66 Responses to "Paleoclimate: The End of the Holocene"
Boukesays
At -80 latitude 12kybp, mean december insolation anomaly is negative, mean june insolation anomaly is neutral, but mean anual insolation anomaly is strongly positive. Something interesting must be happening in spring and/or autumn, can anyone elaborate?
Any idea why error bars are getting substantially larger as present is approached? What’s happened to the Roman and Medieval warm periods? What’s happened to the cooling in between, when 9 m high ice ridges, coming from the Black sea, were towering over the walls of Byzantium (Istambul now)?
garethsays
@ Bouke
Fig.1 (Climate forcing reconstructions for use in PMIP simulations of the last millennium (v1.0)9(2011)
G. A. Schmidt .) Shows the much larger insolation changes around the eqinoxes than the solstices.(since CE 850)
*
gmd-4-33-2011.pdf
Nicksays
On figure 3.
Why do the error bounds on the right hand side increase?
Surely with measurement of temperatures, the error bounds must decrease?
ie. We know current temperatures accurately, but will be unsure of temperatures 10,000 years ago?
[Response: The error bars on the Marcott et al work are because (unusually) there are less records included as you come up to the present. This is related to the difficultly in retrieving and dating the top of ocean sediment cores, while it is relatively easy to date the the termination of the glacial period (and beginning of the Holocene). – gavin]
HarryWiggssays
Berenyi, given your…track record…please show me the supporting data that shows this isn’t just something you’ve once again made up.
“…when 9 m high ice ridges, coming from the Black sea, were towering over the walls of Byzantium (Istambul now)?”
timg56says
Dr Schmidt,
You say that the increase in uncertainty at the far end of the graph is due to few samples available. The authors have indicated that portion of their study is “not robust”. So why use it?
When the results for the last few decades of a 2 millenial period are uncertain and not robust, including them risks the credibility of the entire study.
[Response: Our opinions on this will obviously differ, but including the later points along with the uncertainties allows people to assess this for themselves. Plus inclusion of data that overlaps in time but does not have the same uncertainty (i.e. PAGES-2K, HadCRUT4) provides some context. Pointing out where parts of a reconstruction have more uncertainties than others adds to its credibility in my opinion. – gavin]
stefansays
That portion of the data is shown for comparison – of course the instrumental measurements (shown in red in the first graph) are much more reliable for the modern time, as I discuss in the article. -stefan
Can’t you read graphs? There’s a bump between 0 and 1000AD, and the error bounds give enough wiggle room for the MWP and Roman Warm periods.
Or is it that the wiggle room and bump isn’t large enough for your preconceptions?
Gruntersays
Mon cher M. Berenyi,
If you read the post carefully, both the reason for increasing error bars, and “what happened” to the Medieval Warm Period and the Little Ice Age are addressed — and they are in fact present in the graph (Fig. 1) — just not perhaps as you expected to see them, but as consistent with a long term trend.
But I am remiss if my comment is actually troll-feed.
Axelsays
Interesting post. So what about the 5000 year puzzle? You seem to leave this hanging or am I missing something?
It would help to have a 10,000 year history of natural and anthropogenic albedo change as well.
KRsays
I ran a Fourier filtering experiment using the Marcott et al reported frequency functions for their processing, and obtain results roughly identical to Grant Foster – any Holocene era temperature changes of a magnitude similar to current warming would indeed have shown up quite clearly in the Marcott analysis. (Not to mention that current warming simply won’t reverse/vanish on the same time-scale as it has ramped up, due to the persistence of CO2…)
Modern warming indeed appears unique in the Holocene era.
Tad Boydsays
It appears from the graph (Figure 3 blue line) that the unique rapid rise started in the late 1800′s.
1.) Does this suggest that humans were already putting out enough CO2 to cause global warming at that time?
or
2.) Even though the rapid rise is unique, it may have been natural (from the late 1800′s to 1940 – end of the blue line)?
or
3.) Something else… (my eyeballing of the graph was wrong, premise of my question was wrong, etc)?
Thanks,
Tad
Note: this may be a duplicate. I noticed comments making it through moderation time stamped after I’d asked my question. Please delete if my original post actually made it and just hasn’t been moderated yet. Thanks.
If I recall correctly, Marcott using the high frequency noise in the shorter Mann et al 2008 reconstruction to estimate what type of shorter-term variability might be removed over the whole holocene due to coarse proxy resolution. This yields his Figure 3, where they argue that the decade from 2000–2009 has not yet exceeded the warmest temperatures of the early Holocene (5,000 to 10,000 yr B.P.) but it is warmer than 72 percent of the record.
I wonder if you could do a similar analysis, but look at a frequency density function of 100-year (or 50-year) trends instead of looking at a frequency density function of anomalies. Its not perfect, of course, as there is no reason to think that the Mann et al 2008 reconstruction is really characteristic of shorter term (< 400 year) variability throughout the holocene, but the results might be interesting. I strongly suspect they would show the recent period as somewhat unique.
I am a 64 year old man in fair health, with chronic progressive aches and pains. But if I take the average readings of my health from the recent thirty years of my life, one has to say that I am vital and strong. (cough, cough)
And just this morning, I was thrilled to notice the water in my ice cube trays had frozen solid. After I add a little ethanol, I expect to greatly enjoy myself later on. But I dare not use either piece of evidence to prop up a deluded notion that I remain a young man on a cooling planet.
Cheers !
Lawrence Dawsonsays
And so, unless we are able to do something about climate change, we shall be entering the obcene era.
Anonymous Cowardsays
Tad Boyd #13,
“It appears from the graph (Figure 3 blue line) that the unique rapid rise started in the late 1800′s.
1.) Does this suggest that humans were already putting out enough CO2 to cause global warming at that time?”
Yes, but not enough for the resulting global warming to obviously jump out of the random variations.
For context, here are a couple of graphs featuring relevant estimates: http://cdiac.ornl.gov/trends/emis/graphics/global.total.jpg http://cdiac.ornl.gov/trends/co2/graphics/lawdome.gif
You should generally not trust random graphs. Even if there’s a .gov in the URL suggesting they’re not simply made up, you shoudn’t trust the impression you get for eyeballing graphs that may have been chosen to produce a particular impression. However, this being realclimate, you may hopefully trust that misleading or badly outdated data will be shot down.
Note that the more CO2 there is in the atmosphere, the less impact every additional mole has.
Also note that deforestation had a large impact on atmospheric CO2 concentrations relative to the burning of fossil fuels before the end of the 19th century.
“2.) Even though the rapid rise is unique, it may have been natural (from the late 1800′s to 1940 – end of the blue line)?”
I’m not crazy about the word “natural” in this context because of the large impact of pre-industrical human activity.
Obviously temperatures were already affected by elevated levels of CO2.
But because there have been a lot of random variations, I’m not sure the circa 1875-1940 global warming was all that rapid or unique unless you consider it as part of the longer industrial-age warming trend which is of course remarkable indeed.
But no doubt other commenters would have something more cogent to say on the matter.
David B. Bensonsays
Tad Boyd @13 — Anthropogenic changes to so-called natural climate trends began to be quite sizable with the clearing of forests in Europe and North America for ever increased agricultural fields. Coal, Satan’s cobbles, started being burned in appreciate quantities by 1750 CE and there was already appreciable heavy industry by about 1850 CE.
That the trend in global temperature only becomes positive around 1880 CE is an indication of what is called climate inertia combined with the declining orbital forcing which had to be overcome.
owl905says
“What’s happened to the Roman and Medieval warm periods? What’s happened to the cooling in between, when 9 m high ice ridges, coming from the Black sea, were towering over the walls of Byzantium (Istambul now)?”
There were no ice ridges. And since the walls of Constantinople were 12 meters in height, a 9-meter ‘ice ridge’ wouldn’t ‘tower over them’. There were recorded episodes of the Marmara Sea icing over in the 1st century CE, the 4th century CE, and a succession of frozen sea winters from 800-1300 – but no 9meter ice ridges. Yavuz et. al. “The Frozen Bosphorus”, 2007.
andrew adamssays
#9
If you read the post carefully, both the reason for increasing error bars, and “what happened” to the Medieval Warm Period and the Little Ice Age are addressed — and they are in fact present in the graph (Fig. 1) — just not perhaps as you expected to see them, but as consistent with a long term trend.
Yes, it occurred to me before that the Marcott reconstruction kind of puts the MWP into perspective. Prior to the last century it looks like we had a cooling trend of about 5k years, so it would be expected that temperatures in Medieval times would be warmer than in most of the last 700-800 years and, in the absence of modern anthropogenic warming, warmer than today.
So if there was a temporary but slight deviation from the long term trend, and throw in a bit of regional variation, then it could well be the case that NH temps in medieval times were particularly warm, even approaching today’s levels (or exceeding them in some locations). But this would not be evidence that warming to the extent we have seen over the last century occurred naturally at that time without any human influence. I guess to be fair that it also counters the argument that the MWP is evidence for high climate sensitivity.
Surely the one thing this post is at pains to point out is that it does not accurately propose the level at which temperatures began to turn and thus when “the unique rapid rise started” is also not on offer.
However I think your point is that the driver of such a rise would have to be strong enough by 1940 to be responsible for the loin’s share of the 0.35C rise that we know from thermometers had occurred by 1940. (Note that HadCRUT4 shows (as graphed here) declining temperatures 1850-1908 and then a 0.47C rise to 1940.) Perhaps you are also wondering how far back such a driver would have a significant impact on temperature so as to start that “unique rapid rise.”
If C02 is considered as that driver (not a ridiculous idea in principle, although it is more complicated than that as intimated @19) how much forcing and thus how much temperature rise could we expect from our CO2 emissions by, say, 1900 or 1940?
On the back of a fag packet. From the graph presented by Scripps Institute CO2 measured from ice cores had risen 20ppm by 1900 or 16% of the CO2 rise to date. By 1940 35ppm = 30%. The forcing per ppm is greater at lower CO2 levels and the slower rate of CO2 rise would mean more of the forcing was potentially balanced by temperature rise. But, ignoring that, a simple pro rata rise per ppm yields +0.13C (1900) +0.24C (1940).
Again very simplistically, if the wobbles from the Marcott et al reconstruction are seen as a possible size of natural low frequency wobbles of the order of 0.1C peak to peak, the idea that “the unique rapid rise” should have started before 1900 would fit with CO2 as the dominant driver. The size of natural high frequency wobbles may or may not be why HadCRUT4 shows a minimum in 1908. Certainly by 1940 a CO2 forcing would be dwarfing those natural low frequency wobbles and this appearing as a significant feature on a graph of millennial temperatures.
This lengthened reconstruction of global temperatures is no longer forming the shape of a hockey stick. Given hockey sticks are traditionally made from Mulberry and that Mulberry has a characteristic of growing slowly when mature (at least under natural circumstances), would it be fitting to christen the lengthened reconstruction developed here by Marcott et al as the “Mulberry Bough”.
Although myself I would end the trace at 2012 with just a marker to show the 2100 projection, it surely would remain plain to any observer with half a brain that the spurt of growth we see on the end of that Mulberry Bough is not natural.
FPsays
Are there any Geologists claiming that the planet has been warming for the last 11000 years? Were there ever any Geologists making that Claim? And have they revised their position recently similar to the way the Geological Society revised their position statement on recent warming ?
FPsays
Here, is the AAPG claiming the earth to be warmer in the last 10,000 years…
” In recent decades global temperatures have risen. However, our planet has been far warmer and cooler today than many times in the geologic past, even within the past 10,000 years.”
~ What is their evidence of that? Or is their only argument: “Well, it could have happened, it is possible, and it could be hidden because the data is not granular… ” Or do they have real evidence?
Tad Boydsays
Tad Boyd @13
Found that Gavin had replied to my question but it was sent to the borehole [#1300].
[Response: Other people can chime in – but I think it’s more useful to think of the early 1800’s as being a time when shorter term natural forcings (particularly volcanoes and solar) were pushing climate cooler than the long term trend would imply. Without anthropogenic influences there would have been a recovery of sorts but only to the long term trend – what has actually happened is vastly different. – gavin]
Thanks all for your responses.
I’d had the idea that more recent (than pre-1900) very high human emissions of CO2 drove global warming (the SUV/Commercial air flight era). I was aware of the idea that human activity much earlier than that had started to bring about global warming but did not know if this was generally the view of actual climate scientists. I don’t usually comment because I’m not qualified to make a point, but occasionally do post a question to try to get clarification on what actual climate scientists believe vs. all the other ideas out there and have gotten good direction here at RealClimate (especially from Gavin).
From other commenters that were kind enough to respond to my question I’ve gotten – we (humans) were warming the planet (offsetting cooling) early on (1700’s and 1800’s). Gavin indicates we would have seen a recovery of sorts without human influences but not what has actually happened.
MARodger – You laid out the influences of 20ppm CO2 and 35ppm CO2 increases. (Note – in my reading when Stephan was talking about the unique rapid rise under Figure 3, I was focused on the Marcott et al. blue line and thought that was the context for his description but using HadCRU as the context for the unique rapid rise Stephan is talking about works too as the rapid rise pre 1940 in red, is even more dramatic). Your response helps a great deal to sharpen my clumsy question.
Stefan and/or Gavin – I was assuming that the 1940 and before portion of the rise (Marcot et al. blue line, but HadCRU red line works too) was at least part of what Stefan was referring to as the unique rapid rise but MARodger has indicated my assumption is off in some manner so any instruction regarding that is appreciated. If my assumption is valid in some sense, is the uniqueness of the pre 1940 rapid rise the result of the human activity part of the 20ppm and 35ppm CO2 increases MARodger discusses?
Sorry if MARodger’s response should have sufficed. It is possible I am in the <50% brain category. I do appreciate that actual climate scientists are willing to interact at this level helping separate what the scientists believe vs. the rest.
Introduction to Geological Perspectives of Global Climate Change
Power Point Presentation
Lee C. Gerhard
History has seen many memorable public confrontations between belief systems and science data. Despite the scientific merit of the data, belief systems are powerful endemic and forces against which science must struggle. Some modern examples are evolution and global climate change..
Notes:
Two versions of the presentation are included, one for scientists, without on-slide comment, and one for the lay public with some additional notation.
These presentations will be updated as new information becomes available.
The notes for the scientist version contain many of the base references; a reading list, partly annotated, is appended to this introduction.
So — “evolution and climate change” — I wonder what he means by that?
In Fig 2 I am having a hard time reconciling Mean Dec and Mean Annual. The Mean June makes perfect sense – high insolation in N. Hemisphere extending to Arctic. The Mean Dec does not show high insolation in S. Hemisphere or Antarctic yet the Annual Mean then shows high insolation in Antarctic.
Also, with the large solar forcing 8-10K ago “more than 30 watts per square meter” (in summer I assume) I would have expected even higher temperatures than modern 20th century. Why is that expectation wrong?
Boukesays
@26
Quote from that .doc by Lee C. Gerhard:
The mission of the Intergovernmental Panel on Climate Change (IPCC), a United Nations organization, is not to study causes of climate change, but to document only one cause, human impacts on climate.
[the UN] Endorses the action of the World Meteorological Organization and the United Nations Environment Programme in jointly establishing an Intergovernmental Panel on Climate Change to provide internationally co-ordinated scientific assessments of the magnitude, timing and potential environmental and socio-economic impact of climate change and realistic response strategies
When I read these two things, I get the urge to add Lee C. Gerhard to my list of intellectually bankrupt people.
Romainsays
Bouke,
Care to explain this extract from the “history” page of the ipcc.ch site.
Nothing about NOT human-induced climate change…
“Today the IPCC’s role is as defined in Principles Governing IPCC Work, “…to assess on a comprehensive, objective, open and transparent basis the scientific, technical and socio-economic information relevant to understanding the scientific basis of risk of human-induced climate change, its potential impacts and options for adaptation and mitigation. IPCC reports should be neutral with respect to policy, although they may need to deal objectively with scientific, technical and socio-economic factors relevant to the application of particular policies.”
[Response: Understanding “the scientific basis of the risk of human-induced climate change” obviously requires knowing the context of natural climate change and variability – explaining the amount of space in the IPCC reports given to issues associated with paleo-climate, ENSO, the AMO, signal-to-noise calculations, detection and attribution etc. This idea that IPCC doesn’t look at internal variability or natural forcings is just bogus. – gavin]
Nicksays
Why is the right hand side figure not in the center of the error bounds?
Further to comment @25-27.
The actual slides are in this pdf. There is another version of notes & slides here. It dates back to 2007 and is very silly stuff.
we investigate organic carbon sedimentation patterns and surface water productivity changes in response to Holocene Previous HitclimateTop variability in northern high latitudes. We studied 197 surface sediment samples, 10 short (ca. 10-30 cm long) and 2 long (3-4 m) cores representing the last 10000 years in the western sector of the Barents Sea between Spitsbergen and the Norwegian mainland.
The Barents Sea is a shallow (mean depth ca. 200 m) Arctic Ocean shelf sea which is partially covered by sea ice in the northeast in the winter. Warm, saline Atlantic water (AW) enters the Barents Sea in the southwest and flows east- and northward until it is subducted under cold, fresh Arctic water (ArW) which enters the Barents Sea from the northeast and flows southwestward. The region where the AW is subducted under the ArW is called the Polar Front (PF). Its position is mainly topographically controlled but also depends on the relative strengths of the two water masses. This is also the region of the winter ice margin. Previous research has shown that the Barents Sea is one of the most productive shelf seas in the world.
…
We use OF-Mod 3D, an organic facies modeling software developed by SINTEF Petroleum Research, to reconstruct PP changes and organic carbon accumulation across the western Barents Sea throughout the past 10000 years. OF-Mod 3D is a predictive, process-based, forward-modeling tool used to calculate organic matter preservation in a 3D grid throughout the modeled domain. The surface sample data set is used to calibrate the model to the present-day situation and we will show the spatial distribution of modeled PP throughout the Barents Sea region. We include the position of the PF in the model as a northern boundary for PP during the winter and compare organic matter accumulation in the presence and absence of sea ice.
Well, look around there first, don’t take the worst you can find and write off the rest unseen. That one’s a dinosaur, you expect those. They’re holdovers from the Antideluvian Age, er something.
Petroleum geologists have to understand modeling and climate.
owl905says
Keying off 26 and 27:
Gerhard’s attempts a smear with “The mission of the Intergovernmental Panel on Climate Change (IPCC), a United Nations organization, is not to study causes of climate change, but to document only one cause, human impacts on climate.”
In a lay-down, he’s right. Our climate would not have nearly the focus, the research, the reviews, and the controversy, if it was just ‘understanding it all’. But while Gerhard thinks he’s exposing a secret agenda scam, he’s actually admitting that he can’t join the dots. He doesn’t understand that rising GHG pollution is contributing to a disruption of the climate so geologically sudden and ubiquitous in extent, that the parallels best matching it are extinction events. That’s exactly why the IPCC synthesizes a global state of the change every X years. Gerhard displays a kind of Victorian attitude that somehow if the IPCC just stopped talking about, it would be less of a problem.
wilisays
MARodger @ 23: I was thinking the same thing, but what I see is more like a kind of ergonomically made scythe with a curved handle. (links to images seem to be too long for the filter)
Meanwhile, on the topic of paleo-climate, Hansen has a new piece out in Philosophical Transactions of the Royal Society A:
#23 >Given hockey sticks are traditionally made from Mulberry…
Hockey sticks were never made from mulberry…originally made from hop hornbeam (Ostrya virginiana), then later ash, birch, poplar, and willow. Mulberry is not a commercially viable wood.
“1860s Hockey taken to India. Stickhead made shorter; move from Ash to Mulberry timber for the stick head.”
Romainsays
Gavin,
“This idea that IPCC doesn’t look at internal variability or natural forcings is just bogus.”
Yes it’s bogus. Of course they look at it. Whether or not they FOCUS on it is the question.
What is behind the quoted paragraph when you read it at face value is that this internal variability is just background (proof is, it’s not even mentioned). They say they assess impacts, mitigation and adaptation of HUMAN-induced climate change. Implying that the IPCC is here to confirm a preconceived theory/idea: HUMAN-induced climate change is the most important to care about. IPCC is not here to care about the impacts of natural variability. The scope of work is clear.
I guess it is because internal variability had already been found to have negligible impact compared to human-induced at the time IPCC was created. But then I hear people saying: it’s hard for IPCC people to question the premises on which it has been created.
[Response: This is just very strange. The IPCC is indeed designed to focus on the potential for anthropogenic impacts on climate and I don’t see what is so bad about that. The answer might well have been that there weren’t any important ones. Other review panels (on the Supersonic Stratospheric Transports etc.) come up with not much and are generally set aside – this happens all the time. The IPCC premise is that there is a potential issue worth investigating (a true statement), not that climate sensitivity is some fixed number or that natural variability is negligible. The idea that scientists would work on an assessment that they knew to be pointless is nuts. It’s not like these things are fun. – gavin]
David C.says
Can anyone point me to articles discussing the accuracy of the various proxies themselves? I apologize for my ignorance on this, but to me it seems our understanding of the relationship between the proxy data and temperature should be calibrated and tested against the observed temperature record. The error bars seem to indicate that we know the exact global temperature within 0.2 degrees C 1000 years ago, but where we have actual temperature data, the error margin is more than a degree (which more than covers the observed warming).
In short, do the error bars indicate that science is 95% confident in the real global temperature to within less than 1 degree C for the last few thousand years, or that it is 95% confident that the proxies, using the best available techniques to calibrate calibrate with global temperature, is accurate to within 1 degree C?
> David C.
An explanation of that will either assume you did pass Statistics 101, or that you did not. Have you that background in statistics already? If not, some background is needed.
You’ve run into a problem that confuses a lot of people.
in 2005, a team led by Sarah Belia conducted a study of hundreds of researchers who had published articles in top psychology, neuroscience, and medical journals. Only a small portion of them could demonstrate accurate knowledge of how error bars relate to significance. If published researchers can’t do it, should we expect casual blog readers to?
Confidence Intervals
First off, we need to know the correct answer to the problem, which requires a bit of explanation….
No, I’m not going to try to explain it, I’m a student here myself. Just sayin’, this is an area that takes serious effort to get even a fair idea of what they’re really saying.
None of your paraphrases above seems, to me, close to the mark.
You do present your enquiries in an interesting way, so I don’t know but perhaps this might help. (Note that I am by no means a “climate scientist,” actual or otherwise.)
Because Marcott et al only shows long-term fluctuations, a robust comparison between the blue shoot at the end of the Fig 3 trace and HadCRUT4 is always going to be difficult, especially with the Marcott et al error bars flying off so rapidly. And also note the comment in the post about the “flexibility” of such a “join” although this does not affect the size of the Marcott & the HadCRU rises.
Perhaps to compare apples & apples, HadCRUT4 should be represented far less precisely, say by just 3 x 55-year averages. 1877 -0.32C, 1932 -0.19C, 1987 +0.16C. The BEST land temperature record suggests that HadCRUT4 is not showing all of this “strong rising trend” because it appeared to start earlier than 1850 in the BEST data. So, like the 5 final green dots from PAGE2K, the 1800-1940 0.25C rise in the Marcott et al blue trace is not far from what we see in the thermometer records.
Thus far this analysis is fuzzing out the short term wobbles. But you perhaps allude to wondering how much of the pre-1940 temperature rise (presumably the 1910-40 period) is wobble and how much is “strong rising trend.”
The climate forcings that lie behind the recent wobbles and the “strong rising trend” of HadCRUT4 can be calculated with varying accuracy. The graphs here by Sato et al presents forcings 1880 to date. Note the green plot – this is mostly but by no means all CO2 and that it is not flat back in 1880 (my point @26 with the +20ppm & +35ppm). This green plot is the big positive driver behind the “strong rising trend” but there are also very significant negative drivers.
It is a major task of climatology to establish these forcings with more accuracy and to marry the forcings with the temperature record. While this work remains incomplete, there exists room for speculation about natural oscillations, speculation that deniers love to over-amplify into reasons for ignoring that green plot in the Sato et al graph. But my take-away from the Sato et al graph is that the green plot is a little too scary to be ignored.
Peter Smithsays
For most of the time covered by these graphs, the thermal mechanism would appear to be more-or-less in a steady state, just quietly following various changes in the forcings. We do not appear to be in a steady state at the moment.
If we assume the CO2 concentrations stay at the current levels, and if we ignore any positive feedback from methane and so on, is it possible to calculate what temperature we might get to, given enough time?
Anonymous Cowardsays
Peter Smith #45,
That’s the big question; what the sensitivity metric was created for.
Assuming all forcings (methane, smog and stuff) except CO2 at pre-industrial levels and atomspheric CO2 at the current level, “fast” feedbacks (such as snow cover but excluding the very slow melting of the large ice masses) should get the average global temperature to around 0.52 * sensitivity above the pre-industrial average (if I recall correctly).
Now sensitivity is likely to turn out to be around 2 to 4 centigrades so (ignoring the many caveats) the answer you’re looking for would be between +.7 to +1.8 on the graph at the top of the page.
Jim Eagersays
Re Peter Smith @ #45, it is instructive to look at what earth’s climate was like the last time its atmosphere contained 400 ppm CO2, which would be around 3 million years ago during the mid-Pliocene. Global mean temperature then was 2-3C higher than today (and much higher towards the poles), it’s thought there was a near constant El Nino state, and the West Antarctic ice sheet had collapsed, raising sea level by as much as 25 meters. That said, at about this time the Panama seaway closed, which dramatically changed ocean circulation patterns, and uplift of the Rocky Mountains was also taking place, so the mid-Pliocene is far from a perfect analogy.
John Lsays
I saw this headline in Science:
Researchers Wary as DOE Bids to Build Sixth U.S. Climate Model
All: keep an eye out for Bill Ruddiman’s Earth Transformed, which is supposed to be out in October (after some confusion about dates.) I think this sheds more light on the last ~8,000 years, relevant both to Marcott, et all and PAGES2K. Compared to past interglacials (when well-aligned, which took a lot of work), the usual slow CH4/CO2 downtrends had been slowed well before the Industrial Revolution started.
The cover illustrates the part of the story that comes from Chinese rice paddy archaeology and methane curves compared to other interglacials.
For anyone attending AGU in December, Bill will be giving the Tyndall Lecture.
pete bestsays
considering that humans have now emitted 550 billion tonnes of co2 to date and 1 trillion tonnes emitted brings about the 2C danger threshold (often spoken about by those concerned about such things)and we emit now around 33 billion tonnes rising at 2-3% per annum means that in just a few decades from now the trillion tonnes would have been passed.
Is it all bad – probably not – but its not all good either and some will definitely suffer from increased flooding and droughts, food shortages and more than likely war as a consequence of such things occurring. It might already be occurring in Syria and Egypt due to food pressures caused by ACC.
the higher the temperature gets the worse it will probably be although I am sure that places such as southern England can continue to reap the rewards of growing pinot noir and chardonnay grapes for sparking fizz.
Lynn Vincentnathansays
This is going to be quite upsetting to the MWP climate skeptics that think the MWP was the warmest period ever, warmer than the mid-Eocene high point, than the PETM, than the end-Permian.
And what do I find in that 1st graph — it was warmer 7,000 years ago (at the -5,000 point) than during the MWP.
They’re going to get really mad, then work like devils on finding some way to deny it and resurrect their MWP as the warmest of all. :)
At -80 latitude 12kybp, mean december insolation anomaly is negative, mean june insolation anomaly is neutral, but mean anual insolation anomaly is strongly positive. Something interesting must be happening in spring and/or autumn, can anyone elaborate?
Any idea why error bars are getting substantially larger as present is approached? What’s happened to the Roman and Medieval warm periods? What’s happened to the cooling in between, when 9 m high ice ridges, coming from the Black sea, were towering over the walls of Byzantium (Istambul now)?
@ Bouke
Fig.1 (Climate forcing reconstructions for use in PMIP simulations of the last millennium (v1.0)9(2011)
G. A. Schmidt .) Shows the much larger insolation changes around the eqinoxes than the solstices.(since CE 850)
*
gmd-4-33-2011.pdf
On figure 3.
Why do the error bounds on the right hand side increase?
Surely with measurement of temperatures, the error bounds must decrease?
ie. We know current temperatures accurately, but will be unsure of temperatures 10,000 years ago?
[Response: The error bars on the Marcott et al work are because (unusually) there are less records included as you come up to the present. This is related to the difficultly in retrieving and dating the top of ocean sediment cores, while it is relatively easy to date the the termination of the glacial period (and beginning of the Holocene). – gavin]
Berenyi, given your…track record…please show me the supporting data that shows this isn’t just something you’ve once again made up.
“…when 9 m high ice ridges, coming from the Black sea, were towering over the walls of Byzantium (Istambul now)?”
Dr Schmidt,
You say that the increase in uncertainty at the far end of the graph is due to few samples available. The authors have indicated that portion of their study is “not robust”. So why use it?
When the results for the last few decades of a 2 millenial period are uncertain and not robust, including them risks the credibility of the entire study.
[Response: Our opinions on this will obviously differ, but including the later points along with the uncertainties allows people to assess this for themselves. Plus inclusion of data that overlaps in time but does not have the same uncertainty (i.e. PAGES-2K, HadCRUT4) provides some context. Pointing out where parts of a reconstruction have more uncertainties than others adds to its credibility in my opinion. – gavin]
That portion of the data is shown for comparison – of course the instrumental measurements (shown in red in the first graph) are much more reliable for the modern time, as I discuss in the article. -stefan
Marvellous stuff.
Berényi Péter,
Can’t you read graphs? There’s a bump between 0 and 1000AD, and the error bounds give enough wiggle room for the MWP and Roman Warm periods.
Or is it that the wiggle room and bump isn’t large enough for your preconceptions?
Mon cher M. Berenyi,
If you read the post carefully, both the reason for increasing error bars, and “what happened” to the Medieval Warm Period and the Little Ice Age are addressed — and they are in fact present in the graph (Fig. 1) — just not perhaps as you expected to see them, but as consistent with a long term trend.
But I am remiss if my comment is actually troll-feed.
Interesting post. So what about the 5000 year puzzle? You seem to leave this hanging or am I missing something?
Thanks
It would help to have a 10,000 year history of natural and anthropogenic albedo change as well.
I ran a Fourier filtering experiment using the Marcott et al reported frequency functions for their processing, and obtain results roughly identical to Grant Foster – any Holocene era temperature changes of a magnitude similar to current warming would indeed have shown up quite clearly in the Marcott analysis. (Not to mention that current warming simply won’t reverse/vanish on the same time-scale as it has ramped up, due to the persistence of CO2…)
Modern warming indeed appears unique in the Holocene era.
It appears from the graph (Figure 3 blue line) that the unique rapid rise started in the late 1800′s.
1.) Does this suggest that humans were already putting out enough CO2 to cause global warming at that time?
or
2.) Even though the rapid rise is unique, it may have been natural (from the late 1800′s to 1940 – end of the blue line)?
or
3.) Something else… (my eyeballing of the graph was wrong, premise of my question was wrong, etc)?
Thanks,
Tad
Note: this may be a duplicate. I noticed comments making it through moderation time stamped after I’d asked my question. Please delete if my original post actually made it and just hasn’t been moderated yet. Thanks.
If I recall correctly, Marcott using the high frequency noise in the shorter Mann et al 2008 reconstruction to estimate what type of shorter-term variability might be removed over the whole holocene due to coarse proxy resolution. This yields his Figure 3, where they argue that the decade from 2000–2009 has not yet exceeded the warmest temperatures of the early Holocene (5,000 to 10,000 yr B.P.) but it is warmer than 72 percent of the record.
I wonder if you could do a similar analysis, but look at a frequency density function of 100-year (or 50-year) trends instead of looking at a frequency density function of anomalies. Its not perfect, of course, as there is no reason to think that the Mann et al 2008 reconstruction is really characteristic of shorter term (< 400 year) variability throughout the holocene, but the results might be interesting. I strongly suspect they would show the recent period as somewhat unique.
> the top of ocean sedimentary cores
The top is almost always inhabited — the result is “bioturbation … rapid removal of sediments from the sediment surface (ingestion) followed by injection of this material (defecation) a few centimeters below the sediment surface. This process has significant implications for the age of surficial sediment and for discerning change in sediment contaminant concentrations following change in contaminant inputs. ”
In an undisturbed site where nothing lives in the mud, you could get annual or even seasonal layers (varves“).
It’s not a big problem. It’s one consideration when getting information out of core samples.
I am a 64 year old man in fair health, with chronic progressive aches and pains. But if I take the average readings of my health from the recent thirty years of my life, one has to say that I am vital and strong. (cough, cough)
And just this morning, I was thrilled to notice the water in my ice cube trays had frozen solid. After I add a little ethanol, I expect to greatly enjoy myself later on. But I dare not use either piece of evidence to prop up a deluded notion that I remain a young man on a cooling planet.
Cheers !
And so, unless we are able to do something about climate change, we shall be entering the obcene era.
Tad Boyd #13,
“It appears from the graph (Figure 3 blue line) that the unique rapid rise started in the late 1800′s.
1.) Does this suggest that humans were already putting out enough CO2 to cause global warming at that time?”
Yes, but not enough for the resulting global warming to obviously jump out of the random variations.
For context, here are a couple of graphs featuring relevant estimates:
http://cdiac.ornl.gov/trends/emis/graphics/global.total.jpg
http://cdiac.ornl.gov/trends/co2/graphics/lawdome.gif
You should generally not trust random graphs. Even if there’s a .gov in the URL suggesting they’re not simply made up, you shoudn’t trust the impression you get for eyeballing graphs that may have been chosen to produce a particular impression. However, this being realclimate, you may hopefully trust that misleading or badly outdated data will be shot down.
Note that the more CO2 there is in the atmosphere, the less impact every additional mole has.
Also note that deforestation had a large impact on atmospheric CO2 concentrations relative to the burning of fossil fuels before the end of the 19th century.
“2.) Even though the rapid rise is unique, it may have been natural (from the late 1800′s to 1940 – end of the blue line)?”
I’m not crazy about the word “natural” in this context because of the large impact of pre-industrical human activity.
Obviously temperatures were already affected by elevated levels of CO2.
But because there have been a lot of random variations, I’m not sure the circa 1875-1940 global warming was all that rapid or unique unless you consider it as part of the longer industrial-age warming trend which is of course remarkable indeed.
But no doubt other commenters would have something more cogent to say on the matter.
Tad Boyd @13 — Anthropogenic changes to so-called natural climate trends began to be quite sizable with the clearing of forests in Europe and North America for ever increased agricultural fields. Coal, Satan’s cobbles, started being burned in appreciate quantities by 1750 CE and there was already appreciable heavy industry by about 1850 CE.
That the trend in global temperature only becomes positive around 1880 CE is an indication of what is called climate inertia combined with the declining orbital forcing which had to be overcome.
“What’s happened to the Roman and Medieval warm periods? What’s happened to the cooling in between, when 9 m high ice ridges, coming from the Black sea, were towering over the walls of Byzantium (Istambul now)?”
There were no ice ridges. And since the walls of Constantinople were 12 meters in height, a 9-meter ‘ice ridge’ wouldn’t ‘tower over them’. There were recorded episodes of the Marmara Sea icing over in the 1st century CE, the 4th century CE, and a succession of frozen sea winters from 800-1300 – but no 9meter ice ridges. Yavuz et. al. “The Frozen Bosphorus”, 2007.
#9
If you read the post carefully, both the reason for increasing error bars, and “what happened” to the Medieval Warm Period and the Little Ice Age are addressed — and they are in fact present in the graph (Fig. 1) — just not perhaps as you expected to see them, but as consistent with a long term trend.
Yes, it occurred to me before that the Marcott reconstruction kind of puts the MWP into perspective. Prior to the last century it looks like we had a cooling trend of about 5k years, so it would be expected that temperatures in Medieval times would be warmer than in most of the last 700-800 years and, in the absence of modern anthropogenic warming, warmer than today.
So if there was a temporary but slight deviation from the long term trend, and throw in a bit of regional variation, then it could well be the case that NH temps in medieval times were particularly warm, even approaching today’s levels (or exceeding them in some locations). But this would not be evidence that warming to the extent we have seen over the last century occurred naturally at that time without any human influence. I guess to be fair that it also counters the argument that the MWP is evidence for high climate sensitivity.
Is this a fair interpretation?
Tad Boyd @13.
Surely the one thing this post is at pains to point out is that it does not accurately propose the level at which temperatures began to turn and thus when “the unique rapid rise started” is also not on offer.
However I think your point is that the driver of such a rise would have to be strong enough by 1940 to be responsible for the loin’s share of the 0.35C rise that we know from thermometers had occurred by 1940. (Note that HadCRUT4 shows (as graphed here) declining temperatures 1850-1908 and then a 0.47C rise to 1940.) Perhaps you are also wondering how far back such a driver would have a significant impact on temperature so as to start that “unique rapid rise.”
If C02 is considered as that driver (not a ridiculous idea in principle, although it is more complicated than that as intimated @19) how much forcing and thus how much temperature rise could we expect from our CO2 emissions by, say, 1900 or 1940?
On the back of a fag packet. From the graph presented by Scripps Institute CO2 measured from ice cores had risen 20ppm by 1900 or 16% of the CO2 rise to date. By 1940 35ppm = 30%. The forcing per ppm is greater at lower CO2 levels and the slower rate of CO2 rise would mean more of the forcing was potentially balanced by temperature rise. But, ignoring that, a simple pro rata rise per ppm yields +0.13C (1900) +0.24C (1940).
Again very simplistically, if the wobbles from the Marcott et al reconstruction are seen as a possible size of natural low frequency wobbles of the order of 0.1C peak to peak, the idea that “the unique rapid rise” should have started before 1900 would fit with CO2 as the dominant driver. The size of natural high frequency wobbles may or may not be why HadCRUT4 shows a minimum in 1908. Certainly by 1940 a CO2 forcing would be dwarfing those natural low frequency wobbles and this appearing as a significant feature on a graph of millennial temperatures.
This lengthened reconstruction of global temperatures is no longer forming the shape of a hockey stick. Given hockey sticks are traditionally made from Mulberry and that Mulberry has a characteristic of growing slowly when mature (at least under natural circumstances), would it be fitting to christen the lengthened reconstruction developed here by Marcott et al as the “Mulberry Bough”.
Although myself I would end the trace at 2012 with just a marker to show the 2100 projection, it surely would remain plain to any observer with half a brain that the spurt of growth we see on the end of that Mulberry Bough is not natural.
Are there any Geologists claiming that the planet has been warming for the last 11000 years? Were there ever any Geologists making that Claim? And have they revised their position recently similar to the way the Geological Society revised their position statement on recent warming ?
Here, is the AAPG claiming the earth to be warmer in the last 10,000 years…
” In recent decades global temperatures have risen. However, our planet has been far warmer and cooler today than many times in the geologic past, even within the past 10,000 years.”
~ What is their evidence of that? Or is their only argument: “Well, it could have happened, it is possible, and it could be hidden because the data is not granular… ” Or do they have real evidence?
Tad Boyd @13
Found that Gavin had replied to my question but it was sent to the borehole [#1300].
[Response: Other people can chime in – but I think it’s more useful to think of the early 1800’s as being a time when shorter term natural forcings (particularly volcanoes and solar) were pushing climate cooler than the long term trend would imply. Without anthropogenic influences there would have been a recovery of sorts but only to the long term trend – what has actually happened is vastly different. – gavin]
Thanks all for your responses.
I’d had the idea that more recent (than pre-1900) very high human emissions of CO2 drove global warming (the SUV/Commercial air flight era). I was aware of the idea that human activity much earlier than that had started to bring about global warming but did not know if this was generally the view of actual climate scientists. I don’t usually comment because I’m not qualified to make a point, but occasionally do post a question to try to get clarification on what actual climate scientists believe vs. all the other ideas out there and have gotten good direction here at RealClimate (especially from Gavin).
From other commenters that were kind enough to respond to my question I’ve gotten – we (humans) were warming the planet (offsetting cooling) early on (1700’s and 1800’s). Gavin indicates we would have seen a recovery of sorts without human influences but not what has actually happened.
MARodger – You laid out the influences of 20ppm CO2 and 35ppm CO2 increases. (Note – in my reading when Stephan was talking about the unique rapid rise under Figure 3, I was focused on the Marcott et al. blue line and thought that was the context for his description but using HadCRU as the context for the unique rapid rise Stephan is talking about works too as the rapid rise pre 1940 in red, is even more dramatic). Your response helps a great deal to sharpen my clumsy question.
Stefan and/or Gavin – I was assuming that the 1940 and before portion of the rise (Marcot et al. blue line, but HadCRU red line works too) was at least part of what Stefan was referring to as the unique rapid rise but MARodger has indicated my assumption is off in some manner so any instruction regarding that is appreciated. If my assumption is valid in some sense, is the uniqueness of the pre 1940 rapid rise the result of the human activity part of the 20ppm and 35ppm CO2 increases MARodger discusses?
Sorry if MARodger’s response should have sufficed. It is possible I am in the <50% brain category. I do appreciate that actual climate scientists are willing to interact at this level helping separate what the scientists believe vs. the rest.
Thanks,
Tad
> our planet has been far warmer and cooler today …
The AAPG authors:
http://www.aapg.org/eseries/StaticContent/AAPG_files/html/bio527.html
Their approach starts and ends with politics and money, not climatology:
http://www.kansasenergy.org/documents/Gerhard_slide_notes.doc
So — “evolution and climate change” — I wonder what he means by that?
In Fig 2 I am having a hard time reconciling Mean Dec and Mean Annual. The Mean June makes perfect sense – high insolation in N. Hemisphere extending to Arctic. The Mean Dec does not show high insolation in S. Hemisphere or Antarctic yet the Annual Mean then shows high insolation in Antarctic.
Also, with the large solar forcing 8-10K ago “more than 30 watts per square meter” (in summer I assume) I would have expected even higher temperatures than modern 20th century. Why is that expectation wrong?
@26
Quote from that .doc by Lee C. Gerhard:
Quote from the resolution that started the IPCC:
When I read these two things, I get the urge to add Lee C. Gerhard to my list of intellectually bankrupt people.
Bouke,
Care to explain this extract from the “history” page of the ipcc.ch site.
Nothing about NOT human-induced climate change…
“Today the IPCC’s role is as defined in Principles Governing IPCC Work, “…to assess on a comprehensive, objective, open and transparent basis the scientific, technical and socio-economic information relevant to understanding the scientific basis of risk of human-induced climate change, its potential impacts and options for adaptation and mitigation. IPCC reports should be neutral with respect to policy, although they may need to deal objectively with scientific, technical and socio-economic factors relevant to the application of particular policies.”
[Response: Understanding “the scientific basis of the risk of human-induced climate change” obviously requires knowing the context of natural climate change and variability – explaining the amount of space in the IPCC reports given to issues associated with paleo-climate, ENSO, the AMO, signal-to-noise calculations, detection and attribution etc. This idea that IPCC doesn’t look at internal variability or natural forcings is just bogus. – gavin]
Why is the right hand side figure not in the center of the error bounds?
Further to comment @25-27.
The actual slides are in this pdf. There is another version of notes & slides here. It dates back to 2007 and is very silly stuff.
AAPG: http://www.searchanddiscovery.com/
collection of papers and graphics.
There may be some interesting material, e.g.
Modeling Holocene Primary Productivity Changes in the Barents Sea
#27–“I get the urge to add Lee C. Gerhard to my list of intellectually bankrupt people.”
No obvious reason to resist the urge.
Well, look around there first, don’t take the worst you can find and write off the rest unseen. That one’s a dinosaur, you expect those. They’re holdovers from the Antideluvian Age, er something.
Petroleum geologists have to understand modeling and climate.
Keying off 26 and 27:
Gerhard’s attempts a smear with “The mission of the Intergovernmental Panel on Climate Change (IPCC), a United Nations organization, is not to study causes of climate change, but to document only one cause, human impacts on climate.”
In a lay-down, he’s right. Our climate would not have nearly the focus, the research, the reviews, and the controversy, if it was just ‘understanding it all’. But while Gerhard thinks he’s exposing a secret agenda scam, he’s actually admitting that he can’t join the dots. He doesn’t understand that rising GHG pollution is contributing to a disruption of the climate so geologically sudden and ubiquitous in extent, that the parallels best matching it are extinction events. That’s exactly why the IPCC synthesizes a global state of the change every X years. Gerhard displays a kind of Victorian attitude that somehow if the IPCC just stopped talking about, it would be less of a problem.
MARodger @ 23: I was thinking the same thing, but what I see is more like a kind of ergonomically made scythe with a curved handle. (links to images seem to be too long for the filter)
Meanwhile, on the topic of paleo-climate, Hansen has a new piece out in Philosophical Transactions of the Royal Society A:
http://m.rsta.royalsocietypublishing.org/content/371/2001/20120294.full
“Climate sensitivity, sea level and atmospheric carbon dioxide”
Pretty sobering stuff. Here’s the discussion at CP:
http://thinkprogress.org/climate/2013/09/17/1892241/hansen-climate-sensitivity-uninhabitable/
#23 >Given hockey sticks are traditionally made from Mulberry…
Hockey sticks were never made from mulberry…originally made from hop hornbeam (Ostrya virginiana), then later ash, birch, poplar, and willow. Mulberry is not a commercially viable wood.
http://en.wikipedia.org/wiki/Ice_hockey_stick
#38–My initial reaction, too, but you’re not thinking of the correct type of hockey for this context:
http://en.wikipedia.org/wiki/Field_hockey_stick
“1860s Hockey taken to India. Stickhead made shorter; move from Ash to Mulberry timber for the stick head.”
Gavin,
“This idea that IPCC doesn’t look at internal variability or natural forcings is just bogus.”
Yes it’s bogus. Of course they look at it. Whether or not they FOCUS on it is the question.
What is behind the quoted paragraph when you read it at face value is that this internal variability is just background (proof is, it’s not even mentioned). They say they assess impacts, mitigation and adaptation of HUMAN-induced climate change. Implying that the IPCC is here to confirm a preconceived theory/idea: HUMAN-induced climate change is the most important to care about. IPCC is not here to care about the impacts of natural variability. The scope of work is clear.
I guess it is because internal variability had already been found to have negligible impact compared to human-induced at the time IPCC was created. But then I hear people saying: it’s hard for IPCC people to question the premises on which it has been created.
[Response: This is just very strange. The IPCC is indeed designed to focus on the potential for anthropogenic impacts on climate and I don’t see what is so bad about that. The answer might well have been that there weren’t any important ones. Other review panels (on the Supersonic Stratospheric Transports etc.) come up with not much and are generally set aside – this happens all the time. The IPCC premise is that there is a potential issue worth investigating (a true statement), not that climate sensitivity is some fixed number or that natural variability is negligible. The idea that scientists would work on an assessment that they knew to be pointless is nuts. It’s not like these things are fun. – gavin]
Can anyone point me to articles discussing the accuracy of the various proxies themselves? I apologize for my ignorance on this, but to me it seems our understanding of the relationship between the proxy data and temperature should be calibrated and tested against the observed temperature record. The error bars seem to indicate that we know the exact global temperature within 0.2 degrees C 1000 years ago, but where we have actual temperature data, the error margin is more than a degree (which more than covers the observed warming).
In short, do the error bars indicate that science is 95% confident in the real global temperature to within less than 1 degree C for the last few thousand years, or that it is 95% confident that the proxies, using the best available techniques to calibrate calibrate with global temperature, is accurate to within 1 degree C?
@41 – Climate proxies
http://en.wikipedia.org/wiki/Proxy_%28climate%29
> David C.
An explanation of that will either assume you did pass Statistics 101, or that you did not. Have you that background in statistics already? If not, some background is needed.
You’ve run into a problem that confuses a lot of people.
No, I’m not going to try to explain it, I’m a student here myself. Just sayin’, this is an area that takes serious effort to get even a fair idea of what they’re really saying.
None of your paraphrases above seems, to me, close to the mark.
Tad Boyd @26.
You do present your enquiries in an interesting way, so I don’t know but perhaps this might help. (Note that I am by no means a “climate scientist,” actual or otherwise.)
Because Marcott et al only shows long-term fluctuations, a robust comparison between the blue shoot at the end of the Fig 3 trace and HadCRUT4 is always going to be difficult, especially with the Marcott et al error bars flying off so rapidly. And also note the comment in the post about the “flexibility” of such a “join” although this does not affect the size of the Marcott & the HadCRU rises.
Perhaps to compare apples & apples, HadCRUT4 should be represented far less precisely, say by just 3 x 55-year averages. 1877 -0.32C, 1932 -0.19C, 1987 +0.16C. The BEST land temperature record suggests that HadCRUT4 is not showing all of this “strong rising trend” because it appeared to start earlier than 1850 in the BEST data. So, like the 5 final green dots from PAGE2K, the 1800-1940 0.25C rise in the Marcott et al blue trace is not far from what we see in the thermometer records.
Thus far this analysis is fuzzing out the short term wobbles. But you perhaps allude to wondering how much of the pre-1940 temperature rise (presumably the 1910-40 period) is wobble and how much is “strong rising trend.”
The climate forcings that lie behind the recent wobbles and the “strong rising trend” of HadCRUT4 can be calculated with varying accuracy. The graphs here by Sato et al presents forcings 1880 to date. Note the green plot – this is mostly but by no means all CO2 and that it is not flat back in 1880 (my point @26 with the +20ppm & +35ppm). This green plot is the big positive driver behind the “strong rising trend” but there are also very significant negative drivers.
It is a major task of climatology to establish these forcings with more accuracy and to marry the forcings with the temperature record. While this work remains incomplete, there exists room for speculation about natural oscillations, speculation that deniers love to over-amplify into reasons for ignoring that green plot in the Sato et al graph. But my take-away from the Sato et al graph is that the green plot is a little too scary to be ignored.
For most of the time covered by these graphs, the thermal mechanism would appear to be more-or-less in a steady state, just quietly following various changes in the forcings. We do not appear to be in a steady state at the moment.
If we assume the CO2 concentrations stay at the current levels, and if we ignore any positive feedback from methane and so on, is it possible to calculate what temperature we might get to, given enough time?
Peter Smith #45,
That’s the big question; what the sensitivity metric was created for.
Assuming all forcings (methane, smog and stuff) except CO2 at pre-industrial levels and atomspheric CO2 at the current level, “fast” feedbacks (such as snow cover but excluding the very slow melting of the large ice masses) should get the average global temperature to around 0.52 * sensitivity above the pre-industrial average (if I recall correctly).
Now sensitivity is likely to turn out to be around 2 to 4 centigrades so (ignoring the many caveats) the answer you’re looking for would be between +.7 to +1.8 on the graph at the top of the page.
Re Peter Smith @ #45, it is instructive to look at what earth’s climate was like the last time its atmosphere contained 400 ppm CO2, which would be around 3 million years ago during the mid-Pliocene. Global mean temperature then was 2-3C higher than today (and much higher towards the poles), it’s thought there was a near constant El Nino state, and the West Antarctic ice sheet had collapsed, raising sea level by as much as 25 meters. That said, at about this time the Panama seaway closed, which dramatically changed ocean circulation patterns, and uplift of the Rocky Mountains was also taking place, so the mid-Pliocene is far from a perfect analogy.
I saw this headline in Science:
Researchers Wary as DOE Bids to Build Sixth U.S. Climate Model
http://www.sciencemag.org/content/341/6151/1160.summary
“Many researchers are excited about the nascent project, but others worry it could divert resources from existing collaborations.”
Stefan: nice post, thanks.
@29 Bouke, see DeSmogBlog entry for Lee C. Gerhard.
All: keep an eye out for Bill Ruddiman’s Earth Transformed, which is supposed to be out in October (after some confusion about dates.) I think this sheds more light on the last ~8,000 years, relevant both to Marcott, et all and PAGES2K. Compared to past interglacials (when well-aligned, which took a lot of work), the usual slow CH4/CO2 downtrends had been slowed well before the Industrial Revolution started.
The cover illustrates the part of the story that comes from Chinese rice paddy archaeology and methane curves compared to other interglacials.
For anyone attending AGU in December, Bill will be giving the Tyndall Lecture.
considering that humans have now emitted 550 billion tonnes of co2 to date and 1 trillion tonnes emitted brings about the 2C danger threshold (often spoken about by those concerned about such things)and we emit now around 33 billion tonnes rising at 2-3% per annum means that in just a few decades from now the trillion tonnes would have been passed.
Is it all bad – probably not – but its not all good either and some will definitely suffer from increased flooding and droughts, food shortages and more than likely war as a consequence of such things occurring. It might already be occurring in Syria and Egypt due to food pressures caused by ACC.
the higher the temperature gets the worse it will probably be although I am sure that places such as southern England can continue to reap the rewards of growing pinot noir and chardonnay grapes for sparking fizz.
This is going to be quite upsetting to the MWP climate skeptics that think the MWP was the warmest period ever, warmer than the mid-Eocene high point, than the PETM, than the end-Permian.
And what do I find in that 1st graph — it was warmer 7,000 years ago (at the -5,000 point) than during the MWP.
They’re going to get really mad, then work like devils on finding some way to deny it and resurrect their MWP as the warmest of all. :)