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My take on Climate Change

Oberon

Well-Known Member
Well although some human problems are overreacted, what about sea level rise?

Sea level rise could indeed have dire effect. But again, this is based on certain assumptions which are at the moment just that: assumptions. The amount of glaciers and sea ice has varied widely throughout the history of the earth, and will continue to regardless of humans. If we are contributing to it, this is something we need to address, but again we don't really know based on current evidence whether we are. Sea level changes are notoriously difficult to measure.


1 metre predicted by the IPCC is considered by many to be conservative and some predict 3 to 5 metres which would be very bad and hurt the economy, this still leaves out feedbacks such as glacier dynamics like the Larsen B ice shelf problems.

There are several studies contradicting (and ignored by) the IPCC. Also, certain melting (like parts of Antarctica) has been occuring for thousands of years.


Hurricane Katrina was very bad, a warming world will have worse. Droughts are getting worse and might cause a famine. Heat waves will cause large problems with Heat stroke and other heat related deaths and disease. Heat will increase the area where mosquitoes can live and therefore increase the range of malarial disease. Water acidifications will hurt animals with shells of calcium carbonate apparently it is the sort of thing usually seen only every 300 million years( reference).

These effects of global warming are among the LEAST demonstrated by research. Again, if you would like references, I can provide them. But many of the side effects of warming like storms and droughts are far more prevalent in public media than in actual scientific research.

Again, with respect to this post and the several posts I wrote explaining my position, if you would like greater detail or references just let me know.
 
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evolved yet?

A Young Evolutionist
Sea level rise could indeed have dire effect. But again, this is based on certain assumptions which are at the moment just that: assumptions. The amount of glaciers and sea ice has varied widely throughout the history of the earth, and will continue to regardless of humans. If we are contributing to it, this is something we need to address, but again we don't really know based on current evidence whether we are. Sea level changes are notoriously difficult to measure.
There are several studies contradicting (and ignored by) the IPCC. Also, certain melting (like parts of Antarctica) has been occuring for thousands of years.

Sea level changes are being measured by satellites very easily( if it were humans doing the measurements directly you would have a point). Yes, I would like a reference to the contradicting studies. Yes melting has been happening for a long time but the point is that it is speeding up.
NEJM -- Climate Change and Human Health
These effects of global warming are among the LEAST demonstrated by research. Again, if you would like references, I can provide them. But many of the side effects of warming like storms and droughts are far more prevalent in public media than in actual scientific research.
They are actually very dangerous and hurricane Katrina is considered by thousands of scientists to be the first weather event directly attributable to climate change.

Again, with respect to this post and the several posts I wrote explaining my position, if you would like greater detail or references just let me know.
These I do think should be referenced.
 

Oberon

Well-Known Member
I'm teaching and doing admin work until this evening, but I will respond in full then. In the meantime, I do have some issues with your questions I hope you can address.


Sea level changes are being measured by satellites very easily( if it were humans doing the measurements directly you would have a point). Yes, I would like a reference to the contradicting studies. Yes melting has been happening for a long time but the point is that it is speeding up.
NEJM -- Climate Change and Human Health

They are actually very dangerous and hurricane Katrina is considered by thousands of scientists to be the first weather event directly attributable to climate change.
.

You have throughout this thread referred to a number of websites. But webswites frequently contaibn false or misleading information. It would be helpful to me if you could reference the academic literature (i.e. peer-reviewed journal articles or works published by academic presses) from which you get your data. Thanks.
 

evolved yet?

A Young Evolutionist
These are the sources and references of the article.
Source Information

Dr. Epstein is the associate director of the Center for Health and the Global Environment, Harvard Medical School, Boston.

An interview with Dr. Epstein can be heard at MMS: Error.

References

Houghton JT, Ding Y, Griggs DJ, et al., eds. Climate change 2001: the scientific basis: contribution of the Working Group I to the third assessment report of the Intergovernmental Panel on Climate Change. Cambridge, England: Cambridge University Press, 2001.
Hassol SJ. ACIA, Impacts of a warming Arctic: arctic climate impact assessment. Cambridge, England: Cambridge University Press, 2004.
Leaf A. Potential health effects of global climatic and environmental changes. N Engl J Med 1989;321:1577-1583. [Web of Science][Medline]
McMichael AJ, Campbell-Lendrum DH, Corvalán CF, et al., eds. Climate change and human health: risks and responses. Geneva: World Health Organization, 2003:250.
Epstein PR, Diaz HF, Elias S, et al. Biological and physical signs of climate change: focus on mosquito-borne diseases. Bull Am Meteorol Soc 1998;78:409-17.
 

Oberon

Well-Known Member
Sea Level:

First, what is supposed to be causing it? Melting of ice due to warming. Let's grant for a moment that this is happening at a rate fast enough to be serious. The question still remains what is causing the warming? For example, could it be solar influences? See e.g.

Camp, C. D., & Tunk, Kk. (2007). Surface warming by the solar cycle as revealed by the composite mean difference projection. Geophysical research Letters 34.
Douglass, DH, Clader, DB, & Knox, RS. (2004). Climate sensitivity to Earth to solar irradiance: update. Paper presented at 2004 Solar Radiation and Climate (SORCE) meeting on Decade Variability in the Sun and the Climate, Meredith, New Hampshire, October 27-29, 2004

Harrison, R. G., & Sephenson, D. B. (2006). Empirical evidence for a nonlinear effect of galactic cosmic rays on clouds. Proceedings of the Royal Society London, Ser. A, 462, 1221-1233.


Kirkby, J. (2008). Cosmic rays and climate. Surveys in Geophysics 28 pp. 222-275.

Scarfetta, N., West B. (2007). Phenomenological reconstructions of the solar signature in the northern hemisphere surface temperature records since 1600. Journal of Geophysical Research 112.


Shaviv, N J. (2005) On climate response to changes in the cosmic ray flux and radiative budget. Journal of Geophysical Research 110.


Svensmark, H. (2007). Cosmoclimatology: A new theory emerges. Astronomy & Geophysics 48.


Svensmark H. et al (2007). Experimental evidence for the role of ions in particle nucleation under atmospheric conditions. Proc. Roy. Soc. A 463 385-396

Tinsley, B. A. & Yu, F. Atmospheric Ionization and Clouds as Links Between Solar Activityand Climate. American Geophysical Union monograph, 141, 321-340.

Usoskin, I. G. et al (2003). Millenium-scale sunspot number reconstruction: Evidence for an unusually active sun since the 1940s. Physical Review Letters 91.21

Viezer, Jan. (2005). Celestial Climate Driver: A perspective from four billion years of the carbon cycle. Geoscience Canada 32.

And, of course, in order for GHGs to be the cause of melting, the there need to be positive feedbacks, but is this the case? See e.g.

Compo, G. & Sardeshmukh, P.D. (2008). Oceanic Influences on Recent Continental Warming. Climate Diagnostics Center, Cooperative Institute for Research in Environmental Sciences, University of Colorado, and Physical Sciences Division, Earth Sytem Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, Co.

Kininmonth, W. (2004). Climate Change: a natural hazard. Multi-Science Publishing, Brenwood.

Koutsoyiannis, D. et al. (2008). On the credibility of climate predictions. Hydrological Sciences/Journal des Sciences Hydrologiques, 53 (4), 671-684.

Lindzen, et al. (2001). Does the earth have an adaptive infrared iris? Bulletin of the American Meteorological Society 82, 417-432.

On the problems with surface records, see in particular:

De Laat, A.T.J., & Maurellis, A.N. (2006). Evidence for influence of anthropogenic surface processes on lower tropospheric and surface temperature trends. International Journal of Climatology 26

McKitrick, R.R., & Michaels, P. J. (2007). Quantifying the influence of anthropogenic surface processes and inhomogenities on gridded global climate data. Journal of Geophysical Research 112.

But let's turn specifically to the issue of melting ice. How about the largest mass of ice on the planet? Antarctica? First, it has been melting over the last 6000 years. However, it seems that the rate of melting is either decreasing or that the ice has actually increased over the past 30 years. See, e.g.:

Liu, J., Curry, J. A., & Martinson, D. G. (2004). Interpretation of recent Antarctic sea ice variability. Geophysical Research Letters 31

Vyas, N. K., Dash, M. K., Bhandari, S. M., Khare, N., Mitra, A., and Pandey, P. C. (2003). On the secular trends in sea ice extent oer the antarctic region based on OCEANSAT-1 MSMR observations. International Journal of Remote Sensing 24.

Parkinson, C. L. (2002). Trends in the length of the southern Ocean sea-ice season, 1979-99. Annals of Glaciology 34.

Of course, much of the focus on glacial melting has centered on the arctic. But even the IPCC admits (2007, p. 252), “a few areas have cooled since 1901.”

Also, the other problem is that the period of recent warming comes right after a period of cooling, during which arctic ice increased, and before that, ice decreased due to a period of warming which had nothing to do with AGW. In fact, this period of warming may be causally related to the current melting (see e.g. Professor Mahoney’s seminar given in 2007 at the University of Colorado). Also, the warming in the arctic may have nothing to do with AGW. See e.g. Semenov, V. A., & Bengtsson, L. (2003). Modes of the Wintertime Arctic Air Temperature Variability. Geophysical Research Letters 30.

Perhaps most importantly, though, is the history of melting in the past, even the recent past. Dahl-Jensen et al (1998) note that both the Holocene Climate Optimum and Medieval Warming period were warmer in Greenland than today. As for how fast or rapid warming can occur naturally, see e.g. Bard, E. 2002. Climate shock: Abrupt changes over millennial time scales. Physics Today 55(12).

In Greenland, there is evidence for cooling and again an increase in the amount of ice. See, e.g., Hanna, E. & Cappelen, J. (2002). Recent climate of Southern Greenland. Weather 57 as well as Hanna, E. and Cappelen, J. (2003). Recent cooling in coastal southern Greenland and relation with the North Atlantic Oscillation. Geophysical Research Letters 30.

The point is, glaciers everywhere advance and retreat all the time (see e.g. Braithwaite, R. L. (2002). Glacier mass balance: The first 50 years of international monitoring. Progress in Physical Geography 26.
 
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Oberon

Well-Known Member
But let’s look directly at sea level changes for a moment. You mention that satellites show sea level changes. But guess what It is always changing, sometimes very fast, sometimes slowly (see e.g. Shakleton, N. J., Lamb, H. H., Worssam, B. C., Hodgson, J. M., Lord, A. R., Shotten, F. W., Schove, D. J., & Cooper, L. H. N. (1977). The oxygen isotope stratigraphic record of the Late Pleistocene). Over the past 100,000 years or so, there have been many, many sea level rises and falls (see, e.g. Dansgaard, W., & Oeschger, H. (1989). Past environmental long-term records from the Arctic. In H. Oeschger & C. C. Langway, The environmental record in glaciers and ice sheets. Wiley.)

I can provide more studies on glacial and sea level variability if you wish (just ask), but let’s move on to hurricanes, storms, etc.

Will global warming cause more storms, hurricanes, and similar severe weather? We don’t know. For example, one study (Wilson, R. M. (1999). Statistical aspects of major (intense) hurricanes in the Atlantic basin during the past 49 hurricane seasons (1950-1998): Implications fo the current season. Geophysical Research Letters 26) found warmer temperatures means fewer hurricanes. While there were an increase in hurricanes in the late 90s, this had nothing to do with AGW (see e.g. Goldenberg, S. B., C. W. Landsea, A. M. Mestas-Numez, and W. M. Gray (2001).The recent increase in Atlantic hurricance activity: Causes and implications. Science 293.) In fact, storms in general seem to have been more severe in the past according to some studies (e.g. Dawson, A.G., Hickey, K., Holt, T., Elliott, L., Dawson, S., Foster, I.D.L., Wadhams, P., Jonsdottir, I., Wilkinson, J., McKenna, J., Davis, N.R. and Smith, D.E. (2002). Complex North Atlantic Oscillation (NAO) Index signal of historic North Atlantic storm-track changes. The Holocene 12: 363-369.) Additionally, this may have been due to colder temperatures (ibid, but see also Clarke, M., Rendell, H., Tastet, J-P., Clave, B. and Masse,
L. (2002). Late-Holocene sand invasion and North Atlantic storminess along the Aquitaine Coast, southwest France. The Holocene 12).

In fact, even the 2001 IPCC report stated that there was little evidence for increased severe weather due to AGW.

Ok, I’ve been writing for a while now. Feel free to ask for more references or follow-up questions.
 

evolved yet?

A Young Evolutionist
First, what is supposed to be causing it? Melting of ice due to warming.
Actually 40% of the Sea level rise is thermal expansion, 40% is mountain glacier melting, and 20% is ice caps. What frightens scientists is the chance that they will speed up like what happened at the Larsen B ice shelf.
Let's grant for a moment that this is happening at a rate fast enough to be serious. The question still remains what is causing the warming? For example, could it be solar influences? But let's turn specifically to the issue of melting ice. How about the largest mass of ice on the planet? Antarctica? First, it has been melting over the last 6000 years. However, it seems that the rate of melting is either decreasing or that the ice has actually increased over the past 30 years.
It is more likely that the ice was increasing in-fact till recently the warming air could hold more vapour( and more precipitation.)
Also, the other problem is that the period of recent warming comes right after a period of cooling, during which arctic ice increased, and before that, ice decreased due to a period of warming which had nothing to do with AGW. In fact, this period of warming may be causally related to the current melting (see e.g. Professor Mahoney’s seminar given in 2007 at the University of Colorado). Also, the warming in the arctic may have nothing to do with AGW. See e.g. Semenov, V. A., & Bengtsson, L. (2003). Modes of the Wintertime Arctic Air Temperature Variability. Perhaps most importantly, though, is the history of melting in the past, even the recent past. Dahl-Jensen et al (1998) note that both the Holocene Climate Optimum and Medieval Warming period were warmer in Greenland than today. As for how fast or rapid warming can occur naturally.
The effects of AGW are worldwide well the effects of the Warming period were mainly centred around Europe and Greenland.
The point is, glaciers everywhere advance and retreat all the time (see e.g. Braithwaite, R. L. (2002). Glacier mass balance: The first 50 years of international monitoring. Progress in Physical Geography 26.
Yes, but rarely at this pace.
 

evolved yet?

A Young Evolutionist
Well, first of all I don't like the term climate change, because that's what the climate does. It changes.
I like it because it is not necessarily warming, although in many and most locations it is warming. Maybe the best term is Extreme Anthropogenic Climate Change.

1. The science behind the models

Most of the worry about what will happen and what is happening is based on several independently developed very complex models of our atmosphere. We plug CO2 (and other GHG) levels into these models and view the results, which are needless to say very bad.
Yes but sometimes very accurate:
does_carbon_dioxide_fig3new.jpg

However, while there are several models referred to in the literature, and they do differ, all of them share several important assumptions about the climate and none of them accurately model the climate (which is impossible at the moment as we don't understand too many important parts about it, particularly clouds). So, where could they be wrong?
They use different variables but they all agree that the world is warming possibly 4 degrees by the end of the century.
The most important assumption for catastrophic warming is, as I said, the assumption in the models of a strong positive feedback. However, not only are many important parts of the climate system not understood, there is evidence that the climate has negative feedback systems which will either lessen the impact of GHG emissions to the point where we don't really have to worry anytime soon or will negate them entirely.
Also important are some of the reasons for assuming positive feedbacks. Some of these come from our incomplete understanding of the climate (e.g. the water vapor thing I mentioned in my last post), but many come from other observations, two of which are vital to mention here. The first is reconstructions of past climate. If we reconstruct thousands of years of temperature, and the result is fairly flat except for the current warming, then there may be good reason to believe that the climate is very sensitive to our impact on it (i.e. positive feedbacks). However, the first problem is that the reconstructions most focused on only go back about 2000 years or less. That's nothing, even considering only the time humans have been around. So even if Mann's original hockey-stick (the one which showed almost no fluctuations) was correct, we are still left with other periods of large warming and cooling (e.g. the Holocene Climate Optimum). I think that the main impetus for the graphs going back 1500 years or so is for the effect they have on public opinion. After all, if we look at the record over millions of years, we see massive fluctuations which must be explained.
Many models do not even use these in the unknown feed backs and although this may make them less accurate, it makes them less prone to bias.
Also, as I noted earlier, there are problems with most of these reconstructions. It appears that many scientists seem to use proxy series that they know are corrupt because, when the statistical algorithms are used to sort the data, these series will weight they final shape in such a way as to generate a more hockey-stick like graph. In fact, even the temperature record (i.e. the period of time for which we have actual instruments like thermometers measuring the temperature) has problems. Of course, virtually no expert believes that the instrumental temperature record is so off we can't say that the earth has warmed. But there is reason to believe that it is exaggerated.
I won't contest the exaggeration because this goes along with the 'band-wagon' idea.
Also, while most people who read about climate change think that the warming of the 20th century is all because of GHGs, according to scientists (and I mean the ones that believe we are causing the warming) only the period after about 1970 is the result of increases in GHGs. Yet there is a warming of an equal length at the beginning of the 20th century. Also, it may be that the hottest year on record dates from that period.
I won't contest that after 1970 is when EACC started.
There is also a period of cooling prior to the current warming thought to be caused by us and after the first 20th century warming not related to GHGs.
Just wondering about a source.
The second issue with the feedback assumption that doesn't come from climate dynamics is the assumption that nothing other than GHGs could cause the current warming, and therefore there must be strong positive feedbacks because we also know that without them the GHGs couldn't cause the warming. Only this may well not be true. There have been a number of studies, including quite recent ones, which indicate that the current warming may be caused by something else. For example, a series of studies by several important researchers over the last 20 years or so deal with a totally different climactic factor which may be the cause of observed warming (as far as I know, the most recent peer-reviewed study on this particular cause of warming was published last year, but there may be more recent ones). This research deals with cloud-seeding caused by Galactic Cosmic Rays (which result from stars billions of miles away). There is a large and growing amount of evidence that these rays cause "cloud seeding" in the lower atmosphere, increasing cloud coverage, which in turn raises the temperature.
Another possible cause has to do with the PDO. Then there are theories about solar influence. Then there are those who say we don't know enough about the climate system to say what is causing the warming, and point to past warming periods for which AGW can't be responsible (and often enough also point to problems in the temperature record, which may mean that the warming isn't as drastic as it looks). Some of these are more widely accepted and/or studied than others, but the point is the assumption that nothing else could explain the current warming other than human released GHGs combined with positive feedbacks is contradicted by many, many recent studies. This doesn't prove the theory wrong, and certainly the AGW proponents have published their own studies in which they argue against all of these mechanisms of warming to explain the current trend, but the point is the debate isn't over.
I wonder how big a factor these other things are.
BTW we are at a solar minimum right now.
 

Oberon

Well-Known Member
Actually 40% of the Sea level rise is thermal expansion, 40% is mountain glacier melting, and 20% is ice caps. What frightens scientists is the chance that they will speed up like what happened at the Larsen B ice shelf.

Yes, but again there is the question of what is causing warming and sea level changes. I cited several studies demonstrating that sea level and glacial changes happen regardless of warming (or cooling, in fact) and are constantly shifting.

It is more likely that the ice was increasing in-fact till recently the warming air could hold more vapour( and more precipitation.)

You're missing the point. Satellite and surface stations show cooling around much of antarctica to this day a continued increase in ice in many places.

The effects of AGW are worldwide well the effects of the Warming period were mainly centred around Europe and Greenland.

That simply isn't true. Check out the website I cited which contains references to peer-review studies showing warming all over the globe.

Yes, but rarely at this pace.

Not according to the studies I cited (and others) which show drastic changes can occur and have occurred very quickly.

They use different variables but they all agree that the world is warming possibly 4 degrees by the end of the century.

They all rely on similar assumptions.

Many models do not even use these in the unknown feed backs and although this may make them less accurate, it makes them less prone to bias.


You are quite wrong. ALL models use the feedbacks, because without them there is no problem with the warming. Find me one model which does not have strong positive feedback parameters and posits dangerous warming.

Just wondering about a source.

Check out NASA or the CRU's instrumental surface temperature record.

I wonder how big a factor these other things are.
BTW we are at a solar minimum right now.

Read the studies. And GCRs have nothing to do with solar cycles.
 

evolved yet?

A Young Evolutionist
Yes, but again there is the question of what is causing warming and sea level changes. I cited several studies demonstrating that sea level and glacial changes happen regardless of warming (or cooling, in fact) and are constantly shifting.
This I require a source for.


You're missing the point. Satellite and surface stations show cooling around much of antarctica to this day a continued increase in ice in many places.
That is why it is called Anthropogenic Climate Change not Global Warming.

That simply isn't true. Check out the website I cited which contains references to peer-review studies showing warming all over the globe.
Which one is that?

Not according to the studies I cited (and others) which show drastic changes can occur and have occurred very quickly.
They have occurred, but not recently because we have had a stable climate for the last 11000 years( since we came out of the last ice age)
They all rely on similar assumptions.
Similar because they are often agreed upon in the scientific community.
You are quite wrong. ALL models use the feedbacks, because without them there is no problem with the warming. Find me one model which does not have strong positive feedback parameters and posits dangerous warming.
Sorry could not find one, I guess I should of checked, but it still doesn't stop the fact that the tundra is releasing GHG's, as well as Albedo:
ill_maps-Albedo-Effect.jpg

And Burning forests( from increased temperature/dryness), as well as the increased amount of El ninos( as well as decrease in La ninas).
Check out NASA or the CRU's instrumental surface temperature record.
I'm not sure if the one found is the same one because can't find what you are talking about:
Data.GISS: GISS Surface Temperature Analysis (GISTEMP)
Read the studies. And GCRs have nothing to do with solar cycles.
You still haven't answered the question of how big a role solar output has had on CC.
 

Oberon

Well-Known Member
This I require a source for.
Braithwaite, R. L. (2002). Glacier mass balance: The first 50 years of international monitoring. Progress in Physical Geography 26.



That is why it is called Anthropogenic Climate Change not Global Warming.

And exactly how does temperature rising cause cooling?




Which one is that?

Dr. Idso and other experts run this site, which includes a project on the Medieval Warming Period. While I'm not personally a fan of Idso, the site is a great place for peer-reviewed literature by many, many, many scientists on evidence for the MWP all over the globe.


They have occurred, but not recently because we have had a stable climate for the last 11000 years( since we came out of the last ice age)

Actually we haven't. Let's look at a few sources here. First, let's go back to that 11,000 year mark. Here we have retreat of glaciers, climactic and sea level changes, all widespread, extreme, and cyclical. See, e.g.:

Emei, K.-C & Dawson, A. G. (2003). Holocene paleoclimate records over Europe and the North Atlantic. The Holocene 13:305-309.

Feurdean, A. (2005). Holocene forest dynamics in northwestern Roumania. The Holocene 15: 435-446.

Chen, F.-H., Cheng, B., Zhao, Y., Zhu, Y, & Madson, D. B. (2006). Holocene environmental change inferred from high-resolution pollen record, Lake Zhueze, arid China. The Holocene 16: 675-684.

Hu, F. S., Kaufman, D., Yoneji, S., Nelson, D., Shemesh, A., Huang, Y., TIan, J., Bond, G., Clegg, B., & Brown, T. (2003). Cyclic variation and solar forcing of Holocene climate in the Alaskan subarctic. Science 301: 1890- 1893.

Yu, Z., Campbell, I. D., Campbell, C., Vitt, D. H., Bond, G. C., & Apps, M. J., (2003). Carbon sequestration in western Canadian peat highly sensitive to Holocene wet-dry cycles at millennial timescales. The Holocene 13: 801-808.

Yu, S. –Y. (2003). Centennial-scale cycles in middle Holocene sea level along the southeastern Baltic Coast. Bulletin of the Geological Society of America 115: 1404-1409.

The Holocene warming, which was post 11,000, was global (see, e.g. Enzel, Y., Ely, L L., Mishra, S., Ramesh, R., Amit, R., Lazar, B., Rajaguru, S. N., Baker, V. R., & Sandler, A. (1999). High resolution Holocene environmental changes in the Thar Desert, northwestern India. Science 284: 125-128)

and it was warmer than today (see e.g. S. P. Huang, H. N. Pollack, and P.-Y. Shen. (2008) A late Quaternary climate reconstruction based on borehole heat flux data, borehole temperature data, and the instrumental record. Geophysical Research Levels 35.

What is perhaps even moreinteresting than the cyclical rapid warming here is the periods of cooling during the overall warming (not unlike the c. 30 year cooling in the 20th century between two periods of warming). The effects of the cold periods are interesting and may be seen in e.g. Miao, X., Mason, J. A., Swineheart, J. B., Loope, D. B., Manson, P. R., Goble, R. J., & Liu, X. (2007). A 10,000 year record of dune activity , dust storms, and severe drought in the central Great Plains. Geology 35: 119-122.

Then, from c. 9000 BCE to c. 8500 BCE we have dramatic and probably widespread cooling:
(writing all these names is annoying, so from now on I will just use et al and the lead author)

Barber, D. C., et al. (1999). Forcing of the cold event 8,200 years ago by catastrophic draining of Laurentide lakes. Nature 400: 344-348.

Douglass, D. C., et al. (2005). Evidence of early Holocene glacial advances in sourthern South America from cosmogenic surface-exposure dating. Geology 33: 237-240.

This was shortly followed by another cold period: Rohling, E. J., & Pälike, H. (2005). Centennial-scale climate cooling with a sudden event around 8,200 years ago. Nature 434:975-970.

In fact, I could go on and on citing studies on often extreme climate variability in the past 11,000 years. However, let’s turn to the more recent past
 

Oberon

Well-Known Member
First is Dr. Loehle's study on temperature reconstruction not using proxies other than tree-rings I referred to earlier:


And, although varies estimates differ, as noted in Jan Esper et al. (2005). Climate: past ranges and future changes. Quaternary Science Reviews 24, p. 2165, “When matching existing temperature reconstructions over the past 1000 years, although substantial divergences exist during certain periods, the timeseries display a reasonably coherent picture of major climatic episodes: ‘Medieval Warm
Period’, ‘Little Ice Age’ and ‘Recent Warming.’” They also note the problems inherent with these constructions particularly when it comes to validation of certain proxy series (e.g. tree rings) with the instrumental records.

In short, there is plenty of research on climactic variability, sharp declines and increases in temperature, sea-level changes, etc, during the past 11,000 years.


Similar because they are often agreed upon in the scientific community.

No, they aren’t. They all assume a large positive feedback but the existence of this feedback has been questioned on multiple levels, from the observational record of past temperatures to other natural forcings and so forth. I’ve already cited a number of studies on past climates, but for feedbacks and other natural mechanisms see e.g.

Loehle, C. (2004). Climate change: detection and attribution of trends from long-term geologic data. Ecological Modelling 171: 433-450.

Lindzen, R. S., & Choi, Y-S. (2009). On the determination of climate feedbacks from ERBE data. Geophysical Research Letters 36.

Lindzen, R. S. (1991). Some uncertainties with respect to water vapor’s role in climate sensitivity. Proceedings of NASA workshop on the Role of Water Vapor in Climate Processes.

Compo, G. & Sardeshmukh, P.D. (2008). Oceanic Influences on Recent Continental Warming. Climate Diagnostics Center, Cooperative Institute for Research in Environmental Sciences, University of Colorado, and Physical Sciences Division, Earth Sytem Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, Co.

Kininmonth, W. (2004). Climate Change: a natural hazard. Multi-Science Publishing, Brenwood.

Koutsoyiannis, D. et al. (2008). On the credibility of climate predictions. Hydrological Sciences/Journal des Sciences Hydrologiques, 53 (4), 671-684.

Lindzen, et al. (2001). Does the earth have an adaptive infrared iris? Bulletin of the American Meteorological Society 82, 417-432.

And so forth. The point is, the bulk of the modeled assumptions relies on a) reconstructions of past climates which show considerable variable and are often plagued with complications and 2) theoretical assumptions about climactic systems like clouds and water vapor, only cloud dynamics are barely understood and as the citations above show there is doubt as to the feedback effect of water vapor. The other big reason for the assumption is the conclusion that nothing else could account for the warming, but the studies I cited previously on solar, GCRs, and other natural variations (combined with temperature record issues) show that that may not be the case at all.

Sorry could not find one, I guess I should of checked, but it still doesn't stop the fact that the tundra is releasing GHG's, as well as Albedo:

Albedo is simply a measure of reflection of radiativity. Lots of natural systems effect total reflectivity on a global scale. It isn’t that the tundra is releasing GHG’s, it’s that not all of them are absorbed and therefore the atmospheric levels of GHGs are increasing. But again, none of the models or experts believe that this alone is really a problem. It is the feedbacks speculated to result from the increase in GHGs.

And Burning forests( from increased temperature/dryness), as well as the increased amount of El ninos( as well as decrease in La ninas).

I'm not sure if the one found is the same one because can't find what you are talking about:
Data.GISS: GISS Surface Temperature Analysis (GISTEMP)

Well, let's break this down a bit. First, we have the global instrumental record, e.g. the as given by the 2007 IPCC report here. Now, notice even here that there is a period of warming from about 1900 onwards, followed by 20+ year dip as the globe cooled, and then the modern warming. Also interesting is that this graph only goes to 2000. This is probably because the global records show no warming trend since 1998. This was admitted even by Jones, and see also here for more detail. Also, in one of the released CRU emails, a lead proponent of AGW Kevin Ternberth stated that "The fact is that we can’t account for the lack of warming at the moment and it is a travesty that we can’t." Then there is the problem of how accurate the instrumental record is. The issue is that for a lot of this period we many places all over the globe had spotty records at best. The US is one of the few places to have a consistent instrumental record, but here we get a different picture:

From the NCDC:
graph-Aug2023_42_080371704101.gif



Here the two warming trends are far more similar, and are represented by a more thorough, consistent, and complete temperature record than has been available for the globe.


You still haven't answered the question of how big a role solar output has had on CC.

Again, it isn't just solar output. But looking only at that for a moment, in Scafetta, W. (2009). Empirical analysis of the solar contribution to global mean air surface temperature change. Journal of Atmospheric and Solar-Terrestrial Physics 71: 1916–1923 , we see that an estimated 65% of warming since 1980 is caused by the sun.

Perhaps more important, or more interesting to say the least, is the effect of GCRs.

Again, see e.g. Camp, C. D., & Tunk, Kk. (2007). Surface warming by the solar cycle as revealed by the composite mean difference projection. Geophysical research Letters 34.
Douglass, DH, Clader, DB, & Knox, RS. (2004). Climate sensitivity to Earth to solar irradiance: update. Paper presented at 2004 Solar Radiation and Climate (SORCE) meeting on Decade Variability in the Sun and the Climate, Meredith, New Hampshire, October 27-29, 2004

Harrison, R. G., & Sephenson, D. B. (2006). Empirical evidence for a nonlinear effect of galactic cosmic rays on clouds. Proceedings of the Royal Society London, Ser. A, 462, 1221-1233.


Kirkby, J. (2008). Cosmic rays and climate. Surveys in Geophysics 28 pp. 222-275.



Shaviv, N J. (2005) On climate response to changes in the cosmic ray flux and radiative budget. Journal of Geophysical Research 110.


Svensmark, H. (2007). Cosmoclimatology: A new theory emerges. Astronomy & Geophysics 48.


Svensmark H. et al (2007). Experimental evidence for the role of ions in particle nucleation under atmospheric conditions. Proc. Roy. Soc. A 463 385-396

Tinsley, B. A. & Yu, F. Atmospheric Ionization and Clouds as Links Between Solar Activityand Climate. American Geophysical Union monograph, 141, 321-340.

Viezer, Jan. (2005). Celestial Climate Driver: A perspective from four billion years of the carbon cycle. Geoscience Canada 32.


These studies suggest the current warming trend is not the result of positive feedbacks but cloud dynamics caused by natural factors (i.e. GCRs).
 
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evolved yet?

A Young Evolutionist

Braithwaite, R. L. (2002). Glacier mass balance: The first 50 years of international monitoring. Progress in Physical Geography 26.
I can not find the full text of this, is there anyway you could provide a link?


And exactly how does temperature rising cause cooling?[/COLOR
]
Like I said it is not all rising, there is cooling in-fact national geographic had a poster of it( since I couldn't find the original this will just look like the original):
climate-change.jpg





Dr. Idso and other experts run this site, which includes a project on the Medieval Warming Period. While I'm not personally a fan of Idso, the site is a great place for peer-reviewed literature by many, many, many scientists on evidence for the MWP all over the globe.
I will direct you to this site that uses over ten different proxies and only one is tree rings:
http://coast.gkss.de/staff/storch/pdf/moberg.nature.0502.pdf



Actually we haven't. Let's look at a few sources here. First, let's go back to that 11,000 year mark. Here we have retreat of glaciers, climactic and sea level changes, all widespread, extreme, and cyclical. See, e.g.:

Emei, K.-C & Dawson, A. G. (2003). Holocene paleoclimate records over Europe and the North Atlantic. The Holocene 13:305-309.

Feurdean, A. (2005). Holocene forest dynamics in northwestern Roumania. The Holocene 15: 435-446.
Forest dynamics in northern Romania, would that involve tree rings...
Chen, F.-H., Cheng, B., Zhao, Y., Zhu, Y, & Madson, D. B. (2006). Holocene environmental change inferred from high-resolution pollen record, Lake Zhueze, arid China. The Holocene 16: 675-684.

Hu, F. S., Kaufman, D., Yoneji, S., Nelson, D., Shemesh, A., Huang, Y., TIan, J., Bond, G., Clegg, B., & Brown, T. (2003). Cyclic variation and solar forcing of Holocene climate in the Alaskan subarctic. Science 301: 1890- 1893.

Yu, Z., Campbell, I. D., Campbell, C., Vitt, D. H., Bond, G. C., & Apps, M. J., (2003). Carbon sequestration in western Canadian peat highly sensitive to Holocene wet-dry cycles at millennial timescales. The Holocene 13: 801-808.

Yu, S. –Y. (2003). Centennial-scale cycles in middle Holocene sea level along the southeastern Baltic Coast. Bulletin of the Geological Society of America 115: 1404-1409.

The Holocene warming, which was post 11,000, was global (see, e.g. Enzel, Y., Ely, L L., Mishra, S., Ramesh, R., Amit, R., Lazar, B., Rajaguru, S. N., Baker, V. R., & Sandler, A. (1999). High resolution Holocene environmental changes in the Thar Desert, northwestern India. Science 284: 125-128)

and it was warmer than today (see e.g. S. P. Huang, H. N. Pollack, and P.-Y. Shen. (2008) A late Quaternary climate reconstruction based on borehole heat flux data, borehole temperature data, and the instrumental record. Geophysical Research Levels 35.

What is perhaps even moreinteresting than the cyclical rapid warming here is the periods of cooling during the overall warming (not unlike the c. 30 year cooling in the 20th century between two periods of warming). The effects of the cold periods are interesting and may be seen in e.g. Miao, X., Mason, J. A., Swineheart, J. B., Loope, D. B., Manson, P. R., Goble, R. J., & Liu, X. (2007). A 10,000 year record of dune activity , dust storms, and severe drought in the central Great Plains. Geology 35: 119-122.

Then, from c. 9000 BCE to c. 8500 BCE we have dramatic and probably widespread cooling:
(writing all these names is annoying, so from now on I will just use et al and the lead author)

Barber, D. C., et al. (1999). Forcing of the cold event 8,200 years ago by catastrophic draining of Laurentide lakes. Nature 400: 344-348.

Douglass, D. C., et al. (2005). Evidence of early Holocene glacial advances in sourthern South America from cosmogenic surface-exposure dating. Geology 33: 237-240.

This was shortly followed by another cold period: Rohling, E. J., & Pälike, H. (2005). Centennial-scale climate cooling with a sudden event around 8,200 years ago. Nature 434:975-970.

In fact, I could go on and on citing studies on often extreme climate variability in the past 11,000 years. However, let’s turn to the more recent past
Okay in the last 8100 years.:)
 
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Oberon

Well-Known Member
I can not find the full text of this, is there anyway you could provide a link?
I have the physical text from my university library, but I will look for an electronic version.
Like I said it is not all rising, there is cooling in-fact national geographic had a poster of it( since I couldn't find the original this will just look like the original):
climate-change.jpg
of couse climate varies. Temperatures do not rise universally. The point is that GHGs do not cause cooling so you can't point to increased ice or lowered temperatures as evidence of human induced warming



I will direct you to this site that uses over ten different proxies and only one is tree rings:
http://coast.gkss.de/staff/storch/pdf/moberg.nature.0502.pdf

But they show the medieval warm perion and the little ice age! The variability in climate is there in the reconstruction. Now, while they not that they don't think the MWP was as warm as the 1990s, they also admit the real limits on their reconstruction. The. Main point is they show the variability and note that this means we need more info about natural climate change!


Forest dynamics in northern Romania, would that involve tree rings...
Not for reconstructing temperatures. Just for looking at growth and change patterns aqnd so forth.

Okay in the last 8100 years.:)

Apart from my graphs and sources the study you just linked shows large-scale natural climate variability.
 

evolved yet?

A Young Evolutionist
I have the physical text from my university library, but I will look for an electronic version.
I wish I had access to a university library:(.
of course climate varies. Temperatures do not rise universally. The point is that GHGs do not cause cooling so you can't point to increased ice or lowered temperatures as evidence of human induced warming
What about aerosols and artificial light reflectors?
But they show the medieval warm perion and the little ice age! The variability in climate is there in the reconstruction. Now, while they not that they don't think the MWP was as warm as the 1990s, they also admit the real limits on their reconstruction. The. Main point is they show the variability and note that this means we need more info about natural climate change!
Yes and they provide support for EACC. As well as stating the evidence for a non-global medieval warming period. And wiki supports a non-global medieval warming period too!
Not for reconstructing temperatures. Just for looking at growth and change patterns aqnd so forth.
Well then why do you use them as evidence in a climate reconstruction.
Apart from my graphs and sources the study you just linked shows large-scale natural climate variability.
Yes but not as big as today's( look at their graphs again).
 

Oberon

Well-Known Member
What about aerosols and artificial light reflectors?

All sorts of things can cause cooling or warming. My point was in reference to the melting of glacials for antarctica and that while they have been melting for 6000 years, it appears that anarctica is cooling and in places the ice is thickening. This hardly disproves AGW, but it certainly doesn't support it.

Yes and they provide support for EACC. As well as stating the evidence for a non-global medieval warming period.

FIrst, they while the posit explanations for the various temperature trend, nothing in their study actually supports this. They are simply referring to some other theoretical and empirical previous work. However, other studies would disagree with their reasoning. Also, the study does nothing at all to show the "non-global medieval warming period" because the proxy series were limited to the northern hemisphere. The study simply showed that the proxies they used demonstrated both the MWP and LIA, and also that certain limitations make is impossible to say if the the 20th century was really the warmest (they don't actually come out and say that, they just talk about the limitations).


And wiki supports a non-global medieval warming period too!

Wiki can be edited by anyone. Have a look around in that site I gave you. It has lots and lots and lots of studies on temperature reconstructions from all over the globe which show the medieval warm period.

Well then why do you use them as evidence in a climate reconstruction.

Climate reconstruction is not the same as temperatue reconstruction. It is one thing to note that trees are growing a lot and therefore a hospitable climate is highly likely. It is another to try to correlate tree rings with ACTUAL temperatures over given periods of time, particularly given the numerous other factors involved. More problematic still, is that while some series have been validated and calibrated to the instrumental record, others have not and are still used.

Yes but not as big as today's( look at their graphs again).

On the other hand, they admit the limitations in such proxy reconstructions. It is quite possible that the MWP was warmer. What is really important, however, is that we don't have a flat global climate for thousands and thousands of years, and then all of the sudden the recent warming. We have a fluctuating climate influenced by many, many different and interacting variables over time.
 

evolved yet?

A Young Evolutionist
All sorts of things can cause cooling or warming. My point was in reference to the melting of glacials for antarctica and that while they have been melting for 6000 years, it appears that anarctica is cooling and in places the ice is thickening. This hardly disproves AGW, but it certainly doesn't support it.
I was just trying to show it doesn't disprove it and increasing Antarctic ice does not disprove AGW.
FIrst, they while the posit explanations for the various temperature trend, nothing in their study actually supports this. They are simply referring to some other theoretical and empirical previous work. However, other studies would disagree with their reasoning. Also, the study does nothing at all to show the "non-global medieval warming period" because the proxy series were limited to the northern hemisphere. The study simply showed that the proxies they used demonstrated both the MWP and LIA, and also that certain limitations make is impossible to say if the the 20th century was really the warmest (they don't actually come out and say that, they just talk about the limitations).
They are confined to the NH, but they have some in china, and Arabia.


Wiki can be edited by anyone. Have a look around in that site I gave you. It has lots and lots and lots of studies on temperature reconstructions from all over the globe which show the medieval warm period.
I have no reason to distrust the information or a reason to think someone would post lies on wiki.
Climate reconstruction is not the same as temperatue reconstruction. It is one thing to note that trees are growing a lot and therefore a hospitable climate is highly likely. It is another to try to correlate tree rings with ACTUAL temperatures over given periods of time, particularly given the numerous other factors involved. More problematic still, is that while some series have been validated and calibrated to the instrumental record, others have not and are still used.
Okay.
On the other hand, they admit the limitations in such proxy reconstructions. It is quite possible that the MWP was warmer. What is really important, however, is that we don't have a flat global climate for thousands and thousands of years, and then all of the sudden the recent warming. We have a fluctuating climate influenced by many, many different and interacting variables over time.
Well I don't think they would have such a high margin of error for your prediction to be possible.
 

Oberon

Well-Known Member
I was just trying to show it doesn't disprove it and increasing Antarctic ice does not disprove AGW.

They are confined to the NH, but they have some in china, and Arabia.

And all yet they still show the MWP.


I have no reason to distrust the information or a reason to think someone would post lies on wiki.

I was having a debate on here a while back on the precautionary principle, and how we shouldn't do something just to do something because actions have consequences. I used the example of DDT, which was banned, and millions of people died. Someone else quoted wiki on the carcinogenic nature of DDT. The wiki article said that their was "strong epidemiological evidence that DDT causes" an then listed several cancers. I noted that wiki wasn't a valid source, and this went back and forth, until I finally looked at the three sourced cited. Every single one stated that there was little to know evidence that DDT was carcinogenic.

In this case, I happen to be aware of lots and lots of temperature proxy series examined all over the globe which show the MWP. I am aware of global multiproxy reconstructions that show a warmer MWP (I cited one here).


Well I don't think they would have such a high margin of error for your prediction to be possible.
The difference between the modern warming and the MWP in the study you cited wasn't very great.
 

evolved yet?

A Young Evolutionist
And all yet they still show the MWP.
I couldn't find the data they had on the Chinese and Arabian temperature reconstructions.
I was having a debate on here a while back on the precautionary principle, and how we shouldn't do something just to do something because actions have consequences. I used the example of DDT, which was banned, and millions of people died. Someone else quoted wiki on the carcinogenic nature of DDT. The wiki article said that their was "strong epidemiological evidence that DDT causes" an then listed several cancers. I noted that wiki wasn't a valid source, and this went back and forth, until I finally looked at the three sourced cited. Every single one stated that there was little to know evidence that DDT was carcinogenic.
Are you saying it's a bad thing we banned DDT? If you are I'll start up a one on one debate with you.
In this case, I happen to be aware of lots and lots of temperature proxy series examined all over the globe which show the MWP. I am aware of global multiproxy reconstructions that show a warmer MWP (I cited one here).
What about the Antarctic Ice cores.
The difference between the modern warming and the MWP in the study you cited wasn't very great.
In the course of things 0.6 degrees Celsius is actually quite a-lot.
 
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Oberon

Well-Known Member
I couldn't find the data they had on the Chinese and Arabian temperature reconstructions.

Welcome to paleoclimatology. The point is there reconstruction shows an MWP in the northern hemisphere, where there proxies were from.

Are you saying it's a bad thing we banned DDT? If you are I'll start up a one on one debate with you.

Just review here:
For example, in chapter 7 of Phantom Risk (MIT press 1993) Bruce Ames and Lois Gold (both from UC Berkeley) goes over the myths associated with pesticides in general and DDT in particular.
"Many people view DDT as a particularly dangerous synthetic pesticide because of its bioconcentration and its years-long persistence in the environment. However, DDT is remakably non-toxic to mammals, has saved millions of human lives,; it accuses no demonstrable harm to people. As the first major synthetic insecticide, DDT replaced lead arsenate, which before the modern era was a major pesticide, and is carcinogenic and even more persistent in the environment."

This is why one doesn't use wiki.

Let's look at these sources for the moment. The Lancet article cited states:

"Although DDT is generally not toxic to human beings and was banned mainly for ecological reasons, subsequent research has shown that exposure to DDT at amounts that would be needed in malaria control might cause preterm birth and early weaning, abrogating the benefit of reducing infant mortality from malaria. Historically, DDT has had mixed success in Africa; only the countries that are able to find and devote substantial resources towards malaria control have made major advances. DDT might be useful in controlling malaria, but the evidence of its adverse effects on human health needs appropriate research on whether it achieves a favourable balance of risk versus benefit."

The authors then review all of this, yet a reply within the same journal and issue states this:​

Bis(4-chlorophenyl)-1,1,1-trichloroethane (DDT) has been shown, over the past 60 years, to be one of the few affordable and effective tools against malarial vector mosquitoes, which account for more than 300 million cases of disease and more than 1 million
deaths every year. However, the Review by Walter Rogan and Aimin Chen
(Aug 27, p 763),1 which aims to balance the risks and benefits of DDT, consists
mainly of hypothetical concerns while the reality of human suffering gets
short shrift. Rogan and Chen discuss several possible toxic endpoints, including those
involving neurobehaviour, cancer, and reproductive health. Yet they point to
no evidence that DDT, used as a malaria preventive, causes actual harm to
human beings. For each category of illness or dysfunction offered as support
for their precautionary approach, there is either no or at best weak data to support
a connection to DDT. Rogan and Chen concede that even the few studies
that seem to point to a possible adverse effect—shortened gestation and
decreased time until weaning—havenot been associated with actual adverse
health outcomes.They call for data from trials. But what sort of trials would suit them when 5000 die every day, and the weapon to prevent these needless deaths has been
known to be effective since the 1940s? Rogan and Chen’s only evidence of
harm comes from animal experiments, yet they state that “Various reproductive
and hormonal endpoints have been examined . . . and although associations
have been recorded, causal links have not been confirmed”, and “In people,
DDT use is generally safe”. Should our concerns not be, mainly,
with people? Especially when the people being discussed are dying on
such a scale from a preventable disease? If this were a laboratory experiment,
some debate on the issue might be tolerated. But when on one side of the
scales are studies that are “not so flawed that the findings can be dismissed”,
while on the other side are millions of sick and dead African children,
this academic discussion is unacceptable"
What about the Antarctic Ice cores. [/QUOTE]

Reference
Castellano, E., Becagli, S., Hansson, M., Hutterli, M., Petit, J.R., Rampino, M.R., Severi, M., Steffensen, J.P., Traversi, R. and Udisti, R. 2005. Holocene volcanic history as recorded in the sulfate stratigraphy of the European Project for Ice Coring in Antarctica Dome C (EDC96) ice core. Journal of Geophysical Research 110: Do6114, doi:10.1029/2004JD005259.
Description
The authors analyzed sulfate ice core stratigraphy from Dome C, Antarctica (75.10°S, 123.40°E) to obtain a record of Holocene volcanic eruptions, which they compared with other volcanic indices throughout Antarctica. Sulfate depositional fluxes of individual volcanic events were found to vary greatly among the different sites, which variation was attributed to changes in atmospheric circulation driven by climate forcing; and the team of ten researchers concluded that "changes in the extent and intra-Antarctic variability of volcanic depositional fluxes may have been consequences of the establishment of a Medieval Warming-like period that lasted [from about 1000] until about 1500 AD."

Reference
Hemer, M.A. and Harris, P.T. 2003. Sediment core from beneath the Amery Ice Shelf, East Antarctica, suggests mid-Holocene ice-shelf retreat. Geology 31: 127-130.
Description
Changes in the location of the edge of the Amery Ice Shelf were inferred from measurements of biogenic opal, absolute diatom abundance and the abundance of Fragilariopsis curta found in sediments retrieved from beneath the ice shelf at a point that is currently 80 km from land's edge. The MWP at ca. 750 14C yr BP was likely warmer than at any time during the CWP.

Reference
Khim, B.-K., Yoon, H.I., Kang, C.Y. and Bahk, J.J. 2002. Unstable climate oscillations during the Late Holocene in the Eastern Bransfield Basin, Antarctic Peninsula. Quaternary Research 58: 234-245.
Description
General climatic features were inferred from a study of the grain size, total organic carbon content, biogenic silica content and, most importantly, magnetic susceptibility of 210Pb- and 14C-dated sediments retrieved from the eastern Bransfield Basin (61°58.9'S, 55°57.4'W) just off the northern tip of the Antarctic Peninsula. Most of the Medieval Warm Period (AD 1050-1550) was warmer than the Current Warm Period.

And so on.

[/QUOTE]In the course of things 0.6 degrees Celsius is actually quite a-lot.[/quote]

It could be, but you have to understand how large the margin of error in paleoclimatology can be. Look at the difference between the classic hockey-stick graph and the study you cited. Again, other studies show a warmer MWP. The problem is that it is extremely difficult to determine precise measurements like .6 degrees. For example, just using the instrumental record, not only do we have to account for so many factors besides AGW influencing the record (e.g. the UHI or land changes), but the advanced statistics in averaging out temperatures given that the globe just isn't covered with thermometers.

This becomes far more tricky when you are dealing with far less data with which to work. Hence the variability in the reconstructions. What we can see, however, is clear signs of abrupt and serious NATURAL climate fluctuations. This doesn't mean we aren't contributing to the current trend, but as the authors of the study you cite point out, it does mean we need to better account for natural climactic influences.
 
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