Unprecedented warming?
There's a lot of debate about the `Medieval Warm Period'. But I've always been intrigued by the warm period of 7,000 years ago, known as the Holocene Optimum, and I have been doing some digging to find out just how warm it was. I've come away rather amazed.
Have a look at this image, which uses stalagmites in caves to estimate ancient temperatures (as graphed by Wilis Eschenbach)
Now have a look at this image, which uses oxygen istopes to measure temperature in ice cores:
Notice how very similar they are, and notice in particular how they both say that the last few centuries are by far the coldest period of the current interglacial. The Little Ice Age, they call it with good reason. Far from being unprecedentedly hot, the current world has only just recovered from being almost unprecedentedly cold – for the interglacial. (The sole exception, after the Younger Dyas ended, is the sudden and brief plunge in temperatures that happened 8,200 years ago.)
Again and again you read remarks like this, from a study of stalagmites in South Africa: `Maximum Holocene cooling occurred at AD 1700’.
By contrast the start of the interglacial was much warmer than today. How much warmer?
Between 8,000 years ago and 5,500 years ago the Greenland temperature apparently never got as low as today, and was sometimes -- 6,900 years ago and 7,700 years ago – even more than 3C warmer than today.
It follows that any suggestion that Greenland will melt at temperatures 3C warmer than today is unlikely to be true. The disappearance of Arctic Ocean sea ice during part of the summer would probably not be unprecedented either: the northern shore of Greenland shows evidence of driftwood and beach ridges raised by large waves during the Holocene Optimum on a coast that is nowadays ice-locked most of the year – implying that the Arctic Ocean was much freer of ice in summer than it is today
Polar bears would have taken refuge on land for a few weeks or months – as they do in Hudson’s bay today.
But what about the rest of the planet? Throughout the northern hemisphere ice cores, lake sediments, marine sediments, pollen, tree lines and glacier histories all point to a culmination of the warmth around 7,000 years ago. By then, birch and larch trees grew much further north in all of Siberia than they do today, and one group of scientists reckons that Arctic Siberia experienced July temperatures a remarkable 2.5C-7C warmer than today.
A study of sea sediment cores in the Chukchi Sea shelf in the Arctic Ocean concluded that `during the middle Holocene the August sea surface temperature fluctuated by 5°C and was 3-7°C warmer than it is today'.
Yes, you read that right: up to SEVEN DEGREES CENTIGRADE.
China too abounds in evidence of warmth around 7,000 years ago
Ah, says the `climate consensus', but the Holocene Optimum was confined to the northern hemisphere during summer. Not so. Evidence from high latitudes in the southern hemisphere also shows warmth at the same time: Antarctic ice cores, Tasmanian and south African cave stalagmites. New Zealand glaciers, alkenones (algae derived fats) in seabed cores off Chile – they all point to a warm climate in the early Holocene before 7,000 years ago.
Well all right, said the IPCC, but the tropical oceans were cool, even though the high latitudes were warm.
Really? The only evidence comes from eight seabed cores taken from areas of ocean upwelling, which show slight warming rather than marked cooling since 7,000 years ago. But more cool upwelling generally indicates more warming elsewhere, so it is not clear what these eight cores are saying. The discovery of remains of alpaca moss (Distichia) from 5,000 years ago and 500 metres higher in the Peruvian Andes than it now grows, at a low latitude in the southern hemisphere (the plants had been covered by advancing glaciers some time after 5,000 years ago) seems at least to throw the burden of proof back on those who would argue for the Holocene Optimum being a solely non-tropical phenomenon.
And some of the speleothems in the first chart come from Costa Rica, southern China, Panama and Borneo. Tropical enough for you?
The Sahara, too, hints at a warm planet 7,000 years ago. The Sahara is always very arid during ice ages when the cool oceans starve it of seasonal rain. Its green and moist periods come during the warmest parts of interglacials. Its most recent really wet period lasted from 8,500 years ago to 5,300 years ago, coinciding with Greenland’s least cold time. In this so called `African Humid Period’, the Sahara was covered in forests, grasslands, and permanent hippo-filled lakes, and people drew rock art of crocodiles. The drying of the damp Sahara, after 5,300 years ago, coincides with a marked cooling in Greenland.
Remember 7,000 years ago is not the deep past. It is three millennia after the establishment of agriculture; settlements like Jericho were already 2,000 years old.
Ask yourself this: if the heat of 7,000 years ago, so widespread around the globe and so pronounced in the far north, did not cause planetary catastrophe, why should the lesser warmth of this century?
Comments (22)
Here is a page with a bunch of other historical temperature charts indicating modern temperatures are not so "unprecedented".
http://www.c3headlines.com/temperature-charts-historical-proxies.html
Dear Matt:
I heard an interview with you on public radio last week as I was driving through New York City, and I enjoyed it very much. However, I have a question about this blog posting. I followed the link that you provide to studies showing that mid Holocene warming also occurred in the Southern hemisphere at high latitudes. It is an NCDC web page that collates speleotherm data from studies around the world. I looked at the southern hemisphere data sets and only one of the abstracts mentions mid-holocene warming. As I looked further on the NCDC site I found the following page, which seems directly contradictory to your position: http://www.ncdc.noaa.gov/paleo/globalwarming/holocene.html
I agree with your general premise that scientists tend to paint overly pessimistic pictures of environmental problems - not surprising since research funding depends on convincing the public that an issue is sufficiently critical to justify the expense of studying it. However, I think you may have strayed too far in the other direction in your zeal to rationalize on optimist's view of climate change. The fact that humans survived a warm period in the mid-Holocene says little about how we might be affected by similar warming today, when hundreds of millions of people live at or near current sea level. Ironically, neolithic humans were probably better able to adapt to climate change than current humans, by virtue of their nomadic lifestyle. In any event, while I disagree with your interpretation of climate science, I share your optimism that we will solve this problem. Thank you for your thought-provoking writing.
Thanks, John, yes, the link only supports part of the statement about southern hemisphere warmth. It has two speleothem studies of relevance.
Tasmania: "Overall, the records suggest that the warmest climate occurred between 8000 and 7400 yr BP, followed by a wettest period between 7400 and 7000 yr BP.''
South Africa: "The Early Holocene experienced warm,
evaporative conditions with fewer C4 grasses. Cooling is evident from ~6 to 2.5 ka, followed by warming between 1.5 and 2.5 ka and briefly at ~AD 1200. Maximum Holocene cooling occurred at AD 1700. "
As for the alkenones, they are discussed in another link I give elsewhere:
http://climateaudit.org/2007/01/02/lorenz-et-al-2006-tropical-cooling/
On reflection `high latitude' wrongly implies "far south". I should have said temperate or high latitude.
As for the other sources, I was relying on the IPCC chart reproduced here:
http://climateaudit.files.wordpress.com/2007/01/figure6_9.jpg
Matt - good piece, but this puzzled me "...any suggestion that Greenland will melt at temperatures 3C warmer than today..." I've never heard the suggestion that Greenland will melt, just that it will lose its glacial cover and end up being, er, green. And that we'll all be inundated by the resulting meltwater. Perhaps I have misunderstood you, but if so, so will the warmist rabble...
I recently purchased a copy of this book, and would like to draw attention to the very serious issue with the use of sources. I have paid particular attention to the claims made in relation to climate change. In particular I note the following the following four claims that need clarification on the part of the books author.
Claim 1: Mann Hockey stick is broken
The footnote listed on page 415 that discusses “previous warm episodes” such as the "medieval warming period" (MWP) is used to buttress his points on page 334> However, when one reads the footnote we see the following written by Ridley:
“The famous hockey stick seemed to prove that the Medieval Warm Period never happened has since been comprehensively discredited. It relied far too heavily on two sets of samples from bristlecone pine trees and Siberian larch trees that have since been shown to be highly unreliable; it spliced together proxies and real thermometer data in a selective way, obscuring the fact that the proxies did mirror modern temperatures, and it used statistical techniques that made a hockey stick out of red noise..”
The hockey stick is not "broken". This is a claim made by the "climate change sceptics" that has been refuted many, many times.
Indeed, your supporting materials for this are taken from Steve McIntyre's blog Climate Audit and from Loehle's paper which stops measuring temperatures at 1935, well before the known post-war rise in temperatures. Additional studies and research have confirmed the Mann hockey stick. You make use of several papers from Energy & Environment, a journal of dubious quality, to support your arguments. Climate Audit is source with no scientific credibility.
Claim 2: Polar bear populations are growing
On pages 338-339 you makes the following claim:
“The polar bear, still thriving today (eleven of the thirteen populations are growing or steady), may contract its range further north, but it already adapts to ice-free summer months in Hudson’s bay by fasting on land till the sea re-freezes…”
Dr. Ridley, the US Geological Survey has recently noted that:
“The U.S. Geological Survey predicts two-thirds of the world’s polar bears will disappear by 2050, based on moderate projections for the shrinking of summer sea ice caused by global warming. The bears would disappear from Europe, Asia, and Alaska, and be depleted from the Arctic archipelago of Canada and areas off the northern Greenland coast. By 2080, they would disappear from Greenland entirely and from the northern Canadian coast, leaving only dwindling numbers in the interior Arctic archipelago.”
(See Arctic Climate Impact Assessment (2004). Impact of a Warming Arctic: Arctic Impact Climate Assessment. Cambridge: Cambridge University Press. ISBN 0 521 61778 2. OCLC 56942125.)
I note that the population of polar bears declined by 22% between 1987 and 2004 (see "Effects of earlier sea ice breakup on survival and population size of polar bears in western Hudson Bay". Journal of Wildlife Management (Bethesda: The Wildlife Society) 71 (8): pp. 2673–2683)
Claim 3: Ocean acidification is a "back-up plan" devised by environmental pressure groups
You makes the following claim:
"Ocean acidification looks suspiciously like a back-up plan by the environmental pressure groups in case the climate fails to warm: another try at condemning fossil fuels..." page. 340
Ocean acidification is a well studied phenomena and of genuine concern. I am not sure how Dr. Ridley has come to the conclusion that this is a suspicious plan unless one has a conspiratorial world view.
I would direct you attention to the following paper: Paleo-perspectives on ocean acidification, Trends in Ecology & Evolution, Volume 25, Issue 6, 332-344, 30 March 2010.
The abstract notes:
"The anthropogenic rise in atmospheric CO2 is driving fundamental and unprecedented changes in the chemistry of the oceans. This has led to changes in the physiology of a wide variety of marine organisms and, consequently, the ecology of the ocean. This review explores recent advances in our understanding of ocean acidification with a particular emphasis on past changes to ocean chemistry and what they can tell us about present and future changes. We argue that ocean conditions are already more extreme than those experienced by marine organisms and ecosystems for millions of years, emphasising the urgent need to adopt policies that drastically reduce CO2 emissions."
Claim 4: no species extinction due to climate change
You make the following claim:
"...so far, despite two bursts of twentieth-century warming, not a single species has unambiguously been shown to succumb to global climate trends" page.338
I would draw your attention the following research: Erosion of Lizard Diversity by Climate Change and Altered Thermal Niches, Science 14 May 2010, Vol 328 no.5980 pp.894-899"
The authors of the paper note in the abstract:
"It is predicted that climate change will cause species extinctions and distributional shifts in coming decades, but data to validate these predictions are relatively scarce. Here, we compare recent and historical surveys for 48 Mexican lizard species at 200 sites. Since 1975, 12% of local populations have gone extinct. We verified physiological models of extinction risk with observed local extinctions and extended projections worldwide. Since 1975, we estimate that 4% of local populations have gone extinct worldwide, but by 2080 local extinctions are projected to reach 39% worldwide, and species extinctions may reach 20%. Global extinction projections were validated with local extinctions observed from 1975 to 2009 for regional biotas on four other continents, suggesting that lizards have already crossed a threshold for extinctions caused by climate change."
I believe the peer reviewed literature is clear on the issue Dr. Ridley.
Conclusion
I strongly urge people to fact check Dr.Ridley's work, as I believe I have found substantial errors in the use of his sources.
A review of his notes for Chapter 10 shows a very restrictive use of source: material from "Watts up with that?", The Cato Institute, Climate Resistance.org, Climate Audit.org, the disputed work of Bjorn Lomborg's "Cool it!" and many other sources of dubious quality.
The posting by "Mike" (Mike Who?) seems particular shameless in its use of ad hominem calumnies. Frequent assertions that sources are "discredited," "of dubious quality," (but without citation of authority), "is source with no scientific credibility," may or may not be true, but "Mike" fails to adduce suthority better than his own opinion. He cites one paper's claim that physiological "models" are VERIFIED (emphasis mine) by "observed local" phenomena "and extended projections worldwide." May I suggest that theoretical models are not verified reliably by limited local observations taken together with "extended projections worldwide." Even a mere M. S. like your current correspondent knows that such as these do not verify, do not validate, proposed conclusions in the physical sciences. And the "Mann hockey stick?" Is this the same "hockey stick" propagated by the scandalous behavior of the Hadley research unit, whose director had to resign in disgrace over his and his unit's manipulation and concealment of real-world scientific measurements and data, and its production of research "results" of truly dubious quality? ? I think so. As the past 10 years of declining annual average global temperatures have been revealed despite the IPCC's and the Hadley's efforts at their concealment, the "hockey stick" is now taking its well-earned place in the pantheon of history alongside the Solar Constant, phlogiston, and the Luminiferous Ether.
Mike's comments re the Hockey Stick are most peculiar. How can the ending of the Loehle series in 1935 be relevant to the question of temperatures in the Medieval Warm Period?
@GoGoBigO: it wasn't the "Hadley research unit" whose fast and loose ways with evidence were revealed by Climategate, it was the Climate Research Unit at the University of East Anglia. The common confusion arose, I suspect, because the two research outfits collaborate.
Agree. We'll all be fine. Don't panic. Don't do anything different. Get a nice tan!
Mike's comments re the Hockey Stick are most peculiar. How can the ending of the Loehle series in 1935 be relevant to http://www.uggbootsspeichern.com/the question of temperatures in the Medieval Warm Period?
5 Myr of Climate Change
Posted by madmikedavies
most discussions centre around short term climate shifts. The climate for the last 20kyr has been atypical as we should be currently under 1km of ice in northern europe. The answer is in the last 5 Myr of climate change where continental ice formation has increased the negative insolation by a factor of up to 5 see graph
http://commons.wikimedia.org/wiki/File:Five_Myr_Climate_Change.png
temperature variation is +/- 1degC at Vostok temps >0degC
temperature variation is +/- 2degC at Vostok temps ave -2degC
temperature variation is +/- 5degC at Vostok temps ave -4degC
temperatures below 0degC and ice in any form but especially ice ages are animicable to carbon based life
[...] file, please ask for it in the comment section below.) As the world warms it is getting wetter. As Matt Ridley writes in his book The Rational Optimist: If you take the IPCC’s [International Panel on [...]
How can the ending of the Loehle series in 1935 be relevant to http://www.prowordpress.net/the question of temperatures in the Medieval Warm Period?
amazing study...really a great job!
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I had the same suspicion that the world was much warmer in the past. I think many people are just talking about global warming because it is cool to be doing so. But not many people put the time to study what is actually happening. Then take the right measures to leave a better planet behind. http://www.refinancehomemortgageloan.net
No, I do not agree. World was a very cool place compared to now. Because of the global warming, we will all melt down in a 10 years or so! We must be very careful taking care of your universe.
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I think you may have strayed too far in the other direction in your zeal to rationalize on optimist's view of climate change. The fact that humans survived a warm period in the mid-Holocene says little about how we might be affected by similar warming today <a href="http://mummymakersdaughter.com"> ancient egypt</a>
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This review explores recent advances in our understanding of ocean acidification with a particular emphasis on past changes to ocean chemistry and what they can tell us about present and future changes.
http://mummymakersdaughter.com
You can even see an Ice Age that gripped the planet between -12000 and -9000 B.C. The temperatures are a serious deviation from the warmth that's gripped the Earth for the past 10,000 years.
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