By Roy W. Spencer, Ph. D., October 11th, 2009
It is claimed by the IPCC that there are ‘fingerprints’ associated with global warming which can be tied to humanity’s greenhouse gas emissions, as if the signatures were somehow unique like real fingerprints.
But I have never been convinced that there is ANY fingerprint of anthropogenic warming. And the reason is that any sufficiently strong radiative warming influence – for instance, a small (even unmeasurable) decrease in cloud cover letting in slightly more sunlight starting back in the late 1970’s or 1980’s– would have had the same effect.
The intent of the following figure from Chapter 9 in the latest (AR4) version IPCC report is to convince the reader that greenhouse gas emissions have been tested against all other sources of warming, and that GHGs are the only agent that can cause substantial warming. (The snarky reference to “proof” is my addition.)
But all the figure demonstrates is that the warming influence of GHGs is stronger than that from a couple of other known external forcing mechanisms, specifically a very small increase in the sun’s output, and a change in ozone. It says absolutely nothing about the possibility that warming might have been simply part of a natural, internal fluctuation (cycle, if you wish) in the climate system.
For instance, the famous “hot spot” seen in the figure has become a hot topic in recent years since at least two satellite temperature datasets (including our UAH dataset), and most radiosonde data analyses suggest the tropical hotspot does not exist. Some have claimed that this somehow invalidates the hypothesis that anthropogenic greenhouse gas emissions are responsible for global warming.
But the hotspot is not a unique signature of manmade greenhouse gases. It simply reflects anomalous heating of the troposphere — no matter what its source. Anomalous heating gets spread throughout the depth of the troposphere by convection, and greater temperature rise in the upper troposphere than in the lower troposphere is because of latent heat release (rainfall formation) there.
For instance, a natural decrease in cloud cover would have had the same effect. It would lead to increased solar warming of the ocean, followed by warming and humidifying of the global atmosphere and an acceleration of the hydrologic cycle.
Thus, while possibly significant from the standpoint of indicating problems with feedbacks in climate models, the lack of a hotspot no more disproves manmade global warming than the existence of the hotspot would have proved manmade global warming. At most, it would be evidence that the warming influence of increasing GHGs in the models has been exaggerated, probably due to exaggerated positive feedback from water vapor.
The same is true of the supposed fingerprint of greater warming over land than over the ocean, of which there is some observational evidence. But this would also be caused by a slight decrease in cloud cover…even if that decrease only occurred over the ocean (Compo, G.P., and P. D. Sardeshmukh, 2009).
What you find in the AR4 report is artfully constructed prose about how patterns of warming are “consistent with” that expected from manmade greenhouse gases. But “consistent with” is not “proof of”.
The AR4 authors are careful to refer to “natural external factors” that have been ruled out as potential causes, like those seen in the above figure. I can only assume this is was deliberate attempt to cover themselves just in case most warming eventually gets traced to natural internal changes in the climate system, rather than to that exceedingly scarce atmospheric constituent that is necessary for life of Earth – carbon dioxide.
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Paul Vaughn (17:56:11):
Thank you for the precis of Barkin’s work. I must confess that its relationship to analysis of climate variations escapes me at the moment, unless you’re thinking of n-order effects of geomagnetism upon the solar wind etc.
I’m also acquainted with different jargon in different disciplines. The deliberate reliance of AGWers upon the inapplicable runaway instability of positive feedback, however, goes well beyond the scientific pale. It reminds me of the Queen in “Alice in Wonderland” who claimed that “words mean what I want them to mean.”
Pamela Gray:
In their singular preoccupation with the radiative effects trace gases, they don’t seem to want to understand the life-history and the multiple true effects of the major greenhouse gas. Earth is not a black body.
John S.: I don’t think the problem is the scientists lack of understanding of some aspects of system theory but is instead your lack of understanding of some aspects of climate science.
True, although this is really just a transfer of energy from the surface to further up in the troposphere where the water condenses and releases latent heat. At the end of the day, what matters is how much energy is transferred out of the earth-atmosphere system into space and this can only happen by radiation. That said, the fact that the mid- and upper-troposphere is expected to warm more than the surface does introduce a negative feedback called the “lapse rate feedback” (because to restore radiative balance, what is important is the rise in temperature in the upper troposphere and because that area is expected to warm more than the surface, the surface doesn’t have to warm as much as the upper troposphere in order to restore radiative balance). This negative feedback is included in all of the climate models…and, in fact, because much of the same convective physics controls it and the water vapor feedback, the sum of these two feedbacks tends to vary less from model to model than the strength of each of these feedbacks individually.
I’m confused. In what way do you think that the scientists don’t recognize the limits imposed by saturation? They understand this very well.
Now you are getting into the cloud feedback issue, which is quite complex. As both the amount of water vapor increases and the temperature (and hence the saturation vapor pressure) increases, it is not entirely clear from first principles what clouds will do. You are correct that increases in clouds tend to reduce insolation although they also reduce the transfer of of infrared radiation to space. (I suppose that they might block some of the infrared radiation coming at them from above as you suggest, although there will be less of this because of the decrease in temperature with height.) In general, low clouds block more energy from the sun than they reduce infrared radiation from leaving the earth whereas high clouds block less energy from the sun than the amount by which they decrease infrared radiation leaving the earth.
I don’t actually hear very many cries of “runaway greenhouse”. It can occur in theory (with Venus as a likely example) but in practice it is not the regime we are likely to be in. Tipping points are a different story and involve issues of nonlinear dynamics and hysteresis. For example, the process of building up land ice sheets and breaking apart land ice sheets is not reversible because the ice sheets don’t just decrease by melting but can break up and disintegrate or slide into the sea. There are also possible tipping points involving ocean currents and the release of stores of carbon into the atmosphere (e.g., due to melting permafrost).
I don’t think this is really correct. There are in fact lots of cases in nature of positive feedbacks that lead to instabilities. Pretty much whenever you see an interesting pattern such as a snowflake, sand dunes, a “washboard” effect on a dirt road, or the stripes on a zebra, what you are seeing is the result of a linear instability leading to pattern formation. (Of course, nonlinear terms come in and eventually restabilize the system so it doesn’t run off forever. Even Venus did not rise to infinite temperature!) Here is a rather famous review article on the subject within the field of crystal growth from the physics literature, circa 1980: http://prola.aps.org/abstract/RMP/v52/i1/p1_1
Anyway, this is pretty much irrelevant for the question of current climate change because we are not talking about instabilities. As I noted, in what is apparently the system theory lingo, the net feedbacks in the climate system are expected to be negative when the radiative feedback described by the Steffan-Boltzmann Equation is included in the sum of feedbacks (and, indeed, it is very much a feedback on the original radiative perturbation). However, the net feedbacks excluding the radiative feedback due to the S-B Equation can be positive, which means that the temperature change due to a change in CO2 can be larger than that predicted solely by applying the S-B Equation to the radiative effect of the change in CO2 alone.
In fact, I don’t think you have shown any evidence that climate scientists do not understand their system because they don’t understand system theory.
Joel (13:54:33)
What a load of dissemblimg *ollocks.
” it is not entirely clear from first principles what clouds will do”
It is entirely clear when you look at ITCZ Cu-Nims and consider the vertical wind-speeds within them.
Evaporation removes heat from the surface of the water very effectively due to the latent heat of vaporization, this damp air is flung 15 miles upward where it reflects incoming radiation as it radiates away its extra heat. While the reflection of incoming heat stops at sundown surface evaporation and stratospheric radiation continue into the night.
Thus logic and observation of those living in the tropics confirm that Cu-Nims have an important cooling effect, and hence strong negative feedback. That this is an inconvenient truth to alarmists, like the MWP, does not entitle it to be ignored for their convenience.
“In fact, I don’t think you have shown any evidence that climate scientists do not understand their system because they don’t understand system theory.”
The evidence that the modellers have no idea is in the fact that their predictions fail. That they cannot model the effects of Cu-Nims so they ignore them shows they don’t actually take science seriously.
I don’t understand how anyone claiming to be a scientist can support these charlatans.
Sandy says:
From “Global Warming: The Hard Science” by L.D. Danny Harvey (2000):
So, while I commend you guys for your intuition on this, it is always good to be sure that you are not re-inventing the wheel. These effects are understood and are included in the models. While there may be some technical arguments to be made about how well they are parametrized, to claim that they are not included is simply incorrect. (Note also that since the parametrization of this convection tends to influence both the positive water vapor feedback and the negative lapse rate feedback in the same way, the differences that the models with the different parametrizations have in the individual feedbacks tends to be larger than the differences in the sum of the feedbacks, since models with a larger positive water vapor feedback also tend to have a larger negative lapse rate feedback and vice versa.)
By the way, the irony in all this, as I have noted before, is that those people who are arguing that “the hot spot doesn’t exist” in the tropical troposphere are essentially arguing against the negative lapse rate feedback that Sandy was describing.
Joel Shore (13:54:33):
Nothing you present is news to me. It might be news, however, to nature itself. In a nutshell, “climate scientists” confuse the a-term with the b-term in the demo DE I presented, thereby jacking up the response effects of what are really minor changes in the a-term. The treatment of cloud effects in GCMs is far from realistic, as field measurements amply show. Don’t have time for a treatise. Cheers!
Joel Shore (07:13:11) :
Richard says: “The fact is all the models come up with what should be a hotspot over the tropics between 30 N and S and at a height of 10 km (figure 9.1 f ), which is not there.
The IPCC admits that observations show more warming at the surface than in the troposphere in stark contrast to the models and says that a possible reason is an error or errors common to all models.
I would tend to agree with this explanation and think that the simplest explanation would be feedback mechanisms that work against warming”.
..So, explain to me this:
.. Given that the most direct effect of there being no “hotspot” is that the models have a negative feedback, the lapse rate feedback, that is not justified if no hotspot exists, why do you think the lack of a hotspot means the feedbacks are more strongly-negative?
Joel Shore I am an engineer, not a climate scientist, I cant be bothered trying to explain why exactly the hot spot is not there. I am pointing out that the models show it and the observations show it is not there. The theory says it should be. The theory is wrong here and in many places. There are more things in the atmosphere and on earth than are thought up by you or the IPCC. That is what I am trying to get you to understand.
The lapse rate is not the only negative feedback one can think of. If warming causes more water vapour, it is conceivable that more water vapour can cause more clouds. More low clouds can be a negative feedback. There are somethings that keep our climate stable within certain bounds and it fluctuates naturally between those limits. So far we are within those limits.
Find out the facts and then theorise why this is so. Do not try and fit the facts into the hypothesis.
CO2 may cause a slight additional warming to any natural warming taking place. But CO2 is not a driver of our climate, just an impotent follower of the natural processes. It has consistently failed to stop the earth cooling when it has cooled repeatedly during the ice ages and the cool periods in between, like the little ice age.
Why cant you understand these simple things?
OMG…. Are you guys STILL going at it????? My God! It’s been TWO WEEKS!!!!
Oh well, as long as you’re having fun, carry on! 🙂
Richard says:
If you are expecting there to never be any puzzles or disagreement between theory and data then you are asking way too much because no theory and no observational data set are ever without their problems. The fact is that historically there was initially major disagreement between the satellite data and the models and over time, both as errors in the data were found and the data set became larger, the disagreements essentially all disappeared…resolved in favor of the models.
The only one that still possibly remains is the “hotspot” (tropical tropospheric amplification) in the tropics and even here it is not clear if the disagreement is statistically significant once the spread in the models and the errors, including possible systematic errors, in at least some of the observational satellite and radiosonde data sets are accounted for. And, as I have noted, the fact that the tropical tropospheric amplification clearly does occur for the temperature fluctuations on the order of several months to a few years time scale considerably limits the possibilities for how the models could be incorrect. In fact, I have yet to hear of a coherent conjecture of what could be wrong that could be fixed so as not to mess up the agreement with models at those timescales while curing the supposed problem at the multidecadal timescales.
Well, many things are “conceivable”. But, there has been no convincing evidence for such a feedback. And, contrary to your claims, those people who study paleoclimate do not conclude that the climate is too stable relative to what the models suggest but rather, if anything, somewhat the opposite: “that the climate system is very sensitive to small perturbations and that the climate sensitivity may be even higher than suggested by models” ( http://www.sciencemag.org/cgi/content/summary/sci;306/5697/821 )
Over the timescales of hundreds of millions of years to billions of years, there may be some need to explain why our climate has remained within certain bounds (e.g., the Faint Young Sun Paradox http://en.wikipedia.org/wiki/Faint_young_Sun_paradox ). However, on these timescales there are likely to be geochemical feedbacks involving greenhouse gases that can explain this…and in fact are likely needed to explain how the earth recovered from a snowball or slushball earth scenario ( http://en.wikipedia.org/wiki/Snowball_earth ).
Our current understanding of climate and the role of CO2 and other greenhouse gases in affecting it did not come about because of some massive collusion of scientists. It came about because it best explains the facts and data…and, in fact, despite the fact that there was a lot of resistance to various aspects of it for quite some time. (For example, there were questions about whether the CO2 from burning fossil fuels would actually accumulate in the atmosphere and questions regarding how increases in CO2 would translate into increases in radiative forcing.) The theory had to win over many skeptics, in the true sense of the word over the last century or so…and, unfortunately, many of the arguments today made against it relate to scientific issues that were settled decades ago.
Perhaps for the same reason that most scientists in the field can’t – because most of the available evidence does not support them.
Joel Shore (18:41:56) : no theory and no observational data set are ever without their problems.
The AGW has much more than its fair share of its “problems” to be classed as a theory and hence cannot be looked upon as the gospel truth – in fact far from it.
Joel Shore: The only one that still possibly remains is the “hotspot” (tropical tropospheric amplification) in the tropics
Thats not the only one that “possibly remains. Others are Global temperatures failing to warm; Peer-reviewed studies predicting a continued lack of warming; a failed attempt to revive the discredited “Hockey Stick”; inconvenient developments and studies regarding rising CO2; the Sun; Clouds; Antarctica; the Arctic; Greenland’s ice; Mount Kilimanjaro; Causes of Hurricanes; Extreme Storms; Extinctions; Floods; Droughts; Ocean Acidification; Polar Bears; Extreme weather deaths; Frogs; lack of atmospheric dust; Malaria; the failure of oceans to warm and rise as predicted and many others.
Joel Shore: Over the timescales of hundreds of millions of years to billions of years, there may be some need to explain why our climate has remained within certain bounds
I am not talking about Hundreds of millions or billions of years but just ,10,000 years of our present Holocene interglacial. Our present warming is nothing unusual withing this period and some so called “scientists” have attempted fraudulently to concoct evidence to refute this which makes the AGW hypothesis all the more suspect.
The Holocene Climatic Optimum (wonder why it was called optimum? which means the best or most favourable), which lasted for 4,000 years the temperatures were upto 4 C warmer near the North Pole, 6 to 9 C warmer in northern central Siberia. The Medieval Warm period was upto 1.2C warmer than today.
So not only only are we less warm today than we have been naturally in the past, but these much warmer temperatures caused the Earth no catastrophe. Today we are jumping up and down because it is alleged, by a highly suspect hypothesis, that the Earth might warm by 3C.
Joel Shore: Richard: “Why cant you understand these simple things?”
Perhaps for the same reason that most scientists in the field can’t – because most of the available evidence does not support them.
That is not true the evidence does not support the AGW hypothesis and we do not know what most scientists think about this matter.
The hypothesis needs to explain these past warming and subsequent cooling events first before it can have any credibility about its future predictions.
And the perpetrators of this fraud need to be held to account.
Bernie Madoff has been sentenced to 150 years for defrauding investors of $18 billion. The perpetrators of this fraud have defrauded the public of much more.
My post has got swallowed…