Global climate
Global climate statistics, such as the global mean temperature, provide good indicators as to how our global climate varies (e.g. see here). However, most people are not directly affected by global climate statistics. They care about the local climate; the temperature, rainfall and wind where they are. When you look at the impacts of a climate change or specific adaptations to a climate change, you often need to know how a global warming will affect the local climate.
Yet, whereas the global climate models (GCMs) tend to describe the global climate statistics reasonably well, they do not provide a representative description of the local climate. Regional climate models (RCMs) do a better job at representing climate on a smaller scale, but their spatial resolution is still fairly coarse compared to how the local climate may vary spatially in regions with complex terrain. This fact is not a general flaw of climate models, but just the climate models’ limitation. I will try to explain why this is below.
Regional climate characteristics
Most GCMs are able to provide a reasonable representation of regional climatic features such as ENSO, the NAO, the Hadley cell, the Trade winds and jets in the atmosphere. They also provide a realistic description of so-called teleconnection patterns, such as wave propagation in the atmosphere and the ocean. These phenomena, however, tend to have fairly large spatial scales, but when you get down to the very local scale, the GCMs are no longer appropriate.
Minimum scale
There are several reasons why GCMs do not provide a representative description of the local climate (i.e. exactly where I live). For one, the grid mesh, on which they compute the physical quantities relevant for the climate, is too coarse (typically 200km) to capture the local aspects. The figure on the left shows a typical land-sea mask for a GCM.
The distance between two grid points in a GCM (or an RCM) is the minimum scale (~200km). The coarse resolution typically used in the GCMs till now has implied that the topography has been smooth compared to the real landscape and that some countries (e.g. Denmark and Italy) are not represented in the models (one exception is one Japanese GCM with an extremely high spatial resolution).
Sub-grid processes are represented by parameterisation schemes describing their aggregated effect over a larger scale. These schemes are often referred to as ‘model physics’ but are really based on physics-inspired statistical models describing the mean quantity in the grid box, given relevant input parameters. The parameterisation schemes are usually based on empirical data (e.g. field measurements making in-situ observations), and a typical example of a parameterisation scheme is the representation of clouds.
Surface processes
Climate models need boundary conditions describing the surface conditions (e.g. energy and moisture fluxes) in order to yield a realistic representation of the climate system. Often simple parameterisation schemes are employed to provide a reasonable description, but these do not capture the detailed variations associated with small spatial scales.
Skillful scale
Shortcomings associated with parameterisation schemes and coarse resolution explain why one gridpoint value provided by the GCMs may not be representative for the local climate. A concept called skillful scale has sometimes been employed in the literature, most of which have been linked to a study by Grotch and MacCracken (1991) who found model results to diverge as the spatial scale was reduced. Specifically, they observed that:
Although agreement of the average is a necessary condition for model validation, even when [global] averages agree perfectly, in practice, very large regional or pointwise differences can, and do, exist.
Although it is not entirely clear whether this study really touched upon skillful scale, it has since been cited by others, and used to argue that the skillful scale is about 8 gridpoints. Nevertheless, since the 1991-study, the GCMs have improved significantly, and the GCMs now are run for longer periods and with diurnal variations in the insolation.
Regionalisation
The figure above gives an illustration of the concept of regionalisation, or so-called downscaling. The left panel shows a typical RCM land-sea mask, giving a picture of its spatial resolution. The middle panel shows a blurred satellite image of Europe, which can illustrate how the sharp details are lost yet providing a realistic large-scale picture. The unblurred image of Europe is shown in the right panel. An analogy for the data from GCMs is looking at a blurred picture (middle above) while regional modeling (RCMs) and empirical-statistical downscaling (ESD) is putting on the glasses to improve the image sharpness (right above).
Both RCMs and GCMs give a somewhat ‘blurred’ picture albeit to different degrees of sharpness, and RCMs and GCMs are similar in many respects. However, GCMs are not just ‘blurred’ but also involve some more serious ‘structural differences’ such as an exaggerated Gibraltar Strait (see land-sea mask above), and the Great Lakes area, or Florida, Baja California are quite different and not just blurred (see figure below). Such structural differences are also present in RCMs (eg. fjords), but on much smaller spatial scales.
(Source: Strand, NCAR)Yet the images shown here for present climate models do not really show features down to kilometer scales that may influence the local climate where I live, such as valleys, lakes, mountains and fjords, even for RCMs (the lower right panel shows an optimistic projection for improved spatial resolution in GCMs for the near future). The climate in the fjords of Norway (can be be illustrated by the snowcover) is very different from the climate on the mountains separating them. In principle, ESD can be applied to any spatial scale, whereas the RCMs are limited by computer resources and the availability of boundary data.
What is the skilful scale now?
My question is whether the concept of a skillful scale based on old GCMs still apply for the state-of-the-art models. The IPCC AR4 doesn’t say much about skilful scale, but merely states that
Atmosphere-Ocean General Circulation Models cannot provide information at scales finer than their computational grid (typically of the order of 200 km) and processes at the unresolved scales are important. Providing information at finer scales can be achieved through using high resolution in dynamical models or empirical statistical downscaling.
The third assessment report (TAR) merely states that ‘The difficulty of simulating regional climate change is therefore evident’. The IPCC assessment report 4 (chapter 11) and the regionalisation therein will be discussed in a forthcoming post.
As if the truth was not enough…! Gavin, I presume you will lead us through this latest seminal paper by J Hansen et al.
Dangerous human-made interference with climate: a GISS modelE study:-
http://www.atmos-chem-phys.net/7/2287/2007/acp-7-2287-2007.pdf
Quote: ‘CO2 emissions are the critical issue, because a substantial fraction of these emissions remain in the atmosphere ‘forever’, for practical purposes (Fig. 9a). The principal implication is that avoidance of dangerous climate change requires the bulk of coal and unconventional fossil fuel resources to be exploited only under condition that CO2 emissions are captured and sequestered. A second inference is that remaining gas and oil resources must be husbanded, so that their role in critical functions such as mobile fuels can be stretched until acceptable alternatives are available, thus avoiding a need to squeeze such fuels from unconventional and environmentally damaging sources.
No problem.
Timothy Chase in #44 cites the essay by Annan & Connolley as an authority on the subject of chaotic climate. But that essay is curiously written, the first part very good, the latter part containing errors, and curiously chosen qualifiers… [cut]
[Response:If you think there are errors, do feel free to mention them; I’m not aware of any. For a fuller view of my opinions on this, see http://mustelid.blogspot.com/2005/06/climate-is-stable-in-absence-of.html – William]
I think that the jury is still out on this question. Correct me if I’m wrong. We haven’t been observing the climate system long enough at high enough resolution to be able to say with confidence whether abrupt regional shifts can occur unpredictably in response to the internal dynamics of global heat transfer. My hunch FWIW is they can, and I sense this was Pielke’s point in that thread… [cut]
Maybe the experts here can answer me a related question. Are there potentially multiple global circulatory ‘modes’ (for lack of a better word), and if so, would all these modes be equal in their capacity to dissipate global heat to space? My hunch is that different modes are possible, and that there is no reason to expect them to be equal in dissipative efficiency. If so, then abrupt climate change (regional, if not global) can be expected through internal chaotic dynamics alone.
[AGW alarmists, please note I am not denying anything about the 20th c. temperature trend. I am referring to past climate, something we are forced to view through a foggy lens that becomes increasingly foggy the further we look back.]
To be concrete, consider the example of a coastal city whose climate is warmed by a warm ocean current. If the circulation were to shift, and that current now ran cold, that climate would shift abruptly colder and drier. First, I do not believe the occurrence of such shifts is predictable. Second, I believe they can arise dynamically, without the assistance of any forcing agent. Third, if such shifting were to take place at multiple locations at inter-continental scales, there’s no telling in advance how the global temperature might change. I invite you to overturn these belief statements.
Apologies in advance for awkward use of climatological language.
Attention pressure-change folks — as long as the Earth’s volume is unconstrained, and it is, its surface pressure is not going to vary very much. Basically the surface pressure is going to be:
P = (M / A) g
where M is the mass of the atmosphere (say, in kg), A is the Earth’s surface area (square meters), and g the surface gravity (meters per square second). The answer comes out in Pascals. Working it backwards from sea-level pressure you get a figure of 5.27 x 1018 kg for the mass of the atmosphere. The actual figure is about 5.14 x 1018 kg, because some of the volume that would be atmosphere is taken up by surface relief.
Canonical values for those who want to play with the equation: reference atmospheric pressure is 101,325 Pascals, the Earth’s surface area is about 5.1007 x 1014 m2, and g averages 9.80665 m s-2.
There are pressure variations due to local weather and such physical effects as Bernoulli’s law, which relates pressure and wind velocity. But it’s never very much.
Over geological time, the Earth’s air pressure has probably varied significantly. A primordial hydrogen-helium atmosphere may have given way to a massive steam atmosphere due to the heat of accretion and outgassing, which in turn gave way to a carbon dioxide atmosphere, etc. But the Earth’s atmosphere has had a very consistent makeup for the last several million years at least.
Bender,
Your whole argument is fundamentally flawed. You are ignoring the fact that the models have already made a number of predictions that have panned out. They predicted global warming, polar amplification, stratospheric cooling, and the magnitude of the cooling from the eruption of Mount Pinatubo, all of which have been confirmed empirically. When we can see that the models work, arguments that they can’t work are out of court from the beginning. As Heinlein put it, when you see a rainbow you don’t stop to argue the laws of optics. There it is, in the sky.
People just need to realise about this problem
Re#45 Ray misses the point, the question isn’t about intensive properties.
There is a mean baromatic pressure at my locale, averaged over many years, let’s say exactly 760mm or 1 bar. If I diligently collect daily data for 1 year and the average pressure for that year is 765mm, I would presume that one interpretation might be that there has been fairer weather there than usual for that particular year.
Who measures the possible change in the absolute air pressure globally?
The composition of the atmosphere as ppm by volume may remain constant, apart from the mean increase year on year of ca.delta 2ppm by volume of CO2. Hence, if you refuse to discuss it fair enough. I presume you assume the mass of the atmosphere is conserved.I would be surprised if it were conserved even over a short period such as a century. Were it also increasing, although it wouldn’t figure in the radiation balance, it certainly would further enhance the GHG effect.
[edited]
B.R. Says in #50:”It is a time spirit working here, one of rebellion against the industrial revolution, a romantic longing to a virgin world, that brings people to target our capitalist consumption society.”
Sorry, this is absolute horse puckey. B.R., do you even know any scientists? I doubt most of these guys even own a copy of Walden Pond! And if they do, it’s probably on their iPod. There is no spirit of rebellion. This is not about ideology, but rather about evidence. The science is pretty much incontrovertible–we are changing the climate. What is less certain is what the effect of these changes will be. However, we will be better able to deal with those changes if we manage the rate at which they occur by limiting our greenhouse gas emissions. If you want to protect our “capitalist society”, you had better act now before draconian measures are needed.
“Attention pressure-change folks — as long as the Earth’s volume is unconstrained, and it is, its surface pressure is not going to vary very much.”
if P = (M / A) g, will not V, T and P all vary during the day/night cycle?
How do you model the changes in water rich gas V,T and P when the day/night cycle involves water pricipitation?
This is an actual question, a point scoring? What happens to the gas law assumptions when you are dealing with the transition from a single to two phase system, that is water as a gas and then water in the form of droplets. Are the changes manifest in temperature, pressure or volume?
Is a model of the Earth atmosphere as a ballon reasonable?
DocMartyn, in terms of global properties like whether the atmosphere obeys the ideal gas law etc, consider that ~80% of the atmosphere is N2, with most of the rest being O2, Argon… Most of these molecules are rather inert and stable, so any deviations from ideality are small and mainly only observable at very high or very low pressures.
The atmosphere behaves as a fluid held in place around Earth by the gravitational field. The geomagnetic field is what insulates it from the solar wind so the outer layers are not ripped away. In terms of expansion, I would think that this would be dominated by the outer atmospher–which accounts for most of the volume and little of the mass. The thing is we know how gases behave as a function of temperature and pressure. There’s no new physics here.
Nigel Williams (#38) wrote:
Hardly.
What it supports is the conclusion that you shouldn’t have a local yahoo and total nitwit in charge of the equations. They work very well when they are the correct ones, – as long as the gravity model does. And people want to save time going from point A to point B, therefore the gravity model works quite well.
However, in modeling traffic they run into a real problem because they are basing their equations off of an equation that calculates speed as a function of volume – which assumes a one-to-one. That assumption breaks down in the context of high congestion where a given volume (cars per hour passing a given point) corresponds to a continuem of speeds.
And what can we conclude from that? Volume isn’t a very good variable for calculating speed in times of high congestion. Unfortunately it is pretty much all they have. Density (vehicles per lane mile) would work far better at all speeds. Unfortunately, it is far more difficult to measure density – you can’t just run a weight sensitive rubber pipe across a road to measure that.
However, in climate modeling, which is admittedly far more complicated, you have a great deal more variables to play with – and a great deal of climate modeling is based upon principles of physics – quite possibly all of it. Of course, one might ask whether there might be some unknown or perhaps even unknowable force which will suddenly cause our models to break down – something that no matter how well they might work reality will take a left when we were expecting a right even though our equations were quite accurate all the way up to that point, accurately describing a whole host of phenomena in large variety of contexts up until that magical point.
But one could say the same thing about physics.
There are problems with the climate models we currently have. We know that their estimates are conservative. We haven’t taken into account all of the positive feedbacks relating to ice or the carbon cycle. But virtually all of the feedbacks that we know we are missing are positive feedbacks, and as such, we are able to say that the models are conservative. Given the positive feedbacks, it is quite likely that projections are rosier than what we will actually face, and therefore the urgency with which we should act is greater than what they currently project. However, the carbon cycle is an area of active research as is the cryosphere, so it is quite likely that models will even more accurate in the future.
This rises above politics, gentlemen. I am uncomfortable with environmentalism, I often think it is taken too far, but this science. Given what is at stake, we must learn to work together despite our differences.
When you say “skillful scale” do you just mean effective resolution?
Think of a sine wave. Regardless of the grid size (or equivalent grid size for a spectral model), you need two grid lengths (or three grid points) to minimally resolve half of the wave. You need four grid lengths (five grid points) to minimally resolve a full wave pattern. In numerical weather prediction, the effective resolution is typically taken to be about ten grid lengths. Phenomena smaller than that are not well-resolved at grid scale, so they should be parameterized.
So, a regional numerical weather prediction model with grid resolution of 10 km can adequately resolve meteorological phenomena of length scale ~100 km.
GCM’s these days may have resolutions of around 1 deg or 111 km, so their effective resolution would be more than 1000 km. That’s the length scale of features that they can adequately resolve.
Bzzt! The link behind the name in #55 is another “search engine optimizer” and “global warming awareness” competition counter.
Re#53 Barton’s quote “But the Earth’s atmosphere has had a very consistent makeup for the last several million years at least.”
By “make up” I presume you mean, firstly, composition eg. O2 20.95% by volume or Ar 0.93% by volume.
The O2 content and N2 contents are biologically controlled, way above thermodynamic values. The Ar isn’t the known cosmic abundance, which is pertinent to 36Ar. 36Ar and the other noble gases Ne up to Xe are million folds depleted on Earth, lost during planetary accretion whereas water H20 was presumably retained as hydrates. Atmospheric 40Ar has been built up slowly by radioactive decay of 40K. This is the one atmospheric gas that one could say, secondly,that “it’s mass balance has been effectively constant over millions of years”.
Where’s the evidence that the M has remained constant for millions of years let alone hundreds? Plenty of scientists make this assertion but where is the empirical evidence to support it? It’s one thing to cite CO2 concentrations, tens of thousands of years ago as ppm by volume but in doing so you make the hidden assumption that mass is conserved.
Geochemical abundances of elements in the Earth’s crust are notoriosly innaccurate in several instances. For instance the molecule water, or water budget, in oceans and lakes etc neglects the more than 10% mass that has been subducted at plate boundaries. Years ago Walker upset the carbon budget by a wild unsubstantiated claim that the mantle contained contained at least seven fold the mass of carbon estimated for the crust, yet granites and basalts are vastly depleted in volatiles.
Does anyone know of anyone who calculates the year on year mean sealevel atmospheric pressure for the globe inorder to check its constancy? Since 40Ar is essentially constant in mass it would be nice to see the other ephemeral gases related to it before paying sole attention to intensive properties. If the mass balance changes, due to N2 and O2 variations, the effect on GHG ppm by volume concentrations certainly will also vary, even though the diatomic gases don’t contribute to GW.
Re 63. Graham, Sorry, but if there was a point in there I missed it. I rather doubt that the biosphere impacts the 80% nitrogen content of the atmosphere. I don’t even know what you mean when you say the geochemical abundances of elements in Earth’s crust are inaccurate–with respect to what. They can certainly be measured to arbitrary accuracy, don’t you agree? Do you mean that they vary from place to place? As to H2O, it is important in mantle chemistry, but volcanos also give off a lot of water vapor–it’s probably balanced. I can see why O2 might change wrt very large changes in biomass, but not Nitrogen. And as far as conservation of mass, can we at least stipulate the laws of physics?
There’s one for the standards committee.
“…. a standard atmosphere at sea level is approximately equal to 760 millimeters of mercury, 29.92 inches of mercury, 1.013 bars, 1013 millibars, 14.70 pounds force per square inch, 2116 pounds force per square foot, or 101.325 kilopascals.”
(Quote from a page with one of the better rants I’ve seen about measurement units:
http://ourworld.compuserve.com/homepages/Gene_Nygaard/hectopas.htm )
So, it makes sense to define atmospheric pressure at sea level, because, well, that’s the bottom of the atmosphere, ignoring places like Death Valley that are basins below sea level. What difference will it make when sea level rises? This is where the contemporary rate of change — so much faster than anything anticipated when the standards were defined — can be a puzzle.
Now raising your barometer ten meters is certainly going to show a difference, if it’s a good tool. My old Thommen altimeter certainly detects that change.
But if you then also raise sea level by ten meters to catch up with the barometer — moving the whole atmosphere up the same distance as the barometer — how much difference do you get? The atmosphere’s a thin spherical shell and you’ve increased the inside radius of the atmosphere ten meters.
Actually, Hank, it’ll get more complicated than that. We’re changing solid H2O to liquid, so it will flow toward the equator to balance centripetal acceleration. Earth may become more oblate and sea level may rise more in the tropics than at the poles; the rate of rotation might change (albeit very slightly). I’ll leave that to my buddies with the atomic clocks and platinum-paladium blocks to figure out.
Re #65 Hank,
For an increase in altitude of 300 feet the temperature decreases by 1 deg F. So raising sea level by 10 m (approx. 30 feet)will raise the temperature everywhere that land still exists by 0.1 deg. F.
However, barometric pressure depends on the weight of the column of air above that point, and since there is no change to the total air covering the Earth when sea level rises, the barometer readings will increase by the amount of air in a 10 meter column at any fixed point at or above the new sea level.
Cheers, Alastair.
Re #54 How about Arctic warming in the 1930s-40s?
[Response:See the Delworth and Knutson (2000) article in Science. They use simulations of a coupled model to show that this could easily have arisen from the intrinsic natural variability of the climate at multidecadal timescales. -mike]
Re: reply in #68
And so the exact same thing – an unusually large realization of internal multidecadal variability of the coupled ocean-atmosphere system – can not possibly be occuring today?
[Response: No. Precisely the same thing could of course be happening today. However, such internal variability (both in this model, and all other current generation coupled climate models) is unable to generate a century-long trend in global mean temperature anywhere close to that observed for the past century. Indeed, it is precisely this issue which is addressed in a rigorous, quantitative manner by model-based detection and attribution studies. See our previous review of the topic. -mike]
Please note: the conclusion here would depend on one’s uncertainty surrounding the interactions among the model’s estimated parameters. (I don’t take these estiamtes as error-free.) So … what’s the chance that the CO2 sensitivty forcing coefficient is off by 10% 20% 50%?
I’ve read AR4. Please don’t assume I haven’t.
[Response: I wouldn’t assume you not to have read the report. However, based on your comments above I might call into question your comprehension of its content. -mike]
“Alastair
For an increase in altitude of 300 feet the temperature decreases by 1 deg F. So raising sea level by 10 m (approx. 30 feet)will raise the temperature everywhere that land still exists by 0.1 deg. F.”
I was under the impression that ice was less dense than liquid water, so melting ice into liquid water will reduce the surface/water volume of the Earth.
Moving the atmospheres 5.14 x 10^18 kg a distance of 10 meters requires a potential energy of 5×10^16 J.
Re#64 Ray, we agree where O2 in the atmosphere comes from. It comes partly from the tiny fraction of reduced carbon in biomass that is buried and becomes fossil carbon ie. as coal, kerogen(from which come hydrocarbon gases and oil).The ratio of reduced carbon to carbonate carbon in the crust is thought to be ca. 1 part in 4 or 5. Free O2 also comes from the incorporation of sulphide(and free sulphur from bacterial reduction) as pyrite, also coeval with kerogen formation. At the same time sulphate(as anhydrite or gypsum)is buried but not in similar environments. The ratio of sulphate to reduced sulphur is thought to be ca. 1 to 1. What limits O2 increase is oxidation. Ferrous iron is dominant in the crust,8.6% by mass it rusts through to ferric hydroxide hydrate,(Fe(OH)3.5H20.
In terms of abundances in the crust, oxygen like Si and Al is huge. For every 1 atom of carbon in the crust in general there are ca. 30 each for O, Si and Al. For every 1 atom C there is thought to be ca. 0.5 atoms S in the crust, but the sulphur abundance is imprecisely known(ca. 20% error!). For every carbon atom there are 4 atoms of iron Fe(largely ferrous)and for calcium and magnesium also.
Distribution of elements is not even throughout sedimentary basins, unlike the basaltic crust of the young ocean floors. Thus 10% of the salt(NaCl)content of the oceans is buried beneath the Mediterranean; this figure probably includes associated anhydrites(sulphates), known as sabhkas in the present day Arabian/Persian Gulf. The limited areas of sedimentation are controlled by biomass.
Nitrogen is very low in igneous and basic rocks, it tends to be recycled in kerogens and coals. Whereas atmospheric abundances for O and C are tiny in comparison with the crust, nitrogen accumulates in the atmosphere. It is highly unstable there as every storm produces nitrate, a limited nutrient in the oceans and soils as it is rapidly incorporated as biomass in DNA and proteins. Nitrogen is under as much control by biomass as is oxygen! So for 1 atom of C in the crust how much nitrogen is there in the crust plus atmosphere? No-one knows the error is likely to be several fold. Although not a noble gas, it is depleted relative to cosmic abundance. On a reduced accreting Earth N as ammonia? was lost.
Our Earth, re- climate change, it is often presented as a giant acid/base system(are the oceans becoming more acdic. For millions of years the silicate and borate buffers help maintain ph at ca. 8.2, even with the introduction of volcanic acid volatiles, largely SO2 cf. CO2)). The oceans never become too saline due to evaporite basin formation.
Urey portrayed the acid plus base =salt plus water reaction as the reaction of – calcium carbonate(CaCO3) plus silica(SiO2) to give wollastonite(CaSiO3,igneous at depth) plus CO2 and its reverse.
The Earth’s crust is also a giant oxidation/reduction system-
C + 2Fe2O3 reacts to give 4FeO plus CO2. Those ferric atoms chelate 10 molecules of water, that so happens if you multiply up for the 2.2*10^22kg crust to give 1.46* 10^21kg of water,very close to the known mass of water on Earth.
Up to 36% of the mass of the Earth is free iron(Fe). Homogenise everything and we would return to a highly reduced planet. Brian Mason in the 60’s calculated that since the last 570 million years(Phanerozoic)biomass has recycled a total mass of elements equivalent to more than 50 fold the Mass of the Earth! The mass and composition of the atmosphere is under total control by the biosphere.
Re- mass conservation. Geochemists use an identical atmospheric mass, namely 5.12*10^18kg, dry air, as the rest of you, but we don’t know what it was 100years ago let alone thousands or millions.
Cosmophysicists, cosmochemists and physicists express solar abundances and cosmic abundances as atoms per 1000 atoms Si; climate scientists probably don’t bother.Let’s call these silicon chauvinists. Carbon biomass chauvinists, who aren’t short and vice versa are interested in climate change. Were one to approach the atmosphere,crust and oceans from the biomass point of view it would look like on an atom per atom basis, as I introduced earlier-
C(1)1, S(0.5), Ca4, Fe4,Mg4,H2O(10)……..Si30,O30,Al30
or
S1, C2, Ca8,Fe8 etc.. if you are a sulphur chauvinist.
When I read that the CO2 content of the atmospheree. say in the Younger Dryas at ca. 10000yr was 270ppm by volume, I automatically think but what was its total mass in the atmosphere? Is the atmospheric mass conserved over that time period? I don’t know; I just hope someone wouldstart to measure it with the motivation that Keeling had, and not to continually assert it is conserved without measuring it.
Re: reply in #69
“models … unable to generate a century-long trend in global mean temperature anywhere close to that observed for the past century”
I understand the reasoning, but why “century-long”?
You have the 1930s-40s warmth – an a posteriori “fit” as an anomaly, the 1960s-70s aerosol cooling (another a posteriori “fit”, uncertainty about which is well-known), and the recent 1998-2007 leveling-off of global mean temperature. That leaves two only *two* decades, not ten decades, that need explaining: 1980s-90s. So why not *probable*, why only “possible” that this was an anomalous warming pulse similar to that of the 1930s-40s? 20 years’ worth of anomaly is not as unlikely as 100 years’ worth. Especially relevant considering PDO went inexplicably positive in 1976. That’s presumably a good chunk of the puzzle?
Anomaly after anomaly after anomaly. That’s chaos, no?
Thanks for the replies. Much appreciated. We need to get this right and there’s not much time.
Re #71:
Atmospheric pressure times surface area is, by definition, the mass of the atmosphere. There are no magical forces holding it up, and the only force pulling it down is gravity, which exerts a force proportional to the mass. We know that barometric pressure has been reasonably constant (on average, excluding storms, etc.) since the invention of the barometer by Torricelli nearly 400 years ago. Given the climate swings in that length of time, it’s safe to assume that the mass of the atmosphere is reasonably constant over century-long periods and over periods of cooling as well as warming.
> 1998-2007
How much do you believe a nine-year trend is more reliable than a five-year trend?
Do you believe it’s any different when the first year of the nine years picked is an El Nino year?
http://scienceblogs.com/stoat/upload/2007/05/5-year-trends.png
“Anomaly after anomaly after anomaly. That’s chaos, no?”
No, anomaly after anomaly after anomaly is called giving up. Persisting in investigating the anomalies until you understand their cause–that’s called science.
Actually there were may atmospheric scientists in the 50s-70s that attributed the lack of warming to aerosols from combustion of fossil fuels–the models now say that was a highly credible hypothesis. The anomalous warming in the late 30s and early 40s is still considered anonmalous. However, I do not consider this a satisfactory “resolution”. It may have been a more or less local effect, but even that is not known at present.
Physicists like me get nervous when people attribute warming to “natural variability”. The energy has to come from somewhere–particularly as much energy as we are seeing dumped into the climate system in the current warming epoch. Again, climate scientists have a self-consistent and highly plausible picture. It cannot be the sun, as solar output has not increased enough. It cannot be water vapor–too variable. Next in line is CO2. If you dismiss that, well, you got a source with a few yottajoules (always wanted to use that prefix!) sitting around?
ray ladbury (#75) wrote:
Pinatubo basically cinched it for a great many scientists that aerosols could produce global dimming and mask the effects of global warming. Likewise, we know that there was a drop in temperature as the result of flights being grounds after 9/11 – from what I understand. The effects of aerosols is measurable and regular.
After the fact? Nope. Ad hoc? Certainly not.
Then of course, if one takes any one decade of the twentieth century in isolation, few are statistically significant. Any one year by itself is even less “significant.” But the overall trend is quite significant – and in line with the positive feedback relationship we have seen between CO2 and temperature over, what is it now?, one million years? A heckofalot to explain away as coincidence – and that is basically what one is doing when one attempts to explain fairly well-defined patterns simply by reference to “chaos.”
FurryCatHerder
“We know that barometric pressure has been reasonably constant (on average, excluding storms, etc.) since the invention of the barometer by Torricelli nearly 400 years ago.”
Why should pressure remain constant when temperature changes?
What is the basis for this statement?
DocMartyn, think about the physics. What is the cause of the pressure? The column of air above the point on the ground. Even if the air expands, you will have the same weight of air above that point, so the pressure (weight of the air column divided by area) will remain the same.
#74, #75, #76: You guys are parsing the text (#72) and poking holes without attacking the argument – and in doing so you’re, to some extent, making my argument for me. Shall I explain, or are your minds made up already?
RE#72, bender, As far as the PDO going ‘inexplicably positive’ in 1976, do you want to provide a reference to that?
This argument, that all climate variability is due to various ‘natural cycles’, all of which just happen to be in a positive phase (the AMO, the PDO, etc.), isn’t supported. Every time that there is some unusual warming trend, the skeptics immediately claim it was due to some cycle – warm winter in the US? It must be El Nino, no matter how weak. Record warmth in Russia? It must be the AMO, or the NAO. Warmer sea surface temperatures in the Atlantic? It must be that the AMO is in a positive phase. Or it’s the natural sunspot cycle.
So, how do you tell if you are looking at a trend or at a cyclic phenomena, or a cyclic phenomena superimposed on a trend? You can throw your hands up in the air and claim it’s all chaos – or you can take another look at the link posted in the response to your post: Attribution of 20th Century climate change to CO2.
You run the model without the anthropogenic greenhouse forcing and see what the internal variability is. Then you add in the anthropogenic forcing – then you go and compare the model runs to observations.
From Delworth and Knutson: (you edited their results – the part you left out is in bold: “…the warming of the early 20th century could have resulted from a combination of human-induced radiative forcing and an unusually large realization of internal multidecadal variability of the coupled ocean-atmosphere system.” Bit deceptive, isn’t that?
We now assess whether internal variability alone can account for the observed early 20th century warming, or if the radiative forcing from increasing concentrations of GHGs is also necessary. Over the period 1910-1944 (which encompasses the warming of the 1920s and 1930s), there is a linear trend of 0.53 K per 35 years in observed global mean temperature. If internal variability alone can explain this warming, comparable trends should exist in the control run. Linear trends were computed over all possible 35-year periods, using the last 900 years of the control run (i.e., years 101-135, 102-136, …, 966-1000). For each 35-year segment, the time-varying distribution of observed data over the period 1910-1944 was used to select the model locations for calculating the global mean. The maximum trend in any 35-year period of the control run is 0.50 K per 35 years. This suggests that internal model variability alone is unable to explain the observed early 20th century warming.
If internal variability can’t explain the weaker trend earlier in the century, why would you expect it to now, when the trend is much stronger? Keep in mind also that no amount of internal variation can increase the global temperature – that’s just conservation of energy.
[Response: You’re last statement is not quite correct. Internal variations that lead to either a net change in albedo or to greenhouse effects can lead to a global temperature changes. For instance, El Nino events have a global warming impact, and modelled changes in ocean circulation (such as in the N. Atl.) – even though they mostly redistribute heat – can effect sea ice extent and clouds to produce a net cooling. So, while these changes are small compared to the forced changes, they are not zero. – gavin]
The basis for the statement? Depends. What are you holding constant, what are you varying, what are you measuring?
http://www.chemistry.ohio-state.edu/betha/nealGasLaw/frb4.3.html
Torricelli’s instrument measures the weight of the atmosphere. http://www.imss.firenze.it/vuoto/index.html
Temperature (and latitude) correction tables for using a mercury barometer anywhere in the world (with interpolation) here:
Handbook of Chemistry and Physics: http://216.149.237.254/ei-chemnet/
Temperature Correction for Barometer Readings 83 Ed., p. 15-23
Ike Solem (#80) wrote:
Ya gotta remember – parsing an argument into points so that you can respond to them – that is what is really unfair. Parsing quotes into pieces that are useful despite what an author actually wrote – is useful. And we shouldn’t give anyone problems if they find that they have to parse the evidence – so that they never have to acknowledge its full weight. It just isn’t about the evidence. Its about winning – and reality would be an unfair advantage – so it can’t be about that, either.
Come on and give the guy a chance…
A personal view – for what it is worth…
The denialists aren’t out to destroy the world.
What motivates them is something much more mundane: defending their turf or their tribe against their enemies – in the context of an “us vs. them” view of the world. At root, this seems to be a form of primitive tribalism. But what they seem to have forgotten is that they are part of a larger tribe. To be fully human requires you to recognize the humanity in others – even when they don’t seem to recognize it in themselves. If they are truly honorable warriors, if they honor reality, truth and their own humanity, they will come to the defense of their greater tribe – when it needs them most.
Layer upon layer upon layer of unsupported presumptions, it’s hard to know where to begin.
-It’s not MY model that can’t explain the 1930s-40s Arctic warmth; it’s Hansen’s. Don’t ask me to explain what they can’t.
-mike in reply to #69 is arguing that the anomalous trend is “century long”; but the only trendy part that’s inexplicable is the 1980s-90s portion. You are parsing #72, taking exception to the wording, but not addressing the argument there.
-Ike thinks one can estimate the system’s internal variability by removing the forcings from the model. That’s the hope. But that presumes the models are structurally appropriate. THAT is what I’m disputing. That’s the argument.
-Hank thinks I’m cherry-picking 1998 to exaggerate my point about recent temperatures plateauing; I’m not. They have flattened by any measure, and whether that’s a cyclic deviation or not Hank hasn’t explained why these deviations from a smooth trend happen. They’re not MY bumps; they’re Hank’s. I’m not claiming they’re “natural variability”; Hank is. Natural variability is not something I like to dismiss. It’s something one is sometimes forced to set aside.
-Ike accuses me of selectively quoting for the purposes of deception – which is not an honorable thing to accuse someone of. I’m trying to keep my arguemnts relatively clean to keep them brief. The extra bit doesn’t refute my argument at all; it just helps puts it in context. I’m ok with that.
-Timothy Chase claims reality is on his side, giving him an unfair advantage. Well, Timothy, if the science is SO settled where does mike’s “could, of course” come from in #69? You do not have a monopoly on the truth. mike sees a small crack there. You do not?
-Many here show an unflappable faith in the models, which suggests to me you have no experience in modeling complex dynamic stochastic systems.
-If the weather system is chaotic, then the climate system is chaotic too. I know you don’t agree with this, but I think you may be wrong. Read the full thread by Annan & Connolley and pay close attention to the comments by Pierrehumbert and Held. (That material, though good, is two years old, so also check the more recent literature.)
-If the climate system is (even “sometimes”) chaotic (yes, I know: you dispute even this), then how do you correctly parameterize the numerically stable models such as to mimic the unstable climate? This is a serious problem; it is no joke. My cartoon name is a joke; these points I raise are not. Get past the labels.
-“anomaly after anomaly after anomaly” is me “giving up”? My friend, ray ladbury, do you know what irreducible uncertainty is? It is the futility of what you are suggesting: never give up. When you hit the wall of chaos, you had better know it, and you had better be ready to give up to save your sanity. Hansen et al 2007 suggest exactly this: giving up on the Arctic warming of the 1930s-40s. Why don’t you criticize them?
-PDO dynamics: google PDO will get you started. Hare coined the term. Start there.
Gentlemen, please examine your assumptions. I’m not trying to win a debate or convince anyone of anything. I just think you are not being sufficiently self-critical when it comes to these models, how they are parameterized and what they do and don’t allow you to infer. Remember that attribution is fundamentally a modeling exercise. This argument that weather is chaotic and climate is not – think about it. Chaos is not just inexplicable ups and downs. Only in temporal models does it take that simplistic form. Chaos in spatiotemporal models is marked by bizarre spatial structures (circulatory pathways) that persist for a while, but fade as inexplicably as they emerged. If your models don’t produce that kind of behavior, are they trustworthy? Open question.
That is enough for now. I apologize for the rambling. I think you are trying hard, but maybe have lost your objectivity. There’s lots to pick at in this comment, I know. Please don’t pick. Please hit the argument square on. Think “home run”.
[Response: Your big question concerns the potential structural instability of models, and by extension the structural instability of the real climate. That’s fine, but none of the variations in climate over the last century fall outside of the envelope of forced+internal variation of the structurally stable system so provide no evidence for a deeper instability. Similarly, over the Holocene, with its large precessional trend, there is no such evidence. We do see evidence for threshold behaviour – the drying of the Sahara around 5500 BP that was likely caused by vegetation/climate interactions, but this is still a forced response to the insolation change. Only during the glacial periods (with the Dansgaard-Oeschgar cycles and Heinrich events) do you have evidence for spontaneous and large changes in climate – and even then, this was centered on the North Atlantic and almost certainly involved ice sheet dynamical instabilities.
Thus for the system we have encapsulated in GCMs today (which don’t generally contain either dynamic vegatation or ice sheet dynamics), there is no strong evidence that this system is chaotic anywhere near the part of phase space where we happen to lie. What about evidence from the models themselves? In my experience, I have never seen a GCM demonstrate significant structural instability for any kind of physically valid tweak (coding errors are another story of course). The closest you get is something like THC hysteresis seen in some of Stefan’s work, but again, there is no evidence that we are near those transitions today. However, probably the best argument for structural stability is simply that where the forcings are the same, the response of the system is very similar. Orbital cycles etc. over the last million years, while they have caused enormous climate change, keep producing pretty much the same climate change.
There is of course no possible ‘proof’ that the climate is not near some structural instability, but there is no need for this hypothesis to explain most of what is seen. However, I would hardly take comfort in than thought, and if anything, it might cause one to be more concerned about our future trajectory. – gavin]
Ike Solem stated: “You run the model without the anthropogenic greenhouse forcing and see what the internal variability is. Then you add in the anthropogenic forcing – then you go and compare the model runs to observations.”
If the climate model is pre-determined to be a fixed-point equilibrium in the absence of external perturbations (as it was frequently stated or implied by their authors), no internal variability could be possibly observed or exist.
[Response: The GCM equilibrium is in a statistical sense, as you well know, and there is plenty of internal variability. – gavin]
“Keep in mind also that no amount of internal variation can increase the global temperature – that’s just conservation of energy.”
I usually keep in mind that if the system is open (like Earth), energy is not conserved.
Cheers.
Hi, sorry to violate posting guideline “3) Only comments that are germane to the post will be approved…..”
But something has been bugging me all day about the ~800 year temp/C02 lag in ice cores. Hoping someone at RealClimate can come through or point me in the right direction!
Realclimate talks about positive feedback of CO2 released from ocean from solar forcing in the article “The lag between temperature and CO2. (Gore’s got it right.)”. But it begs the question, what is the _mechanism_ that stops this positive feedback loop once it’s started? And if the feedback effect tapers off over time would you not expect the CO2 and temperature to peak around the same time? Is this explained in more detail somewhere?
Discussion is closed on that article, but hoping for an answer….
Thanks.
[Response: In the climate context feedbacks don’t lead to unconstrained effects because of the eventual dominance of the long wave cooling (i.e. the fact that IR goes like T^4). The post https://www.realclimate.org/index.php/archives/2006/07/runaway-tipping-points-of-no-return/ tries to explain that. – gavin]
Many thanks re-Torricello’s expt, a fascinating read after babelfishing. I did the very experiment in high school physics back in the early 60’s, comes out about 29.5″ Hg in average weather no doubt, the error is in the 3rd place.
I still have the 75th anniversary edition of the Handbook of Chemistry and Physics, 1988-189(69th edition)when everyone was still using 1952 data, done in Arizona for the dry air presumably.
Quote-“FurryCatHerder
“We know that barometric pressure has been reasonably constant (on average, excluding storms, etc.) since the invention of the barometer by Torricelli nearly 400 years ago.”end quote.lol
We also know that the volume composition of CO2 in the atmosphere is 330ppm from the same edition, the error is in the third digit.lol
It appears to me that the physicists are a bit too theoretical. Why don’t you actually go out or stay in(there’s no difference)and do the experiment and come up with a more modern and more accurate value instead of perpetually citing 760mm Hg as a standard atmosphere? You blithely state and assume that there’s no change in the mass of the atmosphere over hundreds or even thousands of years.
Yes, we all know. The pressure at my locale got up to 788mm for a whole week! last autumn and as low as 738mm recently. Of course if I did the measurements over a long period, corrected for altitude, temperature and humidity and everyone else did so then we would get a weighted mean that could be compared with the last reported value established in 1952!
Bender
Do you think that a chaotic system can not be forced from outside? Think of a pot with boiling water. The bubbles in the pot behave totally chaotic. You never can tell where the next bubble will come up. Complete chaos. However, if you turn down the heating of the hot plate to somewhere just below 100 degrees, there will still be bubbles, still chaotic, but you will see that in the mean they are smaller and there are less. You still can’t predict the behaviour of the bubbles, but you can predict a trend in number and extent. Just because there is an external forcing of the system and you know the physics. If you increase the heat, you can predict again that the bubbles will get bigger and more numerous.
Conclusion: If you are not able to predict the behaviour of the chaotic system, it nevertheless might be possible to predict mean effects (or a change of statistical quantities of the system) of external forcings, using the knowledge of physical processes.
The climate system is not too far away from that example, although much more complex. There are some sort of bubbles (like warm and cold air masses, eddies on the small scale, tropical storms on a larger scale) which are coming up and vanishing more or less randomly. There are some stores (like ocean or terrain), there are feedbacks, etc. Quite a complex system with plenty of chaos. However, if you turn up the hot plate, i.e. if you impose an external forcing, it might nevertheless be possible to predict some effect on the mean state of the system. Just because we know the physics.
Do you think there is no effect on climate if solar radiation changes? Do you really think there is no effect of aerosols in the air (be it from a volcano or from combustion)? Do you think the physical measurements and knowledge about radiative effects of gases or particles in the air is just rubbish?
If not, it is very weird to assume that changes in the external forcings have no effect on the climate system. If you turn up the hot plate, and that is what we are doing, there will be a predictable effect. Of course, we cannot predict exactly what will happen even in the mean state, because the system is very complex and there are a lot of feedbacks (i.e. we e.g. do not know the thickness of the pot and ist composition exactly), but we can still predict that there will be heating and to some extent the upper and lower boundaries of the heating.
We know that we turn up the hot plate, we know the physics, and we see the effects that we expect from our knowledge. Of course you can come and say, oh well, look at this chaos in the pot, there are small and large bubbles, you can’t know anything about it. You cannot predict the bubbles with your model, so just forget about predicting, sometimes we see more bubbles, sometimes a little bit less, it is just chaos.
Do you really want to tell us, that we have turned up the hot plate, we see much more and bigger bubbles and we should think that this has nothing to do with the hotter plate, that it is just chaos? That we do not know anything because we do not know everything?
Re #86 The continental ice sheet lie in the northern hemisphere and as they retreat the forests spread north. That together with the formation of peat bogs locks up much of the carbon. Meanwhile, the Milankovitch cycle moves on and a now cooling Pacific Ocean starts absorbing more CO2 which reinforces the cooling.
But it is not ONLY CO2 which is driving the glacial interglacial cycles. Methane, water vapour, ice albedo, and the solar effects from the Milankovitch cycles all play a part. But where the land is ice covered, water vapour has little influence, so it is carbon dioxide with the ice albedo effect that plays the dominant role.
You might conclude from that it is only the high latitudes that will suffer from an increase in CO2, but the if the polar regions warm then the the equatorial regions will have nowhere to dump their excess heat, and they too will warm.
It is much too complicated for Al Gore to be able to explain it fully to the man in the street, but he is essentially correct.
[[Where’s the evidence that the M has remained constant for millions of years let alone hundreds? Plenty of scientists make this assertion but where is the empirical evidence to support it? ]]
Where is the empirical evidence that it was different? No change is the null hypothesis. If you want to prove it was different, you’ll have to come up with empirical evidence yourself. You can’t say, “it might have been different, therefore it probably was.” The burden of proof is on the affirmative; support your contention that M changed.
[[Re- mass conservation. Geochemists use an identical atmospheric mass, namely 5.12*10^18kg, dry air, as the rest of you, but we don’t know what it was 100years ago let alone thousands or millions.]]
We’ve had barometers since the 1600s, Graham.
[[Why should pressure remain constant when temperature changes?
What is the basis for this statement? ]]
The fact that there’s no lid on the atmosphere.
[[Gentlemen, please examine your assumptions. I’m not trying to win a debate or convince anyone of anything. I just think you are not being sufficiently self-critical when it comes to these models, how they are parameterized and what they do and don’t allow you to infer. ]]
And again, I point out that the models have successfully made at least four major predictions all of which have been empirically confirmed, so insisting that they’re unreliable is just stupid.
“Heavier than air flight is impossible.”
“Look, there’s an airplane!”
“The pressure effects simply aren’t enough to lift the wing.”
“It’s in the air! Look! There’s nothing under it!”
“And redirection of the air flow simply can’t generate enough force to continuously life the airframe.”
“It’s flying!”
Etc.
[[It appears to me that the physicists are a bit too theoretical. Why don’t you actually go out or stay in(there’s no difference)and do the experiment and come up with a more modern and more accurate value instead of perpetually citing 760mm Hg as a standard atmosphere? You blithely state and assume that there’s no change in the mass of the atmosphere over hundreds or even thousands of years.]]
[edited]what part of “we’ve been measuring it for 400 years” do you not understand? We don’t “assume” the mass of the atmosphere has been constant, we bleeding measure it! BTW, scientists DO regularly do the calibration experiments for standard measurements. Google NIST and CODATA.
Bender, the argument you are making is fundamentally anti-scientific. First, there is no evidence climate is chaotic. Certainly there seem to be epochs in the history of the planet where the climate was more or less predictable, but on the whole you can say that climate certainly is predictable in a piecewise fashion. However, even if climate were chaotic, that does not make it a scientific no-man’s land. Energy is still conserved, and since energy is increasing–by yottajoules, there must be a source of that energy. If the source is not increased greenhouse activity from anthropogenic CO2, what is it? You seem to want to say it is a coupling between atmosphere and ocean. I think that if you look at the likelihood of enough coupling to bring about GLOBAL effects of the magnitude, you’ll find it is vanishingly small. We could compute the likelihood ratio of anthropogenic causation vs. atmosphere-ocean coupling as a test, but I’m pretty sure you’d come out on the losing end of that comparison.
So, even if the climate were chaotic, the only possible cause for the added energy we are seeing is still anthropogenic CO2. We can still say some very general things about the dynamics of a chaotic climate. First, by adding energy to the system, we make more phase space available to it, making it LESS predictable. Second, the past 10000 years have been a period of exceptional climatic stability, so it the climate is chaotic, we must be near some sort of strange attractor–some quasi-stable equilibrium. By adding energy, we perturb the system away from that attractor, making it more likely to become MUCH LESS PREDICTABLE. Given that all of human civilization has developed during this period of climatic stability, I would see that as a pretty severe threat. So in some ways, the argument that we must do something about climate change is strengthened, not weakened, if climate is chaotic.
You seem to see chaos as some sort of fetish. It is not. Chaotic systems still obey laws and in some ways the very fact that you can’t model them deterministically makes them easier to deal with. You just have different expectations.
You also seem to feel that the conclusion that humans are changing climate rests in some way on the validity of the models. It does not. There simply isn’t another source of energy large enough to explain the increased energy we are seeing in the system. All the climate models do is tell us what some results of those changes may be. Without the climate models, we are flying blind, and I would think that would argue for greater caution rather than less.
On the other hand, as I said, there’s no real evidence that climate is chaotic. The models have done an excellent job of getting the trends–and even many of the details–right. They’ve done much better than would be expected by chance. So it would appear that we have two different approaches. Your anti-scientific approach says climate cannot be modeled, whereas the climate scientists are modeling it.
Re #88
“Do you think that a chaotic system can not be forced from outside?”
No. In fact, I know that it can.
In Re #87:
The weather guys do it every day. The pressure rises and falls with the passage of various storm systems and other such things. And yet, it keeps coming back to the same range of values for “high” and “low”. 26.5″ of mercury is still a pretty nasty hurricane, and 30″ of mercury is still a nice, clear high pressure system parked in your neighborhood. It’s been that way my entire life, and I’ve been 29 for quite a few years now ;)
87 contd. Just returned from the allotment. I’m an old retired scientist now but I keep experimenting.
It’s about two generations ago that Preston Cloud Jnr(he kept the title into his old age and I’d claim is the father of paleoclimatology) reviewed paleo atmosphere data. I remember he used the size of Carboniferous spiders((mass goes as r^3, surface area goes as r^2,bugs breath through pores in their exoskeleton)to infer an atmospheric composition of oxygen at 30% by volume. He thought this was an upper limit for oxygen based upon the fact that wet vegetation would spontaneously combust. Before Cloud I think Berkner and Marshal related all atmospheric limits to PAL(Present atmospheric level)at 1 bar. Cloud perpetuated this as a Carboniferous maximum for O2 as 30%PAL.
Berkner and Marshal,as a known consequence of photodissociation of water in the atmosphere set the Precambrian levels of oxygen max at 0.1% PAL. By the mid sixties it was noticed that connective tissue proteins, we know as collagen and their calcified representative in bone and shell, contained an amino acid(it’s one of the twenty common ones)called hydroxyproline that is synthesised from proline by a univeral enzyme called, you guessed it, hydroxyproline. This enzyme relies on the presence of free oxygen and if the cultures are exposed to levels of O2 less than 1-2%PAL at 1 bar they cannot synthesise skeletal tissue. Cloud used this information to extrapolate back to the Cambrian faunal explosion(ie.hard parts that were more easily fossilised)to predict that by end Cambrian times the oxygen conent of the atmosphere was at least 1% PAL.
It wasn’t until the discovery of the 200bar PAL Cytherian atmosphere of Venus that scientists began to wonder how atmospheric pressure varied on Earth. Were one to oxidise all carbon on Earth and place it as CO2 in our atmosphere, then based upon known geochemical abundance, the answer came out at 90-100bar. Why did Venus, so alike as a sister planet, contain twice as much carbon as Earth? As I mentioned above, based upon the scarce abundance of diamonds, more common at 200km in the Upper Mantle, a well known geochemist stymied such calculations by implying that the mantle contains at least 7 fold more carbon than the crust!Geochemical abundances of elements are highly contentious.
Could those bugs survive at much lower O2 levels at 2 bar total pressure or whatever pressure? There’s only one gas that fills the bill for the Phanerozoic, the last 570 million years of history and that is nitrogen. When we predict paleo CO2 contents as ppm by volume it is always related back to a 1 bar total pressure. Waters in the Jurassic seas of the UK, when the paleo dispostion of the lower half of the UK was subtropical were very warm , upper 20’s , we know this from oxygen isotope fractionation for conditions relevant to PAL 1 bar, and the temperatures do appear reasonable for the sub tropics.
I’m an old guy now, retired to a field where there’s no competitive edge other than the voracious appetite of bugs. ” There’s no reason to believe there’s been any change of the mass of the atmosphere or I fail to see the relevance etc”. True I’m old but not too physically inconvenienced, I stay fit, and my mental processes don’t appear to be affected at all apart from my forgetfulness re- home objects. Time passes by too quickly now, hopefully it’s psychological time,so much so that I don’t remember how I found the time to put in 12 hr days at work. Reading some of the comments, pertinent to this rather peripheral topic I get the feeling that many, a generation younger than myself whose axes are still bright, talk as if they are an even older generation of Greek Scientists.
Leave the arrogance and wisdom to the elderly.
Could anyone with a spare GCM and DC force total pressure to 1.1 *PAL 1 bar just for the fun of it.
>74, etc., “cherry picking” or somebody’s “bumps” is rhetoric —- get the numbers and do the math yourself, or see it done, but understand it:
http://scienceblogs.com/stoat/2007/05/the_significance_of_5_year_tre.php#more
(black lines data, thicker black same but smoothed, thin straight lines non-sig trends; thick straight blue lines sig trends)
So … I’ve been playing with EdGCM overnight, and it’s interesting, but entirely too coarse for my tastes.
Does anyone know of a free (as in freedom of the press, not free beer) GCM with a finer resolution that could produce reasonable model results in a month or so? Also, if the models will run on SMP Windows boxen that would be great — I have access to large amounts of idle time on some 8-way 3GHz Xeon machines.