My take on Climate Change

[jmvizanko]

Ah climate change. That issue that seems to beget more than its fair share of antiscience attitude and lack of scientific understanding, right up there with evolution. What are the facts? 1. The greenhouse effect is a real, observed phenomenon that contributes to the nature of the Earth's climate. 2. Humans have artificially raised the CO2 concentration in the atmosphere by using so many fossil fuels.

That anybody denies the first fact means they might as well denounce the truth of all science. The greenhouse effect is simply a consequence of quantum mechanics, that theory that has given us everything from cell phones to computers. That anybody can observe all the millions of cars driving day in and day out in just their area of the world, and then make the claim that there is no merit behind the observations of our increasing atmospheric CO2, seems equally as ignorant. For anybody with even a basic understanding of physics and chemistry, to believe that these two facts combined can have no effect on the physical processes that make our atmosphere drive our climate must mean they actually don't have a basic understanding of either physics or chemistry.

But what are the actual effects of these two facts? There are many physical variables whose superposition drives what our climate is like. Outside of the greenhouse there is solar output, the reflectivity of sunlight off of clouds and ice, and the negative and positive feedback of plants in response to altered CO2 levels, just to name a few of many. All of these add into a wave of sorts, that varies naturally without any human interaction. But changing any one variable is not likely to be canceled out by the others, and positive feedback can even mean that the opposite happens: they make it worse.

To think that a differing greenhouse effect will not shoot the climate off into a different direction is akin to thinking that throwing a rock into a pond will not cause any waves. Sure there are already waves there, but how likely is it that all the waves from the rock will perfectly cancel each other out? Sure a meteor could hit the pond (analogous to the enormous CO2 increase if say, every supervolcano on earth blew up tomorrow). But we cant plan for such events. So why should we not want to keep the pond in the state it is, considering it has been very conducive for us living for quite some time?

Of course, for even those that understand that the science behind these ideas is valid, there remains much debate about what should be done about it. Surely reducing our use of fossil fuels and replacing them asap will help. But unless everybody dies tomorrow, or we decide to throw out our energy use altogether, the world's immense population means that these goals will not solve the problem fast enough to make a difference. The only real hope lies in being able to directly counter our CO2 output with direct sequestration, and develop energy alternatives as soon as possible. And if we get affordable sequestration methods, at the very least we will be able to cancel out our effect on CO2.

In other words, we need to be throwing as much money and research at these two technologies as possible, if we are serious in wanting to actually cure the problem. It is far enough along that only our technology can save us, and hopefully it can. You might as well not feel too bad about taking that extra long shower, because either we'll find the cure, or our children are screwed.

 

[Oberon]

The two most important things, I think, which require additional research are understanding the various feedback mechanisms involved in climate (particularly cloud dynamics) and being able to accurately and robustly document past climate (which includes not only better statistical techniques and proxies in paleoclimatology, but also a thorough accounting for the UHI in modern reconstructions). Also, as the release of emails from CRU show, there needs to be an increase in providing open access to raw data, codes, and methods used in climate study. It's pretty sad that it takes the efforts of a retired mining engineer to discover (and publish) problems in the principal component analysis of one of the most (formerly) widely cited paleoclimate reconstructions. Finally, models are just that: models. There is an over-reliance on models by the AGW proponents, particularly given widespread acknowledgement that there are important and fundamental climate mechanisms we don't understand.

 

[jmvizanko]

The two most important things, I think, which require additional research are understanding the various feedback mechanisms involved in climate (particularly cloud dynamics) and being able to accurately and robustly document past climate (which includes not only better statistical techniques and proxies in paleoclimatology, but also a thorough accounting for the UHI in modern reconstructions).

As much as it is imperative to more fully understand feedback mechanisms, I think it is still fundamentally a good assumption to assume that whatever they may be, they are not likely to perfectly cancel out our effects and keep the climate where its been for the last 10,000 years of civilization.

Also, as the release of emails from CRU show, there needs to be an increase in providing open access to raw data, codes, and methods used in climate study. It's pretty sad that it takes the efforts of a retired mining engineer to discover (and publish) problems in the principal component analysis of one of the most (formerly) widely cited paleoclimate reconstructions.

No argument there. Science has an especially beautiful component: the fact that authority can be trumped by any one person who can make a better argument.

Finally, models are just that: models. There is an over-reliance on models by the AGW proponents, particularly given widespread acknowledgement that there are important and fundamental climate mechanisms we don't understand.

All the more reason to throw more money into climate research. I think I can safely assume that whatever models are being made, they are not nearly exhaustive or complete enough.

 

[Oberon]

This is in part a reply to the above, but also an expansion of what I wrote previously.

First, my own personal stance or guesses based on the current state of research. The earth has warmed in the last century (although most expert AGW proponents believe only the period after the 1970s or so is anthropogenic warming). Virtually all experts agree that are temperature record is accurate enough to conclude that (with the exception of a tiny handful, e.g. Vincent Gray). Also, CO2 has increased thanks to human activity. There is evidence that we humans are causing the earth to warm, and evidence that this may be very dangerous to us (and other life forms and ecological systems).

As much as it is imperative to more fully understand feedback mechanisms, I think it is still fundamentally a good assumption to assume that whatever they may be, they are not likely to perfectly cancel out our effects and keep the climate where its been for the last 10,000 years of civilization.

That’s the problem. The climate has gone through some dramatic changes in the last 10,000 years, and even in the last 1000 years. The “classic” hockey stick temperature record (MBH) is no longer tenable and even the IPCC dropped it. Paleoclimatology is a difficult science (I mean, even using direct temperature readings is fraught with statistical and other methodological issues, let alone using proxies). Dendroclimatology is particularly risky, because many of the tree proxy series used are not reliable indicators of temperature. That being said, various local and global climate reconstructions have found different results, but for the most part the MWP can be seen as global and as significant. The question is whether it topped the 20th century warming. Some reconstructions suggest it did. Many do not (including Mann’s more recent reconstruction, which does show the MWP). However, going back further we have even more cycles, including the Holocene Climate Optimum, which was probably warmer than the 20th century. And, of course, we have had dips which caused damage as well, forcing settlers out of Greenland and Iceland.

Feedbacks are vital because the models are designed (in part due to the incorrect assumption of a static overall climate trend) so that manipulating certain variables will have drastic consequences. It is of course well known that the effect of CO2 alone is negligible. The models assume a positive feedback, but there have been several studies to suggest that the earth has ways for adjusting to changes in the atmosphere. After all, all of weather is primarily a result of thermodynamic principles whereby heat is moved around. If the feedbacks are negative, or at least enough feedbacks are negative (or strongly negative), then the little warming caused by greenhouse gasses is not problematic at all (at least in terms of climate change).

We definitely need more research into certain aspects of climate which are ignored (or unfunded) because they focus on areas of climate forcings unrelated to greenhouse gasses, such as GCRs. We need to better maintain and account for the sites at/in which our temperature instruments are kept (e.g. not right outside air-conditioners or above asphalt. Inquiries into shady dealings in climate science (including funding by companies trying to promote skeptical views for money) must be fair and thorough. The Muir-Russel inquiry was a travesty dwarfed only by the inquiry of M. Mann. They never talked to the critics. They didn’t look at most of the data. They specifically avoided specific topics. And Muir wasn’t even there the only time Phil Jones was interviewed! We certainly need to continue funding, and looking for alternative energies, but we also need to open up climate science. As Wegman noted long ago, too much of the top names in climatology just review each other’s papers and work to keep critical views out. So much of climate science involves other disciplines (statistics, physics, mathematics, etc). As J. R. Christy noted not long ago in a speech, climate science could benefit greatly by incorporating more experts like these, particularly those who are not only familiar with models but the problems which occur between models and reality.

Finally, science is not driven by consensus. Consensus is often great, particularly when it is based off of decades and decades of research, but the important thing is to looks at the studies. And there is no part of AGW theory that isn’t found to be problematic in some recent studies, even though so-called authors of “skeptical” papers are finding it harder and harder to be published.

All the more reason to throw more money into climate research. I think I can safely assume that whatever models are being made, they are not nearly exhaustive or complete enough.

Absolutely.

 

[Cypress]

One must not be a scientist to understand that all the cars & factories have an effect on our planet and the climate.
Best we can do is put as much money as possible into research & developement of alternative form of energie, such as sun, wind and water.

 

[Oberon]

One must not be a scientist to understand that all the cars & factories have an effect on our planet and the climate.
Best we can do is put as much money as possible into research & developement of alternative form of energie, such as sun, wind and water.

There is no doubt that increasing levels of carbon dioxide can have an effect. It may very well have a disastrous effect. However, the climate is a dynamical system with multiple feedback systems. No climate scientist thinks that the greenhouse gases we emit are what is causing the warming. Rather, those who believe that the warming is anthropogenic believe there is a positive feedback cycle which drastically raises the otherwise small increase in temperature caused by CO2.

 

[Cypress]

There is no doubt that increasing levels of carbon dioxide can have an effect. It may very well have a disastrous effect. However, the climate is a dynamical system with multiple feedback systems. No climate scientist thinks that the greenhouse gases we emit are what is causing the warming. Rather, those who believe that the warming is anthropogenic believe there is a positive feedback cycle which drastically raises the otherwise small increase in temperature caused by CO2.

Ok, then we better should do something about this positive feedback.
What ****** me off is that Africa, the continent that with the smallest contribution, faces the hardest results.

 

[Oberon]

Ok, then we better should do something about this positive feedback.
What ****** me off is that Africa, the continent that with the smallest contribution, faces the hardest results.

That's the problem. We don't know if the feedback is positive. In other words, some studies, including recent ones, provide evidence for negative feedbacks (i.e. the increased temperature from greenhouse gases is compensated for by certain climate systems). There are a number of problems in any science, especially new ones, but two of the biggest (related) problems in climate science are an over-reliance on models which we KNOW are wrong and a strong desire just to do something even though it might not help at all. Certainly, there is plenty we can and should do, such as research into alternative energies, using more nuclear power and making it safer, continue to design cars with better and better fuel efficiency, and so forth. But many solutions people throw out are drastic, terrible, and probably worthless. I would also add that too often scientists are loathe to say "we just don't know." If one looks through the massive amount of climate research, there is an enormous amount of study on the effects of human activity on the environment (probably because such studies get more funding and because they are easier). This is great, don't get me wrong, but there is so much we don't know about climate variability that isn't receiving enough attention. We know very well that climate changes. That's what it does. Yet while we have some ideas and some research, there is so much we don't know about what drives climate and what natural feedbacks are in place to regulate climate.

To pick one example that is amazing to me, very recently a good deal of research has been done on the effects of galactic cosmic rays. These are from stars that exploded however many millions of years ago from all over the place that continue to enter our atmosphere. Numerous studies suggest GCRs work as cloud "seeders," i.e. they form nuclei around which clouds are formed. This is especially true, it seems, for low-level clouds, which appear to be one of the biggest factors in increases in temperatures. In other words, exploding stars billions and millions of miles away could very well be responsible for the observed temperature rise which is usually thought to be the result of greenhouse gases.

Certainly, this theory is not uncontested. The point is, however, that before we consider plans like Kyoto, we need to know a lot more than we do. The precautionary principle is a terrible principle to go by, because while doing nothing can be bad, so can doing something. Here's my take in brief:

What we should do-

1. We should definitely continue to fund climate studies
2. However, all such studies should require that the scientists make available all of their raw data, corrected data, codes, and methods.
3. We should continue to research alternative energies and improve those we have.
4. Climate science is too close-knit of a communitiy, and needs and influx of specialists in related areas (statisticians, physicists, mathematicians, economists, etc).
5. The IPCC protocols and procedures need to be totally revamped and reviewed
6. The climate science community needs to stop hampering and excluding those who they consider "deniers" (a term which often includes even those who believe in anthropogenic global warming, like Pat Michaels, but don't believe it is as bad as many of the AGW proponents). Science is all about skepticism. Even if the skeptics are completely wrong, funding their research and publishing their papers can only improve our understanding of science and increase communication among experts.
7. Politics will always be a component in issues such as these, but those who have followed the story of the release of emails at CRU and know the background of the emails will lose all confidence is the only steps taken are the ridiculous "inquiries" at CRU and Penn state. They didn't even look at all the emails, or most of the relevant studies, nor did they even interview the critics discussed in the emails.
8. Paleoclimatologists not only need more interaction with the statistical community (although, thankfully, the situation is much better since the hockey-stick fiasco), they need to stop using proxy series that aren't reliable. If a proxy series diverges from the temperature record, it isn't reliable. Period. Even the NAS panel ruled against using certain dendro series which are still used.
9. There are temperature recording stations all over the world now, thankfully. However, as a long project by amateurs (who went out and photographed the instrument sites) showed, these are often poorly maintained and placed in areas which will bias readings. And that's just in the US. We don't know how bad the situation is in other countries.
10. Satellites are THE BEST tools for measuring global temperature, and should be given pride of place.

Some things which require increased research in climate science
1. Feedback systems, feedback systems, feedback systems. This is perhaps the most important thing we need to get right.
2. Cloud dynamics are a fundamental component in climate. We know far too little about them.
3. Thanks to CERN and the dedicated efforts by Svensmark and others, there is now a fair amount of research into GCRs, but more is needed.
4. Most temperature reconstructions correct for UHI effects using outdated research. Researchers need to continue to attempt to understand all effects of surface processes on temperature readings and do a better job of incorporating them into temperature reconstructions.
5. The PDO may play a vital role in climate regulation, and more research is needed.
7. While we have seen record highs in the last 10 years, the temperature average has remained steady. The models did not predict that. We need better models. The climate is a dynamical system and research into such systems is very new.
8. There remains important discrepencies both between satellite readings and AGW theory, and between satellite readings and surface temperatures. Although the situation is not as bad as when the NAS basically said in 2001 "we have no idea why this is" there is still a lot that needs to be resolved.

That's all I have off the top of my head for now.

 

[Terrywoodenpic]

The warming of the planet is observable.

The totality of the mechanisms causing it are not.

More money and effort go into trying to disprove it and anti propaganda, than in doing anything about it.

It would make sense to take warming as a fact... and do everything in our power to reduce man's contribution to warming effects.

 

[Oberon]

The warming of the planet is observable.

I agree. And as I think I noted earlier, this is one place where virtually all experts agreee (maybe 2 or 3 don't out of thousands).

The totality of the mechanisms causing it are not.

Again, I agree.

More money and effort go into trying to disprove it and anti propaganda, than in doing anything about it.

Here I don't agree. In actually, enormous amounts of funding goes into study human influences on climate. Scientists who research natural warming mechanisms have trouble getting any funding. Anthropogenic global warming is big business, and countries like America and the US pour far, far, far, more money into research on human activity on climate than on natural climate variability.

As for the propaganda and private funding, there is a lot of money and dis/misinformation thrown around on both sides.

It would make sense to take warming as a fact... and do everything in our power to reduce man's contribution to warming effects.

Again, I agree, but with a caveat. There are costs to actions as well as inactions. For example, it would make little sense to spend trillions of dollars and cause massive problems in third world countries just if the expected benefit of this action was, say, a .1 degree celsius decrease in the warming trend over the next century.

 

[evolved yet?]

Originally Posted by Oberon
It's pretty sad that it takes the efforts of a retired mining engineer to discover (and publish) problems in the principal component analysis of one of the most (formerly) widely cited paleoclimate reconstructions.

Look at this:
climategate scientist cleared of misconduct They were cleared because they did not fudge the data..

 

[evolved yet?]

That’s the problem. The climate has gone through some dramatic changes in the last 10,000 years, and even in the last 1000 years. The “classic” hockey stick temperature record (MBH) is no longer tenable and even the IPCC dropped it. Paleoclimatology is a difficult science (I mean, even using direct temperature readings is fraught with statistical and other methodological issues, let alone using proxies).

Actually the graph still stands Hockey stick controversy

See the medieval warm period on the graph? It's way below current temperatures...

 

[Oberon]

Look at this:
climategate scientist cleared of misconduct They were cleared because they did not fudge the data..

First, the publications by MM in the peer-reviewed literature don't have anything to do with fudged data. They have to do with problems in Mann's methodology, i.e. his use of non-reliable proxies, failure to meet statistical significance (and using improper correlation procedures at that) and problems with his PCA algorithm.

As for the inquiries into the emails, the scientists/CRU were cleared because none of the "inquiries" actually looked at much of anything. Mann's was just a joke. The oxborough report didn't bother to look at the science. NONE of the inquiries ever bothered to speak to any of the critics or those mentioned in the emails. As for the Muir-Russel report, the one that was supposed to be the most thorough, the guy didn't even bother to show up the only time Phil Jones was interviewed. They basically just asked the CRU guys what they meant and did and went with that. That's like auditing a company by asking them to explain their financial data to you and never bothering to check it. The inquiry was so bad that they botched even the non-technical aspects. Muir Russel claimed that Jones' email to "delete all emails" didn't violate any FOIA legislature because at that point no FOI had been submitted. Only it is part of public record that David Holland sent his FOI two days before the email, at which point the emails show a flurry of activity including the "delete all emails." You'd think that, if they couldn't bother to interview the critics, couldn't bother to look through the studies other than the ones given to them by CRU, they could at least look at dates.

Actually the graph still stands

Yeah, according to Mann and wiki. Of course, not only did the Wegman panel completely criticize all of Mann's statistical procedures, even the NAS panel ruled that bristlecone series should be avoided in reconstructions, and yet they are used. Why? Because, like other series, even though they fail to correlate with the temperature record, they show the hockey-stick shape necessary for the principal component algorithm to pull out that hockey stick out of red noise. If you use other proxies, which do correlate with the temperature record, you get a different picture:

 

[evolved yet?]

The 'Hockey Stick' Graph still stands

 

[evolved yet?]

First, the publications by MM in the peer-reviewed literature don't have anything to do with fudged data. They have to do with problems in Mann's methodology, i.e. his use of non-reliable proxies, failure to meet statistical significance (and using improper correlation procedures at that) and problems with his PCA algorithm.

As for the inquiries into the emails, the scientists/CRU were cleared because none of the "inquiries" actually looked at much of anything. Mann's was just a joke. The oxborough report didn't bother to look at the science. NONE of the inquiries ever bothered to speak to any of the critics or those mentioned in the emails. As for the Muir-Russel report, the one that was supposed to be the most thorough, the guy didn't even bother to show up the only time Phil Jones was interviewed. They basically just asked the CRU guys what they meant and did and went with that. That's like auditing a company by asking them to explain their financial data to you and never bothering to check it. The inquiry was so bad that they botched even the non-technical aspects. Muir Russel claimed that Jones' email to "delete all emails" didn't violate any FOIA legislature because at that point no FOI had been submitted. Only it is part of public record that David Holland sent his FOI two days before the email, at which point the emails show a flurry of activity including the "delete all emails." You'd think that, if they couldn't bother to interview the critics, couldn't bother to look through the studies other than the ones given to them by CRU, they could at least look at dates.



Yeah, according to Mann and wiki. Of course, not only did the Wegman panel completely criticize all of Mann's statistical procedures, even the NAS panel ruled that bristlecone series should be avoided in reconstructions, and yet they are used. Why? Because, like other series, even though they fail to correlate with the temperature record, they show the hockey-stick shape necessary for the principal component algorithm to pull out that hockey stick out of red noise. If you use other proxies, which do correlate with the temperature record, you get a different picture:

Hmmm no source for your information that the hockey stick doesn't stand, wonder why...
BTW I really hope you less then live 3 metres above sea level

 

[Oberon]

The 'Hockey Stick' Graph still stands

That's great that you can throw websites at me. Unfortunately, it simply isn't true. Not even Mann's latest graph shows the same hockey-stick shape, and despite numerous attempts by a select group of researchers (all reviewing each other's papers), they can't get the hockey stick shape without bad statistics and bad proxies. The graph I posted above was from a study which used non-tree-ring proxy data. Mann did this in 2008, didn't come up with the same hockey stick (his graph showed a MWP, but below modern temps), only he used the Tiljander sendiments which everyone agreed (especially the researcher who published the proxy series) were corrupt. And without tree-rings or Tiljander proxies, Mann couldn't bring his reconstruction back before 1500.

Also, in addition to Wegman's critique of Mann's procedures and data handling, even the NAS report faulted Mann in numerous places:

A second area of criticism focuses on statistical validation and robustness. McIntyre and McKitrick (2003, 2005a,b) question the choice and application of statistical methods, notably principal component analysis; the metric used in the validation step of the reconstruction exercise; and the selection of proxies, especially the bristlecone pine data used in some of the original temperature reconstruction studies. These and other criticisms, explored briefly in the remainder of this chapter, raised concerns that led to new research and ongoing efforts to improve how surface temperature reconstructions are performed.

As part of their statistical methods, Mann et al. used a type of principal component analysis that tends to bias the shape of the reconstructions. A description of this effect is given in Chapter 9. In practice, this method, though not recommended, does not appear to unduly influence reconstructions of hemispheric mean temperature; reconstructions performed without using principal component analysis are qualitatively similar to the original curves presented by Mann et al. (Crowley and Lowery 2000, Huybers 2005, D’Arrigo et al. 2006, Hegerl et al. 2006, Wahl and Ammann in press). The more important aspect of this criticism is the issue of robustness with respect to the choice of proxies used in the reconstruction. For periods prior to the 16th century, the Mann et al. (1999) reconstruction that uses this particular principal component analysis technique is strongly dependent on data from the Great Basin region in the western United States. Such issues of robustness need to be taken into account in estimates of statistical uncertainties.

Huybers (2005) and Bürger and Cubasch (2005) raise an additional concern that must be considered carefully in future research: There are many choices to be made in the statistical analysis of proxy data, and these choices influence the conclusions. Huybers (2005) recommends that to avoid ambiguity simple averages should be used rather than principal components when estimating spatial means. Bürger and Cubasch (2005) use several dozen statistical methods to generate examples of reconstructions; these reconstructions differ substantially even though they are based on the same data. Many of these issues can be decided by using the validation data to select among competing models and focusing on the prediction intervals associated with a reconstruction (see Chapter 9). When the prediction intervals are taken into account, the differences among competing reconstructions may be deemed small relative to the large uncertainty of each individual estimate.

Regarding metrics used in the validation step in the reconstruction exercise, two issues have been raised (McIntyre and McKitrick 2003, 2005a,b). One is that the choice of “significance level” for the reduction of error (RE) validation statistic is not appropriate. The other is that different statistics, specifically the coefficient of efficiency (CE) and the squared correlation (r 2 ), should have been used (the various validation statistics are discussed in Chapter 9). Some of these criticisms are more relevant than others, but taken together, they are an important aspect of a more general finding of this committee, which is that uncertainties of the published reconstructions have been underestimated.

Committee on Surface Temperature Reconstructions for the Last 2,000 Years. Surface Temperature Reconstructions for the Last 2,000 Years.
Washington, DC, USA: National Academies Press, 2006. pp. 112-113.

 

[evolved yet?]

What is wrong with tree ring data?

 

[Oberon]

Based on the analyses presented in the original papers by Mann et al. and this newer supporting evidence, the committee finds it plausible that the Northern Hemisphere was warmer during the last few decades of the 20th century than during any comparable period over the preceding millennium. The substantial uncertainties currently present in the quantitative assessment of large-scale surface temperature changes prior to about A.D. 1600 lower our confidence in this conclusion compared to the high level of confidence we place in the Little Ice Age cooling and 20th century warming. Even less confidence can be placed in the original conclusions by Mann et al. (1999) that “the 1990s are likely the warmest decade, and 1998 the warmest year, in at least a millennium” because the uncertainties inherent in temperature reconstructions for individual years and decades are larger than those for longer time periods, and because not all of the available proxies record temperature information on such short timescales. However, the methods in use are evolving and are expected to improve.

Committee on Surface Temperature Reconstructions for the Last 2,000 Years. Surface Temperature Reconstructions for the Last 2,000 Years.
Washington, DC, USA: National Academies Press, 2006. p 115.



Prior to about 1600, information is sparser and the pattern of change is not necessarily synchronous, but periods of medieval warmth are seen in a number of diverse records, including historical information from Europe and Asia; cave deposits; marine and lake sediments; and ice cores from Greenland, Ellesmere Island, Tibet, and the equatorial Andes.

Committee on Surface Temperature Reconstructions for the Last 2,000 Years. Surface Temperature Reconstructions for the Last 2,000 Years.
Washington, DC, USA: National Academies Press, 2006. p 116.



• There are very few degrees of freedom in validations of the reconstructed temperature averaged over periods of decades and longer. The RE validation metric used by Mann et al. (1998, 1999) is a minimum requirement, but the committee questions whether any single statistic can provide a definitive indication of the uncertainty inherent in the reconstruction. Demonstrating performance for the higher-frequency component (e.g., by calculating the CE statistic) would increase confidence but still would not fully address the issue of evaluating the reconstruction’s ability to capture temperature variations on decadal-to-centennial timescales.

• Using proxies sensitive to hydrologic variables (including moisture-sensitive trees and isotopes in tropical ice cores and speleothems) to take advantage of observed correlations with surface temperature could lead to problems and should be done only if the proxy– temperature relationship has climatological justification.

• The observed discrepancy between some tree ring variables that are thought to be sensitive to temperature and the temperature changes observed in the late 20th century (Jacoby and D’Arrigo 1995, Briffa et al. 1998) reduces confidence that the correlation between these proxies and temperature has been consistent over time. Future work is needed to understand the cause of this “divergence,” which for now is considered unique to the 20th century and to areas north of 55°N (Cook et al. 2004).

• For tree ring chronologies, the process of removing biological trends from ringwidth data potentially obscures information on long-term changes in climate.

• Temperature reconstructions for periods before about A.D. 1600 are based on proxies from a limited number of geographic regions, and some reconstructions are not robust with respect to the removal of proxy records from individual regions (see, e.g., Wahl and Ammann in press). Because the data are so limited, different large-scale reconstructions are sometimes based on the same datasets and thus cannot be considered as completely independent.

• Reconstructions of low-frequency variations in the temperature record that make use of proxies other than tree rings (Moberg et al. 2005b) are limited by the small number of available records, by dating uncertainties, and by the sensitivity of many proxies to hydrologic variables as well as to temperature. These data gaps highlight the need for continued coordinated efforts to collect proxy data over broad geographic regions.

Committee on Surface Temperature Reconstructions for the Last 2,000 Years. Surface Temperature Reconstructions for the Last 2,000 Years.
Washington, DC, USA: National Academies Press, 2006. pp. 116-117.

 

[Oberon]

What is wrong with tree ring data?

1) Too many factors influence rings
2) Too many tree-ring proxy series don't correlate with the temperature record

"Most seriously, typical reconstructions assume that tree ring width responds linearly to temperature, but trees can respond in an inverse parabolic manner to temperature, with ring width rising with temperature to some optimal level, and then decreasing with further temperature increases (D’Arrigo et al., 2004; Kelly et al., 1994). This response is most likely due to water limitation at higher temperatures, because higher temperatures increase evaporation rates. The result of this violation of linearity is to introduce tremendous uncertainty or bias into any reconstruction, particularly for temperatures outside the calibration range. For example, tree rings in many places show recent divergence from observed warming trends, even showing downward trends (Briffa et al., 1998a,b; Pisaric et al., 2007). In a recent circumpolar satellite survey covering 1982 to 2003 (Bunn and Goetz, 2006), it was found that tundra areas showed increased photosynthetic activity, but forested areas showing a change evinced decreased photosynthesis and this effect was greater where tree density was higher. This effect probably reflects moisture limitations. If the temperature remained at the present level, over time the forest would adjust its density to come into equilibrium with available water and this decreased growth effect would dissipate. Trees may also respond more to precipitation (e.g., Gedalof et al., 2004) than to temperature, respond to seasonal temperature and moisture shifts as well as to annual means, or shift their response from temperature to precipitation at different times. If climate is reconstructed from tree ring data, therefore, the response will primarily reflect noise, with the average response being flat, which will make it look like past climates have been stable." from Loehle, 2007.

 

[evolved yet?]

(dark blue 1000-1991): P.D. Jones, K.R. Briffa, T.P. Barnett, and S.F.B. Tett (1998). , The Holocene, 8: 455-471. doi:10.1191/095968398667194956
(blue 1000-1980): M.E. Mann, R.S. Bradley, and M.K. Hughes (1999). , Geophysical Research Letters, 26(6): 759-762.
(light blue 1000-1965): Crowley and Lowery (2000). , Ambio, 29: 51-54. Modified as published in Crowley (2000). , Science, 289: 270-277. doi:10.1126/science.289.5477.270
(lightest blue 1402-1960): K.R. Briffa, T.J. Osborn, F.H. Schweingruber, I.C. Harris, P.D. Jones, S.G. Shiyatov, S.G. and E.A. Vaganov (2001). , J. Geophys. Res., 106: 2929-2941.
(light green 831-1992): J. Esper, E.R. Cook, and F.H. Schweingruber (2002). , Science, 295(5563): 2250-2253. doi:10.1126/science.1066208.
(yellow 200-1980): M.E. Mann and P.D. Jones (2003). , Geophysical Research Letters, 30(15): 1820. doi:10.1029/2003GL017814.
(orange 200-1995): P.D. Jones and M.E. Mann (2004). , Reviews of Geophysics, 42: RG2002. doi:10.1029/2003RG000143
(red-orange 1500-1980): S. Huang (2004). , Geophys. Res Lett., 31: L13205. doi:10.1029/2004GL019781
(red 1-1979): A. Moberg, D.M. Sonechkin, K. Holmgren, N.M. Datsenko and W. Karlén (2005). , Nature, 443: 613-617. doi:10.1038/nature03265
(dark red 1600-1990): J.H. Oerlemans (2005). , Science, 308: 675-677. doi:10.1126/science.1107046
(black 1856-2004): Instrumental data was jointly compiled by the w:Climatic Research Unit and the UK Meteorological Office Hadley Centre. Global Annual Average data set TaveGL2v [2] was used.

Here is the sources of those datas, if you look at these sources they don't all use tree rings.