Arguments
Empirical evidence that humans are causing global warming
What the science says...
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Less energy is escaping to space: Carbon dioxide (CO2) acts like a blanket; adding more CO2 makes the 'blanket' thicker, and humans are adding more CO2 all the time. |
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Climate Myth...
There's no empirical evidence
"There is no actual evidence that carbon dioxide emissions are causing global warming. Note that computer models are just concatenations of calculations you could do on a hand-held calculator, so they are theoretical and cannot be part of any evidence." (David Evans)
At a glance
Empirical evidence? None? That's a big bold statement to make, so let's take a look. 'Empirical' is defined as something that may be actually measured and presented as a finding. Let's treat the topic as a criminal prosecution. The accused is CO2 and the accusation is that its increased levels through our emissions are warming the planet. As with all court cases, it's important to present an accurate account of events. So firstly, we'll examine the background to this particular case.
It all started in the 1820s, when French physicist Joseph Fourier had worked out that, at its distance from the Sun, Earth should be very cold. He proposed that Earth's atmosphere must contain something that kept the planet warm, like some invisible blanket. His ideas were, it turned out, correct albeit incomplete.
Some decades passed before the nature of Fourier's blanket was discovered. This was done through a series of experiments involving various gases. Interestingly, two investigators worked on it independently, John Tyndall, in the UK and Eunice Foote in the USA. Impressively, their results were virtually identical.
Foote, writing in 1856, was the first scientist to state that carbon dioxide can trap energy. She predicted that if there had been more CO2 in the atmosphere at times past, an increased temperature would have prevailed. That was something the geologists already knew. Tyndall went on to write, in 1861, that on top of carbon dioxide, hydrocarbons - such as methane - would have even greater effects at very low concentrations. The greenhouse effect and its key players had been identified.
The landmark paper, "The Carbon Dioxide Theory of Climatic Change", was published just under a hundred years later. Essentially, it stated what we know now. Without the atmosphere and its greenhouse gases, Earth would be an uninhabitable iceball. As Fourier started to reason all that time ago, greenhouse gases act like a blanket. They keep Earth warm by inhibiting the escape of energy back into space. Humans are adding CO2 to the atmosphere, mainly by burning fossil fuels, thereby intensifying the effect.
That's the background. As we emit more greenhouse gases, the effect is like wrapping yourself in a thicker blanket. Even less heat is lost. So how can we tell that? How can we find hard evidence, like good CCTV footage of our suspect up to their mischief?
How about measuring it?
Satellites orbiting our planet carry sensitive instruments on board. Through them we can measure how much energy is arriving from the Sun. We can measure how much energy is leaving the Earth, out into space. So right there we have two things to compare.
What do the measurements tell us? Over the last few decades since satellites became available, there has been a gradual decrease in the energy heading from Earth's surface back into space. Yet in the same period, the amount of energy arriving from the Sun has hardly changed at all. Something is hanging onto that energy and that something is getting stronger. That something is carbon dioxide - doing exactly as Foote and Tyndall said it would 160 plus years ago.
Verdict: guilty on all counts.
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Further details
The well-established theory that man-made CO2 is causing global warming is supported as well as any chain of evidence in a rock-solid court case. CO2 keeps the Earth warmer than it would be without it. It has done so for most of geological time. Humans are adding substantial amounts of CO2 to the atmosphere, mainly by burning fossil fuels. Empirical evidence abounds to support the contention that the rising temperatures are being caused by that increasing CO2.
The Earth is wrapped in an invisible blanket
It is the Earth’s atmosphere that makes most life possible. To understand this, we can look at the moon. On the surface, the moon’s temperature during daytime can reach 100°C (212°F). At night, it can plunge to minus 173°C, or -279.4°F. In comparison, the coldest temperature on Earth was recorded in Antarctica: −89.2°C (−128.6°F). According to the WMO, the hottest was 56.7°C (134°F), measured on 10 July 1913 at Greenland Ranch (Death Valley).
Man could not survive in the temperatures on the moon, even if there was air to breathe. Humans, plants and animals can’t tolerate the extremes of temperature on Earth unless they evolve special ways to deal with the heat or the cold. Nearly all life on Earth lives in areas that are more hospitable, where temperatures are far less extreme.
Yet the Earth and the moon are virtually the same distance from the sun, so why do we experience much less heat and cold than the moon? The answer is because of our atmosphere. The moon doesn’t have one, so it is exposed to the full strength of energy coming from the sun. At night, temperatures plunge because there is no atmosphere to keep the heat in, as there is on Earth.
Without the atmospheric greenhouse effect, Earth would be approximately 33°C (59.4°F) cooler than it actually is. That would make most of the surface uninhabitable for humans. Agriculture as we know it would be more or less impossible if the average temperature was −18 °C.
Greenhouse gases act like a blanket, keeping the Earth warm by preventing some of the sun’s energy being re-radiated from Earth's warmed surface, back out into space. If we add more greenhouse gases to the atmosphere, the effect is like wrapping yourself in a thicker blanket: even less heat is lost. So how can we tell what effect CO2 is having on temperatures, and if the increase in atmospheric CO2 is really making the planet warmer?
The heat-trapping effects of CO2 and other greenhouse gases were discovered in the mid-19th century but we can do more sophisticated stuff these days. We can measure the heat energy going into Earth's climate system and that coming back out.
In 1970, NASA launched the IRIS satellite measuring infrared spectra. In 1996, the Japanese Space Agency launched the IMG satellite which recorded similar observations. Both sets of data were compared to discern any changes in outgoing radiation over the 26 year period (Harries et al. 2001). What they consistently found was a drop in outgoing radiation.
This change in outgoing radiation was consistent with theoretical expectations. Thus the Harries paper found "direct experimental evidence for a significant increase in the Earth's greenhouse effect". This result has been confirmed by subsequent papers using data from later satellites (Griggs & Harries 2004, Chen et al. 2007). In the same period, the amount of energy arriving from the sun has hardly changed at all.
When there is more energy coming in from the Sun than there is escaping back out to space, it should come as no surprise to learn that our climate is accumulating heat. The planet's total heat build up can be derived by adding up the heat content from the ocean, atmosphere, land and ice (Murphy et al. 2009). Just since 1998, the planet has accumulated heat energy equivalent to the yield of 3,260,000,000 Hiroshima-sized atomic bombs.
The primary greenhouse gases responsible for the trapping of heat – carbon dioxide (CO2), methane (CH4), water vapour, nitrous oxide and ozone – comprise around 1% of the air. The main components of the atmosphere – nitrogen and oxygen – are not greenhouse gases, because they are virtually transparent to long-wave or infrared radiation.
For our next piece of evidence, we must look at the amount of CO2 in the air. We know from bubbles of air trapped in ice cores that before the industrial revolution the amount of CO2 in the air was approximately 280 parts per million (ppm). In June 2013, the NOAA Earth System Research Laboratory in Hawaii announced that, for the first time in millions of years, the amount of CO2 in the air had gone above 400 ppm. It's now getting on for 420 ppm. That information gives us the next piece of evidence; CO2 has increased by 50% in the last 150 years.
The Smoking Gun
The final piece of evidence is ‘the smoking gun’, the proof that CO2 is causing the increase in temperature. CO2 traps energy at very specific wavelengths, while other greenhouse gases trap different wavelengths. In physics, these wavelengths can be measured using a technique called spectroscopy. Here’s an example:
Fig. 1. Spectrum of the greenhouse radiation measured at the surface. Greenhouse effect from water vapour is filtered out, showing the contributions of other greenhouse gases (Evans et al. 2006).
The graph shows different wavelengths of energy, measured at the Earth’s surface. Among the spikes you can see energy being radiated back to Earth by ozone (O3), methane (CH4), and nitrous oxide (N20). But the spike for CO2 on the left dwarfs all the other greenhouse gases, and tells us something very important: most of the energy being trapped in the atmosphere corresponds exactly to the wavelength of energy captured by CO2.
Summing Up
Like a detective story, first you need a victim, in this case the planet Earth: more energy is remaining in the atmosphere.
Then you need a method, and ask how the energy could be made to remain. For that, you need a demonstrable mechanism by which energy can be trapped in the atmosphere, and greenhouse gases provide that mechanism.
Next, you need a ‘motive’. Why has this happened? Because CO2 has increased by nearly 50% in the last 150 years and the increase is mostly from burning fossil fuels.
And finally, the smoking gun, the evidence that proves ‘whodunit’: energy being trapped in the atmosphere corresponds exactly to the wavelengths of energy captured by CO2.
The last point is what places CO2 at the scene of the crime. The investigation by science builds up empirical evidence that proves, step by step, that man-made carbon dioxide is causing the Earth to warm up.
Finally, the myth-creator refers to climate models as "concatenations of calculations you could do on a hand-held calculator". That statement demonstrates nothing more than a limited grasp of what models are and do and is rebutted at this post in our series.
Last updated on 9 July 2023 by John Mason. View Archives
We know that the climate was warmer in the geological past than it is now. What do we know of the factors ( particularly co2) that caused the decrease in temperature from the warmest time?
From that, are we able to calculate how much the climate would be warming without human generated co2 emissions
jl5501 @301 : The answer to your first question is multi-faceted, regarding past influences. In the short-term viewpoint of recent centuries, the biggest factor is atmospheric CO2 (plus its feedbacks). In the longer term i.e. megayears, you will find large influence from the subtle shifts of interaction between the gradually changing cycles of the planet's orbital shape and inclination of the axis, as well as continental drift [affecting ice-related albedo].
Go to this site's Home Page, and check out the various Climate Myths ~ and in particular, Number 14 which addresses the recent cycling of Ice Ages. The chart there may give you the impression that a new ice age might be "expected" in 10,000 years or so . . . but in the text you will notice that the next [natural] deep cooling from orbital/tilt interactions will be a weak effect . . . and so the next "due" Ice Age might well be (hypothetically) due in 30,000 years or longer ~ yet in reality ( and owing to the the recent high levels of human generated co2 ) that due-to-arrive Ice Age will be scotched by the present higher than natural CO2 in the air and by the warmed-up oceans and by the dissipating North Polar ice. So . . . a long, long wait for new ice ages . . . and an unpleasant time for the next few centuries, from the overheating of our planet.
jl5501 - there are a number of approaches to this. On page 405 of IPCC WG1 (chapter 5), you will find results of 9 studies with different methods summerized. The range of the ECS from these studies is still wide. Another recent study is discussed here. Accurately determining both past temperatures and particularly past forcings is not a trivial exercise.
The problem I see with this theory is that it seems to discount the effect of redirected energy by the increased CO2 before it reaches the lower atmosphere. Insulation works both ways. Put a dark background behind a 2 way mirror and almost light is reflected: put a light source behind it and it becomes see through. Changes to landscape are as much a factor as any in my belief. My imperical evidence is easier to prove; just check out the daily high and low temperatures of any metropolitan area and the rural areas next to them and see the contrast.
blue65 @304:
1) The incoming radiation is for the most part, Short Wave radiation to which CO2 is transparent. Hence there is not significant redirection of "... energy by the increased CO2 before it reaches the lower atmosphere". It is the contrast between transparency to incoming radiation, and relative opaqueness to outgoing radiation that it is the key feature of greenhouse gases, and which makes them greenhouse gases.
2) Changes in the landscape are a factor, and are itemized by the IPCC as Land Use Changes (LUC). Overwhelmingly the effect of LUC is to reflect more solar radiation back out to space (increase albedo), thereby cooling the planet. However, the effect is small relative to the effect of changing concentrations of greenhouse gases and aerosols. The effect is itemized on the chart below as "Albedo change due to land use":
3) The temperature effects of cities relative to countrysides are a combination of changes in albedo but that is variable (concrete has reduced albedo but ashpalt has increased albedo); changes in thermal inertia, with most modern construction materials having low thermal inertias relative to plant matter (probably due to limited water content); and a large number of sources of industrial waste heat in cities (the "urban heat island effect"). Changes in albedo from cities also result from increased aerosol production which also effects countryside downwind from cities (an effect that has been detected). The net effect can be to warm or to cool cities relative to the local countryside. The total globally averaged effect is small relative to the forcing from greenhouse gases.
We have direct evidence, as the following news article and original paper show.
http://newscenter.lbl.gov/2015/02/25/co2-greenhouse-effect-increase/
http://www.nature.com/nature/journal/v519/n7543/full/nature14240.html
The above describe direct measurement of the incoming and outgoing radiation of the Globe at various wavelengths over a decade, and show that it is directly due to more CO2.
Maybe I miss something but there seems to be something wrong with the line of argument.
First argument “we’re raising CO2 levels” seems plausible, there is a clear exponential rise of CO2 that correlates to the increase in population.
Second argument “CO2 traps heat”: that is probably true but irrelevant for the reasoning before we have established that there is a phenomenon that we need to explain.
Third argument: “The planet is accumulating heat”: yes, the diagram clearly shows a drastic increase. But the time period starts 1960, if you instead look from 1880 you get a slightly different picture: the temperature has increased during the 20 century but in more of a linear fashion. If the heating of the planet was caused by human action then the smoking gun would be a correlation between CO2 levels and temperature but there is none. the number of people and emission of greenhouse gases are increasing exponentially, air and sea temperatures are increasing linearly.
I don’t have a personal opinion in this, but from a purely logical standpoint there seems not to be any evidence that climate change is man made.
[PS] What theory would predict, is that climate moves in response to NET forcings, not just CO2. Please these articles here and here for further discussion. You might also like to review basic, laboratory-based physics in a textbook to review your assessment that CO2 trapping heat is only "probable".
It was the third argument that was the important one: “The planet is accumulating heat” which it obviously does. If the heating of the planet was caused by human action then the smoking gun would be a correlation between CO2 levels and temperature but there is none, the number of people and emission of greenhouse gases are increasing exponentially, air and sea temperatures are increasing linearly. The effect could be lagging but then why don't we see a tendency of an exponential curve in temperature? And if the effect is lagging, why do we see such a clear onset of the rise?
jobel @308, the formula for forcing from CO2 is:
1) ΔF = 5.35 x ln(C/Co)
where ΔF is the change in forcing, C is the current CO2 concentration, Co is the initial CO2 concentration, and ln(x) is the natural logarithm of x.
Increasing the CO2 concentration from 287 parts per million by volumn (ppmv) to 400 ppmv at a constant exponential rate requires an annual increase of 0.2% each and every year. That exponential growth rate, therefore, provides an approximate model of the increase in CO2 levels from 1850-2016. Plugging that into formula (1), we have that each year on average, the forcing goes up by 0.0107 W/m^2 (for a total increase of 1.77 W/m^2). Because the increase is in forcing is the same each year, the increase in forcing is linear.
The temperature increase due to a change in forcing is given by the formula
2) ΔT =λ x ΔF
where λ (the lower case greek letter lambda) is the climate sensitivity factor, and ΔT is the change in temperature. For the year to year increase, the relevant climates sensitivity factor would be that for the Transient Climate Response, and is approximately 0.4 oC/(W/m2). That yields a 0.0043 C per annum temperature increase from our model, or an estimated 0.7 C increase in Global Mean Surface Temperature over the interval 1850-2016. (Of course, it will not be precisely that because CO2 is not the only changing forcing.) Crucially, because temperature is linearly related to changes in forcing, a linear change in forcing will result in a linear change in temperature.
That is not some obscure result or fancy theory. It is the theory you purport to criticize; and that theory predicts that an exponential increase in CO2 concentration will result in a linear temperature increase. Despite this, you claim that the approximately linear increase in temperature given an approximately exponential increase in atmospheric CO2 disproves the theory. That is, you claim because the situation is as the theory predicts, the theory is disproven. Being generous we will attribute that attrocity of reasoning to ignorance, although it takes a lot of gall to so condemn a theory you are so patently ignorant of.
Finally, as a minor point, the correlation of CO2 concentration to GMST (BEST land/ocean) over the period 1850-2013 is 0.902. Even your claims of fact are eggregiously false.
Thanks Tom for your answer. No need to be unfriendly, I am just curious. I thought it was obvious from my post that I am a layman, I am looking at it from a pure logical viewpoint. That said, I realize that I did a major error in my first post. I wrote about correlation between CO2 and temperature, but I meant number of people and global temperature levels. Very sorry about that!
So here is the third argument rephrased correctly:
“The planet is accumulating heat”: yes, the diagram clearly shows a drastic increase. But the time period starts 1960, if you instead look from 1880 you get a slightly different picture: the temperature has increased during the 20 century but in more of a linear fashion. If the heating of the planet was caused by human action then the smoking gun would be a correlation between number of people and global temperature but there is none. the number of people are increasing exponentially, global temperature increasing linearly.
Sorry for the error, hope that someone can explain this in layman's terms
jobel @310:
In layman's terms the explanation is simple. Your purported facts are fictions.
The temperature series has not increased in a linear fashion except since shortly after 1960. And over the period 1960-2013 population also increased in a linear fashion (trend: 80.4 million per annum; Standard Deviation: 0.36 million; r squard: 0.999; correlation:0.999). Overall the correlation of population to Global Mean Surface Temperature from 1880-2013 was 0.900 From 1850-2013 it was 0.897, not as good as the 0.902 correlation between CO2 and GMST, but very impressive all the same.
You write that "If the heating of the planet was caused by human action then the smoking gun would be a correlation between number of people and global temperature but there is none." The key problem for you, however, is that there is a correlation - a high correlation - between population and temperature. That means when you asserted the contrary you simply made up a "fact" to suite your argument. It also means that if you actually believed that "If the heating of the planet was caused by human action then the smoking gun would be a correlation between number of people and global temperature", you would not accept that the global warming in the 20th century was anthropogenic.
Of course, by reverting to population rather than CO2 concentration, you are moving further away from the theory you purport to criticize. The warming is not a direct function of human population - but of increased greenhouse gas forcing. And while human population growth has contributed to the growth in emissions, and hence to the growth in temperatures; they do not have a linear relationship. Indeed, per capita emissions have grown approximately quadratically:
(Source)
Temperature, in the mean time, grows with the forcing, ie the log of concentration. Combined the two effects mean that temperatures will grow at slightly below a linear rate relative to population. To determine the actual rate, however, we would need to compare the growth of all forcings vs population. That becomes a complicated and obscure way to check a theory which stands up to far more obvious and direct tests.
Finally, when you say a theory is refuted "looking at it from a pure logical viewpoint" you are saying the adherents to that view have made fundamental errors of reasoning that are easilly exposed. You are saying of the climate scientists who developed that view that they are either incompetent or dishonest. That hardly seems like a friendly approach to me. If you want friendly, try being a little less arrogant and begin with the assumption that the scientists are competent so that if you think you have a knock down argument against them, you are probably wrong. By all means then ask us to identify where the error lies - but don't assume that the thousands of scientists are wrong because of your bee coaster argument that you have not bothered fact checking.
It was a simple question from an interested layman, not critique. From this you extrapolated a non-existing disdain for all climate scientists. I was apparently not humble enough in my question. Anyway, thanks for your reply, it answered my question, kind of.
[PS] Jobel, you make a fair complaint, and Tom, I think your response was overly, and unnecessarily, aggressive. Sadly, SkS sees far too many fake skeptics, would-be Galileo's and other idiots. Frequent responders are inclined to assume the worst. I would ask everyone to be careful with tone.
Jobel
An important point to consider. Changes in CO2 concentration are expected to produce an accumulation of heat. But where the heat is likely to go is the issue. All parts of the system will need to warm - atmosphere, oceans, land surface and Cryosphere (via ice melting). However it takes very different amounts of heat to produce the same temperature change - air is easy, water in the oceans is the big one. So we would expect most of the excess heat to go into the oceans, still only producing a small temperature change.
Which is what we are seeing. Around 93% of the heat being added to the system is appearing in the oceans. The rest is divided roughly between heating land, air and ice. So when you only look at what is happening to surface air temperatures you are looking at a very small part of the system. The tail rather than the dog. And since energy can also flow between the various parts of the system, changes in the energy flows between the air and oceans can have sigificant impacts on air temperatures while only impacting the ocean slightly.
So the air temperature record is looking at a small part of the system, thermodynamically, and a rather noisy part.
One site showing changes in ocean heat content is NODC here. The most relevant graph is panel 2 in the animation, 0-2000 meters.
[Rob P] Image embedded.
Thanks everyone for taking the time to answer my question, I really appreciate it!
I have yet to find the answer to the following problem. Consider the atmosphere of Venus is almost 100% CO2. Not quite, but close enough. The surface temperature is about 800 degrees. Let's ignore for now the fact that Venus is closer to the sun which would make the effect of CO2 less. And also ignore that the atmospheric pressure is much higher than that of Earth. So, 100% CO2 would make the temperature 800 degrees warmer, 1% would make it 8 degrees warmer and .01% would make it .08 degrees warmer. The .01% number is roughly the increase in CO2 over older estimates. Now if we factor in that Venus is much closer to the sun and the atmosphere of Venus contains a whole lot more CO2, the .08 degree number would drop much more. It would seem by this method that the actual effect of CO2 is not large. I have sent this little story to various people and no seems to want to respond. Anyone?
Hi Jeff
The relationship between CO2 and temperature is not linear - it's loglinear. decreasing the atmospherice concentration of CO2 by 1% does not decrease the amount of energy reradiated back to the surface by 1%.
Jeff18 @315, the temperature response to increased CO2 in the atmosphere approximates to a linear increase for each doubling of CO2. Thus, you will get the same temperature response for increasing the CO2 concentration from 140 ppmv to 280 ppmv (ie, from half the industrial to the industrial concentration) as you would for increasing it from 280 to 560 ppmv.
Clearly this relationship does not hold across all concentrations of CO2, for if it did, there would be an infinite temperature increase from 0 ppmv to any finite value. Checking with modtran, the relationship holds from approximately from 16 to 4000 ppmv, ie, the full range of reasonable expectations of past and future CO2 concentrations on Earth - but it is not straighforwardly transferable to the situation on Venus.
Further complicating things, temperature varies with the fourth root of energy, so that a linear increase in forcing (W/m^2) will be associated with a less than linear increase in temperature, particularly when there is not fluid H2O on the planet as with Venus. Consequently no simple rule of thumb formula will give very accurate results for the effect in changes in CO2 concentration for Venus. This is important because applying the loglinear (linear increase with each doubling) mentioned by Tristan as a best approximation would lead us to expect a surface temperature on Venus elevated by only 80oK, which is far to small. Better results can be obtained by using the formula that surface temperature equals the lapse rate times the effective altitude or radiation to space of IR radiation from the atmosphere, where that altitude is determined by radiation models of Venus' atmosphere. Better still is the application of the full theory of the greenhouse in the form of climate models, which can predict with reasonable accuracy the actual surface temperature (and have done so since 1980).
Finally, I suggest you read this post by Chris Colose, and that we conduct any further discussion on this in that thread (where it is on topic).
Jeff18.
That isn't the way to calculate it.
Here is how the greenhouse effect works.
Putting these together, the balance temperature for Earth is-18C. The average altitude where the transition to optical thinness occurs is around 5 km up. So this level in the tmosphere tends towards -18C. Then the Lapse rate warms the air below and cools the air above this altitude. So the surface is at around -18 +(5 * 6.5) = +14.5 C. About right. And the 10 km level is at around -18 -(5 * 6.5) = -50.5 C About right.
Lets do the math for Venus.
With that super dense atmosphere its effective emission altitude is over 50 km up. Its balance temperature is actually lower than the Earth. Although it is closer to the Sun and receives twice as much sunlight, it is far more reflective. Earth reflects around 30% of the sunlight that strikes it and only absorbs 70%. The Bond Albedo of Venus is 0.9 so Venus only absorbs 10% of the sunlight that strikes it so only 2/7ths of what the Earth absorbs. So its equilibrium temperature is actually more like -85 C
And the Lapse Rate on Venus is around 10.2 C/km. It is this much higher because there is no condensation of water which lowers the Lapse Rate on Venus.
So putting the numbers together -85 + (10.2 * 50+) gives over 425 C - about right.
I will briefly add that, were we to ignore complications and work back to a climate response based on the difference between Venus' and Earth's surface temperatures by the loglinear rule, we would estimate the climate response per doubling of CO2 to be 70o K. Obviously too large, for reasons given @317, but certainly not the basis for concluding that CO2 can have no significant effect on global temperatures (the conclusiong Jeff18 is angling for). The 70oK figure, like Jeff18's 0.08oK temperature impact for 25% of current CO2 concentrations on Earth, are both examples of Garbage In, Garbage Out.
Noting that we are off-topic on this post (as pointed out @317), this is a brief extra point to the foregoing.
The climate of Venus is overwhelmingly CO2 and this does provide a strong greenhouse effect. But the temperature of Venus requires more as a pure CO2 greenhouse contains many holes in the IR spectrum. (This is expained well p57-58 in Chapter 3 Goody & Walker 1973.) These holes are now known to be plugged by H2O & SO2 but these require to be at a level that does not greatly increase albedo & cool the planet. (See this paper by Bullock & Grispoon.)
I thank you all for your response. I didn't consider my comment to be off topic as I am concerned with the effect of CO2 on the atmosphere and was just using Venus as an example. Apparently not a very good example so scratch that one. From what Tom said, the increase in temperature from CO2 going from .04% to .05% would be less than what we have seen from the CO2 going from .03% to .04%. But what are the actual number? What is the temperature change due to CO2 alone and how do we know it's CO2 and not some other factor? I'm sure you are familiar with the show Mythbusters. In one episode they filled a tank with CO2, put in a block of ice, shined a light on it and compared that to a similar tank filled with air. The ice in the CO2 thank melted faster. No big surprise there. But no actual numbers either. I would like to have seen a tanks with 100% CO2, 10%, 1%, .1%, .01%, and zero and compared the melting rate in each. Then I would have a better idea of the effect of CO2. Anyone have some actual numbers?
320. MA Rodger
"The climate of Venus is overwhelmingly CO2 and this does provide a strong greenhouse effect."
But at 1 atm pressure there seems to be no effect of co2. What the temperature is at higher pressure closer to the surface is not caused by the greenhouseeffect. Or do you have experimental data showing how co2 can increase the intensity from ~2500W/m^2 to ~15000W/m^2?
HB @322.
You presumably mean 1 bar when you say "1 atm pressure." On Venus 1 atm of pressure is about 90 bar and the surface temperature 462ºC. What your energy flux figures are meant to represent is not immediately clear to me. A simple S-B calculation suggests the Venusian surface emits some 17,000W/sq m as opposed to the Earth's 400W/sq m. I'm assuming the "~2500W/m^2" figure you quote is a stab at the Venusian insolation. But I could be wrong.
I am no expert on the Venusian atmosphere but likely Robinson & Catling (2013) know a thing or two. Their figure 1 (below) uses data from Moroz and Zasova (1997) for its Venus Temperature-Pressure trace and shows Venus at 1 bar to be significantly warmer than Earth at 1 bar. This elevated temperature (350 K) exceeds a pro rata temperature wrt Earth due to the elevated Venusian insolation. Thus the GHG effect on Venus at 1 bar exceeds the full Earth atmosphere GHG effect. What contribution CO2 makes to this high-altitude Venusian GHG effect is a further issue. I assume your comment concerning this, that "there seems to be no effect of co2" has no evidential basis. But I could be wrong. So please surprise me if you can!
323. MA Rodger at 01:25 AM on 29 December, 2016
HB @322.
You presumably mean 1 bar when you say "1 atm pressure." On Venus 1 atm of pressure is about 90 bar and the surface temperature 462ºC. What your energy flux figures are meant to represent is not immediately clear to me. A simple S-B calculation suggests the Venusian surface emits some 17,000W/sq m as opposed to the Earth's 400W/sq m. I'm assuming the "~2500W/m^2" figure you quote is a stab at the Venusian insolation. But I could be wrong."
2500W/m^2 is insolation, that is correct. But I think it is a bit more. Why do I need to be exact? Do you have an argument based on the difference of 2000W between 15-17000W?
Did you really not understand that I used 1atm as it is on earth?
"I am no expert on the Venusian atmosphere but likely Robinson & Catling (2013) know a thing or two. Their figure 1 (below) uses data from Moroz and Zasova (1997) for its Venus Temperature-Pressure trace and shows Venus at 1 bar to be significantly warmer than Earth at 1 bar."
With more than 90% co2 in the atmosphere you would expect a bit more, wouldn´t you?
2500/4=625W/m^2
But for a slowroller like venus you should use the hemisphere:
2500/2=1250W/m^2
350K=850W/m^2
"This elevated temperature (350 K) exceeds a pro rata temperature wrt Earth due to the elevated Venusian insolation. Thus the GHG effect on Venus at 1 bar exceeds the full Earth atmosphere GHG effect. What contribution CO2 makes to this high-altitude Venusian GHG effect is a further issue. I assume your comment concerning this, that "there seems to be no effect of co2" has no evidential basis. But I could be wrong. So please surprise me if you can!"
So because people believing in greenhouseffect can´t understand the planetary temperature of Venus surface where co2 is so hot and dense that it is in a critical state, we can assume that a gas that is not a heat source, is the cause of high temperature?
I would choose almost any other explanation than that. All of them would include heat generation of some sort. Since that is what it takes to heat something up.
HB
You are missing one important point. Albedo. Venus is highly reflective with a Bond Albedo of between 0.75 to 0.9. So it only absorbs 10%-25% of the sunlight that strikes it. Incontrast the Earth absorbs around 70% of the sunligt that strikes it So, although it is much close to the sun, Venus actually absorbs less energy from the Sun than the Earth does.
Next, for the temperature at the surface to be high doesn't require heatgeneration. It only requires heat tranport from the upper atmosphere to the surface.
See my comment at 318. The atmospheric Lapse Rate determines th surface temperature, based on the upper atmosphere temperature which is set by radiative balance and GH gases - for Venus mainly CO2.
I suggest you do some reading to understand how vertical air movements, which can transport heat up or down, create the Lapse Rate.