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The debate over man made global warming has become quite politicized, so I think that it’s an appropriate topic for this forum. I’ve been very up front about my position on the global warming debate. I’m skeptical that man made CO2 emissions are causing catastrophic warming. In this posting, I’ve given a overview of my reasoning. This posting is organized into the following categories:

I. Definitions
II. Strawman Delimas
III. A Summary of the Scientific Case for Catastrophic global warming.
IV A Rebuttal of Three Scientific arguments for Catastrophic global warming.

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I. Definitions:

Alarmists: Those who believe that man made CO2 emissions are causing catastrophic warming. This term is not intended to be derogatory, but merely a descriptive term to distinguish people from those who believe that we do not need to be alarmed.

Skeptics: Those who are not convinced that man made CO2 emissions are causing catastrophic warming.

Anthropogenic Global Warming (AGW): The “anthropogenic” term means “human,” or man-made global warming. However, I consider the term to be ambiguous, since I’ve seen it used to imply that man merely has a non-zero impact on global temperatures, as well as implying that man has a dominating influence on the climate change. It also can include man made influences which are not due to CO2, such as land use, deforestation, other gases, etc…


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II. Straw Man Dilemmas: Here are two snippets that I’ve seen used as reasons to cut CO2 emissions. I thought that it would be a good idea to get these out of the way first.

Strawman #1: It’s indisputable that global warming is real and is happening now. Therefore, we need to cut CO2 emissions.

Strawman #1 Rebuttal: Most believe that there has been some warming over the past 150 years. However, this does not say anything about the cause. Many believe that the Earth cooled as it went into the Little Ice Age about 500 hundred years ago, and then started warming about 150 years ago as we came out of it. The existence of warming over the past 100-150 years does not mean that man-made CO2 emissions are causing most of it.

Strawman #2: It’s indisputable that CO2 causes global warming. Therefore, we need to cut CO2 emissions.

Strawman #2 Rebuttal: All scientists acknowledge that CO2 absorbs infrared energy, and that all other things being equal, increasing CO2 levels is likely to increase global temperatures. However, there are several other known factors which are known to affect the climate. In order to show that CO2 emissions should be lower, it would need to be proven that expected CO2 levels are causing a significant part of the climate change beyond what would be expected from natural variation.

Both of these strawman issues above often lead to the flawed and sometimes leading question: Do you believe in global warming? Often, the questioner really means: “Do you believe that man-made CO2 emissions are causing catastrophic warming?” In this case, I’d answer “no.” However, if the question is answered as it was asked, I’d have to say that “yes, there probably has been some warming over the past 150 years.” Problems occur when the questioner makes one assumption and the answerer makes another assumption about the question. For example, I’ve seen discussions where this question is answered by a skeptic who replies “no” and then the questioner ridicules the skeptic by stating something like “every respectable scientist believes in global warming”



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III. A Summary of the Scientific Case for Catastrophic global warming.

Items A, B, & C below are what I consider to be the main categories for the scientific case for catastrophic warming caused by man-made CO2 emissions. I give brief description below, and section IV will give quick rebuttals for each of these three categories.

A. Paleoclimate reconstructions which show almost 1000 years of stable temperatures followed by ~100 years of dramatic temperature increases which roughly coincide with increased levels of CO2 in our atmosphere.

B. Models which show that the recent warming could only be explained by increased levels of CO2. Natural variations have been studied, and their influence is too small to have this much impact.

C. Ice core data which shows a correlation between CO2 levels and temperatures.



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IV. A Rebuttal of Three Scientific arguments for Catastrophic global warming.

A Quick Rebuttal of Paleoclimate Reconstructions: : The most famous of these is the Mann-Bradley-Hughes (MBH) hockey stick that was used in the report from the 2001 Intergovernmental Panel on Climate Change (IPCC). One of the key problems with this study is that the hockey stick result relies on a set of data made from bristlecone pines from the western part of the United States. Additionally, this study used a non-standard statistical method which gave inappropriately large weighing to this series. Also, many of the trees that he measured were “strip barked,” where at least some of the outer bark has died, which affects growth rates. The original researcher, Don Graybill, a dendrochronologist, who collected the data for this set of bristlecone pines, stated that tree ring measurements from these pines should not be used for temperature reconstructions.

If the bristlecone pines are removed from the data set, the hockey stick shape goes away. There have been a few attempts to show that other studies with different data asset have also replicated the MBH hockey stick, such as this spaghetti graph. However, many of these reconstructions have the same bristlecone series used in MBH, which dominates their results. Other reconstructions have dominating series with other data quality issues, and some have allegedly been cherry picked to give the desired results. Even if you believe that the dominating series are valid data, I think that it’s hard to argue that these results are robust if the hockey stick shape disappears if a single data series is removed.

Michael Mann, of the original MBH articles, more recently published a hockey stick shaped reconstruction in 2008 which did not use any tree ring measurements. However, the hockey stick shape relied on a single set of lake bed sediments (Tiljander). Other non-tree data was used in the study. However, if the Tiljander sediment measurements were removed, the hockey stick goes away. Again, this is hardly a robust result if the hockey stick shape goes away if a single data series is removed. Worse still, the “foot” of the hockey stick is from a period of time in which the original data collectors said cannot be used for temperature reconstructions because sediments were contaminated by upstream dredging. WORSE STILL, the sediment density data shows strong COOLING during this period, and not warming. Mann’s publication simply used an algorithm which places a negative calibration for the sediments in order to obtain the result that he wanted. Mann has vigorously defending the calibration technique and has sharply criticized those who claim that he has used his data “up side down.” In my opinion, the critics are correct, and Mann’s defense relies on the parsing of words. I have also read that Mann has attempted so show that his 2008 results are robust, but showing that the hockey stick shape remains even when the Tiljander sediment density measurements are removed, but that his analysis actually replaces the Tiljander measurements with a data series that contains Bristlecone pine data.

Rebuttal of the other arguments will come in a followup posting.

Hey Jason,

I have to say the term "alarmist" is pejorative; it implies irrationality. A better term would be pragmatists. "Skeptics" on the other hand implies rationality and is complimentary; maybe they could be could denialists (but that would be pejorative--and it's not a word).

In any case, this debate seems to come down to who you believe. Wikipedia has a nice survey of opinions of various organizations and individuals (http://en.wikipedia.org/wiki/Scientific_...e_change). When assessing whether to believe someone or not, you have to ask a) what are their creds., and b) if they have other factors influencing their expressed opinions. I have seen a few apparently credentialed scientists opinions stating humans have insignificant impact, and many un-credentialed scientists/engineers (such as Rutan--not a climate scientist) who have expressed this as well--but no organized research. But I have seen many more, and more credentialed scientist take the opposite position. Moreover, there are many organized studies that support this.

My position is that most people agree the earth is warming, so the question is, is the man-made part of that significant? Most/all of the credible (not funded by oil, e.g.) organizations/studies seem to take no opinion or an opinion of "yes" on this question. I don't see any taking a position of "no". Therefore, given the possible consequences (accelerated melting of ice caps, more severe hurricanes, flooding, etc.) of continued increased warming, prudence would direct us to take action to curb this.

I think this topic has become a religion by some on both sides, but prudence dictates you take action to curb greenhouse emissions. I happen to be swayed by the studies, organizations and individual scientists who believe there is an impact over the individuals (I am not aware of any credible studies--just opinions of other studies) who say there is not.

Hello Refil!

Thank you for your comments. I’ve actually given a fair amount of thought into how to best refer to all sides of this argument, but I still haven’t found terms that I’m completely happy with. “Alarmists” wasn’t intended to be pejorative, but I can see how some might see it that way. I saw a special on PBS where they referred to the two sides as “scientists” and “skeptics,” which I didn’t think was quite fair, because it implies that none of the skeptics are scientists, and that no scientists are skeptics. “Denialists” is common used these days as an obviously derogatory term for skeptics. When I think of “pragmatist” in this context, I think of a third group that many refer to as “Luke Warmers,” who are people who believe that man-made CO2 emissions may be causing significant climate change, but that the most practical solution is probably just to adapt, rather than trying to severely cut back on CO2 emissions. I’ve seen the term “warmers” used, but that seems a bit ambiguous to me. It doesn’t distinguish between the luke warmers who believe that, yes, there’s warming, but it’s nothing to be too alarmed about. I’d put Bjorn Lomborg in that category. I’ll keep my ears open and continue to look for a better term than “alarmist.” “Highly Concerned Warmer” is too long

I partially agree with concept that the debate comes down to who you believe. Unfortunately, this creates a situation where we are left with situation that is defined by an appeal to authority with a tendency toward ad hominems.

Quote:When assessing whether to believe someone or not, you have to ask a) what are their creds., and b) if they have other factors influencing their expressed opinions.

I think that even those criteria are troublesome in this debate. People have argued that anyone with any connections to the petroleum industry can’t be trusted because there is the motivation of money. However, I think that the money argument goes both ways, since climate scientists are almost exclusively dependent on government grants. Additionally, there is an increasing lobby from industries that benefit from subsidies for low CO2 technologies. In the 2012 budget, there is $1 billion for “International Climate Assistance.” The president’s proposed budget for 2012 has $2.6 billion for the “U.S. Global Change Research Program’

In the end, however, I think that this not very helpful. What if the bad guy is correct? If Hitler says that one plus one is two, it’s still two.

Having said that, I do believe that there are some characteristics which can be more reliably used to judge someone’s credibility and reliability as a scientific resource. For instance, do they make their data available so that their work can be replicated, even by academic opponents? Do they have a tendency to hide data that doesn’t support their conclusions? Do they shield their work against critical scrutiny, or do they welcome it? If they don’t appear to behave ethically and within the bounds of scientific integrity, then I will tend to require a higher threshold of understanding before I will feel comfortable trusting their work.

I think that the ClimateGate emails conclusively show a lack of integrity on the part of several key climate researchers. Before this incident, however, I was aware of several instances of unethical behavior. The ClimateGate emails made some of these issues more public, and gave some behind-the-scenes input.

One article that I would highly recommend reading is Andrew Montford’s article, Caspar and the Jesus Paper.

For the previous few years, I had been keeping up in real time as these events had been unfolding. Much of the story is about the difficulties encountered by Steve McIntyre, a semi-retired mining executive with an extraordinary understanding of statistics who got involved in paleoclimate recontructions, and has now written multiple peer reviewed papers that have been published in climate journals (and served in the IPCC). Montford’s “Casper and the Jesus paper” is a little long (almost 4000 words), but gives you a good flavor for the types of things going on. Montford is professional science writer, but has an excellent grasp of the technical issues, and an extraordinary ability to summarize.

I rarely recommend books on this subject, because most tend to be slanted and are load with strawman arguments, but I highly recommend Montford’s book, The Hockey Stick Illusion: Climategate and the Corruption of Science. The Casper and the Jesus paper incident is covered in his book. Another thing that I like about Montford’s book is that he goes into sufficient scientific detail so that the reader can understand the key technical issues.

The final point that I’d like to make is that I believe that many of the critical issues in the climate change debate are understandable by mainstream technical people who aren’t necessarily climate scientists. The issue of whether a data is robust, when the trend drastically changes when a single series of tree measurements is removed is fairly understandable. Issues like the upside-down data used in the Tiljander river sediment are not the level of detail you see in a New York Times article, but are easily understandable for many people. I’m planning to add more examples in my followup posting.

Regarding biases, research funded by government grants is in a totally different category that research being funded by private industry. Let's not pretend that the pressures to have a certain outcome in those 2 scenarios would be the same. Companies can unilaterally pull the researching funding at any time if the "findings" are not to the company's liking. Government sponsored research has representatives from every side watching what happens, so no one group has control of funding, and pressuring for a particular outcome. An oil company's reason for being is to sell oil. A report saying that burning fossil fuels greatly increases global warming will negatively impact its bottom line--such research is inherently biased and cannot be taken without a large grain of salt. Government, at least in theory, is supposed to be for the benefit of the citizens, and government research is not subject to nearly as much pressure to produce a pre-determined result.

Regarding, "Climategate"...is this the one and only study on which the "alarmist" have made their argument? Like you said with your Hitler analogy, just because 1 bad actor says 1 + 1 = 2, doesn't mean it's not true. What about all the other research?

Finally, while data and analysis may be understandable by laypeople (non climate scientist), it would be more convincing to have climate scientists who have done the research say that the dangers of global warming (due to man) is over-blown and nothing to worry about. The climate scientist I have heard from are unequivocal that this is real.

Thank you for your comments.

Quote:Regarding biases, research funded by government grants is in a totally different category that research being funded by private industryLet's not pretend that the pressures to have a certain outcome in those 2 scenarios would be the same.

I might agree with that point to an extent, but that’s not the argument that I’m making. There is very little climate change research that is industry funded.

Quote:Government sponsored research has representatives from every side watching what happens, so no one group has control of funding, and pressuring for a particular outcome.

I think that this is debatable in the field of climate research. Many believe that the field is overwhelmingly dominated by advocacy for one side. Richard Lindzen, a tenured professor of atmospheric physics at MIT has stated many times that there are intense political pressures on climate scientists to conform to what he has called climate alarmism. Roy Spencer, a former NASA climate science (currently at the University of Alabama) who pioneered the use to satellites for measuring global temperatures, has stated similar sentiments.

If you included money for advocacy groups who write summaries and reports, then it would still be a very lopsided situation. I’ve read complaints that the petroleum industry has flooded the topic with money. However, some of the numbers that I’ve seen suggest that pro-global warming advocacy has a much larger pool of money than the skeptics. One organization that comes to mind which is know is have skeptical views on the subject is the Heartland Institute, which sponsors a rebuttal the IPCC reports, has a budget that is dwarfed by competing advocacy groups:

WWF..................$700 M
Greenpeace.........$300 M
Pew...................$360 M
Sierra Club............$56 M
Heartland Institute ...... $7 M

Quote:Regarding, "Climategate"...is this the one and only study on which the "alarmist" have made their argument? Like you said with your Hitler analogy, just because 1 bad actor says 1 + 1 = 2, doesn't mean it's not true. What about all the other research?

I’m not sure if I completely understand your comment about climategate.

The Climategate incident wasn’t a study. It confirmed what many believe to be unethical practices among a key group of climate scientists in the field of paleoclimatology. Among the charges against this group are manipulation of data and coordination to suppress publications by critics.

Quote:Finally, while data and analysis may be understandable by laypeople (non climate scientist), it would be more convincing to have climate scientists who have done the research say that the dangers of global warming (due to man) is over-blown and nothing to worry about. The climate scientist I have heard from are unequivocal that this is real.

There a problem in that anyone can pick and choose which climate scientist to ask in order confirm the opinion that they want. If you ask researchers like Richard Lindzen, Roy Spencer, or John Christy, then you’ll get a very different answer than if you ask researchers like Michael Mann, James Hanson, or Phil Jones.

Additionally, there are some independent researchers out there who do not get any funding for their research and publications. I mentioned Steve McIntyre in a previous posting. He does his analysis in his spare time, and doesn’t receive any government or industry funding. He did start accepting some paypal contributions on his blog. Since he began investigating statistical methods used in climate reconstructions, he has made multiple peer reviewed publications and served in the IPPC for the 2007 report. They tended to ignore his input, but he was invited to serve.

I’d like to reiterate two of my earlier points by stating that

• I think that many of us can better assess this by examining the science, rather than trying to evaluate the sources.
• I don’t think that we need to rely 100% on an argument from authority on this issue.
  

I think there have been several issues raised in which an informed personal can make a reasonable judgment call. For instance, with the key Hockey Stick Paper (Mann, Bradley, & Hughes), if the hockey stick trend goes away if a single series of trees (all from the western US) is removed, I think that most people would agree that the trend is not robust. This issue of robustness exists in every example of hockey stick shaped climate reconstruction over the past 1000 years that I am aware of. In another reconstruction (without the bristlecone pines), the hockey stick goes away if a single small series of a few trees from the Polar Urals is removed. By the way, the dendrochronologist who collected the Polar Ural tree core data has added several new trees to his collection, and the hockey stick trend went away. The climate researcher who was using this series, then began substituting another series (Yamal) in order to obtain the hockey stick shape. Steve McIntyre is the guy who uncovered these practices, and the climate scientists who published the original studies have done everything possible to prevent McIntyre from obtaining the raw data. These are the kinds of practices that make me more skeptical of their conclusions.

"I’m not sure if I completely understand your comment about climategate.

The Climategate incident wasn’t a study. It confirmed what many believe to be unethical practices among a key group of climate scientists in the field of paleoclimatology. Among the charges against this group are manipulation of data and coordination to suppress publications by critics."

I understand. I'm saying that it seems that a large part of the counter-argument hinges on climate-gate, as if it totally negates all other research.

Regarding funding of research...are there no studies funded by tax dollars only (i.e., neither by Greenpeace et al, or the oil industry)? What do they say?

"I think that many of us can better assess this by examining the science, rather than trying to evaluate the sources.
I don’t think that we need to rely 100% on an argument from authority on this issue."

To a degree this is true. However, unless you intend to go get a PhD and then do your own research, you have to decide which experts you trust. Aside from one's 1 or 2 fields of expertise in life, you have to trust the opinion of your doctor, mechanic AC repair guy, lawyer, etc. The fact is, even if we have the mental capacity to achieve expertise, we do not have the time to be expert at everything.

Regarding the picking and choosing of scientists to confirm one's opinion...one question to ask is which side has more credible scientists (and studies) from which to pick and choose? Seems there are very few credible scientist on the skeptics side (your list of 3 are the most prominent of a short list, from what I can tell).

Here is a pretty good site I came across that counters a lot of the skeptic arguments:
http://www.skepticalscience.com/Tree-rin...roblem.htm

...including much of the minutia around tree-rings, cones, etc.

Thanks once again for your contribution. I apologize for the delay in my response. My day job has a big release and had demanded much of my time lately. I hope to be more prompt in the future.

(10-07-2012 03:43 PM)refill Wrote: [ -> ]

nomoon Wrote:Nomoon: "I’m not sure if I completely understand your comment about climategate.

The Climategate incident wasn’t a study. It confirmed what many believe to be unethical practices among a key group of climate scientists in the field of paleoclimatology. Among the charges against this group are manipulation of data and coordination to suppress publications by critics."

I understand. I'm saying that it seems that a large part of the counter-argument hinges on climate-gate, as if it totally negates all other research.

I wouldn’t agree that the large part of the counter-argument hinges on climate gate. Every issue disclosed in the climate-gate emails was already known about. People who brought up these issues were ridiculed for even implying that these types of coordinated shenanigans were going on. The emails merely confirmed it. I’d say that climate-gate reduces the credibility of this particular sub-field or climate researchers, and reinforces the argument that we should try to reduce our reliance on argument from authority involving issues with involve their research. I still think that the best arguments rely on examining the science, instead of using arguments from authority.

In the big picture, climate-gate resides in area III.A (Paleoclimate Reconstructions) from my original post. The implication is, if global temperatures were hotter during the Medieval Warm Period (MWP) and possibly the Roman Warm Period (RWP), then the current temperatures are not unprecedented. It would reaffirm that natural variations in climate are larger than the models assume, and that the current temperatures are within the natural variation of climate, and that CO2 isn’t necessary to explain our current state. Disproving the hockey stick wouldn't concretely disprove catastrophic warming from CO2, but it would remove the "unprecedented warming claim" that was used as moderately strong circumstantial evidence to support it.

refill Wrote:

nomoon Wrote:"I think that many of us can better assess this by examining the science, rather than trying to evaluate the sources.
I don’t think that we need to rely 100% on an argument from authority on this issue."

To a degree this is true. However, unless you intend to go get a PhD and then do your own research, you have to decide which experts you trust. Aside from one's 1 or 2 fields of expertise in life, you have to trust the opinion of your doctor, mechanic AC repair guy, lawyer, etc. The fact is, even if we have the mental capacity to achieve expertise, we do not have the time to be expert at everything.

I don’t feel that you need a Ph.D to understand some of the key critical issues. In fact, with this particular public scientific debate, I feel that too many people assume that the issues are not understandable, and therefore, we must rely on authority.

Coincidentally, ClimateAudit has a new posting (Forensic Bioinformatics)on a situation in the field of cancer research that parallels the issue of bad science and manipulation of data. It started when two statisticians tried to replicate work published by a group of cancer researchers at Duke University. They made critical comments in journals, but instead of honestly addressing the criticism, the Duke researchers resorted to rigorously defending the work, and relied on their authority to claim that the criticisms from the non-experts where “deeply flawed” and minor. The criticisms from the statisticians had trouble getting published in mainstream medical journals because their results were “too negative.” An investigation at Duke even cleared the cancer researchers. It wasn’t until later that their story began to unravel when the main researcher’s credibility was undermined for an entirely different issue. The experience from the two statisticians is strikingly similar to the experiences of Steve McIntyre and Ross McKitrick.

refill Wrote:Seems there are very few credible scientist on the skeptics side (your list of 3 are the most prominent of a short list, from what I can tell).

A larger list of skeptical scientists can be found at this Wikipedia link. (Note that climate based Wikipedia articles are closely patrolled by global warming advocates, including William Connolley, who apparently has rewritten over 5000 climate articles. Condescension regarding skeptics can be expected at Wikipedia).

I'll make a comment on the SkepticalScience blog in a followup post.

(10-07-2012 03:43 PM)refill Wrote: [ -> ]Here is a pretty good site I came across that counters a lot of the skeptic arguments:
http://www.skepticalscience.com/Tree-rin...roblem.htm

...including much of the minutia around tree-rings, cones, etc.

In my opinion, there are lots of strawman arguments on the internet that use the simple point-counterpoint format. It frequently turns into either a strawman or false dilemma. In my opinion, SkepticalScience.com is notorious for this type of argument. The article in the link that you gave is an example that discusses the “divergence problem.” Skeptical Science presents the skeptic argument using a quote from Steve McIntyres Climate Audiit. So far, so good.

Quote:Tree-rings diverge from temperature after 1960
Actual reconstructions "diverge" from the instrumental series in the last part of 20th century. For instance, in the original hockey stick (ending 1980) the last 30-40 years of data points slightly downwards. In order to smooth those time series one needs to "pad" the series beyond the end time, and no matter what method one uses, this leads to a smoothed graph pointing downwards in the end whereas the smoothed instrumental series is pointing upwards — a divergence (Climate Audit).

SkepticalScience then gives a condescendingly labeled rebuttal, “What the science says…” The summary paragraph is in the quote below:

Quote:The divergence problem is a physical phenomenon - tree growth has slowed or declined in the last few decades, mostly in high northern latitudes. The divergence problem is unprecedented, unique to the last few decades, indicating its cause may be anthropogenic. The cause is likely to be a combination of local and global factors such as warming-induced drought and global dimming. Tree-ring proxy reconstructions are reliable before 1960, tracking closely with the instrumental record and other independent proxies.

There is no evidence that the divergence problem is “unprecedented.” There are very few temperature sets made before the 20th century, and even those have reduced accuracy, and none of those early temperature records exist near the dominant tree cores. It’s impossible to rule out pre-twentieth century divergences. If the tree cores don’t show warming in the later 20th century, how do we know that the tree cores don’t show warming that occurred earlier. Other temperature reconstructions clearly show a strong Medieval Warm Period (MWP) about 1000 years ago. These tree cores aren’t used in the hockey stick reconstructions.

I came across the Skeptical Science website years ago, and I wasn't impressed. It seemed to a collection of strawman-based one sided arguments.

"There is no evidence that the divergence problem is “unprecedented.” "

How can there be evidence that something is unprecedented? There can be evidence that there is precedence for something, but I don't see how there can be evidence that something is unprecedented.

Can you point to a time when the "divergence problem" occurred before the last few decades? I think the SS article is saying no such data exists. Your argument seems to say since we only go back so far, we should assume that there is precedence. That does not seem prudent, when the data we do have says there is no precedence.

Please identify the "straw man arguments" and "false dilemmas" you refer to.

Regarding the quality of the Skeptical Science website, it seems very well balance to me, responding to skeptical arguments on a point by point basis. If there are straw men, skeptics should identify them. The climate experts will either say why the argument is not a straw man, or concede that the point is irrelevant, or "respond" with silence.

refill Wrote:"There is no evidence that the divergence problem is “unprecedented.” "

How can there be evidence that something is unprecedented? There can be evidence that there is precedence for something, but I don't see how there can be evidence that something is unprecedented.

It sounds like we agree on that issue. It was John Cook (Skeptical Science) who claimed that the divergence problem was unprecedented.

Quote:Can you point to a time when the "divergence problem" occurred before the last few decades? I think the SS article is saying no such data exists. Your argument seems to say since we only go back so far, we should assume that there is precedence. That does not seem prudent, when the data we do have says there is no precedence.

It was Skeptical Science that declared that the divergence in the later 20 twentieth century was unprecedented. We’re supposed to accept that statement, and thus, conclude that none of the selected proxies underestimated the earlier temperatures. Skeptical Science has the burden of proof on that detail. If we don't know whether the divergence of the later 20th century was unprecedented, then the proxies can't prove the non-existence of earlier warming.

The existence of a Medieval Warm Period (MWP) would be proof of a divergence. The existence of a MWP would also contradict unprecedented warming of the 20th century. It’s not surprising that there is significant hostility towards the idea of the MWP among many global warming advocates. David Deming, a professor of Geophysics (with specialization with temperature and heat flow) who has done some work with bore hole temperatures, was contacted by a climate researcher who told him “we have to get rid of the Medieval Warm Period.” The MWP period was generally accepted to exist until the time of the first major Hockey Stick Publication (Mann, Bradley, Hughes).

Skeptical Science has its own version of the debate about the existence of the MWP. It states the skeptic position, and then lays out what I would call a non-critical and one sided argument for his positions. Evidence supporting the skeptic side is not presented or acknowledged.

This link (The Medieval Warm Period – a global phenomenon, unprecedented warming, or unprecedented data manipulation?) gives a summary of some of the evidence supporting the existence of a MWP. Some of the evidence is historical in nature (Vikings settling in a warm Greenland, vineyards in Great Britain, etc…), some from proxy measurements, and some miscellaneous (evidence of smaller glaciers, etc…). From the global warming advocate side, this type of evidence is often dismissed along the lines of this quote from Skeptical Science:

Quote:Skeptical Science:The Medieval Warm Period was not a global phenomenon. Warmer conditions were concentrated in certain regions. Some regions were even colder than during the Little Ice Age. To claim the Medieval Warm Period was warmer than today is to narrowly focus on a few regions that showed unusual warmth

Skeptical Science concludes by stating the following and including the graph below:

Quote:What is more, and as can be seen in Figure 4, globally, temperatures during the Medieval Period were less than today.

That might be convincing if you accepted this at face value and didn’t look at opposing arguments. I’ll list a few:

The graph above is proxy reconstruction with the divergence part deleted from the later 20th century, with thermometer data spliced at the end. We still don’t know whether the earlier proxy data has any hidden divergences.

The Mann et. All 2009 paper with the graph above has many problems that are discussed here: Mann 2008: the Bristlecone Addiction

Among them are the problems with a dominant proxy (the Tiljander sediments which I mentioned in an earlier post) that rely on a nonsensical negative calibration to the sediment data. Mann also uses the flawed bristlecone pines from the western US, which the US National Academy acknowledged shouldn’t be used in temperature reconstructions.

Skeptical Science makes the claim that regional temperature trends can’t be used as evidence of global trends. However, the graph from Mann 2009 is overwhelmingly dominated by the trend from the bristlecones in the western US and a single set of sediment proxies.

As the graphic in this link shows, however, there are several proxies all over the globe which reflect warming during the Medieval period.

refill Wrote:Regarding the quality of the Skeptical Science website, it seems very well balance to me, responding to skeptical arguments on a point by point basis. If there are straw men, skeptics should identify them. The climate experts will either say why the argument is not a straw man, or concede that the point is irrelevant, or "respond" with silence.

In my opinion, the Skeptical Science is not well balanced. Skeptical Science only gives the skeptical side a brief comment, and then attacks it using one-sided arguments. An argument or rebuttal from the skeptical side is not given or even acknowledged.