2011-12-08 23:36:15Pagani et al 2011.Antarctic glacial onset: second draft
John Mason

johntherock@btopenworld...
86.134.20.156

The End of the Hothouse: new study links major atmospheric CO2 drop to the onset of Antarctic glaciation, 33.7 million years ago

by John Mason

Forty million years ago, Antarctica had a pleasantly mild climate, its mountains and shores flanked by swathes of woodland in which a diverse mammalian fauna flourished. Today, it is one of the most inhospitable places on Earth. Throughout this time, the continent has remained in pretty much the same place, straddling the South Pole. It follows that a drastic climatic change must have occurred, but how?

That has been the subject of much research over the years and a good picture has gradually emerged. Now, a new paper in the journal Science has clarified the role of rapidly-declining atmospheric carbon dioxide levels in the temperature-plunge that saw the rapid onset of Antarctic glaciation, 33.7 million years ago. The fall in CO2 concentration was from 1000-1200 ppm down to 600-700ppm, at which point it was cool enough to allow glaciers to start to form. That our current emissions path takes us beyond the latter levels by 2100 means that we are heading straight towards a planet that may no longer sustain polar ice-caps, resulting in a steady melt and relentless sea-level rise that will duly threaten every coastal city in the world. We'll see what the research found out in a moment, but first let's take a quick look at the Cenozoic Era, the geological timespan during which the glaciation of Antarctica began.

The Cenozoic Era: 65.5 million years ago (MA) to the present day

The Cenozoic is subdivided into seven periods of geological time: from oldest to newest the Palaocene (65.5-55.8 MA), the Eocene (55.8-33.9MA), the Oligocene (33.9-23.03MA), the Miocene (23-5.3MA), the Pliocene (5.3-2.6MA), the Pleistocene (2.6MA-11,784 thousand years ago) and the Holocene, from then until the present day. It saw one of Earth's periodic transitions from the Hothouse climate (very warm; no polar ice-caps) to the Icehouse, the latter typified by the geologically recent glacial/interglacial cycles.

The early Cenozoic had a positively balmy climate, including the Paleocene-Eocene Thermal Maximum (PETM on the graphic below). The PETM featured such extreme warmth that subtropical flora and fauna occurred in some Polar regions, as evidenced in the fossil record. During the middle to late Eocene, global temperatures cooled, but around the Eocene-Oligocene boundary they literally fell off a cliff. This was the point at which glaciation rapidly initiated in Antarctica. Through the rest of the Oligocene and into the Miocene, temperate conditions saw Antarctic glaciation advancing and retreating, before the temperature-decline in the late Miocene and Pliocene led down into the Icehouse of the Pleistocene.

Climate trend of the past 65 million years

Above: The Cenozoic climatic trend (green line): figure prepared by Robert A. Rohde (citations via the link).

The cause of the precipitous end-Eocene fall in temperatures has been the subject of much research. The strata dating from this time have been mapped, analysed and their fossil fauna and flora described on an ongoing basis. The new paper in Science has added yet another piece to the jigsaw, refining the use of what was previously a problematic CO2 proxy - something whose properties can be calibrated with CO2 concentration at the time - and reaffirming the role of CO2 as Planet Earth's atmospheric thermostat.

However, the new study has also been doing the rounds in the skeptic sector of the Blogosphere. Typically, and unsurprisingly, the professional-skeptic spin on the paper has involved variations of the following theme: "so the Antarctic was a frozen hell at 600ppm and we are nowhere near that, so what's all the fuss about?"

Ahem.

The first Golden Rule when a new paper comes out is to read it, so let's take a look and see what it actually says. Here's the Abstract - the brief summary of the work that all scientific papers begin with:

Abstract

Earth’s modern climate, characterized by polar ice sheets and large equator-to-pole temperature gradients, is rooted in environmental changes that promoted Antarctic glaciation ~33.7 million years ago. Onset of Antarctic glaciation reflects a critical tipping point for Earth’s climate and provides a framework for investigating the role of atmospheric carbon dioxide (CO2) during major climatic change. Previously published records of alkenone-based CO2 from high- and low-latitude ocean localities suggested that CO2 increased during glaciation, in contradiction to theory. Here, we further investigate alkenone records and demonstrate that Antarctic and subantarctic data overestimate atmospheric CO2 levels, biasing long-term trends. Our results show that CO2 declined before and during Antarctic glaciation and support a substantial CO2 decrease as the primary agent forcing Antarctic glaciation, consistent with model-derived CO2 thresholds.

What does that mean? We can now delve into the paper itself for the meat to put on the bones.

Glaciation always leaves calling-cards

Firstly, due to their very nature, glacial episodes on Earth always leave behind their distinctive geological calling-cards. The onset of mid-Cenozoic glaciation in Antarctica, ~33.7 million years ago, is no exception in this respect. Initiation of this abrupt climatic change is marked by a sudden shift in deep-sea oxygen isotope values and also by two strong signals in the local sedimentary rock sequence: firstly, the sudden introduction of sediments with a glacio-marine origin and secondly a change in in the types of clay-minerals present that identifies a shift in the predominant type of weathering of the rocks of the continent, from chemical dissolution of minerals to a physical erosion regime. So we have known for a long time that Antarctica went from being ice-free to having a system of glaciers, we know that this happened around the Eocene-Oligocene boundary and we know that, geologically-speaking, this change happened rather quickly.

So how did it cool so quickly?

The abrupt cooling episode that led to the appearance of Antarctica's glaciers has been the subject of much research and there have been a number of proposed mechanisms, involving changing concentrations of greenhouse gases, orbital variations and changes to oceanic currents in various combinations.

Brief mention should also be made of the slightly fainter sun at the time: as a main sequence star, the sun has been brightening at a rate of ca. 10% per billion years of geological time, so that 33.7 million years ago it would have been about 0.3% less bright than at the present day. However, this variability clearly occurs over a very long timescale, so that it would not cause a sudden and drastic climate event.

CO2 values in the Hothouse climate of the Eocene (and indeed over the preceding millions of years) were significantly higher (1000-1500ppm) than any relatively recent levels (180-280ppm respectively in glacial-interglacial cycles and ~390ppm and rising in the Industrial Age of today). However, the exact timing, nature and causes of the Cenozoic CO2 decline have remained somewhat elusive. Reconstructions have been attempted by examining the chemistry of alkenones in marine sediments. Alkenones are organic compounds of the ketone family that are in most cases highly resistant in nature. They are produced by a particular class of phytoplanktonic algae and their stable carbon isotope ratios have been used in palaeoclimatology as a method of estimating atmospheric CO2 levels (Pagani, 2002).

Alkenone-based CO2 reconstructions for the period of cooling that led to the onset of Antarctic glaciation have to date been a little problematic. They do indicate that the large CO2 decline occurred in several steps during late Eocene-early Oligocene times from the Hothouse high of 1000-1500ppm.  However, a previous attempted reconstruction showed an increase in CO2 at the time of the cooling and a large decline occurring 2-3 million years after maximum ice-sheet expansion (Pagani et al, 2005). This was found to be at odds with a separate proxy based on boron isotopes (Pearson et al, 2009) which indicated a C02 decline consistent with the Eocene-Oligocene boundary cooling, a subsequent weak rebound then a continued decline. It was also quite at odds with modelled estimates for the CO2 threshold - the level below which a rapid onset of Antarctic glaciation was likely to occur. Why?

The existing, problematic alkenone-based CO2 record is based on samples taken from a variety of environmental settings. In cases where they were obtained from poorly-stratified, nutrient-rich waters, the new paper suggests, it was possible that the samples did not accurately reflect the atmospheric CO2 concentration. In this new study, the authors examined regional differences in CO2-alkenone estimates from six well-separated localities around the globe, representing a range of environmental conditions, in order to investigate the problem further.

The paper goes on to describe in considerable detail how the issues with alkenones as proxies may be addressed, based on biochemistry work with cultures of the alkenone-producing algae in which physical and nutritional conditions could be varied and the results noted. The research led to the understanding that it was in fact very difficult to glean useful reconstructions from high southern latitudes (i.e. the seas around Antarctica) because of uncertainty with respect to these critical physical and nutritional conditions around the Eocene-Oligocene boundary. This was because the rather different geography at the time would have affected ocean circulations - and hence those physical and nutritional constraints - in that particular area, in an unpredictable manner. However, it was found that the uncertainties were greatly reduced at low-latitude sites - of which, in this study, there were two - in the Atlantic Ocean a little south of the Equator. It is upon these two sites, therefore, that the new attempt to reconstruct atmospheric CO2 was focused.

The sites yielded a reconstruction that revealed a persistent and substantial CO2 decline that began approximately two million years before the start of the rapid cooling and continued through and just beyond the event. A slight rise occurred in the mid-Oligocene before a long-term decline then set in towards Miocene times. The decline over the period 35.5-32.5 million years ago was from an initial high of 1000-1200ppm down to 600-700ppm in just three million years. This is consistent with the boron-based study and, importantly, is also consistent with the modelled estimates for the threshold CO2 level required for rapid glaciation in Antarctica (e.g. DeConto et al, 2008). In other words, it is consistent with what the physics would expect.

Other recent research has suggested that the development of the Circum-Antarctic Oceanic Current through the remainder of the Oligocene contributed to the further cooling of the continent due to thermal isolation (Anderson et al, 2011), so that by the Miocene the only vegetation left on Antarctica was localised areas of wooded tundra: some time after 12.8 million years ago this, too, had vanished as the great ice-sheets expanded. In addition, there is the positive feedback of albedo-rise once extensive permanent ice and snow are present, which would also favour further cooling. However, the take-home point of this study is that sharply-falling CO2 levels had the leading role in abruptly transitioning the global climate from the Hothouse to one in which it was cool enough for Antarctic glaciation to commence.

 

Paleoglobe from the late Eocene

Above: The late-Eocene world. Image courtesy of Ron Blakey of CP Geosystems.

Where did the CO2 go?

What processes would have been responsible for the strong CO2 drawdown event that led to this cooling? Burial of organic matter is one way of removing a lot of carbon from the system. This goes on all of the time. Chemical weathering of silicate minerals is another significant and ever-present carbon-sink. But here, we are dealing with a specific event in which a large amount of CO2 was taken out of the system - a carbon cycle "hiccup", if you like.

The Hothouse of the early Cenozoic was accompanied by very widespread tropical to sub-tropical weathering of silicate minerals but at the same time there was also the Alpine-Himalayan Orogeny (mountain-building episode), which commenced in Palaeocene-Eocene times and continued into the Miocene. The massive increase in mechanical erosion as mountain ranges rise leads to two enhanced carbon sinks: firstly a massive increase in surface area available to weathering agents, amongst which dissolved CO2 in rainwater is a lead player (think of the surface area of a lump of rock weighing a kilogram compared to the surface area of a kilo of sand scattered over the ground), and secondly a massive increase in particulate flux i.e. sediment getting swept down rivers - which in turn leads to rapid burial in sedimentary basins, including burial of organic carbon. So as a candidate bulk sink of carbon, it is certainly worthy of further consideration. Large phytoplanktonic algal blooms are another possibility - the mid-Eocene also saw the "Azolla event", a massive bloom of a freshwater fern over the then isolated and highly stratified Arctic Ocean, conditions in which dead organic matter was preserved and buried (e.g. Brinkhuis & Schouten, 2006). Did similar events occur elsewhere in the final years of the last Hothouse Earth?


The implications of this research


The graphic below depicts atmospheric CO2 concentrations, as observed at Mauna Loa from 1958-2008 (black dashed line) and projected from 2008-2100 under the six IPCC scenarios. Given that current emissions are in line with the A1F1 scenario, there seems a high risk of crossing the 600ppm threshold by later this century if the situation remains unmitigated. What does this mean in practice, with respect to the recent paper?

IPCC emissions scenarios

Source: http://www.ipcc-data.org/ddc_co2.html

The Pagani et al (2011) reconstruction suggests that a significant and rapid episode of CO2 drawdown occurred just before and during the cooling that led to the onset of Antarctic glaciation, and the drawdown took CO2 levels to 600-700ppm - below the modelled threshold value for the initiation of Antarctic glaciation. The converse of this is that, in an ice-free world, atmospheric CO2 levels much above 600-700ppm would not favour temperatures low enough for the development of glaciers in that continent.

Heading into a future with CO2 levels in the high hundreds of PPM therefore seems unfavourable for the long-term survival of the ice-sheets of Antarctica. In this context, it is important to remember that the current study deals with the onset of glaciation in Antarctica - as set out above, the extensive ice-sheets came later in the Oligocene and Miocene when CO2 levels were lower still, the Circum-Antarctic Current had fully developed and albedo had increased massively. Skeptical Science has already covered land-ice loss from Antarctica here: the current rate of loss is 100-300Gt/year. Arguments, generated by professional climate change skeptics, that Antarctica is gaining ice are thus off-target: the continent is losing land-ice, whose melting leads to sea-level rise. Fluctuations in sea-ice (which is what these skeptics have seized upon) do not affect sea-levels: indeed, they are to be expected as the input of massive amounts of fresh water from melting land-ice dilutes surface sea-water salinity, thereby raising its freezing-point and promoting sea-ice growth - for the time being.

In conclusion, we are already into a world where the long-term survival of parts of the ice-sheets is not favoured: the further towards the high hundreds of ppm CO2 we head the further we head into a world that does not favour any Antarctic land-ice, although of course to melt all that ice would likely take many centuries. That is no comfort when considering the ecological, humanitarian and economic effects of a steady sea-level rise of several tens of metres over that time, submerging all of our coastal cities one after another. If that's not worth making a fuss about then what is?

Paper under discussion in this post:

Pagani, M., Huber, M., Liu, Z., Bohaty, S.M., Henderiks, J., Sijp, W., Krishnan, S. & DeConto, R.M. (2011): The Role of Carbon Dioxide During the Onset of Antarctic Glaciation. Science, 334, 1261-1264

2011-12-09 05:55:33
Sphaerica

Bob@Lacatena...
76.28.5.93

Excellent article, although the direction the science takes and the conclusions at the end do not directly, clearly refute the phrasing of the denial position offered at the outset:

"so the Antarctic was a frozen hell at 600ppm and we are nowhere near that, so what's all the fuss about?"

I think I'd put a little more emphasis, at the end, on the idea that the current science paints a bleak enough picture with only partial destruction of the Antarctic ice-sheets, and that no one really had ever been predicting the complete loss of all Antarctic ice any time soon. Adding that to the equation at a mere 600 ppm is a very, very bad thing, not something in which to take comfort.

"so the Antarctic was to remain a frozen hell even with climate change and things were still going to be pretty bad, but now we suspect that 600 ppm might push Antarctic over the edge as well... why isn't there more fuss?"

2011-12-09 14:56:09
jyyh
Otto Lehikoinen
otanle@hotmail...
193.199.52.124

I've always thought the cooling of the ACC was the sole cause. It'd have initiated massive algal blooms down south (most zooplankton died for the cold), leading to vastly increased algal carbon sink during this period, but clearly there are also other factors in play. Informative, and the question of where this sequestred carbon is now is important, Thumb.

2011-12-09 18:04:03
John Mason

johntherock@btopenworld...
86.134.20.156

Thanks both. I'll tweak the ending, but also it occurred to me overnight that I could ask Pagani whether there has been any Sr isotope work on late Eocene limestones. It is a line of enquiry that can pick up monstrous chemical weathering episodes - see my ramblings on the Taconic Orogeny & the Hirnantian glaciation in the late Ordovician:

http://www.geologywales.co.uk/storms/hirnantian.htm

I'll email him on that point.

It also occurred to me overnight that I have used the term "skeptic" twice when what I mean is "denialist". Can I use the latter or is it generally frowned upon? "Political opposition" would be my second choice, as I think the term "skeptic" is misused by the media WRT climatology.

Cheers - John

2011-12-10 01:03:32
Daniel Bailey
Daniel Bailey
yooper49855@hotmail...
97.83.150.37

"I have used the term "skeptic" twice when what I mean is "denialist""

My personal preference is fake-skeptic.  Clear, to the point, lacks the taint of "denier" or "denialist".

2011-12-10 01:35:13
John Mason

johntherock@btopenworld...
86.134.20.156

Thanks - have adapted that term and tweaked the ending slightly.

Cheers - John

2011-12-10 16:14:05
Glenn Tamblyn

glenn@thefoodgallery.com...
60.230.159.2

John

I like it. Clear and concise. However one quibble/point and a suggestion.

Q/P:  Currently the language and concepts in this post are towards the upper end of the SkS readership. You might consider adding some simpler statements or more summaries to help the lower level of our readership follow it.

Second point. This does not include any provision for changes in the Sun's output over deep time. The Sun has increased its heat output by about 30% since it was born, call it 4.5 Billion years ago.

Although 35 Myr may seem small compared to the age of the Sun, there is still an effect. By my rough calculation 600ppm 35 Myr ago is the equivalent of around 520 ppm today.So the doubling of CO2e that is the focus of so much attention now also seems to put us into the temperature range where Antarctica could completely deglaciate.

 

And I think the recent IEA report suggested that before the end of this decade installed FF power station capacity would take us to 685 by the end of their economic life. Loose Antarctica or loose Trillions of dollars shutting down capital plant before the end of its life! What was it Hansen said about Faustian Bargains?

2011-12-10 16:16:29
Glenn Tamblyn

glenn@thefoodgallery.com...
60.230.159.2

DB

I like the term 'Professional Skeptic' - not only conveys that the skepticism may 'not be entirely accurate' but also that this isn't just a casual position they have taken, this is a career path.

2011-12-10 19:04:05
John Mason

johntherock@btopenworld...
86.134.20.156

Glenn, thanks. I have incorporated the term.

Have added a number of simplifications/explanations, mentioned the sun, and also summarised in a few words another paper - Anderson et al 2011 (see refs - it's a very interesting paper which is open-source), which looks at the West Antarctic Peninsula and suggests a CO2 plunge kicking things off then the Circum-Antarctic Current (plus albedo-change almost certainly) taking a role later in the Oligocene & Miocene as the last patches of wooded tundra finally succumbed to the advance of the ice-sheets.

How do I go about posting it once it's fully approved? Can someone do that for me?

Cheers - John

2011-12-11 03:00:23
Daniel Bailey
Daniel Bailey
yooper49855@hotmail...
97.83.150.37

John Mason:

Dana and JC usually handle the scheduling of publication of the articles and rebuttals.  I act as backup, when needed.

2011-12-11 04:50:45
John Mason

johntherock@btopenworld...
86.134.20.156

I'll email JC - it's my first post and I should like his approval. There's no great hurry WRT this and it is his site after all.

Have also emailed the guys who produce the palaeoglobes - not Chris Scotese on this occasion but Ron Blakey as he has a lovely one from the late Eocene. It will fit in the middle nicely, should he agree to its use.

Cheers - John

2011-12-11 13:52:07
Rob Painting
Rob
paintingskeri@vodafone.co...
203.173.237.124

John, this is better but is both too long and expects too much of an uninformed reader, i.e our target audience. There's just too much extraneous information.

Here for example: "During the middle to late Eocene the climate cooled, but around the Eocene-Oligocene boundary it literally fell off a cliff. This was the point at which glaciation initiated in Antarctica. Through the rest of the Oligocene and into the Miocene, warm (but not Hothouse senso stricto)"

Senso stricto? Knowing how all those periods relate to each other is not something the casual reader is going to be able to process either.

As the late great Ernest Rutherford, and now the great progosticator Nealstradamus, suggest - how would you explain this to a barmaid? I would suggest breaking it down into headings to aid digestibility too.

Introduction: What are you going to tell/show them?

- paper confirms well-known relationship between global temperature and atmospheric CO2? 

-Antartica began to grow ice sheets when CO2 fell below 600ppm? Before then it was warmer and supported both plant and animal life which no longer exist?

- On current trends, and if this 600ppm represents a threshold between some ice/no ice in Antarctica, then within 70(?) years we have burnt enough fossil fuel to make Antarctica completely ice-free and submerge every coastal city in the world. (You might not want to go there, but this is what is implied if all that ice is lost. It is not an exaggeration, just spell out the timeframe) 

Guts of the post:

-Previous studies of CO2 proxies of the cooling period which initiated icesheet formation, shows they had been misinterpreted?

-New analysis reveals that a drop in atmospheric CO2 from 1200-1000ppm to 700-600ppm coincides with the formation of the icesheet, and is in line with physics?

- Why did it drop?

-Where did the CO2 go?

-Anything else a casual reader might find interesting?

Summary: Reinforce the introduction and any other key points you think the reader should take away. 

Just remember who we are writing for, don't be mislead by commenters who are generally reasonably well informed on SkS threads. They are only a tiny percentage of readership.   

NB: lose the citations at the end. They're just unncecessary clutter. Hyper-link to relevant papers, and try not to go too overboard.

Oh, and congrats on your first blog post here!

2011-12-11 21:17:22
John Mason

johntherock@btopenworld...
86.134.20.156

Rob, thanks.

 

WRT the total melt, I'm not sure we really have much idea how long that will take TBH - however the situation will condemn us to an ongoing rise.

The previous studies were not misinterpreted as such - instead they gave problematic results, which this paper has gone a long way to solve.

I'll give it a final edit, but it has to be appreciated that this is a particularly complex subject and too much brevity can backfire, by leaving out crucial context.

Cheers - John

2011-12-11 21:42:57
Rob Painting
Rob
paintingskeri@vodafone.co...
118.93.31.58

"I'll give it a final edit, but it has to be appreciated that this is a particularly complex subject and too much brevity can backfire, by leaving out crucial context."

John, that is the all too common trap that climate science communicators fall into, myself included. We have to some how condense what the science says into bite-sized servings. If we try to cover everything, then the message will be diluted, or not understood at all. We are not writing to impress each other.

Total melt - many centuries, perhaps over a millenia. Who cares? The average Jane/Joe just needs to know that our actions today will likely result in all coastal cities being inundated in the future. Will Florida even exist anymore? London? New York? That's how serious this is. Once the tipping point is reached there are no rainchecks, postponements or cancellations, that deal is done and dusted. 

Now I agree that not everything we may wish to write about can be covered in a single post, but I reckon this one can, and without losing vital context. And I'm only giving this spiel to you, seeing as this is your first post and it's easier to start off on the right foot. I know it's hard to take this all onboard, it was for me too when Nealstrdamus was (rightly) criticizing me, but I've long since realized he was bang on the button.

 

 

2011-12-11 21:47:32
John Mason

johntherock@btopenworld...
86.134.20.156

Rob, it's much appreciated. Getting started on the right foot makes perfect sense to me!

Leave it with me - churning into Notepad right now!!

Cheers - John

2011-12-11 23:51:08
John Mason

johntherock@btopenworld...
86.134.20.156

OK have a look at the slimmed-down version, folks! A few hundred words less. Please note that I have given the Cenozoic - and the alien, wooded Antarctica - a better introduction too.

Cheers - John

2011-12-12 06:03:03
Rob Painting
Rob
paintingskeri@vodafone.co...
118.92.83.229

John, this is vastly better (from a layman's perpsective), although you could still have shed a tad more jargon. Thumbs up from me bro!

2011-12-12 18:36:50
John Mason

johntherock@btopenworld...
86.134.20.156

Good to go, I guess. Hopefully I might hear from Ron WRT the end-Eocene palaeoglobe today.......

Cheers - John

2011-12-13 18:03:28
John Mason

johntherock@btopenworld...
86.134.20.156

Update: Ron has permitted the use of the paleogloce which I have dropped in to break up the text.

This post is now ready to go on the front end - can Dana or Dan sort that when ready?

Cheers - John

2011-12-14 03:12:06My recommendation
John Hartz
John Hartz
john.hartz@hotmail...
98.122.98.161

The article needs a good introdcutory paragraph telling the reader what's it all about (including major conclusions) and enticing him/her to actually persue the remainder of the article. 

A well-written introductory paragraph should standard fare for all SkS articles.

2011-12-14 04:28:20
John Mason

johntherock@btopenworld...
86.142.20.0

John, I was hoping that the title & first paragraph might draw people in: the former summarises the study and the latter briefly sets out the problem before ending with a tantalising question.

Happy to give the start another rework if necessary, if people agree with you.

Cheers - John

2011-12-14 06:05:22John Mason
John Hartz
John Hartz
john.hartz@hotmail...
98.122.98.161

My recommendation was made based on the text provided in your initial post. If you have subsequently rewritten the initial paragraph, I have not seen the revised version.  

An example of the type of introdctory paragraph that I believe should be standard in all SkS articles is the initial paragraph of Dana's recent article, Huber and Knutti Quantify Man-Made Global Warming. I prodded Dana to add the following opening paragraph before the article was posted. [Dana composed the text. I only urged him to create and insert a new paragraph.]

Huber and Knutti (2011) have published a paper in Nature Geoscience, Anthropogenic and natural warming inferred from changes in Earth’s energy balance.  They take an approach in this study which utilizes the principle of conservation of energy for the global energy budget to determine  and quantify the various contributions to the observed global warming since 1850 and 1950.  Over both timeframes, the authors find that human greenhouse gas emissions are the dominant cause of global warming.

2011-12-14 17:47:25
John Mason

johntherock@btopenworld...
86.142.20.0

John,

Title and first few sentences now say:

The End of the Hothouse: new study links major atmospheric CO2 drop to the onset of Antarctic glaciation, 33.7 million years ago

by John Mason

Forty million years ago, Antarctica had a pleasantly mild climate, its mountains and shores flanked by swathes of woodland in which a diverse mammalian fauna flourished. Today, it is one of the most inhospitable places on Earth. Throughout this time, the continent has remained in pretty much the same place, straddling the South Pole. It follows that a drastic climatic change must have occurred, but how?

That has been the subject of much research over the years and a good picture has gradually emerged. Now, a new paper in the journal Science has clarified the role of rapidly-declining atmospheric carbon dioxide levels in the temperature-plunge that saw the rapid onset of Antarctic glaciation, 33.7 million years ago. The fall in CO2 concentration was from 1000-1200 ppm down to 600-700ppm, at which point it was cool enough to allow glaciers to start to form.

Cheers - John

2011-12-15 03:19:15
dana1981
Dana Nuccitelli
dana1981@yahoo...
64.129.227.4

Let me know when you feel this is ready to publish, John M.

2011-12-15 04:32:54
John Mason

johntherock@btopenworld...
86.142.20.0

Hi Dana,

I'm fairly content with it, but I should like to see if others share John H's concerns WRT the start of the piece, as in the post immediately above. I'm new here in terms of blog posts and want people to be happy with my contributions.

Cheers - John

2011-12-15 04:39:36John Mason
John Hartz
John Hartz
john.hartz@hotmail...
98.122.98.161

Your first two paragprahs fill the bill. If it were my call, I'd combine them into a single paragaprh, but your writing style is your style.

2011-12-15 04:42:22
John Mason

johntherock@btopenworld...
86.142.20.0

Thanks, John. Good to get the clarification. Everyone certainly has their own style, which is a good thing IMO :)

Dana - good to go, and away with the chocks!

Cheers - John

2011-12-15 05:09:30John Mason
John Hartz
John Hartz
john.hartz@hotmail...
98.122.98.161

I just read Rob Painting's concerns about he length of the article. Along those lines, I suggest that you delete the paper's Abstract amd the paragraph before it.

I disagree with Rob about elimainating the "Paper under discussion in this post..." mateiral a tthe end of the paper. I do not believe that readers will see it as clutter. In addition, It is necesary material for the print verison of the article. Embedded electronic links do not show up in the print version.

2011-12-15 05:26:02
John Mason

johntherock@btopenworld...
86.142.20.0

I thought about doing that, John: however, despite the extra word-count, I think it is respectful to any author to include the abstract, and then to comment on the bulk of the paper. It leaves the clear conclusions well-recorded and incapable of misinterpretation. I have done this for years, because I believe that if you are centering an entire post around one paper then it is useful to cite that paper's abstract.

My view is that SkS should always incorporate these verbatim into any blog-posts. Readers will either flick through the first couple of sentences or read all the way to the bottom. And you'll never make one do the other, or vice-versa!

I may be wrong of course!! But it is the pattern I have seen eveywhere.

Cheers - John

2011-12-15 08:42:47John Mason
John Hartz
John Hartz
john.hartz@hotmail...
98.122.98.161

I do not recall ever seeing the complete Abstract of a published paper included in the text of a SkS article.  

If our target audience is indeed the average person, including the Abstract in an article counterproductive.   

2011-12-15 17:00:26
John Mason

johntherock@btopenworld...
86.142.20.0

I guess the point I was trying to make is that the whole idea of any paper having an Abstract is that its findings may be read and reasonably digested by any literate person, although in reality that is not always accomplished by the abstract-writer! I do tend to encourage people to read abstracts simply because I tend to encourage people to get their climatology - at least in good measure - from the horse's mouth, so to speak.

One idea might be to move it down to beneath the reference to the paper: doing so would still see it read by those who want to. What do other regular contributors think? Having made it stand out in bold already makes it skippable by people who would be inclined to skip such a thing.

Cheers - John

2011-12-15 17:52:51
dana1981
Dana Nuccitelli
dana1981@yahoo...
71.137.110.252

I think including the abstract is fine - it's a pretty short one.