SteveF. I think you must be confusing equilibrium with transient sensitivity….there’s quite a difference!

“But we know that climate sensitivity can’t be low (the palaeo record shows it must be around 3 C at least) and this means that continued emissions will produce high levels of warming. ”

Do we? Paleo results are not so simple to interpret, and depend on a set of assumptions which may not be correct. If climate scientists can’t define the current (negative) forcing due to atmospheric aerosols to any better than +/- 80%, how can paleo studies to estimate climate sensitivity be so certain?

What we really do know is 1) that climate models using high climate sensitivity (similar to the paleo values) consistently predict more warming than has been observed, 2) that ocean heat accumulation since 2003 is near zero (in clear conflict with the climate models), 3) that high sensitivity requires long ocean lag periods which are not evident in the ocean heat data, and 4) that a wide range of climate sensitivities is completely consistent with the instrument temperature record, depending on what values for aerosol forcing and ocean lag are assumed.

It is clear that GHGs must warm the Earth’s surface, but the magnitude of the warming matters a lot in terms of what costs can be justified to control emissions of CO2. IMO, we need to be very sure of the magnitude of warming, and pretty sure of its consequences, before obliging most of mankind to large economic sacrifices to avoid/reduce that warming.

Can you point to one example of a proxy they reference where they do not assert an MWP peak?

Ok. Well, there is this one. which states without snark or spin: ” For the Huascaran Glacier (9.11°S, 77.62°W), this work suggests that the MWP was not as warm as the CWP.”

Though is obviously true that their mission is to demonstrate the existence of a global MWP, the Idso brothers do provide descriptions of studies that do not confirm their view that the MWP was as warm or warmer than the present era see this or this one, or this as well as an overall counts of studies that confirm or deny.

Now it’s your turn to find equal candor and snark-free open-minded inclusion of contrary findings on Real Climate or Tamino.

You complain of a selection process at the CO2 Science site so you must be especially outraged by the incredible massage job in Mann 2008 which is apparent when you can see the graphs of the individual data sets that supposedly comprise Hockey Stick II.

You can make a fair criticism about selection of date ranges, interpretation of some studies in the summaries etc in the CO2 Science list. But at least it’s all out front. I don’t have to rely on references to unavailable data sets or absurdly complex algorithms whose purpose appears to be to weight bristlecone pines or selected Finnish lake bottoms.

Andrew

But we know that climate sensitivity can’t be low (the palaeo record shows it must be around 3 C at least) and this means that continued emissions will produce high levels of warming. Doubling C02 can’t produce only 1.5C warming. So likely impacts will be severe and therefore we need to reduce emissions radically.

Actually, the paleoclimate records show that the CO2 sensitivity is only 1.5C per doubling. 3.0C per doubling is consistently too high throughout just about the entire record. I have all the data and will be putting it up in a nice useable form soon for those that want to check for themselves.

You don’t have to. All you have to do is show your evidence and describe your thought processes to a reasonable person. That person (if open minded) will take your presentation seriously.

You are talking about playing some kind of game to appease a certain group of people. I think that’s childish.

Andrew

My point about the graphs posted at Climate Audit (there is also a collection of graphs of the individual studies in Mann’s more recent multi-proxy hockey stick but I don’t have the link at the moment) is that the majority of those studies show a MWP.

The result of Mann et al 2008 shows an MWP, for goodness’ sake!

I generally trust the CO2 Science compendium precisely because they do not suppress, filter out, or weigh the numbers. The composite is messy. They include results that do not confirm their point of view.

On the contrary, they assert that the results confirm their view, even though that is not true! Furthermore, it is nonsense to suggest that they do not ‘filter out’. You must surely be aware that they have selected only proxy data that suggests a pronounced warm period at some time or another which they then label the MWP? Can you point to one example of a proxy they reference where they do not assert an MWP peak? Do you really need me to refer you to proxies which show no such peak, even give or take the couple of hundred years that they allow themselves? Your assertion is demonstrably untrue.

As for Mann 2008, McIntyre said that at first glance they didn’t show a common signal. Of course they don’t show the same signal!

1) Finding conflicting studies the the CO2 Science site may be jarring to people who are used to the appearance of doctrinal purity.

I generally trust the CO2 Science compendium precisely because they do not suppress, filter out, or weigh the numbers. The composite is messy. They include results that do not confirm their point of view.

So congratulations for finding some contrary results among what is offered. No go do a similar search on Real Climate or Tamino to see if anomalous results are acknowledged as candidly.

2) My point about the graphs posted at Climate Audit (there is also a collection of graphs of the individual studies in Mann’s more recent multi-proxy hockey stick but I don’t have the link at the moment) is that the majority of those studies show a MWP. McIntyre is obviously right that they do not all show the same signal–and the contradictory nature of tree ring data seems rather characteristic for the reasons I suggested in my previous post.

In any event, to conclude that such data collectively yields a hockey stick is utterly contrived.

3) The hockey stick is sold to the general public as if the numbers simply present a clear pattern. When McIntyre et al demonstrate that is not the case, the fallback position is that precisely because the data is so contradictory, only the enlightened can see the true pattern using methods that the uninitiated are not entitled to examine.

If the methods are discovered and found wanting, it is irrelevant because the enlightened already just know the hockey stick has been “confirmed” by other studies.

If it turns out the majority of proxy studies do not confirm that, then such a finding is forever suspect unless and until the enlightened choose to perform a similar review.

The issue deserves a response more substantive that the clubby narcissism that seems to be the habit of Team defenders.

6. How Warm Was the Medieval Warm Period? Thomas J. Crowley and Thomas S. Lowery Ambio, Vol. 29, No. 1 (Feb., 2000), pp. 51-54

maximum Medieval warmth was restricted to two-three 20–30 year intervals, with composite values during these times being only comparable to the mid-20 th century warm time interval. Failure to substantiate hemispheric warmth greater than the present consistently occurs in composites because there are significant offsets in timing of warmth in different regions; ignoring these offsets can lead to serious errors concerning inferences about the magnitude of Medieval warmth and its relevance to interpretation of late 20 th century warming.

1. Jones, Terry L.; Schwitalla, Al (2008). “Archaeological perspectives on the effects of medieval drought in prehistoric California”. Quaternary International 188 (1): 41–58. doi:10.1016/j.quaint.2007.07.007.

Oh dear. Andrew, this is not a paper presenting any form of temperature reconstruction. Go look.

2. Keigwin, Lloyd D. (29 November 1996). “The Little Ice Age and Medieval Warm Period in the Sargasso Sea”. Science 274 (5292): 1503–1508. doi:10.1126/science.274.5292.1503.

Yup. LLoyd finds the Sargasso Sea indicated as being warmer in c1000AD than today. Well done!

3. Hu FS, Ito E, Brown TA, Curry BB, Engstrom DR (2001). “Pronounced climatic variations in Alaska during the last two millennia”. PNAS 98 (19): 10552–10556. doi:10.1073/pnas.181333798. PMID 11517320.

Woops. The paper charts the Alaskan lake as being warmer today than at any time during the MWP. Sorry.

4. Bradley, Raymond S. Climate System Research Center. “Climate of the Last Millennium.” 2003. February 23, 2007. [1]; E.L. Ladurie, Times of Feast, Times of Famine: a History of Climate Since the Year 1000 (0(Barbara Bray, tr.) (New York: Doubleday)1971.

Oh dear. Bradley finds:-

One thing that all reconstructions shown in Figure
6.6 clearly agree on is that northern hemisphere
mean temperature in the 20th century is unique, both
in its overall average and in the rate of temperature
increase. In particular the 1990s were exceptionally
warm — probably the warmest decade for at least
1000 years (even taking the estimated uncertainties
of earlier years into account).

I think I’ll give up at that point.

Are you claiming to have read these papers, Andrew? If so, why on earth are you presenting this list as evidence of whatever case you wish to put?

Thank you for your references.

when (if) you convince each author they are wrong come back

I have no expectation at all of considering any such authors to be ‘wrong’ (whatever you mean by that). You don’t say what you think your evidence amounts to in terms of the temperature of a global simultaneous MWP, so I can’t say whether I think you wrong or not.

Before commenting on your list, I need to ask what were your critieria for picking out these particular studies? There are plenty of accusations around of cherry-picking results that suit your prejudices, so can you assure us that you have not done this? I can see no obvious examples of studies which would count as evidence against your view, even though you must know there are plenty to choose from, so I do suspect that you may be doing exactly what some people have falsely accused Briffa of doing.

I’ll spend the time responding to your list in more detail once I know your selection criteria. For now, I’ll state the obvious points that your list is overwhelmingly one of NH locations and you give no indication yourself of the extent to which they do or do not suggest correlated warm periods.

It is not in dispute by me that there was an MWP, but the question of whether such a period was globally simultaneous is another matter, as is the indicative global average temperature during such a period. You must surely be aware that when we compare with present temperatures we do not compare with regions showing the highest anomalies, but with the global average.

I look forward to you clarifying your selection criteria.

Show me where Gavin’s analysis of the English wine tale is so wrong as to render his whole argument invalid, and I will concede.

A quick look at the first pdf linked in that list showed the conclusion I quoted. A list looks impressive, but if it doesn’t support your contention, it is just smoke and mirrors.

Bart, you should read the primary source, Selley’s book on the Winelands of Britain, not the distorted spin put on it by Gavin Schmidt.

I was referring to the fact that many people from outside of the science proclaim loudly that the science is wrong.

If you want such a strong claim to be taken seriously by anyone (besides your fellow shouters and ideological bedfellows), you have to play the game. The science game. Otherwise you’re just one more of those people shouting things like “The earth is flat, hollow, expanding, 6000 years old, and so on” to quote Robert Grumbine.

And about those English vineyards, see eg http://www.realclimate.org/ind.....lish-wine/

“Of course, we can argue about the details until the cows come home (like Steve M is good at), but this doesn’ change the bigger picture..”

Sure it does; the devil is always in the details. Of course increases in greenhouse gases must warm the planet’s surface, but it matters a LOT if the warming is 1.5C for a doubling of CO2 or if it is 4.5C. The key issue is an appropriate (political/taxation/public control) response to increases in CO2, and what is appropriate depends completely on how much warming will take place. To over-hype the potential warming (as I honestly think many do) so as to justify massive changes at enormous cost is just as irresponsible as to claim there is no warming from GHGs. Both avoid the difficult balance that needs to be struck between costs and benefits.

Put simply, we know there is a Greenhouse effect; we know that C02 is a GHG; we know its atmospheric concentration has increased; we have very strong evidence to believe that this increase is anthropogenic; we would expect this to induce warming (which seems to have occurred) and we would expect that this will continue and be significant (define as you want to) because we know sensitivity (within bounds). We also might expect some impacts and that these would likely be negative for human an ecosystems.

Of course, we can argue about the details until the cows come home (like Steve M is good at), but this doesn’ change the bigger picture (and my few dealings with Steve M suggests that he thinks so too).