Large Hardon Collider

[Restrat]

I was incredible disillusioned about academia by my experience in a PhD program. I really love what brought me into my field, but found that the further you go the more you have to give up in order to do whats going to make your school more money so you can keep your job. It's 100% about the money if you work for a research intensive university, money you never see but have to bring in, at least in bio research. In my department one of the top professors never took grad students- he only hired people to work and got post-docs, and since he was an 'expert' in his field he got tons of grants to do so. He wasn't even pretending that grad school was about helping to train the next generation of scientists. The classes were also a joke- they didn't want you to bother with learning anything as it could take away from your research time. We spent the first two weeks doing punnet squares in a graduate level genetics course, and my core microbiology course was actually the undergraduate microbiology 2 course. The grad students had to write one extra paper on a topic of their choice.

[Tristam]

Without CO2, photosynthesis is kinda fucked, isn't it?

It depends on the type of plant and the environment it's in. Some plants respond well to excess CO2, others don't. You're also assuming that temperature increases will stop after they reach this "optimum" which while it may have resulted in a wetter africa, also resulted in desertification of the american midwest (goodbye breadbasket). It was a regional phenomenon.

wiki:
Northwestern Europe experienced warming, while there was cooling in the south.[2] The average temperature change appears to have declined rapidly with latitude so that essentially no change in mean temperature is reported at low and mid latitudes. Tropical reefs tend to show temperature increases of less than 1 °C; the tropical ocean surface at the Great Barrier Reef ~5350 years ago was 1°C warmer and enriched in 18O by 0.5 per mil relative to modern seawater.[3] In terms of the global average, temperatures were probably colder than present day (depending on estimates of latitude dependence and seasonality in response patterns). While temperatures in the Northern Hemisphere were warmer than average during the summers, the tropics and areas of the Southern Hemisphere were colder than average which comprised an average global temperature still overall lower than present day temperatures

edit: And for the whateverth time, there's more to the science than the climate models. The models are only part of the story, and we don't need them to predict warming. Stop pretending like all anyone cares about are the models.

[Eliseos]

I still have the option of going into medical physics, engineering, or getting a physics PhD but getting some lab job where I'm more of an engineer or something else than a physicist. I'm leaning heavily towards one of those now.

Join us engineers!

[Max™]

Again, this is you showing you don't know what the fuck. You don't solve differential equations with a damned calculator, you do it with pencil & paper. The hard ones you solve with Matlab, and that isn't a calculator, it's a computer program. And no, by calculator, you didn't mean Matlab.

Uh, no, by calculator I meant a program that calculates shit, I didn't say pocket calculator, and I'm quite aware that people do math on pencil and paper... thanks for the helpful tip though.

Also, your internet autism is showing because I never said I can solve differential equations in my head. I said I have the tools to be able to solve them, you'd be lost and would have no idea what to do with the problem given to you.

Ah, so I wouldn't know that I'm looking for the instantaneous rate of change of a particular function, or to apply those wonderfully useful things known as calculus methods to attempt to find said derivatives, or to apply those derivatives to find a particular solution?

Or, if one were not fully educated in calculus, they could make use of tools of various degrees of sophistication, http://www.digitalcalculus.com/demo/odecalc.html lots of types online, from free cheap-o ones like those, to higher end versions.

And for the whateverth time, there's more to the science than the climate models. The models are only part of the story, and we don't need them to predict warming. Stop pretending like all anyone cares about are the models.

We can predict the behavior of the climate system a hundred years in the future without computer modeling? Did Eliseos do it on a napkin?

I guess it's my mistake, I didn't know we had empirical evidence of future climate change, got any links?


Incidentally: there will be a total solar eclipse passing over the US in 2017, the maximum eclipse will occur at a point like a hundred miles north-northeast of where I am, at the TN-KY border.

Goes through Oregon to Georgia I think, I'll update with the google map of the path if I can find it.

[Tristam]

We can predict the behavior of the climate system a hundred years in the future without computer modeling? Did Eliseos do it on a napkin?

I guess it's my mistake, I didn't know we had empirical evidence of future climate change, got any links?

Hmm, I guess you didn't read this the last time I provided it. Did they have computers in the late 1800s? Ahrrenius predicted, and was correct, in the changing climate over the next 100+ years after publishing his work. The past 100 years are pretty good empirical evidence.

http://www.aip.org/history/climate/simple.htm

These elementary ideas were developed much further by the Swedish physical chemist Svante Arrhenius, in his pioneering 1896 study of how changes in the amount of CO2 may affect climate. Following the same line of reasoning as Tyndall, Arrhenius pointed out that an increase in the blocking of heat radiation would make for a smaller temperature difference between summer and winter and between the tropics and the poles. (Link from below)
Arrhenius's model used an "energy budget," getting temperatures by adding up how much solar energy was received, absorbed, and reflected. This resembled what his predecessors had done with less precise physics.(15) But Arrhenius's equations went well beyond that by taking into account another physical concept, elementary but subtle, and essential for modeling real climate change. This was what one turn-of-the-century textbook called "the mutual reaction of the physical conditions" — today we would call it "feedback."

Also, that graph you gave is misleading, I know you got it from a denialist site (watts lol, still getting all your info from blogs?), and I'm having a tough time finding the original data, the link they provide goes to nothing. But I don't think it matters because the scale is lots of millions of years. Over that timescale, large changes in landmass position and other effects on climate happen and CO2 remember is both forcing and feedback. In the current cycle of ice ages and interglacials, the planet has never seen CO2 concentrations such as exist today, your graph cites a pagani but doesn't give a year. See Pagani 2005 and look at CO2 ppm. It's been stable for the past 25 MILLION years.

http://www.sciencemag.org/cgi/content/abstract/1110063

"The relation between the partial pressure of atmospheric carbon dioxide (pCO2) and Paleogene climate is poorly resolved. We used stable carbon isotopic values of di-unsaturated alkenones extracted from deep sea cores to reconstruct pCO2 fromthe middle Eocene to the late Oligocene (~45 to 25 million years ago). Our results demonstrate that pCO2 ranged between 1000 to 1500 parts per million by volume in the middle to late Eocene, then decreased in several steps during the Oligocene, and reached modern levels by the latest Oligocene. The fall in pCO2 likely allowed for a critical expansion of ice sheets on Antarctica and promoted conditions that forced the onset of terrestrial C4 photosynthesis."

edit: So it's not that "CO2 acts differently", it's that the conditions of the entire planet were wholly different. You can't compare levels of CO2 now to levels of CO2 400 million years ago because so much other stuff was different that there could be any number of reasons there was more CO2 in the atmosphere.

[Khamsin]

By the way, sorry for the derail but I kinda missed the last 80 pages or so and any keyword I could search for wouldn't help in this thread. Has anything meaningful come from the data collected by the LHC yet? Any major discoveries that I've missed since the evening news decided to cover the latest hollywood breakup instead?

[Woozie]

For the LHC specifically, there has been no huge developements yet.

Also, I don't know if this has been posted before or not

http://www.youtube.com/watch?v=P9dpT...eature=related

Edit:

LOL

http://www.oeffner.net/researchpapers.htm

[Tristam]

They've been doing stuff, but I'm not qualified to say whether this is generally intersting. It seems cool tho.

http://scienceblogs.com/brookhaven/2...e_of_nucle.php

edit: And for the research papers thing, so true... so true...

[Woozie]

Hmm, I haven't heard of that. I'm going to take this article to my professor tomorrow and see if he can explain this to me. I have no idea how significant this is. I barely even understand it.

[Tristam]

Yeah I usually steer clear of the physics based blogs on that site with the exception of Starts with a Bang. That's a good one for explaining stuff to lay audiences. I don't think he's got anything on the LHC in a while tho.

[Max™]

Got the chart off of google images, though I try to avoid linking to sites which are known skeptic/denialist sorts.

Spoiler: show

http://img.photobucket.com/albums/v2...lion_years.jpg
http://www.newscientist.com/data/ima...1647-5_738.jpg

Here's an IPCC one:

Spoiler: show

http://www.ipcc.ch/publications_and_...gure-6-1-l.png

They don't plot temperature estimates further back than roughly the PETM (Paleocene-Eocene Thermal Maximum) though, oddly.

They cover the PETM: http://www.ipcc.ch/publications_and_...ch6s6-3-3.html, yet don't point out that it probably was cooler than the Mesozoic peaks, nevermind the Devonian or the Permian spikes.

Spoiler: show

http://upload.wikimedia.org/wikipedi...ate_Change.png

http://en.wikipedia.org/wiki/File:ra...ate_Change.png
http://en.wikipedia.org/wiki/Paleoclimatology

There's lots of sources out there for this stuff, but you either have to get it off of Wiki, or a skeptic site, as the IPCC doesn't seem to be a fan of admitting there are temperature reconstructions prior to the PETM.

Hmm, I guess you didn't read this the last time I provided it. Did they have computers in the late 1800s? Ahrrenius predicted, and was correct, in the changing climate over the next 100+ years after publishing his work. The past 100 years are pretty good empirical evidence.

http://earthobservatory.nasa.gov/Fea...nius_model.gif
http://earthobservatory.nasa.gov/Fea...servations.gif

Arrhenius showed his physical insight at its best when he realized that he could not set aside another simple feedback, one that would immediately and crucially exaggerate the influence of any change. Warmer air would hold more moisture. Since water vapor is itself a greenhouse gas, the increase of water vapor in the atmosphere would augment the temperature rise. Arrhenius therefore built into his model an assumption that the amount of water vapor contained in the air would rise or fall with temperature. He supposed this would happen in such a way that relative humidity would remain constant. That oversimplified the actual changes in water vapor, but made it possible for Arrhenius to roughly incorporate the feedback into his calculations. The basic idea was sound. The consequences of adding CO2 and warming the planet a bit would indeed be amplified because warmer air held more water vapor. In a sense, raising or lowering CO2 acted mainly as a throttle to raise or lower the really important greenhouse gas, H2O.

Now, keep in mind that the IPCC does this still: http://www.ipcc.ch/publications_and_...3s3-4-2-1.html, https://www.ipcc.ch/publications_and...3s3-4-2-2.html.

Over the ocean, the observed surface specific humidity increases at 5.7% per 1°C warming, which is consistent with a constant relative humidity. Over land, the rate of increase is slightly smaller (4.3% per 1°C), suggesting a modest reduction in relative humidity as temperatures increase, as expected in water-limited regions.

Think about that... the temperature rises, and the relative humidity stays constant.

"Relative humidity represents a percentage of the maximum amount of humidity that can remain in the air, at the given temperature of the air."

Now, if you raise temperatures without adding water vapor, relative humidity drops. If you lower temperatures while maintaining water vapor levels, relative humidity rises.

Due to instrumental limitations, long-term changes in water vapour in the upper troposphere are difficult to assess. Wang et al. (2001) found an increasing trend of 1 to 5% per decade in relative humidity during 1976 to 1995, with the largest increases in the upper troposphere, using 17 radiosonde stations in the tropical west Pacific. Conversely, a combination of Microwave Limb Sounder (MLS) and Halogen Occultation Experiment (HALOE) measurements at 215 hPa suggested increases in water vapour with increasing temperature (Minschwaner and Dessler, 2004) on interannual time scales, but at a rate smaller than expected from constant relative humidity.

"Key point to remember: Given that the amount of water vapor is held constant, then if you
--reduce the temperature, the relative humidity goes up
--increase the temperature, the relative humidity goes down."


I dunno, fuckin' water vapor, how does it work?

[BerenTebogo]

Starts with a bang is A+

[Mizango]

Holy cow, I go away for the weekend and this thread start popping

[Tristam]

The point wasn't that the graph was from a denialist site, the point is that it is misleading for what you are saying, which obviously is why the denialist site used it (in fact, they made it lol). Spikes in CO2 hundreds of millions of years ago are completely irrelevant because the positions of continents are far more important when you compare 100 million year timescales, which I've told you before but you continue to ignore. You said it yourself, mixing of the oceans is very important. Well, the positioning of Antarctica (which got itself nicely situated at the south pole about 25 Mya) changes all that. To say nothing of the influence of the flora/fauna over millenia. The past 25 million years are what is important in this context, and you need to look beyond google/wiki apparently to understand this. If you don't have access to that Pagani 05' paper, go to a library, get access to it, download it and read it.

This is as clearly as I can say it, because the continent of antarctica is currently at the south pole, it impedes rapid mixing of ocean waters and provides a large surface to collect snow/ice. So even though in the distant past, CO2 may have been higher, other geologic factors clearly influenced the climate. These geologic factors are not changing right now (or they are, but so slowly as to be irrelevant).

I don't understand your problem with the humidity of the upper atmosphere either. Do you have a problem with Arrhenius' model? Looks pretty good to me based on what you posted. It's not perfect, but you can understand chemistry and physics and make pretty good predictions without advanced computer models. It's also worth pointing out that we're nowhere near any sort of equilibrium.

Or what exactly is your point. I mean here's the IPCC summary you cite:

"To summarise, the available data do not indicate a detectable trend in upper-tropospheric relative humidity. However, there is now evidence for global increases in upper-tropospheric specific humidity over the past two decades, which is consistent with the observed increases in tropospheric temperatures and the absence of any change in relative humidity. "

So it gets warmer, more water vapor in the upper atmosphere, specific humidity up, relative humidity constant. What am I missing? You could always keep changing the goalposts though. I'm much rather find out what the APS is going to do with those bazillions of climate dollars. Maybe when Woozie goes to Dallas he can infiltrate the climate cabal and get back to us.

[Max™]

Ah, so Arrhenius had a good model, though the assumption of constant relative humidity is absurd, and the predictions were HUGELY off? You think it makes sense to simply peg the level of water vapor exactly to the upper troposphere temperatures? I thought I included a study about the radiosonde methods and the absurd averaging processes applied in those IPCC studies.

An independent check on globally vertically integrated water vapour amounts is whether the change in water vapour mass is reflected in the surface pressure field, as this is the only significant influence on the global atmospheric mass to within measurement accuracies. As Trenberth and Smith (2005) showed, such checks indicate considerable problems prior to 1979 in reanalyses, but results are in better agreement thereafter for ERA-40. Evaluations of column integrated water vapour from the NASA Water Vapor Project (NVAP; Randel et al., 1996), and reanalysis data sets from NRA, NCEP-2 and ERA-15/ERA-40 (see Appendix 3.B.5.4) reveal several deficiencies and spurious trends, which limit their utility for climate monitoring (Zveryaev and Chu, 2003; Trenberth et al., 2005a; Uppala et al., 2005). The spatial distributions, trends and interannual variability of water vapour over the tropical oceans are not always well reproduced by reanalyses, even after the 1970s (Allan et al., 2002, 2004; Trenberth et al., 2005a).

To summarise, global, local and regional studies all indicate increases in moisture in the atmosphere near the surface, but highlight differences between regions and between day and night. Satellite observations of oceanic lower-tropospheric water vapour reveal substantial variability during the last two decades. This variability is closely tied to changes in surface temperatures, with the water vapour mass changing at roughly the same rate at which the saturated vapour pressure does. A significant upward trend is observed over the global oceans and some NH land areas, although the calculated trend is likely influenced by large interannual variability in the record.

Wtf is "globally vertically integrated water vapor" btw?


I know about Antarctica interfering with current circulation, but funnily enough, that isn't cited as the reason for the current ice age cycles. Rather the IPCC says that the reduced CO2 allowed Antarctic glaciation.

Spoiler: show

http://universe-review.ca/I09-03-drift.jpg

Is this paper similar to the Pagani one?

http://droyer.web.wesleyan.edu/PhanCO2(GCA).pdf

CO2-forced climate thresholds during the Phanerozoic

Dana L. Royer

*
Department of Earth and Environmental Sciences, Wesleyan University, Middletown, CT 06459-0139, USA

Oh, what is this: http://www.sciencedaily.com/releases...0622134142.htm

Deep Sea Algae Connect Ancient Climate, Carbon Dioxide And Vegetation

ScienceDaily (June 27, 2005) — New Haven, Conn. --

Assistant Professor Mark Pagani in the Department of Geology and Geophysics at Yale and his colleagues mapped the first detailed history of atmospheric carbon dioxide between 45 - 25 million years ago based on stable isotopes of carbon in a National Science Foundation study reported in Science Express.

"Through the energy we consume, each of us makes a contribution to increasing greenhouse gasses, such as carbon dioxide and methane, in the Earth's atmosphere," said Pagani. "To understand the implications of these actions for the future, scientists look to the past to gain a better understanding of Earth's climate system under high greenhouse gas conditions." The findings were based on calibration of carbon-containing compounds produced by ancient sea surface algae that were recently isolated in deep sea drill cores.
The data indicates that between 45 - 34 million years ago the atmospheric carbon dioxide level was up to five times greater than today, with a sharp decrease and then stabilization to near modern day levels between 34 - 25 million years ago.

During the early part of the Paleogene Period, from 65 - 34 million years ago, global climates were much warmer than today with very little ice present at the poles. The boundary of the Oligocene and Eocene Epochs 33.7 million years ago was marked by rapid global cooling and the formation of large continental ice sheets on the Antarctic.

"Before this study, the relationship between the global climate and the concentration of carbon dioxide in the atmosphere during the late Eocene and Oligocene was largely unknown," said Pagani, who is recognized for his reconstruction of past atmospheric carbon dioxide levels between 25 million and eight million years ago.

They also present intriguing evidence that the sharp drop in carbon dioxide level, between 33 - 25 million years ago, prompted the origin of economically important land plants that are sensitive to atmospheric carbon dioxide levels, such as corn and sugarcane.
"The onset and stabilization of ice sheets at the same time as a decline in carbon dioxide illustrates the importance of atmospheric carbon dioxide as an agent of both climate and biological change," Pagani said.
Collaborators were Brett Tipple from Yale, James C. Zachos and Stephen Bohaty at University of California, Santa Cruz and Katherine Freeman at Pennsylvania State.

The climate money was including the carbon trading money, I assume, and I think the idea was that if you want any of it, funding or otherwise, you can't do anything but support the current political view on climate change. Worked for Gore didn't it?

[Woozie]

More proof that Mother Nature is a huge show off


http://cosmiclog.msnbc.msn.com/_news...n-walk-on-legs

Alan Boyle writes:Bacteria have legs? That suggestion seemed surprising to Gerard Wong, a bioengineering professor at the University of California at Los Angeles, when his students told him they were seeing some strange behavior in movies of the microbes.

"They said, 'You know, we noticed that some of the bacteria — in fact, a lot of them — popped a wheelie and stood up," he recalled. "And I said, 'What are you talking about?'"

But in a sense, it's true: The movies show that the Pseudomonas aeruginosa bacteria wiggle themselves up into a vertical position and move leglike projections known as Type IV pili to wander around a surface. Wong and his colleagues describe the phenomenon in this week's issue of the journal Science.

You'd think that if bacteria could walk, someone would have noticed it long ago. And it may well have been noticed. But as far as Wong knows, his research team's report is the first systematic set of observations of the behavior. He said that once word got out about the pili phenomenon — for example, at an American Physical Society session in March — he started hearing comments that other researchers were seeing the walking as well. And then came the evolution jokes. "In a way, it's kind of like 'bacteria erectus,'" Wong said. What's next? Opposable thumbs?

The funny thing is that Wong's team didn't start out looking for bacteria legs at all. Instead, they were developing an image-processing algorithm to sort through masses of microbe movies, just to check on the effects of the genetic modifications they were making. Pseudomonas aeruginosa is a pathogen that plays a role in cystic fibrosis, and if some genetic twist makes them less able to do their dirty business — which appears to involve forming constrictive biofilms in the lungs — that could suggest new medications for fighting the disease.

About 30,000 Americans have cystic fibrosis, and the median life expectancy for people with the genetic disease is about 38 years. The disease isn't caused by bacteria, but it leaves the lungs more vulnerable to infection by bugs such as Pseudomonas aeruginosa.

"Once the biofilms form, they become very resistant to antibiotics," Wong said. "At some point there's just absolutely nothing you can do."
Crawling bacterium

Gerard Wong / UCLA Bioengineering, CNSI

For directional motion, bacteria generally favor "crawling" in a horizontal orientation, as shown in this schematic.

In addition to reporting the walking behavior, Wong and his colleagues say that there's a link between the prowess of a bacterium's Type IV pili and the ability to form biofilms. The bacteria can use the pili either to walk (in a vertical orientation) or crawl (in a horizontal orientation). Walking seems to be good for wandering around a surface — perhaps to look for food, or to hook up with other bacteria to form a biofilm. Crawling seems to be better for moving directly from one area to another.

Wong and other researchers would love to find a way to disrupt the biofilm-forming process. Understanding the behavior of walking bacteria could eventually lead to new treatments, not only for cystic fibrosis, but for other ills related to biofilms.

"Failures of implants, dental plaque ... those are all biofilms," Wong said. "Being able to control those biofilms could be very important."

So in a sense, Wong's research is aimed at cutting off the legs off harmful bacteria while letting benign microbes go about their business. That goal may be a giant leap for medicine, but there's a benefit to every small scientific step from here to there — including figuring out how bacteria get from here to there.

Videos of walking bacteria, courtesy of Gerard Wong:

* Launch sequence: Bacteria attached to a surface can orient themselves perpendicular to the surface. Such "standing" cell orientations play important roles in their life cycles. One example is how bacteria detach from a surface. Here we see that the bacterium spins on the surface, tilts upward to a near-vertical orientation and then launches from the surface.
* Newborn bacterium walks away: After a bacterium divides into two daughter cells, one of the daughter cells stands up, walks away and then detaches from the surface. This new "walking" mechanism, where the bacterium body is upright and perpendicular to the surface, is distinct from the commonly described "crawling" movement, where a bacterium moves while lying down with its body axis parallel to the surface.
* One goes, one stays: After a bacterium divides, one of the daughter cells stands up before detaching from the surface. The other daughter cell remains behind. This difference in cell fates of two sister cells is observed in most division events.

http://www.popsci.com/science/articl...-trillion-suns

Now that scientists are done making a map of the cosmic microwave background, they can use that detailed map to find hidden treasures from the ancient universe.

Using the South Pole Telescope, they’ve just found a mother lode: the biggest galaxy cluster ever seen, harboring about 800 trillion suns inside hundreds of galaxies.

The huge cluster remained hidden until SPT scientists spotted it by looking for distortions in the cosmic microwave background, the afterglow of the Big Bang. These distortions are created as background radiation passes through a large galaxy cluster, according to the Harvard-Smithsonian Center for Astrophysics.

The cluster, which is found in the southern constellation Pictor the painter, is full of galaxies that formed when the universe was only about two billion years old. They are quite faint and their light is shifted toward the red end of the spectrum, meaning they are very far away; according to the Harvard-Smithsonian center, the cluster’s redshift value puts it roughly 7 billion light-years from Earth.

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Tags
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This means we see the cluster as it appeared 7 billion years ago. If we could see it now, it would probably be about four times this size.

Old, humongous galaxy clusters like this can be used to study how dark matter and dark energy drove the evolution of the cosmos. Gravity holds the clusters and associated inter-galactic gases together, and dark energy drives them apart.

When the universe was less diffuse, gravity had a stronger influence; in a 2009 study, scientists said gravity should have led galaxy clusters to increased 50-fold over 5.5 billion years. But dark energy stunted the spread of these behemoths, and they only grew 10-fold.

Galaxy clusters can help astrophysicists measure dark energy’s equation of state — the magic number that explains cosmic inflation and the accelerating expansion of the universe. The CMB search method provides an accurate cluster mass, which is important for these studies.

The new cluster was found as part of an ongoing survey with the SPT. Researchers will also study the evolution of hot gas within galaxy clusters; study the evolution of massive galaxies within clusters; and identify distant star-forming galaxies.

[Max™]

Bacteria X-games, coming soon.

I wanna see one pop a 1260 Cork!

[Tristam]

Ah, so Arrhenius had a good model, though the assumption of constant relative humidity is absurd, and the predictions were HUGELY off? You think it makes sense to simply peg the level of water vapor exactly to the upper troposphere temperatures? I thought I included a study about the radiosonde methods and the absurd averaging processes applied in those IPCC studies.


I know about Antarctica interfering with current circulation, but funnily enough, that isn't cited as the reason for the current ice age cycles. Rather the IPCC says that the reduced CO2 allowed Antarctic glaciation.

The assumption was made for old models, and the real problem with the Arrhenius model was that he assumed the increases of CO2 would be slow. That's what I meant when I said we're not at a steady state. The rate of addition of CO2 is so fast right now that it would take quite a while for the planet to stop warming even if CO2 were stabilized at present values. He wasn't off by much at all, look at his (2nd) estimate for climate sensitivity, he's at the lower bound of the error (it's on his wiki page). Plus he did all this work with pencil and paper and you can't cut him a little slack?

But for constant relative humidity, I think you're confusing observations with models. The experimental observations noted in the IPCC report indicate somewhat constant relative humidity under some conditions, so it's clearly not absurd though it is not completely conclusive. Even so, modern models do NOT assume constant relative humidity.

http://www.realclimate.org/index.php...odels-part-ii/

"# Do models assume a constant relative humidity?

No. Relative humidity is a diagnostic of the models’ temperature and water distribution and will vary according to the dynamics, convection etc. However, many processes that remove water from the atmosphere (i.e. cloud formation and rainfall) have a clear functional dependence on the relative humidity rather than the total amount of water (i.e. clouds form when air parcels are saturated at their local temperature, not when humidity reaches X g/m3). These leads to the phenomenon observed in the models and the real world that long-term mean relative humidity is pretty stable. In models it varies by a couple of percent over temperature changes that lead to specific humidity (the total amount of water) changing by much larger amounts. Thus a good estimate of the model relative humidity response is that it is roughly constant, similar to the situation seen in observations. But this is a derived result, not an assumption. You can see for yourself here (select Relative Humidty (%) from the diagnostics). "

The ice age scenario is due to both the geological conditions and the loss of CO2 by some means. The positioning of antarctica is a geological forcing, while CO2 was either a forcing (via some mechanism, weathering perhaps) or an amplifying feedback, or possibly both. So both things had to happen. But you can't make the comparison between now and 100 million years ago because we know that CO2 is a forcing today (we're adding it to the atmosphere and understand the chemistry and physics) and all other phenomena are stable over the timescales we're interested in. Put another way, when you're looking at a graph over 400 million years, you're looking at multiple potential forcings acting simultaneously (geology, weathering, sun intensity changes, evolution of photosynthesis, etc etc etc.) and influencing temperature. But your graph doesn't account for all those potential forcings, so while temp and CO2 may not be correlated over 200-400 Mya (guessing here), you don't know what the condition of other long term underlying forcings are. Over the timescales we're interested in today (10s to 100s of years), many of these forcings are known to not be an issue (new photosynthesis evolution hasn't occurred, sun is stable, antarctica hasn't moved alot, volcanism isn't too crazy, and so on).

edit: I saw the nasa feature page you got that graph from, I have a number of problems with it and I'm a bit disappointed in nasa with that article. For instance they don't update it to include the 2006 Dessler paper that takes their calculated changes in relative humidity and throws it through 17 different GCMs with the result being no statistically significant difference between their estimates and the model outputs.

[Tristam]

Bacteria have legs now? Damn... It's only a matter of time before they decide we're not useful and kill us all off.

[Woozie]

I was just telling a friend that bacteria are now one step closer to their end goal of world domination.