Of possible interest to our readers, there was an interview yesterday on the BBC (“Today Programme”) regarding the supposed controversy about the “Hockey Stick”: A climate scientist Professor Michael Mann suggests global warming is caused by mankind (mp3 file). Also available on the BBC website is the real audio file of the interview.
Re #50
Read the study carefully.
The statements:
“the study has made a mistake in assuming that Arctic warming in the mid-19th century is due to an increased greenhouse effect”
“the researchers of the “lake study” were intent on demonstrating the human contribution to warming”,
are not claims made in the study and are beyond the scope of the study.
The study states several times that the majority of observed changes in species composition did not occur at 1850, but occurred recently.
For example:
“Local topographic, morphometric, and geologic factors also influence the nature and magnitude of limnological responses to warming. For example, certain sites [e.g., some shallow ponds (12)] produce relatively low beta-diversity values, despite being situated in regions where adjacent sites have changed more markedly (Fig.2 and Table 1). This finding results from the heightened sensitivities of some shallow ponds to even small climatic changes, which record species shifts both before and after approximately anno Domini 1850, and consequently lower beta-diversity estimates (Table 1). However, only the most recent assemblage changes are ecologically consistent with warming (12), which implies that our statistical treatment provides conservative estimates of ecosystem changes attributable to warming.”
As far as the use of ice cores, when discussing independent climate proxies the study cites to another paper: 6. Overpeck, J., Hughen, K., Hardy, D., Bradley, R., Case, R., Douglas, M., Finney, B.,
Gajewski, K., Jacoby, G., Jennings, A., et al. (1997) Science 278, 1251�1256.
I have not seen this paper, so I do not know if it discusses ice cores. Are ice core useful or necessary? Again this is something that might be beyond the scope of the study.
“the researchers of the “lake study” were intent on demonstrating the human contribution to warming”,
are not claims made in the study and are beyond the scope of the study.
Fine – so why is everyone banging on about it.
However, only the most recent assemblage changes are ecologically consistent with warming (12), which implies that our statistical treatment provides conservative estimates of ecosystem changes attributable to warming.
Excellent – they’re not really claiming anything are they which is pretty much what I thought all along.
Arrrh – another error in #51 I’ve spelt ‘comparative’ wrong.
As far as the use of ice cores, when discussing independent climate proxies the study cites to another paper: 6. Overpeck, J., Hughen, K., Hardy, D., Bradley, R., Case, R., Douglas, M., Finney, B., Gajewski, K., Jacoby, G., Jennings, A., et al. …
I have not seen this paper, so I do not know if it discusses ice cores. Are ice core useful or necessary? Again this is something that might be beyond the scope of the study.
Sorry missed this bit. There are 2 slightly separate issues here.
First of all there’s climate warming which is claimed to be responsible for the ‘changes’. The study appears to have used climate proxies to show that the changes are consistent with a warmer climate. I wouldn’t think there would be much dispute about this.
The second issue is the cause of the warming. Some people (not necessarily the researchers, themselves) seem to have jumped to the conclusion that the warming is human-induced (probably due to fossil fuel burning). As you say this appears to be beyond the scope of the study. But, if they had decided investigate a possible human contribution, they could have examined ice core data. Ice cores contain traces of atmospheric gases (e.g. CO2) which were present in the atmosphere at various periods in time. It may then be possible to show a link between the warming and GHG concentrations as well as a link between the warming and the ecological changes – and conclude that humans caused the ecological changes.
I don’t believe there was sufficient additional (above pre-industrial levels) GHGs in the atmosphere to cause the early changes and possibly some of the later ones as well, so we have to assume that the changes are the result of nature.
I enjoy the interpretations of Googlers. For example: reading papers for which they have no training. An example of this is in post 50; the poster’s concluding paragraph has completely forgotten that the point of the paper (oh, yeah – that) was that there was a study of lake sediments.
Not ice cores, but lake sediments. There already is a record of ice cores. Someone can now look at a record of lake sediments in addition to the ice core record. The lake sediments may be an additional useful dataset to refer to. Maybe not.
But that’s the point – it is a new dataset. And sort of back to the original topic of this thread (oh yeah – that) this is how proxy information is developed.
A tactic of the deniers is to quibble over tiny details to sow doubt. That is a bad tactic on a site created by working scientists.
D
The Lake Study, again
Thanks Dano for your comment.
I do have some professional experience in analysis of aquatic sediments like the ones examined in this study.
The objective of this study was to examine ecosystems and document changes, if any, caused by anthropogenic climate change. To see if anthropogenic climate change has caused changes in ecosystems you must first know what the ecosystems were like before anthropogenic climate change started. To be certain of spotting changes you must find the earliest signs of warming, whether anthropogenic or not, and start the study at or before that time. The authors of this study looked at the proxy data and saw the first signs of climate change in the mid 19th century, hence the use of 1850 as the starting date.
The study can be summarized as follows. Arctic ponds and lakes have only a few types of species and are highly sensitive to change. These factors make them ideal indicators of ecosystem changes. The study examined ponds and lakes and found major changes in the types and numbers of species throughout the arctic. The changes were not biotic (caused by other plants or animals), but were caused by environmental changes. Several anthropogenic factors like pollution and land use were considered, but could not have been the cause for all the changes. The environmental factor that caused the changes in species was climate warming. The greatest changes in the ecosystems occurred when and where anthropogenic climate change was greatest. These findings led the authors of the study to conclude that these ecosystems were being affected by anthropogenic climate change. The widespread nature of these changes then led the authors to conclude that the entire arctic was being affected by anthropogenic climate change.
Like I said before read the study carefully, but this time read it carefully and slowly.
Many thanks to John and Roger (posts 45 & 46)
It will take me quite a few late nights to work my way through these links!
Colin
RE #54 Dano’s comment
This statement: “A tactic of the deniers is to quibble over tiny details to sow doubt” is a very helpful point.
I think on a website that has the goal of providing accurate science for the interested public it is absolutely necessary to point out the tactics that deniers use. If someone spots these tactics and knows that the tactics are just attempts to obfuscate the science, then they can look past these tricks and get to the facts.
Again that was an excellent comment.
Re #10. I tuned into the moral maze as well. George Monbiot did his best to calmly explain the scientific consesus. Lomberg was given far too much kudos when he was introduced, and his methodologies were not challenged enough. Melanie Phillips.. where to start? To summerize – she believes that the entire mainstream scientific community is involved in a socialist conspiricy which has invented global warming, due to a “self-loathing” of the West and capitalism. It doesn’t really matter that she spouts this guff on the Moral Maze. What is more worrying is that she writes such rubbish, unchallenged, in the commentary pages of the Daily Mail, one of the most widely read national newspapers in the UK. For more info on such “journalism” check out this article on George Monbiots website http://www.monbiot.com/archives/2004/04/27/the-fossil-fools/
The objective of this study was to examine ecosystems and document changes, if any, caused by anthropogenic climate change. To see if anthropogenic climate change has caused changes in ecosystems you must first know what the ecosystems were like before anthropogenic climate change started. To be certain of spotting changes you must find the earliest signs of warming, whether anthropogenic or not, and start the study at or before that time. The authors of this study looked at the proxy data and saw the first signs of climate change in the mid 19th century, hence the use of 1850 as the starting date.
Joseph
This is OK as it stands (I’ve now read the paper, BTW). However I think the authors have arrived at some less than clear conclusions.
You say
The objective of this study was to examine ecosystems and document changes, if any, caused by anthropogenic climate change
Fine – no problem there.
To be certain of spotting changes you must find the earliest signs of warming, whether anthropogenic or not, and start the study at or before that time.
mmmmh – right so this is any warming – natural or anthropogenic.
The authors of this study looked at the proxy data and saw the first signs of climate change in the mid 19th century, hence the use of 1850 as the starting date.
So how have they decided which warming is due to anthropogenic causes and which is not. [For the benefit of Dano – this is why I suggested the use of ice core data, i.e. to determine the levels of atmospheric CO2 at the time]
I don’t think that any mid-19th century warming can be attributed to fossil fuel burning. I also think that a number of the people who ‘run’ this web-site would probably agree with me. Gavin in Post #47 provided a somewhat diplomatic response to the issue of ghg content but he did also provide a link which shows all climate forcings since 1850. It would be reasonably easy to show that the human/CO2 effect is minute.
So if mid-19th century Arctic warming is NOT anthropogenic – why do we neccessarily think that the other warming periods discussed in the paper ARE. Could it not be the case that there is a natural cycle of warming and cooling in the Arctic. [Note that British naval records suggest warming and ice retreat in the EARLY 19th century]
The lake study, yet again
It must be a really, really big lake to get this much attention on Realclimate.
First some basic aspects of the scientific process need to be addressed. Individual studies are single steps in a step-by-step process to find factual information. For example, a study proves “A” to large degree of certainty. Taking the next step, other studies examine a smaller issue associated with “A” or what are the effects of “A”. Constant re-examination of the same issue would slow science to a standstill.
The authors of the lake study based their conclusions of what portion of climate change is anthropogenic on the results of earlier studies. That is what the footnotes are for, look at the papers cited: 1. Holland, M. M. & Bitz, C. M. (2003) Clim. Dynam. 21, 221-232; 5. Moritz, R. E., Bitz, C. M. & Steig, E. J. (2002) Science 297, 1497â-1502; 12. Douglas, M. S. V., Smol, J. P. & Blake, W., Jr. (1994) Science 266, 416-419;
13. Sorvari, S., Korhola, A. & Thompson, R. (2002) Global Change Biol. 8, 171-181; 14. Ruhland, K., Priesnitz, A. & Smol, J. P. (2003) Arct. Antarct. Alp. Res. 35, 110-123; 28. Lotter, A. F. & Bigler, C. (2000) Aquat. Sci. 62, 125-141; 34. Birks, H. J. B., Jones, V. J. & Rose, N. L. (2004) J. Paleolimnol. 31, 531-546; 47. Crutzen, P. J. (2002) Nature 415, 23. These studies could address any questions about the amount of anthropogenic climate change.
I will now try to address the specific science questions John Finn asks. First the ice cores, I questioned the ice cores because they might have been examined in the study the authors cite, and without seeing the cited study it is premature to claim they did not examine ice cores. I also brought it up because I was not sure if they were useful to the lake study. The study looked at changes on a scale of a decade or less for over 150 years, can ice cores be that specific? Are ice cores useful for measuring recent (i.e. the past fifty years) changes in greenhouse gases? Are recent ice core GHG measurements equal or superior to direct atmospheric measurements of GHG that are available for this same time span?
The second issue is British naval records. Do they cover the entire arctic? How extensive were they (i.e. yearly or more or less often and in how many areas)? How reliable or robust are they?
The third issue is the extent of anthropogenic climate change. The mid 19th century is early, but since the arctic is highly sensitive and would be among the first areas to show signs of anthropogenic climate warming (the authors use the term “polar amplification”) the late 19th century might not be too early. The recent warming is much more likely to be anthropogenic then any warming the 19th century because the concentration of anthropogenic GHG has greatly increased and therefore the forcing is much greater. According to the authors of the lake study the recent ecological changes and therefore climate changes are unprecedented in the lake sediment record. I quote the study, “Our data show that many arctic freshwater ecosystems have experienced dramatic and unidirectional regime shifts within the last _150 years. For those sites where longer paleoecological records are available, recent changes in species composition appear unprecedented in the context of the last several centuries (13, 34) or even millennia (12, 14).” This is strong evidence that the recent warming is beyond the bounds of the natural cycle of warming and cooling.
I think there is a blurring of opinion verses fact in this lake study debate. Scientific knowledge is based on data and conclusions firmly based on the data. When a large majority of scientists agree on a scientific conclusion it is usually because there is overwhelming proof supporting it. If well-supported and widely accepted scientific conclusions and facts do not agree with what someone prefers or expects this does not mean the scientific facts and conclusions are incorrect or need to be constantly re-examined. When the facts conflict with your opinion or beliefs it is time to change your opinion or beliefs.
In the climate change debate politically and economically motivated people and groups have hijacked the role of scientists and other people with legitimate scientific questions or doubts. The questioning of climate change science is now too often just an attempt to stop or delay the debate in order to prevent the enactment of climate change regulations and has no valid scientific basis. This is unfortunate because it makes the science harder to do and harder for the general public to understand, but this is probably the goal of the denialists.
Finally, there is one more point I must bring up. John Finn stated, “I don’t believe there was sufficient additional (above pre-industrial levels) GHG’s in the atmosphere to cause the early changes and possibly some of the later ones as well, so we have to assume that the changes are a result of nature”. If John Finn believes something we have to go along with his belief. I wonder if he believed I was dating a supermodel, would a supermodel have to start dating me? If that were the case it would be great, but I have some serious doubts about that being true.
If John Finn believes something we have to go along with his belief.
No you don’t. Perhaps I should have said “think” or “my opinion” rather than “believe”, as I am prepared to change my opinion if the evidence warrants it.
I did give the study the benefit of the doubt in an earlier post, but having read it, it doesn’t deserve it. It clearly links ecological changes in the Arctic with ANTHROPOGENIC warming – yet provides no evidence to back up it’s conclusions.
It’s all very well saying the study can’t do everything. Perhaps not but the AGW link is pretty central to it’s findings – which have been seized on by environmentalists and others as yet further evidence …blah blah blah.
On the ice cores – that’s just a suggestion. They may have some alternative method for measuring atmospheric greenhouse gases. If so a brief paragraph, at least, might have been appropriate.
Finally, I’m not sure it’s just my opinion that questions AGW in the mid-19th century. I’ve tried to encourage a response from the realclimate scientists – with a small degree of success. Despite how it may seem sometimes, I do actually respect their knowledge and expertise. But I suspect that they, like me, think that natural variability would have been a much larger factor than ghg increases up to 1900.
In order to and try settle this, I might email the lead author of the study. He has made his email address available, so I assume he will have no objections.
The “lake study” again and again. Considering how much time is being spent on the “lake”, maybe I’ll rent a summer cabin there.
John Finn has tipped his hand. He seems to be politically motivated, but not really interested in the science. His claim that anthropogenic global warming has been “seized on by environmentalists” is evidence of this. Many opponents of climate change science dismiss it as some crackpot environmentalist scheme. If you look at the history of environmental politics in the U.S., environmentalists usually have much more accurate scientific arguments then their opponents, and that is one of the reasons they have been successful. He probably does not like the study because it shows that anthropogenic warming is causing major ecological effects, a conclusion that could have major implications in the political aspects of the climate change debate.
John Finn did not give the lake study the benefit of the doubt. He criticized it without even reading it. He disputed claims, and still is disputing claims, not made by the study. When confronted with quotes from the study that contradict his claims he illogically twists them in a futile attempt to prove that he is right. He brought up ice cores not as a suggestion, but to insinuate that study is not valid without the use of ice cores.
If John Finn were to read the study again, read it slowly and carefully, look at the graphs charts and maps (these are not just pretty pictures) he would see firm evidence for the study’s conclusions. The starting point for the study is 1850 because that is a time before anthropogenic warming clearly occurred in the arctic and not because it is when anthropogenic warming clearly occurred. The study does not claim that anthropogenic warming occurred in the mid 19th century. The study does show that the changes in species (i.e. the relative abundance of a variety of species in an ecosystem; in this case algae, insects and crustaceans in arctic ponds and lakes) are correlated with the accepted science of when anthropogenic warming occurred. In the late 19th century when anthropogenic warming was small, changes in species was small. As anthropogenic warming increased in the early 20th century, species change increased. When the anthropogenic warming was the greatest in the late 20th century, the change in species was greatest. In localities where the warming was the greatest the species change was the greatest, and in localities where there was less warming there was less species change.
John Finn needs to look at the papers the lake study cites when it discusses anthropogenic climate change. This is where the authors of the lake study provide the evidence of anthropogenic warming. They are not just pulling some figures out of a hat. This is the basic scientific process. John Finn has asked Realclimate when anthropogenic warming started and he was told by real climate: “If you mean measurable in terms of clearly coming out of the “noise” in the observations, it appears to be relatively recently (i.e. the last couple of decades). If you mean at what point did anthropogenic CO2 start to have a warming effect, that would be in the late 19th Century – however at that point it was not particularly large compared to the other things going on (volcanoes, solar, land use etc.). – gavin”.
There is scientific consensus about anthropogenic climate warming because there is overwhelming scientific evidence from many different fields of science that support it. John Finn cannot expect the same rehashing of the same questions over and over ad nauseum because he does not like the answer. Science is moving on and John Finn should do the same.
[Response: Please keep comments focused on the science, not the motivations. If this gets more off track, I will shut down the thread. – gavin]
Joseph
I’ll happily withdraw the comment about environmentalists.
I’ll just repeat my argument one more time and allow you to explain to me where it is flawed.
The study claims some ecological changes occurred in the mid-19th century – fine. They claim that proxy data shows that the changes are due (or linked at least) to climate change – again fine. They claim that the climate change was due to human actions (i.e. anthropogenic) – now I have a problem.
The lake study
This is the last time I will be at the “lake”. It’s a nice lake and I have had some fun, but it is time to move on. I would not mind if this thread was shut down.
If I was at work my response to these questions would be “objection, asked and answered”, but I will be civil and try one more time.
First John Finn asks, “How do they know that the mid-19th century warming was human-induced.”
This is not a claim made by the authors of the study
Second John Finn asks, “If the warming which caused the mid-19th century changes was NOT human-induced – how do they know that subsequent warming and ecological changes ARE human-induced.”
What part of the warming is human-induced is based on previous studies, if the studies the authors of the lake study cite are not readily available, you can look at the answers Realclimate has provided.
In addition, the recent ecological changes, not ones in the mid-19th Century, are not like anything seen in the record. I quote the lake study: “recent changes in species composition appear unprecedented in the context of the last several centuries (13, 34) or even millennia (12, 14).” Since the recent species changes are unlike anything in the natural record, and these changes are due to warming that a scientific consensus agrees is human-induced warming, the authors come to a firm conclusion that the ecological changes are human-induced.
That is how science and the scientific studies interpret the data. These are facts and conclusions that are put through a rigorous process to make sure that they correctly explain real world processes. Scientific conclusions are based on much more than guesses or personal preferences.
I’m determined to have the last word on the “last word for now” thread.
Joseph
You seem convinced – or have convinced yourself, at any rate – that the studies cited by the ‘lake study’ and the comments by realclimate support anthropogenic warming in the mid-19th century.
You quote Gavin who says
If you mean at what point did anthropogenic CO2 start to have a warming effect, that would be in the late 19th Century – however at that point it was not particularly large compared to the other things going on (volcanoes, solar, land use etc.). – gavin
Volcanoes (does the plural have an ‘e’?) can have a pretty big effect anyway. But the implication here is that natural changes in solar forcing will be responsible for more warming (and cooling) than anything produced by the additional greenhouse gases – and this is at the END OF THE 19th CENTURY – following a period of much greater volume of CO2 emissions compared to the pre-1850 period.
In other words – as far as the mid-19th century is concerned – the gentle warming produced by the natural 11-year (approx) solar cycle maximum will dwarf any ghg warming. In fact, I doubt whether any increase in ghg concentrations could be detected as distinct from natural variability. Whatever is said in the studies that are cited isn’t going to change that.
Anyway, Joseph – nice to have had this exchange of views. No need to respond – or then I’ll have to :-)
Sorry John but I can’t resist this!
According to one book I read the plural of Volcano doesn’t have an e.
But I’m not so sure
My Ref: Quayle, D. (1992) ‘My Favorite Spellings’ 5th Edition, The White House, USA.
Hugh
I will respond one more time to end on a more positive note. At times I have been uncivil and for this I apologize. There seems to have been a misunderstanding.
John Finn does bring up some good points. Anthropogenic climate change (ACC) in the mid-19th century is something that is debatable, and a study that bases its conclusions on mid-19th century anthropogenic climate change could also be debatable. However, the â��lake studyâ�� in question, “Climate-driven regime shifts in the biological communities of arctic lakes” does not state that there has been mid 19th century anthropogenic climate change or base its conclusions on mid-19th century ACC.
The study is on the PNAS website. The link is at:
http://www.pnas.org/cgi/content/abstract/0500245102v1?ijkey=4a08e009cfa92b2b11078190eb392d7fd376f87c&keytype2=tf_ipsecsha
I never claimed that the lake study is based on mid 19th century ACC or the study claimed that there was ACC in the mid 19th century. I do admit thinking that the study claimed that there has been mid 19th century ACC or is based on mid 19th century ACC is understandable even after reading the abstract or the study itself. Scientific papers are often highly technical and very dense. Missing or misreading one sentence is easy to do, but if that is done the message that the study intends to convey can be misunderstood. The �lake study� does state that there was climate warming starting in the mid 19th century, but does not state it was ACC and its conclusions were not based on mid 19th century ACC. If the study did claim that there was noticeable mid 19th century ACC its conclusions would be weakened.
The �lake study� based some of its evidence on other studies, and if someone wanted to see what evidence the �lake study� used they should look up these studies. There are two studies that the lake study primarily refers to when mentioning ACC.
�Dynamics of recent climate change in the arctic� 5. Moritz, R. E., Bitz, C. M. & Steig, E. J. (2002) Science 297, 1497�1502
It is on the web at:
http://depts.washington.edu/isolab/papers/MoritzBitzSteig.pdf
�Arctic environmental change of the last four centuries� 6. Overpeck, J., Hughen, K., Hardy, D., Bradley, R., Case, R., Douglas, M., Finney, B., Gajewski, K., Jacoby, G., Jennings, A., et al. (1997) Science 278, 1251�1256.
This study can also be found on the web at:
http://www.geo.umass.edu/faculty/bradley/overpeck1997.pdf
The studies conclude that there was no ACC in the mid 19th century or so little ACC that it would show little noticeable effect in the mid 19th century.
Other commentators have asked Realclimate when ACC began to be noticeable and how much of climate change has been caused by natural causes verses ACC.
RC recommended this paper: Crowley, T.J., Causes of Climate Change over the Past 1000 Years, Science, 289, 270-277, 2000, on the �Senator Inhofe on Climate Change� post, comment #15.
RC also provided direct answers, but these have not said there was mid 19th century ACC.
I think the biggest impact of the study is that it concludes that ACC has already having major ecological changes. One of my main interests in climate change is the ecological effects. As far as I know, there is much talk of the potential ecological effects but little evidence for ecological effects that have already occurred or are ongoing. Could anyone at Realclimate recommend papers that discuss current ecological effects of ACC?
If John Finn wants the last word on the �Last Word�, I would happily invite him to respond. Again I apologize for being uncivil.
Folks —
Many thanks for providing this valuable resource. After readng the “dummies’ guide” and listening to the Mann BBC interview, however, I remain puzzled about a couple of aspects of the MM critique and response.
First, the Dummies’ guide (DG) argues (in point 7) that the MM critique is not really about statistical methodology but about what source data should be included, and argues for inclusion of the “bristlecone pine” dataset on the grounds that improves the fit over the 19th century validation period. The DG does not appear to address the MM argument, however, that the hockey-stick shaped result is highly sensitive to the inclusion or exclusion of this one dataset. Is it? In other words, using correct PC methodology, how much does the large-scale hockey-stick shape change if the bristlecone pine data are excluded?
[Response: The issue of the sensitivity of the reconstructions to particular data was addressed in some detail by MBH98. See e.g. the original supplementary table here. The skill (that is, the estimated reliability of) the reconstructions was found to be relatively insensitive to the precise mix of data used over the past several centuries. Further back in time, the potential for a statistically skillful reconstruction becomes more sensitive to the availability of certain key data, including several of the long western North American tree-ring data. This finding is hardly new, however–it was discussed in considerable detail by Mann et al in followup paper to MBH98 published in Geophysical Research Letters in 1999. What is of greater relevance then, is that the basic conclusions of this earlier work, such as the finding that late 20th century warmth is the anomalous in the context of the past millennium or longer, are common to numerous recent studies by different groups, based on a variety of different proxy data and statistical methods. –mike]
Second, a broader question (and one that may not allow a simple definitive answer): the critiques of MM’s arguments in both DG and Mann’s BBC interview appear to suggest that there are fundamental, beginner’s flaws in their analysis. But if this is really the case, how did their paper pass peer review to get published in GRL, which I understand has extremely high standards? We’re not dealing with Baliunas and Soon getting published in “Energy and Environment” here, after all.
[Response: The issue of peer-review and the imperfect nature of the peer-review process, including specific discussion of recent articles published in the journal GRL, was provided by us previously here and here. –mike]
What I’m trying to get is a sense of how solid are the millenial-scale proxy results that the late 20th-C results are well outisde the uncertainty envelope of the past 1K – 2K years — not with respect to partisan nonsense like Baliunas and Soon, but with respct to serious, impartial criticism. Are there serious, honest critics still calling the large-scale result into question?
[Response: As discussed by us elsewhere on this site, the basic conclusions of previous work, i.e. that late 20th century warm is anomalous in the context of the past millennium or longer, is common to numerous other studies that have appeared in the mainstream peer-reviewed literature since MBH98. While the details of past climate history are currently being debated in the litererature, the most recent studies, such as that of Moberg et al (2005) published a little more than a month ago in Nature, affirm this fact–in fact, Moberg et al (2005), while arguing for greater variability than is evident in other studies (including the most recent study published in Science just a couple weeks ago) conclude that late 20th century warmth is likely anomalous in at least the past two millennia, not just the past millennium. –mike]
Many thanks for your help,
[Response: Thanks for your insightful questions. –mike]
Ted Parson