (Center Disk) photospheric temperature is constant over the activity cycles 21, 22, and 23″. I have known Bill Livingston [and White] for over 35 years and he is a very careful and compe

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