Guest commentary by Sarah Feakins
Our recent study in Nature Geoscience reconstructed conditions at the Antarctic coast during a warm period of Earth’s history. Today the Ross Sea has an ice shelf and the continent is ice covered; but we found the Antarctic coast was covered with tundra vegetation for some periods between 20 million and 15.5 million years ago. These findings are based on the isotopic composition of plant leaf waxes in marine sediments.
That temperatures were warm at that time was not a huge surprise; surprising, was how much warmer things were – up to 11ºC (20ºF) warmer at the Antarctic coast! We expected to see polar amplification, i.e. greater changes towards the poles as the planet warms. This study found those coastal temperatures to be as warm as 7ºC or 45ºF during the summer months. This is a surprise because conventional wisdom has tended to think of Antarctica being getting progressively colder since ice sheets first appeared on Antarctica 34 million years ago (but see Ruddiman (2010) for a good discussion of some of the puzzles).
Where did this record come from?
The ANDRILL program is a multinational collaboration involving scientists from Germany, Italy, New Zealand and the United States to drill through ocean sediments around Antarctica. The drilling effort in the austral summer of 2007 involved a rig perched upon the Ross Ice Shelf, drilling down through the ice, 400m of water below that and then grinding down 1km into the sediments. The sediments are bagged and then transported back to the storage facility in Florida from where they are parcelled out to analysis laboratories across the world.
It can take years to process all this sediment and perform all the compositional, elemental and isotopic analyses that need to be done. Numerous scientists work on getting the most information possible out of the core. One of the early findings was the unexpected discovery of abundant pollen in the Miocene part of the core by Sophie Warny (Warny et al, 2009). The pollen came from types of tundra vegetation and indicated summer temperatures above freezing, which was also inferred from the presence of freshwater algae.
After Sophie found the pollen, I began to search for molecular fossils of those same plants. The waxy coating of plant leaves is remarkable for its resilience in sediments. In addition those leaf wax molecules capture an isotopic record of past rainfall. It is these isotopic signatures that allow quantitative insights into temperature and rainfall.
To extract the leaf waxes we don’t look for visual fossils, instead we use organic solvents to dissolve and extract the leaf waxes out from the sediments. Those organic molecules are then purified by passing through a series of filtering steps in the lab. Ultimately we wind up with a pure concentration of the leaf waxes which can be analyzed by mass spectrometry (see photo).
How are the results interpreted?
The leaf wax hydrogen isotope evidence was interpreted in comparison to model experiments. Jung-Eun Lee (JPL) conducted experiments, after adding water isotopes into a model dubbed GRAM (Frierson et al, 2006) because it requires a gram of computational effort rather than a ton in a full general circulation model. With the aid of the isotope-enabled model version, iGRAM, we can simulate the movement of water around the planet and track the water isotopic signatures. The goal was to see if modern relationships between different points in space that have different isotopes in precipitation and temperature are valid when we instead consider changes at the same point over time. Model experiments suggested a small upwards tweak in the temperature reconstructions for the Miocene from 2ºC to 7ºC. These experiments also reveal the dynamics behind the isotopic values: more evaporation from the warmer high latitude oceans and increased rainfall at high latitudes. (Ed. In similar experiments for Greenland (Werner et al, 2000), the changes in the seasonal cycle were important in understanding the isotope paleo-thermometer).
The iGRAM model is however an idealised aquaplanet, (i.e. no continents at all) so it isn’t useful for the interior of Antarctica, but deep sea records suggest that glacial ice volume was about 50% of modern volume at that time. It is however difficult to do full general circulation model experiments for this period because of the difficulty of constraining boundary conditions in the Miocene – what the land surface looked like, what greenhouse gas levels were, etc. An aquaplanet is perhaps good enough for these tests as conditions at the coast are really set by the oceans.
In terms of figuring out how the climate system operates, temperature is one of the simpler variables to reconstruct (not that any of this is really simple). Figuring out how precipitation changes is harder, largely because models can’t capture the scale of clouds let alone raindrops. What the leaf waxes provide is an archive of the isotopic composition of precipitation – much as the ice cores do for the past million years. Of course an ice core is not as simple as a rain gauge, and a plant has biology that an ice core doesn’t, but crucially if plants are growing, leaf waxes are probably preserved in sediments allowing us to push these isotopic records back beyond the ice core records to address questions about what climate was like further back in time.
How robust are these results?
What is reassuring here is that all the lines of evidence presented, from various microfossils, molecular fossils, isotopes and model experiments, all point to temperatures at the coast of Antarctica reaching above freezing point in summer months, probably around 7ºC (45ºF).
Downcore results through the Miocene section show at least two periods of exceptional warmth.
It is in those warm, periods further back in time, that might help us understand a little more about how warmer climate systems operate, and that information might just be important as we contemplate our future.
References
- S.J. Feakins, S. Warny, and J. Lee, "Hydrologic cycling over Antarctica during the middle Miocene warming", Nature Geoscience, vol. 5, pp. 557-560, 2012. http://dx.doi.org/10.1038/NGEO1498
- W.F. Ruddiman, "A Paleoclimatic Enigma?", Science, vol. 328, pp. 838-839, 2010. http://dx.doi.org/10.1126/science.1188292
- S. Warny, R.A. Askin, M.J. Hannah, B.A. Mohr, J.I. Raine, D.M. Harwood, F. Florindo, and . , "Palynomorphs from a sediment core reveal a sudden remarkably warm Antarctica during the middle Miocene", Geology, vol. 37, pp. 955-958, 2009. http://dx.doi.org/10.1130/G30139A.1
- D.M.W. Frierson, I.M. Held, and P. Zurita-Gotor, "A Gray-Radiation Aquaplanet Moist GCM. Part I: Static Stability and Eddy Scale", Journal of the Atmospheric Sciences, vol. 63, pp. 2548-2566, 2006. http://dx.doi.org/10.1175/JAS3753.1
- M. Werner, U. Mikolajewicz, M. Heimann, and G. Hoffmann, "Borehole versus isotope temperatures on Greenland: Seasonality does matter", Geophysical Research Letters, vol. 27, pp. 723-726, 2000. http://dx.doi.org/10.1029/1999GL006075
What is the resolution on these sediments? How far forward in the recent past can you reliably go? The point of the question being… can you say with confidence that the last time the Antarctic coast achieved these temperatures was 15.7 Mya, or is it possible that the same conditions occurred more recently, but the sediment proxy is only valid from X Mya and back?
[With the ultimate point being “can we reliably treat the sediments as evidence that these conditions have not existed in 15 Myr, in which case it is quite possible that global warming somewhere over 2.5˚C will (in time) restore a condition that has not occurred on Earth since then?”]
2nd paragraph reads “11C (20F)”; something isn’t right there…
And now for a question: do we know the atmospheric CO2 at that time?
Thanks
[Response: A change of 11ºC is the same as a change of ~20ºF (19.8 to be exact). Miocene CO2 is surprisingly difficult to pin down – Two relatively recent papers come to quite different conclusions: Tripati et al (2009) say ~400ppmv and Pagani et al (2005) say ~280ppmv (based on quite different techniques). This is discussed in the Ruddiman paper linked above as well. – gavin]
[Response: Actually, I don’t think Miocene CO2 is particularly harder than any other time before we have CO2 from ice cores. All the geochemical proxies have similar problems and uncertainties. The Miocene CO2 problem stands out because the CO2 estimates bump up against values so low it’s hard for known climate physics to explain how warm the climate is. That’s particularly true if Pagani’s value is closer to the truth, but even the higher value in Tripati et al is problematic. Thus, it is particularly important to understand more about the nature of Miocene climate, and ANDRILL is part of that process. Puzzles like this are Nature’s way of reminding us when there is potentially some big gap in our understanding, and such puzzles demand to be resolved. Sometimes, the puzzle is resolved in favor of the models, through continued improvement in the proxies; this happened with the earlier puzzle of relatively warm CLIMAP LGM tropical sea surface temperatures. To some extent, the problem of cool Eocene tropical temperatures was also resolved in favor of models, though the story is still not complete there. But it could also be that the Miocene and Pliocene are telling us that the climate has some as-yet unfathomed way of flipping into a warmer state. Danger ahead? Best not to poke the angry beast. – raypierre]
Bob, this is one of the first reports out of the ANDRILL program — worth looking at how it’s being done. I’ve been waiting eagerly for anything for quite a while, knowing it was coming eventually.
ANDRILL pulled up cores from various sites, put them on ships and sent the material off to research labs all over the world where the cores went into storage or labs. People are working to make sense of the chunks they have, write that up, and get it to a journal. Lots of pieces, widely distributed.
I doubt there’s an overall complete answer to your questions possible until that work is well advanced.
If I knew where to send donations, I’d send them money. It’s quite a project.
It’s just started.
Pretty coolReally fascinating piece. Hate to “ooh and ah,” but it really is amazing to see the backward extension of proxies ‘in process’ as it were.It’s also tantalizing to try and imagine what else might come out of the ANDRILL.
(And a tip of the hat in gratitude for all the hard work behind results like these.)
#2–LH, an ANOMALY of 20 degrees F is indeed roughly equal to 11 C. They weren’t discussing absolute temperature; where they do, the figures are 45 F and 7 C, which is also (roughly) correct.
If we’re nitpicking, the only thing I spotted was “perhpas” for “perhaps” in the second para of “How Are The Results Interpreted.”
For LH:
“how much warmer things were – up to 11ºC (20ºF) warmer … coastal temperatures to be as warm as 7ºC or 45ºF during the summer…”
Did you read that as saying 11C equals 20F? That would certainly be wrong.
In context, read as part of the sentence, I read it as:
Found 7C, 11C warmer than expected (they expected -4F)
Found 45F, 20F warmer than expected (they expected 25F)
Yes, re-read at least once, carefully, in context, those temp references are clear, but maybe it’d be a lot clearer if science quit coddling Americans and instead force them to start thinking in the terms science and the rest of the world does, skip the F translations and it doesn’t bring the thought process to a bump that requires re-reading, or result in misinterpretations. ;)
Response to 1 and 3: This is not really ‘one of the first reports out of ANDRILL’ – there have been many papers out of that program already, quite a few fascinating. see e.g. ‘Modelling West Antarctic ice sheet growth and collapse through the past five million years’, http://www.nature.com/nature/journal/v458/n7236/full/nature07809.html; and ‘Obliquity-paced Pliocene West Antarctic ice sheet oscillations’, http://www.nature.com/nature/journal/v458/n7236/abs/nature07867.html, published in 2008 and 2009. The ANDRILL website gives great information on the project (http://www.andrill.org), with lots of information on project-related publications for professional scientists and the general public.
And yes, the proxy can be used from the present into periods going back many millions of years as long as the right type of sediments is present; methods can (and have been) used on deep-sea cores recovered by the Integrated Ocean Drilling Program, i.e. from other parts of the worlds oceans and from sediments on land.
flxible wrote: “… if science quit coddling Americans and instead force them to start thinking in the terms science and the rest of the world does …”
Yes, by all means let’s “force” Americans to start thinking in terms of Centigrade instead of the Fahrenheit scale with which they are intuitively and viscerally familiar. It’s important to show them the smaller Centigrade numbers, so they won’t immediately “get” just how high these temperatures we are talking about really are. It is much more important to get them to use the “correct” temperature scale than to effectively convey the magnitude of the problem in terms that they can readily understand.
Right?
Hank, thanks. It’s interesting that this is also on the heels of the Lake El’gygytgyn paper, which seems to be similar in many ways. I actually had the same question in that case, but I could tell from the paper itself that the proxies went back at least as recently as the 10,000 ya.
I’ll have to see if I can beg/borrow a copy of the paper from someone.
[Response: Actually there is great story (or three) to be told about the ‘Lake E’ results. The difficulties in getting that core are not widely appreciated! – gavin]
SA – I’m aware of the problem you point out, being an American by birth and a Canadian by choice, but is 20F or 45F going to raise any uneducated American eyebrows? Might sound real nice to a Texan about now. And the “instant translation” is no doubt what tripped LH above. Maybe there could be “popularized translations” into “American” where all stated temperatures were in F? Someday the US will finally generally adopt the C scale, but reading papers with both scales included does disrupt the smoothness of my [and others] thought processes – maybe because I understand both.
I don’t think LH was confused by the translation from C to F. We’ll see if he/she comes back and elaborates.
I know I’m just a dumb American, but I’m perfectly fluent in both centigrade and Fahrenheit, and I can even get along in Kelvin or Rankine if necessary. It’s a pity the rest of the world is so easily confused by the mere suggestion of an alternate temerature scale.
What was the obliquity? Seems like with no tilt, then it doesn’t really matter what the inferred CO2 was is, it’s not causitive but reactive? And no, CO2 could/will not be a forcing on the scale of obliquity (as the precautionary principle seem to lead many here to believe, not speaking of you directly as the article author)?
1) How long did these warm episodes last ? The graph indicates on the order of 1e4-1e5 yr ?
2) How rapid was the onset of these periods ? or is the data not fine enough to tell ?
sidd
Perhaps it would be useful to add that this study is consistent with both deep sea records from around Antarctica (Shevenell et al., 2004 among others) as well as terrestrial records from the Dry Valleys (Lewis et al., 2008). So now we have evidence from different proxies, phases (biogenic carbonates to organic biomarkers to pollen assemblage data), and sediments from different environments (terrestrial to marine) that all show a consistent pattern of climate change in the Pacific Sector of the Southern Ocean and Antarctica during the middle Miocene climate optimum. It is now important for us to determine if this response was similar around Antarctica.
While Middle Miocene CO2 levels need (require) more study, it is important to remember that other forcings and/or feedbacks may also be important.
The ANDRILL record (this study, and the program in generally) is extremely important because it is a proximal marine record that links the terrestrial and deep sea records. We are finally able to recover high quality marine sediments from the Antarctic continental margin that are giving us important opportunities to integrate climate proximal to Antarctica’s ice sheets with detailed records from deep sea sediments from lower latitudes. This is one of MANY high quality studies that have come or are coming out of the ANDRILL program.
To the person who wanted to donate money, contact the ANDRILL program at the University of Nebraska… Alternatively, as a new Assistant Professor, I am currently accepting donations from unconventional sources. Government funds are getting harder to come by these days :)
I would like to point out a correction to the false-color map of Antarctica accompanying the post headline. Siple Dome is presented on the wrong side of the Ross Ice Shelf, it should be marked on the “grid west” side, in the general vicinity of Byrd and WAIS camps.
The dot currently marked “Siple” looks closer to CTAM/Beardmore.
Just a minor comment on an excellent, informative post! Thanks.
[Response: Oops. You are indeed correct. The map came from the article SI, and so someone else will need to fix it (I’ll let them know). In the meantime, I’ll swap in a more correct map… Thanks – gavin]
Amelia: Alternatively, as a new Assistant Professor, I am currently accepting donations from unconventional sources. Government funds are getting harder to come by these days.
If you have not already, consider RocketHub. I just ran into another project that was doing fundraising there and had stellar results; astonishing how much money is laying about idle in the pockets of bystander enthusiasts.
One interesting response of the Miocene biosphere to the thermal stress was the contraction of the equatorial biome to the few plants that could take the heat- in Borneo and Sumatra it reverted into the cycad monotreme that fossilized into the ultraslow sulfur coal strata mined today.
Sarah,
Thanks for this fascinating post on the methodology behind your findings.
What’s really interesting about the warm climates prior to the ice core record (but not too far back….following say, the Eocene-Oligocene transition) is that it probably provides a good template for the long term tail in the future of the Anthropocene (in the absence of geo-engineering strategies). I have in mind the century to millennial timescale response to unabated CO2 emissions.
Substantial evidence exists that the peak warming should increase linearly with our CO2 emissions, peaking at ~2 C per trillion tons carbon emitted, but with global temperature “locked” into that new state even as emissions go to zero. Concerning the longer-term feedbacks, what’s really important for the type of “concentration thresholds” (e.g., 350 ppm, 450 ppm) that some people have proposed is that those concentrations remain elevated above the threshold of choice for thousands of years. Some of these “CO2 targets” are largely based on the threshold CO2 values that were required to initiate Antarctic glaciation.
Another thing to keep in mind is that the Miocene and Pliocene may provide evidence for multiple equilibria in the climate system. The presence of “small but hidden bifurcations” would be extremely interesting. Despite the proxy uncertainty, CO2 values were probably maintained below 700-800 ppm during the entire time period discussed here up until the present. This is true for CO2 proxies based on Boron, stomata, phytoplankton, and others. Plate tectonics is not too different and solar irradiance was not radiatively distinguishable from present-day values. Because of the logarithmic relationship between CO2 concentration and its impact on outgoing radiation, it’s difficult to argue that these fundamental boundary conditions conspired to produce much more than a modern-day equivalent of a doubling of CO2. Yet the climate was much different. Not only is global mean temperature in excess of modern by many degrees, but sea level is much higher (+10-30 m, at least in the Pliocene) implying substantially less ice cover, the meridional temperature gradient is suppressed, and the dynamics is different than today (e.g., a “permanent El Nino like” zonal SST pattern in the Pliocene).
To the extent that multiple states exist, it is very unlikely that the same CO2 threshold that initiated Antarctic glaciation would be the same as the threshold going the other way.
A lot of this seems way out there in terms of timescale, but just think if the Vikings decided to engage in some sort of activity that put us on a climate branch like the Pliocene or Miocene.
To enlarge on the Colose comment–the paleoclimate record shows that the earth can maintain a warmer equilibrium for millions of years, but we don’t understand how the feedbacks rearrange themselves. The Pliocene is more familiar because it behaves like what we would expect from mildly higher greenhouse gases maintained for a long period. The Miocene is uncomfortable because it appears unstable. But, the warm temperatures lasted for multiple millions of years, in addition to even warmer intervals.
The answer is I’m just an idiot who was reading this while doing other work. It’s like speaking a foreign language – if I truly understand Spanish, I don’t convert it to English in my head. I’m fine with the metric system, so if you tell me 67 kilometers I just know how far that is; I don’t try to convert it to miles. But telling me Celsius is like telling me a word that I convert to English in my head, leaving me open to screw up.
Thanks everyone!
This was a great guest article. Thanks to Sarah for contributing it and RealClimate for hosting it.
It’s nice to read climate stories that aren’t driven by “skeptic” fulminating, and I’m glad to see more of them at RC.
Something to keep in mind is that priot to about 4 mya there was a near-equatorial seaway connecting the Pacific and Atlantic oceans. That alone would result in a quite different climate I should think.
This is all the more interesting because of C4 carbon fixation in plants. There’s some thought that relatively low available CO2 was instrumental in the evolution of C4 carbon fixation, but it’s hardly settled, especially because the C4 pathway evolved independently in different families of plants.
“C4 plants arose around 25 to 32 million years ago[10] during the Oligocene (precisely when is difficult to determine) and did not become ecologically significant until around 6 to 7 million years ago, in the Miocene Period.[10]…Today, C4 plants represent about 5% of Earth’s plant biomass and 3% of its known plant species.[13][9] Despite this scarcity, they account for about 30% of terrestrial carbon fixation.[10]”
http://en.wikipedia.org/wiki/C4_carbon_fixation
http://en.wikipedia.org/wiki/Evolutionary_history_of_plants#Evolution_of_photosynthetic_pathways
A summer temperature of 7C along the coast of Antarctica: does that not say that the Antarctic ice sheets were very much present? Greenland gets warm along the coast, too, and the ice is present still: could not the increased humidity make the center of the Antarctic land mass have thicker ice than now?
Was ice rafting of fines obvious or obviously absent?
Amelia, another science-funding site here I’ve sent money through:
http://www.petridish.org/
Paleontology category has no project listed yet.
It’s screened, might be worth a little time to inquire:
http://www.petridish.org/about#for_scientists
(note, “Petridish” is a for-profit; don’t know any details about that)
If temperatures were higher with less ice I understand that sea levels would be increased as we have defined under our current global warming scenarios. In this case the Antarctic Coast would have a completely different profile than today.
Does this work give any insights to the mechanisms of the process of sea level changes?
> any insights to the mechanisms of the process
Sure; look at the online pictures of cores and the magnified images of what makes up the layers, and what changes between layers. Lots.
Hank @30
Having read the article my curiosity was sparked by the statement that the sediments were 400m below sea level. Therefore I’m understanding that sea level dropped with cooling and the formation of ice.
This appears to go against the prediction of our models which predict the opposite effect.
I must be missing something basic here. Any thoughts welcome.
Thanks
Correction to previous post.
Should read “sea level increase with the cooling” not dropped!!!!
Titus, the sediment drill started at 400m because that is the water depth to the present sea bed from the surface.
That doesn’t mean that sea level has changed by 400 meters.
Titus #33,
See this picture, which shows where the water goes to when a continental ice sheet melts.
Yes, sea level comes down as it gets colder, but at the edge of a growing ice sheet, the land subsides faster still… it’s complicated ;-)
Actually it’s even more complicated… not only does the land go down, but sea water is attracted by the mass of the growing ice sheet, and piles up at the margin. See here.
Thank you Hank and Martin for your replies.
I found Martin’s link @35 a very useful reference.
As a layman in this respect I think I’ll just accept Martin’s advice that this is ‘complicated’:)
Regards
TJ
You can find plenty to read about this kind of thing. Here’s one from a while back nicely illustrated:
http://www.sciencedirect.com/science/article/pii/S1571919708000037
Let me see if I can oversimplify here off the top of my head, a common source for such stuff — and perhaps the scientists will be kind enough to laugh and correct my errors.
So start off with an ice free Antarctica — there’s a bunch of large islands and rivers from them drain into the ocean between them and around them. Eventually something changes — the continental drift moves the whole area toward the South Pole, the Earth’s orbit and inclination vary a tiny bit, the area starts to snow more and more, and the ocean between the islands starts to freeze over longer. Eventually the ocean surface stays frozen and the snow starts to build up year after year. After a while the ice gets so thick that, as its own weight builds up, the mass of floating ice pushes downward.
First it pushes the water under it out toward the edges, wherever it can escape; eventually the ice and the water under it start compressing whatever was there into mud and squeezing the mud along with the water out toward the edges of the ice cap. Out at the edges where the ice isn’t as thick, whatever’s being squozen extrudes and spreads out into a river delta at the level of the seabed.
As the ice cap builds larger and wider the ice in contact with the rock advances in all directions toward the edge, grinding and scraping in some places. The bottom of the ice and the water and sediment pushing out ahead of it carve up the seabed.
Then things warm up a bit; the ice retreats along the sea floor, some of it melts from below in the ocean leaving a surface sheet of ice. Whatever likes living in the ocean gets into that water under the ice, some of it dies, and you get a sediment layer full of shells and droppings and whatnot — living organisms make much of that sediment.
Then things warm more, the surface floating ice clears off intermittently at least, and you get an ocean making a sediment layer full of stuff hhat lives along the edge of forming or melting ice, or in blooms during springtime, and also all the organisms that live off of what blooms in the spring there. Different kind of sediment layer.
Then at some point it gets colder longer; there’s more pressure on the ice cap, more mud squeezed out, more ice in contact with the rock pressing out toward the edge. Surface ice stays longer, different kind of sediment layer forms.
Every now and then a slope fails and a mass of muddy water — a “turbidity current” — takes off downslope tearing away and rearranging everything for a great distance, recarving the surface. (One measure of these was when one happened recently and a series of ocean telecommunication cables got broken by it, one after another, over a very long distance.)
Was antarctica any distance from the pole that long back? Given continental drift.
Nope: https://en.wikipedia.org/wiki/Miocene
Thanks again for the reply Hank. Food for thought.
If, as you show, Antarctica is in the same place then the climate must have been very different from what we have today.
In my early education we were taught a theory that the earth had a canopy of water vapor which had the effect of keeping the whole earth in a warm balance. At some point the canopy collapsed and the vapor turned to water and filled the oceans.
This kind of fits as it means the plants would have been in abundance and the seal level lower. Would this theory hold any water? Please excuse the pun!!
https://duckduckgo.com/?q=earth+had+a+canopy+of+water+vapor+
Hank @41.
My question was; “can this theory hold any water” when considering these latest discoveries. It does seem to fit very well.
Reading through some of your links it appears to be an open question. The last time I heard about it was from a park guide at Muir Woods in California (home of the giant Redwoods) who gave a very compelling talk on the likelihood of this climate model. Pity it gets negatively linked to Creationism and therefore easily dismissed in many folks minds.
Titus @42 — Water vapor is (almost) entirely controlled by temperature. The evaporated H2O fairly rapidly condenses out as precipitation.
In the distant past there was more CO2 in the atmosphere than at any time up to a few years ago. The carbon cycle is not well understood, at least by me, but it is clear that CO2 levels have been gradually decreasing, on average, for the past 50+ million years. This is thought to be related to the formation of the Himalayan mountains starting at that time.
You need to find the book that part of your early education came from. See if it has been revised since you were taught that. Science works that way, and there will be much new and different compared to what youngsters were taught years ago.
If what’s taught today is no different that your early education, it’s not science.
A librarian can help you with this. I can’t.
Re 13 Matthew – YES! (Rankine is one up on me – although I understand how it’s constructed, I almost never see it.)
Re 14 thomas hine
– no tilt? Earth, so far as I know anyone knows, has always had significant tilt (maybe not Mars? If the Earth had no moon, the effects of the other planets would lead to wild obliquity variations over time. I suspect that’s not necessarily a general principle of large moons, though. I don’t know exactly what causes the obliquity variability in detail, but in general, precession (that component not caused by the shift in the semimajor axis) is caused by tidal forces of mainly the moon and sun acting on Earth’s equatorial bulge. Since the Earth’s orbit about the sun and the moon’s orbit about the Earth are not coplanar, the moon and sun would independently cause the Earth’s axial wobble to be about different axes, leading to variations in tilt with respect to the other – however, the lunar orbit’s inclination responds to the sun’s tidal force (tidal relative to the Earth-moon barycenter) by wobbling about the same axis (perpendicular to the Earth’s orbital plane) that it causes Earth’s axis to wobble about. So in a rough time-averaged way the moon’s effect should be the same as the sun’s (in terms of direction). But there could be some terms that don’t cancel out when integrating effects over time, given the eccentricities of the orbits, etc(?). But then again, maybe it’s the other planets(?). Also, the Earth’s orbital inclination wobbles due to the other planets – I’d imagine this would affect obliquity in some way. Over geologic time, at perhaps varyind rates owing to continental drift and some other factors (Earth’s spin via coriolis effect’s role in Kelvin waves, and Earth-moon distance itself is very important), the dissipation of tidal energy combined with transfer of angular momentum has sent the moon farther from the Earth and caused the Earth’s spin to slow, which affects precession and obliquity cycles; I don’t know if there’s been any long term obliquity trend from that – maybe early on right after the moon formed? Any celestial mechanics out there to help clarify?
– Co2 not matter? Impossible! (tilt or not) – it absorbs and emits radiation in accordance with the Planck function, Kirchoff’s law (regarding thermal radiation) (most of the atmosphere is close to LTE via high rates of molecular collisions relative to other processes), and Schwarzchild’s equation (regarding optical path length, in case there’s another equation), with, for the absorption band most important in Earth-like conditions, optical cross section peaking near 15 microns and, averaging over individual lines, gaps, and wobbles, approximatly halving per some interval of the spectrum, so that each doubling effectively widens the bite that CO2 takes out of OLR by that amount (basically the same for net tropopause level upward LW flux and surface downward LW flux, although that’s not a bite but an addition – anyway it’s the change in tropopause level flux after stratospheric adjustment (equal to OLR change after stratospheric adjustment) that’s the most important for global average surface temperature because of the way convection can respond to radiative heating), causing an accumulation of energy until the OLR (via temperature increase – the Planck response) and solar heating return to rough time-averaged global balance, given whatever (non-Planck respons) feedbacks (lapse rate, water vapor, clouds, snow/ice, vegetation, etc.) occur.
– “not causitive but reactive?”
it’s both over various time scales; mainly causative over short time scales w/ respect to climate, but it must always react to something (like humans digging up and burning fossil fuels).
– “CO2 could/will not be a forcing on the scale of obliquity”
Who said it was? Although for modelling purposes, if you know how CO2 varied, you can enter it into a model as a forcing (academically, distinction between forcing and feedback can depend on your purposes or what question you are trying to answer or explain, etc.), or you can use climate + model to try to infer CO2 (+CH4, etc.) – generally, as long as you aren’t doing both for the same time period, it’s not circular, I think.
-“(as the precautionary principle seem to lead many here to believe,”
One has nothing to do with the other. Precaution pertains to action given uncertainty, it doesn’t eliminate that uncertainty.
Re 19 Russell – cycad monotreme – is that cycads with monotremes? (I find cycads interesting as I’m not sure offhand if I’ve ever seen one in person).
Re 25 Patrick – “the C4 pathway evolved independently in different families” I didn’t know that; thanks. I wonder about CAM now… (don’t need to reply, I’ll look it up when I get around to it).
Re 40/42 Titus – I heard of that water shell idea, and it was in the context of making a somewhat literal interp. of the Bible seem scientific.
But with an open mind and some fun with physics:
saturation water vapor pressure (w/ respect to a flat surface of pure liquid water) only depends on temperature, not total air pressure, hence the upper atmosphere above the tropopause could become very enriched with water vapor without having it condense (although this would be hard to maintain over a long time, I’d think (?)). Also a relative lack of CCN might allow supersaturation to some extent – I have no idea what extent (as it is, cloud formation can/does require some supersaturation – see ‘Kohler curve’, cloud droplet vs haze particle)
But outside CH4 oxidation, water generally comes from the ocean and works it’s way up through the troposphere into the stratosphere, with most being squeezed out along the way due to condensation such as when following a moist adiabatic ascent – hence water vapor concentration falls ‘precipitously’ with height up through the troposphere. Maybe H2O mixing ratio can increase with height in the stratosphere due to CH4 oxidation or due to localized injections from below that don’t have larger regional effects on the intervening layer (??). Falling space material can be a source.
But molecules bearing H can be broken up, given the energy of some shorter wavelengths of solar radiation, and the H can escape to space (at a rate that increases with the abundance of H-bearing species in the upper atmosphere – see “Biogenic Methane, Hydrogen Escape, and the Irreversible Oxidation of Early Earth” – Catling, et. al. – http://www.sciencemag.org/content/293/5531/839.abstract )
Also, consider that if you have too much column H2O in the upper atmosphere, the pressure necessarily increases (not adiabatically – heat can be radiated away given a little time) from it’s weight, and the first part of this speculation would fail to apply – it would condense out. A rough estimate of the maximum H2O you could store up there could be gotten by taking some representative temperature at the lower portion of where it would be and finding the equilibrium vapor pressure – the weight of the water can’t be greater than that.
And note that while the air isn’t circulated and mixed as vigorously up there as it is below, it does mover around – in particular, mechanical energy radiating as fluid waves transports some of the work output of the tropospheric heat engine upward where it runs an upper-atmospheric heat pump. There are the hemispheric meridionally-overturning Brewer-Dobson circulation and a global overturning above that which will replace much of the upper atmospheric air with air from below within … I don’t know the time period but it’s certainly not too long climatologically and short geologically. In fact, everything below roughly ~ 100 km height is called the ‘homosphere’ because of how well mixed it all is – except for things like water vapor and ozone, whose chemical/physical reactivity and associated concentrations of source and sink can stay a step ahead of mixing. Above the ‘turbopause’ is the heterosphere, where molecular diffusion dominates over turbulent mixing and the composition varies with height with each ‘species’ tending toward a seperate hydrostatic balance (perturbed by sources and sinks, I think).
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Bringing it half-way back to the original topic, I read something a couple of years ago or so about the idea that (localized) glaciation can limit mountain height. I wonder if some higher mountain ranges prior the the Pleistocene might have increased atmospheric poleward heat transport via quasi-stationary waves.
42 Titus,
Yes, all true. It happened about 3.8 billion years ago, though “warm” was probably near molten lava temps.
http://www.chem.duke.edu/~jds/cruise_chem/oceans/ocean1.html
Jim Larsen @46 — Merely boiling hot methinks.
Clarifications/corrections:
re my 45 –
Re 14 thomas hine “Earth,“…”has always had significant tilt”
Well, maybe not before the moon-forming impact (??)
“If the Earth had no moon, the effects of the other planets would lead to wild obliquity variations over time. I suspect that’s not necessarily a general principle of large moons, though.”
– meaning variations in other conditions could allow the Earth to have a relatively steady obliquity without the Moon.
from here:
http://www3.geosc.psu.edu/~jfk4/PersonalPage/PDFs.htm
go to
http://www3.geosc.psu.edu/~jfk4/PersonalPage/Pdf/Persp_Biol_Med_01.pdf
“Peter Ward and Donald Brownlees’s “Rare Earth” – essay review, James F. Kasting
see p.5/15 – if the moon-forming impact hadn’t occured, Earth’s spin may have been slower at first, but wouldn’t have slowed as much over geologic time and could be fast enough today to avoid wild obliquity changes. (A TV show on the subject of the Moon actually went so far as to specify how fast the Earth spun before the impact – I don’t have the notes in front of me but I think they said an 8 (?) hour day, which might have led to a 12 (?) hour day now, whereas after the moon forming impact it was a 6 (?) hour day and slowed to 24 hour day so far (evidence from tidal rhythmites suggests an 18 hour day something like 900 Ma – I don’t know the source for this)
So if the Earth spun fast enough we wouldn’t need the Moon to prevent such wild obliquity variations. I don’t know if/how adjusting other parts of the solar system could/would do the same.
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Re 40/42 Titus
– A rough estimate of the maximum H2O you could store up there could be gotten by taking some representative temperature at the lower portion of where it would be and finding the equilibrium vapor pressure – the weight of the water can’t be greater than that.
– based on the assumption of 100 % H2O above that level. Adjust for differing conditions. more exact: calculate saturation vapor pressure as function of height (according to known or chosen temperature profile) and where it intersects atmospheric pressure – above is 100 % H2O and below the saturation vapor pressure is the partial pressure of water vapor (maximum allowable in equilibrium). Careful about summing amounts over height, because:
partial pressure, locally, is equal to total pressure * molar fraction
however
total pressure (in hydrostatic balance) is equal to the weight (mass*g) per unit area of overlying substance.
For example, with preindustrial CO2 around 280 ppmv, and being approximately well mixed in most of the atmosphere, the partial pressure of CO2 near sea level (absent local sources or sinks) would be approximately 0.28 mb (average sea level pressure is a little over 1000 mb, or 1 bar, or 100 kPa. 1013 mb is closer; it’s 1013.something mb). However, the mass of all the CO2 in the atmosphere contributes a larger amount to the total pressure because the molecular mass is greater than the average air molecule (from memory and by approximation, 44 g/mol / 29 g/mol * 280 ppm mol/mol * 1000 mb = 44/29 * 0.28 mb ~= 0.42(48) mb. H2O is the opposite; it’s molar mass is ~ 18 g/mol (and it’s molar fraction is highly variable, of course).
Related:
specific humidity http://amsglossary.allenpress.com/glossary/search?id=specific-humidity1
mixing ratio http://amsglossary.allenpress.com/glossary/search?id=mixing-ratio1 – but see also http://en.wikipedia.org/wiki/Mixing_ratio
absolute humidity http://amsglossary.allenpress.com/glossary/search?id=vapor-density1 – the molar version of this is one way to define concentration (as in mol/L) – however earlier I refered to concentration when I meant a relative concentration, as in partial pressure/total pressure.
– where molecular diffusion dominates over turbulent mixing and the composition varies with height with each ‘species’ tending toward a seperate hydrostatic balance (perturbed by sources and sinks, I think).
Except perhaps charged particles. I don’t know a lot about that, but when mean free paths get long enough, the effect of the magnetic field starts to show; they locally follow helical paths. This happens to electrons below where it happens to ions, and in between the wind can move ions differently than electrons – this gives rise to the E-region dynamo.
Re Jim Larsen – the timing may have been a bit different than that
“The Hadean-Archaean Environment”, Norman H. Sleep
http://cshperspectives.cshlp.org/content/2/6/a002527.full.pdf+html
suggests liquid water was able to form soon (~10 Myr) after the moon-forming impact, however with enough remaining vapor and CO2 above, the boiling point would be higher.
See also
“Initiation of clement surface conditions on the earliest Earth”
Sleep et al.
http://www.pnas.org/content/98/7/3666.full
Re my 45 re 14 – But there could be some terms that don’t cancel out when integrating effects over time, given the eccentricities of the orbits, etc(?) if I may indulge in tying up a loose end –
Interesting point – the rate of precession pulsates (or at least, it should given the physics – perhaps it is masked by Chandler wobble? – I don’t know) over short time periods. The tidal torque a mass raises on a planet via it’s equatorial bulge is maximum when the mass is overhead at ~ 45 deg latitude (assuming the shape of the planet deviates from spherical with a vertical displacement that is approximately sinusoidal over latitude, which I think is close to accurate, though am not 100 % sure – because I’ve never gone through the math including the amplifying graviational effects of the bulge itself) – it is zero if over the pole or in the equatorial plane. Aside from the effects of eccentricity, Solar-driven precession thus peaks at solstices and is zero at the equinoxes, and in general when obliquity itself is largest, and lunar driven precession relative to the lunar orbital plane (which can cause obliquity to change when not in the plane of Earth’s orbit) peaks when the moon is highest above or below the equatorial plane, and in general when the lunar orbit is tilted opposite the Earth’s tilt.
Meanwhile (if I’ve got this right) the planets collectively ought to cause Earth’s axis to tend to wobble about the angular momentum vector for all (other) planets (excluding intrinsic spins – equatorial bulges have gravity and Earth’s contributes to changes in the orbits of satellites, but for interplanetary interactions the effect should be second-order or less relative to positions, I’d think), and cause the Earth’s orbit (I picture it as a tidal torque on the Eart-Sun system (or Earth-Moon-Sun, actually, and it is the Earth-Moon system’s orbit about the sun) to wobble similarly (at a different rate, and this itself changes Earth’s obliquity independent of torques on the Earth), although ultimately all planetary orbits wobble about the angular momentum vector for all including themselves because those causing wobbles also wobble (but they don’t fall down!). And while total angular momentum is linearly proportional to masses and velocities and positions (though velocities do depend on positions differently), gravity is proportional to distance^-2 and linearized tidal acceleration to distance^-3 – and deviations from such a linear approximation get large when the distance is not so much larger than the dimensions of the system being torqued (and it’s interesting when the tide-producer is inside the system). So perhaps one way to describe it is that planets individually wobble somewhat about the whole but especially about the nearest neighbors, and larger and larger groupings ultimately wobble about the whole (?).
Okay, done.