Arguments
Empirical evidence that humans are causing global warming
Posted on 9 July 2013 by gpwayne
This post is a new 'basic' level rebuttal of the myth: "There is no actual empirical evidence that carbon dioxide emissions are causing global warming."
What the Science Says: Less energy is escaping to space. Carbon dioxide (CO2) acts like a blanket; adding more CO2 makes the 'blanket' thicker
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.
The Earth is wrapped in an invisible blanket
The laws of physics tell us that without the atmosphere, the Earth would be approximately 33°C (59.4°F) cooler than it actually is.
This 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. In other words, it would be freezing cold even at the height of summer.
The reason that the Earth is warm enough to sustain life is because of greenhouse gases in the atmosphere. These gases act like a blanket, keeping the Earth warm by preventing some of the sun’s energy being re-radiated into space. The effect is exactly the same as wrapping yourself in a blanket – it reduces heat loss from your body and keeps you warm.
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?
One way of measuring the effect of CO2 is by using satellites to compare how much energy is arriving from the sun, and how much is leaving the Earth. What scientists have seen over the last few decades is a gradual decrease in the amount of energy being re-radiated back into space. In the same period, the amount of energy arriving from the sun has not changed very much at all. This is the first piece of evidence: more energy is remaining in the atmosphere.
Total Earth Heat Content from Church et al. (2011)
What can keep the energy in the atmosphere? The answer is greenhouse gases. Science has known about the effect of certain gases for over a century. They ‘capture’ energy, and then emit it in random directions. The primary greenhouse gases – carbon dioxide (CO2), methane (CH4), water vapour, nitrous oxide and ozone – comprise around 1% of the air.
This tiny amount has a very powerful effect, keeping the planet 33°C (59.4°F) warmer than it would be without them. (The main components of the atmosphere – nitrogen and oxygen – are not greenhouse gases, because they are virtually unaffected by long-wave, or infrared, radiation). This is the second piece of evidence: a provable mechanism by which energy can be trapped in the atmosphere.
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 thousands of years, the amount of CO2 in the air had gone up to 400ppm. That information gives us the next piece of evidence; CO2 has increased by nearly 43% in the last 150 years.
Atmospheric CO2 levels (Green is Law Dome ice core, Blue is Mauna Loa, Hawaii) and Cumulative CO2 emissions (CDIAC). While atmospheric CO2 levels are usually expressed in parts per million, here they are displayed as the amount of CO2 residing in the atmosphere in gigatonnes. CO2 emissions includes fossil fuel emissions, cement production and emissions from gas flaring.
The Smoking Gun
The final piece of evidence is ‘the smoking gun’, the proof that CO2 is causing the increases 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:
Spectrum of the greenhouse radiation measured at the surface. Greenhouse effect from water vapor is filtered out, showing the contributions of other greenhouse gases (Evans 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 provable 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 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.
Honeycutt #47, Thank you for reading my post and commenting. Where I live, H2O is a very long lived gas. It is always there in very abundant quantity. An individual molecule may leave the atmosphere but it is always replaced by another one, H2O is the primary greenhouse gas and has a whole slew of LWIR absorption bands H2O does not need any other greenhouse gas to exist in the atmosphere in order to provide its greenhouse gas effect. H2O is the weather maker. Ignoring it leaves a big whole in the argument. "Dwarfs all other greenhouse gasses" cannot be inferred from the chart because the greenhouse gas that is responsible for most of the greenhouse effect was filtered out of the chart.
[GPW]: William, there are a few other points I'd like to make about water vapour (UK spelling). CO2 is now a precursor of warming, WV is a function of it. CO2 is well-mixed globally, WV is not. The residence time of CO2 is centuries or even millennia; the residence time of WV is days or weeks.
We humans are not directly adding WV to the atmosphere (although it increases through chemical reaction and increased evaporation). We are adding CO2, methane etc. And finally, the reason WV was left out was explained by DSL earlier (thanks DSL), and in the paper from which the graph was obtained (post #10). I'll repeat the extract of the paper once more:
William,
The fact that H2O levels are high where you live is really missing the point. How long would an artifically induced change in those levels last?
The answer is "a few weeks". If humanity was busily attempting to artifically cause global warming by increasing atmospheric H2O levels, it would fail, because any extra beyond what the atmosphere can carry will simply precipitate out. To increase H2O levels long term requires increasing the temperature, which is exactly how H2O acts as a feedback to warming by CO2.
Contast this with CO2. It will take thousands of years for an increase in CO2 levels to revent naturally. During that entire time, the greenhouse effect is enhanced.
As I mentioned before, H2O is the turbo, CO2 is the accelerator. Travelling at 200 km/h the turbo is probably responsible for quite a lot of the engine's power output, but that doesn't change the fact that the turbo is still a slave to the accelerator and it's the accelerator that's responsible. Nobody's ignoring H2O, we're just focussing on what actually matters when it comes to driving climate change.
William,
One other point:
H2O does not need any other greenhouse gas to exist in the atmosphere in order to provide its greenhouse gas effect.
That's actually not true. With no CO2, the earth would freeze into a snowball and at low enough temperatures there will be no H2O in the atmosphere. The reason the earth escaped snowball earth situations in the past was because CO2 and methane released from vocanoes was not being taken up by rock weathering (due to the rock being covered in ice) allowing the concentrations to reach high enough levels that the greenhouse effect could melt the ice. The transitions between snowball earth and hothouse earth can't be explained without those other greenhouse gasses.
So while H2O provides over half of the total greenhouse effect currently, it only does so thanks to the other greenhouse gasses. Again with the turbo analogy: no matter how powerful a turbo is, it has exactly zero effect when the car is switched off. Drive at 200 km/h and it could well be causing the engine to produce more than twice as much power as an equivalent engine without a turbo, but it's still dependent on the accelerator to do its job.
William Haas, you seem to think that where you live is isolated from the rest of the climate system. Are you sure you want to claim that dropping CO2 completely from the atmosphere would have no appreciable effect on your local water vapor concentration? H2O is a powerful greenhouse gas, but it's also a fast feedback--not a forcing. It responds very quickly to other forcings. Its residence time makes it unable to produce any climate-scale trend in global energy storage (not even close). It follows GHG forcing (rising rapidly). It follows solar forcing (flat or falling for fifty years). Harp on WV all you want, but it doesn't do the driving.
John @ 20: "Problem is that when those events occurred in the past, they gnerally occurred over a geological time scale."
Terranova @ 48: "JH at 20: prove that statment. No models, but proof."
Here you go, Terranova: http://tinyurl.com/l5wz6zc
Ask a broad question, get a broad answer. Did you want John to do your thinking as well? Btw, science is not going to provide you with proof for a positive hypothesis. Perhaps you meant "evidence." If you want absolute certainty, go find a priest.
Jason says " If humanity was busily attempting to artifically cause global warming by increasing atmospheric H2O levels, it would fail,"
True but it's ironic that we kinda are attempting to do just that. Burning hydrocarbons can be summarized by the simplified relation: CH + O2 ---> CO2 + H2O.
So we do release large amounts of water vapor in the atmosphere through the combining of atmospheric oxygen with fossil hydrogen. As I recall, the decrease in atmospheric oxygen has even been observed.
So, William, even if your argument had any validity in physics (which it doesn't), it would constitute even more of a reason to decrease fossil hydrocarbon consumption.
William... "Where I live, H2O is a very long lived gas."
Your comments demonstrate a fundamental lack of understanding of the physics being discussed. WV is not a long lived gas, and as has be stated by others here, is also a condensing gas. CO2, CH4, etc. are all long lived non-condensing gases in our atmosphere.
Think about it this way. What is the WV content of the atmosphere where you are when the temperature goes below zero C?
Terranova @48... "You cannot dismiss the contribution of water vapor."
Definitely not dismissing it in the least. I'm just saying that for the purposes of understanding what human factors of impacting changes in global temperature, the fact that WV is not on the spectral graph has no bearing on the point being discussed.
@Terranova #48:
My satement about the rapidity of climate change being generated by mankind's activities is based upon a body of science very nicely articulated by Gavin Schmidt and Joshua Wolfe in their book, Climate Change: Picturing the Science, W.W. Norton Company Ltd, 2009.
Here's what they say:
This is good information. One thing I am trying to understand. If I look at the current understanding of CO2 levels over millions of years, reconstructed by a variety of methods like ice cores, plant stomata, and geochemistry, all put together, it looks like the levels of CO2 went up and down a lot and were way higher in the past than they were now, like 1000 or 1500 ppm. A recent paper on it is at
http://ajsonline.org/content/311/1/63.short
but there are lots of other papers like that too. So what I am curious about is
1) During a lot of those times millions of years ago, the earth was fairly lush and had a lot of flora and fauna, and I guess evolution was taking place. I think man is supposed to have evolved about then. But if 400 ppm or 1000 ppm are bad for life, why was there so much life going on then? I mean even now there’s a lot of stuff being published about how trees and plants and other flora are using water better, growing faster and things like that, for example the USDA just said trees are using water a lot better at
http://www.nrs.fs.fed.us/news/release/trees-water-atmospheric-co2
2) The CO2 levels went up and down a lot it looks like over millions of years so. I guess that means that a lot of natural processes affect CO2 levels? Or is it just man that does it? I mean what was making the CO2 go up and down for all those past millions of years?
Just curious. Thanks for your reply.
[TD] Excellent questions. For answers to your question 2, see the post How do human CO2 emissions compare to natural CO2 emissions? (after you read the Basic tab, click and read the Intermediate tab) and the post Understanding the long-term carbon-cycle: weathering of rocks - a vitally important carbon-sink.
For one specific example, see CO2 lags temperature - what does it mean?
Videre, regarding your question #1: No one has claimed that 400 ppm or 1,000 ppm of CO2 are bad for life in general. But all individual species have evolved to thrive in certain environments, including a certain range of CO2 levels. When any aspect of their environment changes "slightly" and/or "slowly," individual animals and plants might be able to cope, and even if individuals cannot cope, their species might be able to evolve to cope. But if some aspects of their environment change "too much" and/or "too fast," individual animals cannot cope well or at all, and species cannot evolve fast enough to avoid extinction. Making the whole thing even more precarious are the interdependencies of plant and animal species. If just one species' numbers fall, or if their characteristics or behavior change, a large number of other species can be affected even to the point of extinction. The big problem for us and all other current life is that CO2 is rising so fast that many species cannot evolve or move or otherwise adapt fast enough to the temperature and other climate changes, or to the ocean chemistry changes. For some examples, see the post It's Not Bad, and be sure to read all three tabbed panes (Basic, Intermediate, and Advanced).
Regarding increased CO2 increasing plant growth and using less water: Yes, there are some benefits at some levels of CO2 increase for some plants. But it is not a uniform benefit across all levels of CO2 or plants. And increased growth of crops often means the extra growth goes into of the parts of the plants that humans don't use, such as woody stalks of plants whose leaves and fruit we eat. More importantly, increased CO2 does not come by itself; it causes climate changes such as increased temperature and changed precipitation patterns, and ocean acidification that detrimentally affects fish, coral, and even vast numbers of microscopic creatures on which other creatures in the food pyramid depend.
That’s great, thanks. I looked at the Global Carbon Cycle link. That’s really great. What I don’t understand is that all the other parts of the carbon cycle, like the vegetation and land and the oceans and rock weathering are more than10 times the size of the fossil fuel and land use source, and I guess if they only changed like 5 or 10% they could either decrease or increase the CO2 as much as the fossil fuel burning. So if its just the fossil fuel that makes all the difference, then do we need to assume that all those other much bigger effects are staying constant within a few percent?
Thanks for the link to the CO2 lag link too, but now I am more confused. It says that the initial rise in temperature was caused by astronomical things and then the ocean temperatures rose and CO2 then rose because it is less soluble in oceans if the temperature is higher. I guess that makes sense. But then does that mean that all those million years ago the same thing was going on? And I guess if the CO2 got released after the temperature went up in those long ago times and then started heating things up, I guess I don’t understand what stopped it. The other thing I guess is if the temperatures started going up and caused the CO2 to go up, how do we know that is not what’s happening now. I mean the ocean temperatures look like they are going up. How do we know, I mean from the data, that the CO2 rise in the atmosphere isn’t being caused by the rise in ocean temperature. I guess the other thing is if CO2 lagged temperatures in the past and then the greenhouse effect kicked things up a notch, so it should just keep going up. But if I look at the upper graph on the link, it looks like the temperature went up and then down a lot of times in the past 400 thousand years. So what I don’t get is, if the greenhouse effect kicks in and heats things up, then more CO2 gets released from the oceans, then more greenhouse effect kicks in, it seems like it should just keep going up and up? Or is there something else going on that is causing the temperatures to go up and down in thos 400 thousand years? And i guess if there was something else going and we dont know what it was, how do we know its not going on now?
Thanks for the info on plant and animal species. I guess I was most curious about the cause effect relation between CO2, temperature, and other climate factors.
Videre - it would be better if you put your questions in the relevant thread. Very very briefly (and if you have more then PLEASE respond in the right place):
- natural flows in and out are very large, but also more or less balanced. FF is changing that. If you messed significantly with natural flows, you would be trouble fast.
- CO2 and methane respond to change in temperature regardless of cause of change. They magnify (over very long time scales) any other forcing that changes temperature. Water vapour does same but more or less instantly. However, the feedback is not a runaway (k<<1) so equilibrium is reached. (see here for detail if you dont understand).
Videre... You're asking good questions. Just don't make the mistake of thinking that just because you're coming up with questions that there are no answers.
All too often I've seen folks coming to comment on SkS asking many similar such questions thinking they're somehow figuring out "problems" with climate science. Nothing could be further from the truth.
What they are figuring out is that climate is a very complex area of science. This is also science that dates back to the 1820's and has been very intensely researched for many decades. Greenhouse gas theory is on equal footing with evolution, relativity and germ theory. That we are warming the planet through the combustion of fossil fuels is settled science. As with all theories there are areas we don't yet completely understand. Those areas we don't fully understand are highly unlikely to change the aspects of climate science that have been long settled.
You'd do well to spend some time reading through all the relevant posts here on SkS. And if the posts don't answer your questions fully, feel free to click through to the actual scientific research. Almost every article on this site has direct links to the relevant peer reviewed research.
Remember, most scientific research is being done by people who have dedicated their lives and careers to understanding the areas they're researching. When you come upon something that doesn't make sense to you, that means you're just coming upon something you don't yet understand, and need to understand better.
If you do find things that just aren't making sense to you, as scaddenp said, post a comment in the section of the relevant article. We all keep track of current comments, so your question won't get lost.
Videre
I would second Rob Honeycutt's comment.
Also, to help clarify your thinking, you talk about 'millions of years'. Be clearer in your own mind what time scale you are thinking about because different factors have different significance over scales of millions of years, 10's of millions and 100's of millions.
For example, over very large time scales 10's to 100's of millions of years, one needs to take account of the fact that the Sun wasn't as hot in the past and that higher CO2 concentrations in the past approximately compensate for this. Roughly speaking, every 150-200 million years that we look back in time, CO2 levels need to double, just to compensate for the cooler Sun.
Thanks for the help. I guess I was trying to keep my focus on this thread and just looking at the data.
Scaddenp, I am sorry for coming back to this thread, but it was the moderator who directed me to those other threads as having the answers to my questions about this thread, but when I read the other threads, I just had more questions about this thread so I just posted my observations from those other threads into this thread where it was relevant. I am really trying to get a handle on the maint points of this thread and the information given in this thread.
So if I go down the main points in the summing part at the bottom of the thread with my questions I get something like this:
1. More energy is remaining in the atmosphere. See here when he sent me to the geological pages and the energy balance it looks like more energy has come into the atmosphere lots of times, I think one of the threads says it was astronomical changes like orbits and the sun. So it just looks like there are a lot of things that have and can cause more energy to be in the atmosphere. I mean when he directed me to the CO2 lagging thread, its just weird that more energy was getting into the atmosphere at various times in the past even before the CO2 levels rose.
2. The next is the mechanism by which energy can be trapped in the atmosphere. I guess this makes sense as being a mechanism that can do it, but then the lag problem crops up again because if CO2 lags temperature then it just seems something else traps energy too to start the temperature going up. And I guess if the greenhouse effect traps the energy, while it might not go runaway, if it was high in the millions of years past and still the temperature went down and up and down then is there something else going on too that either gets rid of heat and traps it? Its just weird that if the greenhouse effect traps energy that it wouldn’t just keep trapping energy in the past. The other thing about trapping the energy came up when I looked at the fourth point below.
3. The next one is CO2 increasing 50% in the past 150 years. When the moderator told me to look at the history and I had already looked at the data over millions of years, i think it went back to about 60 Ma, which I thought meant 60 million years, there were a lot of ups and downs, not just going up like doubling like Glenn said. Plus if the ocean temperature is going up and CO2 was going up because of the less solubility of CO2 in water I guess that could explain the CO2 rising now too, like it might have millions of years ago. It made it even worse when I looked at the CO2 balance thread the moderator directed me to where I saw those other ins and outs of CO2 were like about 10 or 20 times as big as the fossil fuel burning and land use. I know scaddemp said those much bigger CO2 sources were more or less balanced, but I thought error bars on measurements in climate science must be like 5 or 10 percent or even larger sometimes and that just a few percent of those big numbers would be a lot larger than the fossil fuel burning contribution to CO2.
4. So the last one I wondered about too, and it is about the energy being trapped in the atmosphere is exactly the energy captured by CO2. So I looked at the link to the conference poster of Evans in 2006 and it had the radiation measurements for all the greenhouse gases but it took out water and wasn’t a peer reviewed paper so I looked at the IPCC last out report, I think its called AR4, which came out in 2007, after the Evans poster. On page 141 in Chapter 2 there’s a Table 2.1 that shows the CO2 radiative forcing in 2005 was 1.66 W/m2 and all the other gases, not CO2, add up to about 0.77 W/m2 so CO2 is about 63% of the total of those gasses. But water still wasn’t in there so I looked on page 204 still in Chapter 2 at the Table 2.12, which gives all the radiative forcings. A lot of them are negative, like ozone and aerosols and all, so if I add up all the negative ones (a big one is the cloud albedo effect) I got negative forcings of -2.1 W/m2 and adding up the total of the positive ones, not CO2, I got a positive 1.35 W/m2. The uncertainties are pretty big on the numbers too so these numbers have intervals around them like a factor of two. So what confused me is that it looks like the CO2 forcing is kind of small compared to the other effects. Just the negative ones look like they can cancel out the CO2 effect. It just seemed weird that so many other effects are going on but somehow it’s for sure that CO2 is the dominant thing.
So anyway, I just wanted to look at the post and the information in it and try to understand the main points, which I thought were all about the empirical evidence that humans are causing global warming by increasing CO2, but wound up having a lot of questions. Sorry if I crossed the threads but I thought they all related to this one, plus I think the moderator pointed some of them out to me as helping understand this thread.
Videre @66:
1) To a first approximation, all energy on Earth comes from the Sun. That energy is then reradiated to space as thermal radiation (IR). The surface temperature required to balance the incoming energy depends on:
a) The amount of energy from the sun which is reflected (albedo);
b) The level in the atmosphere from which energy is radiated to space (the greenhouse effect); and
c) The distribution of heat on the Earth's surface.
The albedo is controlled by the presence and latitudes of snow and ice, the prevalence of clouds and by the prevalence of different types of vegetation. The natural greenhouse effect is controlled by the four major naturally occuring greenhouse gases, ie, H2O, CO2, O3 and CH4. The distribution of heat is controlled by the arrangement of the continents and milankovitch cycles. Variation of any of these factors can result in a change in the Top Of Atmosphere (TOA) energy balance, and hence of the surface temperature. In the face of that, saying that "its just weird that more energy was getting into the atmosphere at various times in the past even before the CO2 levels rose" is, quite frankly, silly.
As it happens, climate scientists have a pretty good idea as to what caused increased warming durring glacial epochs (change in the distribution of heat due to milankovitch cycles, which drove changes in albedo and CO2 and CH4 concentrations as a feedback). They also have a good idea of what those factors would be doing now without human intervention. Specifically, the milankovitch cycle would be cooling the Earth, driving an increase in ice and snow, and a reduction in CO2 and CH4 concentration as a feedback.
2) The entire basis of your second point seems to be the assumption that if increased CO2 traps more heat through the greenhouse effect, then it must over ride all other influences on the Earth's temperature so that countervailing factors cannot result in cooling. Or, to take a specific example, the fact that the CO2 forcing was sufficient for a 6.5 C increase in surface temperature 400 million years ago, would mean (by your logic) the fact that the sun was about 10% cooler that could not possible prevent that increase.
3) We do not know that the current CO2 increase is anthropogenic by measuring all natural fluxes and finding a shortfall. Rather, we have measured the human addition ot CO2 in the atmosphere, and found that less is staying in the atmosphere than we put there. It follows that nature is taking the shortfall out of the atmosphere. So, the error bars on our measurement of natural fluxes is irrelevant, because the error bars on our measurement of anthropogenic emissions are sufficiently small as to leave no doubt. IF you wish to learn, you need to stop constructing straw man versions of purported scientific arguments, and address the actual arguments used by scientists.
4) From table 2.12 of IPCC AR4, the sum of all forcings exluding long lived greenhouse gases is -1.24. The forcing from long lived greenhouse gases is 2.63, leaving a net forcing of 1.39 W/m^2 (just slightly greater than that of CO2 alone). CO2 is the largest single forcing, and the only anthropogenic forcing agent with a duration greater than a century. No other single forcing agent has even half the effect of CO2. Consequently your claim that, "it looks like the CO2 forcing is kind of small compared to the other effects" is pure bunkum.
On all four points it strikes me that you are not an earnest seeker after the truth of the matter, but somebody looking for any fact to twist out of context to avoid accepting the science. You are doing this before you even understand the science, and the result merely makes you look foolish.
This is a nice and simple explanation of the greenhouse effect in action. The effective blackbody temperature of Earth when applying the Stefan-Boltzmann law is -18 or 255K and its observed temperature is 15C or 288K representing a temperature-disparity of 33K. This amounts to a huge 'radiative forcing' by the atmospheric greenhouse. in fact it amounts to 150.35W/sq.m. The idea that CO2's forcing is "small" I guess depends on your definition of `small'. Doubling atmospheric CO2 is enough to produce a radiative forcing of 3.7W/sq. thanks to thousands of line-by-line spectural computations by HITRAN, which even prominent climate skeptics such as Lindzen and Spence acknowledge is true and wholly. 3.7Wsq.m would result in an atmospheric warming of about 1.2C, with the rest accounted for by positive feedbacks inherent in the climate-system. This imples that CO2's direct warming would only need to be amplified by a mere 0.8C by feedbacks to take us to 2C, which is apparently dangerous territory for some scientists. I think skeptics such as the Sky Dragon Slayers could learn thing or two about the greenhouse with the Moon/Earth comparison. Spencer's illuminating saucepan anology and cooked chicken as a way of conceptually proving the existence of the radiative greenhouse effect is probably one of the best I've come across. You guys should do a similar thing.
Thanks that helps. Just trying to understand the science is all. Like Rob said above the standard is evolution and relativity and germ theory. I guess germs they observe all the time in controlled experiments and measure growth and infection rates to better than a percent and evolution I think people observed directly in germs like E. Coli and even saw birds or something evolving in a few years. And relativity, I think they tested relativity in experiments with clocks and lasers and its been tested to precisions like a part in a billion or better. And that means the theory checks out. If I look at the data and then links on here it just looks like the accuracies of the science for CO2 forcing has factors of two running all around which doesn’t seem to be the same as for evolution, relativity and germ theory. But I don’t know for sure.
But thanks for the help really. Sorry if anybody got offended ok. I think everybody here is just great help.
Videre,
Quantum field theory is responsible for "the worst theoretical prediction in the history of physics" by predicting a value for the cosmological constant that is over 100 orders of magnitude larger than that which is actually observed.
To put that into context, there are some 1080 electrons in the universe, from memory.
Compared to that, a factor of two "running around" is absolutely fantastic.
Evolution is actually very similar to AGW in terms of how it has been established as scientific fact. Hint: it's not by watching E. Coli or even birds evolve. And another: it's not surprising that many of the people who deny one also deny the other.
But I think you misunderstand why those factors of two exist. If you're talking about overall climate sensitivity (and not something quite well known, like the factor of two that the water vapour feedback has on CO2, which comes from those same physical thories and measurements), it's because we're dealing with a very noisy system where it's hard to make accurate measurements; in recent times, when we have accurate instruments, the signal is still small, whereas over longer periods of time, when the signal is large, we don't have access to accurate measurements. (Nevertheless, the tightest constraints on climate sensitivity remain those comparing glacials with interglacials because the signal is so large it doesn't matter so much.)
On top of that, it's likely that with all the complex interactions of the different parts of the system, the actual figure changes all the time.
But this doesn't mean that we haven't established the figure accurately enough to take action.
Consider you are driving at high speed towards a brick wall. You're not sure if you're going to hit it in five seconds or ten. Do you lament how difficult it is to judge distances accurately when travelling at high speed, or do you brake?
Thanks that helps a lot. I guess quantum field theory is pretty complicated and probably people pretty much agree lots of it isn’t established for sure. I guess that’s a case where the science isn’t settled. I guess maybe they can test hypotheses for simple stuff like electrons moving fast around atoms and all and even way down to parts per billion, no factors or two or anything. But like in relativity guys have this hypothesis that the end result of something happening is completely predictable by a forcing function, like the mass or the velocity. Or the acceleration. Then they do an experiment like flying something fast like a particle or a clock and then measure the result and it just confirms the whole hypothesis within parts per billion, again no factors of two running around. I guess that’s what I meant. I think in relativity there is a whole lot of stuff going on where people think maybe there’s dark matter and that cosmological constant is either there or not, and I know they can guess some things happen in certain ways, but sometimes they don’t so I guess that part isn’t settled science. The part where they have some effects they think cause things but they can’t do experiments for sure so its not settled. In the evolution thing too it helps that the experiments on whole systems of organisms like E. Coli and be put into a controlled stress situation and observed over lots of generations and sure enough the hypothesis that gene frequencies change over time due to stress works out. That way like for all these other theories I guess they don’t deny or not deny anything they just make a hypothesis then do controlled observations and measure the results, and see if the hypothesis tests okay.
So I was just trying to compare the hypothesis that human production of CO2 forces temperatures up in the same way, like in this thread. You know, getting some kind of result that is the same as the other ones in settled science, where the confidence limits are really strong, for the whole end to end thing, and everything is connected by this really ironclad hypothesis. Like if you increase CO2 exactly by some amount and hold everything else constant, then the temperature goes up just the amount you predict just like you think. Prediction seems pretty important too. It’s pretty hard, I think, especially about the future. I just thought that was how it worked for the other theories in science.
Videre, I responded on the more appropriate thread (CO2 lags temperature) to your point #2 from one of your comments on this thread.
Videre, in your point #2 you wrote "And I guess if the greenhouse effect traps the energy, while it might not go runaway, if it was high in the millions of years past and still the temperature went down and up and down then is there something else going on too that either gets rid of heat and traps it? Its just weird that if the greenhouse effect traps energy that it wouldn’t just keep trapping energy in the past."
The amount of greenhouse gases in the atmosphere varies as a consequence of variations in the natural sources and sinks of greenhouse gases. An example is the increase in CO2 that is a consequence of Milankovich orbital cycles; when the amount of CO2 increases, the greenhouse effect is strengthened. But there are natural sinks of CO2, which means there are natural mechanisms for removing CO2 (and other greenhouse gases) from the atmosphere. If the amount of CO2 removed by the sinks is greater than the amount added by the sources, the amount of CO2 in the atmosphere decreases, which weakens the greenhouse effect. An example is that a major cause of glacial periods ("ice ages") is the Milankovich orbital cycles going the other way than they do when they end a glacial period. As the Sun's rays become less perpendicular to the Northern Hemisphere's surface, the amount of the Sun's energy hitting the ground decreases, which allows ice and snow to remain on the ground longer and to cover more area, which reflects more sunlight, which allows even more ice and snow to exist, which causes cooling of the land, air, and oceans. Cooler oceans can contain more CO2, so the oceans become less of a source of CO2 for the atmosphere, and eventually become cool enough to absorb CO2 from the atmosphere, which weakens the greenhouse effect.
But even more important for you to understand is that CO2 is not the only driver of temperature. If you have questions about that, it is important that you comment on that thread, not this one.
Videre @71, an important trick in science is knowing how to test a theory.
Take special relativity as an example, it has an effect at all velocities, so in principle you could measure the time distortion of two trains passing each other in opposite directions with a relative velocity of 33.33 m/s (100 Km/hour). Even with the most accurate atomic clocks, however, your margin of error would be large. In fact, an equivalent experiment using aircraft only measured time dilation to an accuracy of about 10%, although later repetitions showed an accuracy to within 1.6%.
Alternatively, you could use an Ives-Stilwell experiment, which constrains the error to one millionth of 1%.
A critique of special relativity (and they do exist) who argued that special relativity had been poorly confirmed based on the 10% error margin of the first experiment, while ignoring the existence of the second would not be taken seriously. Yet that is the equivalent to what you have done.
You argue that the rise in CO2 could have a natural source, quoting the large error in measurements of natural fluxes. In doing so, however, you ignore the 2% error in measurement of C14 levels, which show categorically that ocean outgassing or decline in vegetation are not the source of the recent growth in CO2; or the 1.5% error in measurements of C13, which show categorically that volcanoes are not the source. Combined, with an error of around 2%, all natural sources are exlcuded by these two sets of observations - but that, apparently is irrelevant to you.
As to being offended, I am not offended but tired. Tired of the continuous misrepresentation of science by so-called "skeptics"; and tired of purported honest enquirers who show by their actions that they are anything but.
If you are an honest enquirer, you will take a step by step approach to gaining knowledge. You will start with something very basic and ask specific questions about parts of the evidence or argument you do no understand - not in great screeds of text which are likely (designed?) to discourage response, and raising so many issues that many are likely to be ignored - but by short simple questions. One question at a time.
And while you are working through the examples, you are not so arrogant as to believe that issues you can think of in a few seconds with a very limited knowledge of the subject have escaped the attention of the thousands of climate scientists who have spent lifetimes studying the issue in a profession in which careers are made by pointing out the errors of others. Instead you have the humility to realize that if the issue has occurred to you, it has probably been raised and answered before, and you are simply not aware of that fact. And given that humility, you give the climate scientists, rather than bloggers like A Watts (who, lets face it, are in the same position as you in respect to climate science), the benefit of the doubt until you have studied the issue in sufficient detail that you know not only the popular explanation of the issue, but also the historical and current scientific discussion of it.
Videre made this passing statement: "...and wasn’t a peer reviewed paper so I looked at the IPCC last out report, I think its called AR4, which came out in 2007,.."
Given the level of detail in each of his questions, to claim that he "thinks" 2007 IPCC report is called "AR4" strikes me as a huge red flag.
I would put forth that Videre is not someone who is at all curious or skeptical. He's another fake skeptic thinking he can come to SkS to poke holes in the science, which he clearly does not understand.
Videre, you need to come clean here. Everyone here are more than willing to discuss the science with you but you need to be honest in your discussion. No one here wants to talk to someone who is feigning curiousity.
Yeah, Rob, I noticed other oddities about Videre's writing. Sort of an inconsistent hybrid of a young teenager, a wide-eyed adult, and a denier. For example, there are the failures to understand or even notice the most obvious and straightforward concepts in the posts and in our responses, yet detailed attention to and calculations of forcings. But I decided to take him/her at face value, because I don't want to act like a Wattsian, and because lurkers might learn from my responses. Nonetheless, I'm about out of patience....
The vast majority of interested parties are aware that humans are responsible for 'some' warming, but the $64 billion question is, how much warming is human emission of GHGs responsible for?
The short answer:
"Nobody knows."
Earthling,
how much warming is human emission of GHGs responsible for?
Officially, it's very likely that human emissions of GHGs are responsible for most of the warming over the past 50 years. Unofficially, I think you'll find that human emissions of GHGs are responsible for over 100% of the warming that actually occurred (i.e. the temperature would have actually declined without human GHG emissions).
"Nobody knows."
97% of scientists with relevant expertise would disagree. Perhaps it's better not to assume that just because you don't know something then that must mean that nobody else does, either.
Earthling. Actually the warming potential from anthropogenic additions of CO2 are known, sufficiently understood and well-documented in the scientific literature. The standard equation for calculating the radiation-enhancement from CO2 is as follows: RF = ln*5.35(C\C1). The equation in question is derived from HITRAN, which is based on real-world observations (spectrometer/satellite measurements) and determines the radiative forcing characteristics of certain gases in the atmosphere, such as CO2 and CH4. The equation above gives us a radiative forcing of about 3.7W/sq.m for a doubling of CO2 corresponding to a warming of about 1C in the atmosphere. It's also worth pointing out that hardened skeptics such as Lindzen, Spencer, Nova, and many others, all agree with the 3.7W/sq.m of radiative forcing from a doubling of CO2, so it's not really that controversial. So despite claims to the contaray, the warming from human CO2 in the atmosphere is quantifiable and well-accepted - even by skeptics. As Jason pointed out, there's also the small matter that 97% of scientists agree that the planet has warmed since 1860 and that human CO2 has been a significant contributer to that warming.
I've been on a roll and should pull back - but this is too good not to share
Reposted at:
Consensus part 2 - The Empirical Evidence
http://citizenschallenge.blogspot.com/2013/07/consensus-part-2-empirical-evidence.html
~~~~~~~~~~~~~~~~~~~
thanks, :-)
@ Earthling:
Huber and Knutti (2011) quantified that human attribution as being 74% and 122% due to humans (with a best estimate of around 100% human attribution). In other words, natural variability is not responsible for the observed warming trend.
http://www.nature.com/ngeo/journal/v5/n1/abs/ngeo1327.html
Since then, Gillett et al (2012) also examined the human attribution of the warming trend observed. They found that humans are responsible for 102% of observed warming from 1851 to 2010 and 113% of the observed warming from 1951 to 2000 and 1961 to 2010 (averaged together).
http://www.agu.org/pubs/crossref/2012/2011GL050226.shtml
And Sedláček & Knutti (2012) examined ocean and atmosphere warming to ascertain whether recent global warming is consistent with natural variability, or with external forcing (i.e unrelated to internal variability of the climate system). They found that both computer simulations and historical observations are incompatible with natural variability as a possible cause of ocean warming. I.e., natural factors/cycles are not the cause of the ongoing warming we can see and measure.
http://onlinelibrary.wiley.com/doi/10.1029/2012GL053262/abstract
And Jones et al (2013) concludes that greenhouse gases have caused between 100% and 200% of the observed global surface warming over the past 60 years, and other human influences (primarily aerosols) have offset a significant percentage of that warming via cooling effects. Natural temperature influences have had a very slight cooling effect, and natural internal variability appears to have had a fairly significant cooling effect over the past decade, but little temperature influence over longer timeframes.
The results of this study are consistent with the wide body of evidence supporting the settled science that human greenhouse gas emissions are the dominant cause of the current global warming.
http://onlinelibrary.wiley.com/doi/10.1002/jgrd.50239/abstract
Edit: Please read Dana's summary post for a more in-depth treatment:
http://www.skepticalscience.com/a-comprehensive-review-of-the-causes-of-global-warming.html
JasonB, "(i.e. the temperature would have actually declined without human GHG emissions)."
It would seem that we humans have probably done ourselves a favour by acting to avoid a decline in global temperature.
The LIA, wasn't a time I would have enjoyed living in, for me, the 40s were bad enough.
Thanks to all who replied, I'll consider the possibility that humans have caused somewhere around 74 to 122% of warming and compare it to the IPCC WG1AR5:
.
Earthling, I've responded to part of your sentiment here.
Earthling,
That would have to be a record-breaking transition from "It's not us" to "It's good". Well done. Now you just need to familiarise yourself with the consequences of AGW before deciding that it's a good thing.
Thanks to all who replied, I'll consider the possibility that humans have caused somewhere around 74 to 122% of warming and compare it to the IPCC WG1AR5:
"It is extremely likely that human activities have caused more than half of the observed increase in global average surface temperature since the 1950s."
"The greenhouse gas contribution to the warming from 1951–2010 is in the range between 0.6 and 1.4°C. This is very likely greater than the total observed warming of approximately 0.6°C over the same period. {10.3.1}"
I'm not sure what you mean by "compare", do you think your statement is inconsistent with the two quoted? The first is talking about all human activities, the second is specifically talking about greenhouse gasses and echos the comment I made earlier as well as reflecting the most recent scientific literature (which is what the IPCC is actually doing, after all), pointed out already by Daniel Bailey.
"If it doesn’t get warmer over the next years, then it likely will be blamed on the increased share of anthropogenic cooling."
Note that this statement is not from the IPCC WG1AR5. Although it was indented differently, I found the fact it was included in quote marks immediately afterwards and in the same font to be misleading. It's actually a translation of a comment on a blog post!
It also displays a desire not to understand how the system actually works and even criticises genuine scientific attempts to do so when the results don't fit the simplistic strawman that had been constructed.
As far as I can tell, the most critical measurement that would affirm or falsify the theory that manmade GHG emissions are warming the atmosphere is the TOA energy balance. In other words the total amount of energy leaving the atmosphere (SW and LW) needs to be less than the total arriving. I can understand how this is devilishly difficult to measure, but without this information there is no way to know the actual effect that greenhouse gases are having.
Although I accept the theoretical basis of AGW, I have always struggled with the lack of negative feedbacks in the models, particularly cloud feedbacks that increase Albedo and could mean that much of the SW energy that might otherwise hit the surface and be re-radiated as LW may not make it to the surface in the first place and gets reflected straight back out to space.
I have read the article below
http://onlinelibrary.wiley.com/doi/10.1029/2012GL052087/full
which is very interesting but hardly definitive on the TOA balance.
What data sets are there out there detailing incoming and outgoing flows? Are there any satellites doing the job? What is the information on cloud cover, particularly around the tropics where insolation and cloud formation is greatest?
The tropics seem to be the biggest problem, both the lack of a measured / measurable tropical Troposphere "hot spot" and the fact that tropical sea surface temperatures have not risen as the models predict. It looks like to me that there is something special going on in the tropics that the models are missing.
With the surface temperatures showing little visible trend either up or down for some years now the theory goes that the energy accumulating in the atmosphere because of the TOA imbalance must be being sequestered in the deep ocean. However if the evidence for a TOA imbalance is less than rock solid then it could simply be that there is currently a (temporary?) balance at the TOA that means that there is no extra heat being accumulated that needs to be sequestered.
[TD] Clouds both trap outgoing radiation and reflect incoming radiation. Different kinds of clouds have different net results of those two influences. It has turned out to be difficult to measure or model the overall net effect, but that very difficulty is evidence that the net effect is not strongly one way or the other, so reducing the uncertainty about the net effect will not much effect the models' bottom line of projection that warming will be happening sufficiently that we must take action. For further info (and a place for you to comment) on clouds, see the counterargument "Clouds Provide Negative Feedback", noting there are Basic and Intermediate tabbed panes for you to read. See also "Infrared Iris Will Reduce Global Warming."
The tropical hot spot is not an indicator unique to human-caused global warming, as explained in "There's No Tropospheric Hot Spot."
Matthew L - One of the most robust measures of energy imbalance is the rise in ocean heat content, which integrates/averages that TOA imbalance, and those measures indicate ongoing TOA imbalances of ~0.5-0.6 W/m2. There are multiple threads here on Sks regarding ocean heat content, and I would also point to Loeb et al 2012, 'Observed changes in top-of-the-atmosphere radiation and upper-ocean heating consistent within uncertainty'.
"I have always struggled with the lack of negative feedbacks in the models" - Observations on climate sensitivity are in the 2-4.5 C/CO2 doubling range, indicating an overall positive feedback to forcings. Current data on cloud feedback indicates it has a small and probably positive value (Dessler 2010).
"...then it could simply be that there is currently a (temporary?) balance at the TOA that means that there is no extra heat being accumulated...?" - GHG forcings have certainly not halted, OHC is still rising, particularly in the deep ocean, and observations are consistent both with models of ocean circulation (Meehl et al 2011) and measured short term climate variability (Foster and Rahmstorf 2011). Currently there is no evidence whatsoever of a TOA rebalancing.
Matthew L - My apologies, the reference I gave on OHC was for shallow waters only. More appropriate references would be to Meehl et al 2013 on short and medium term variability, Levitus et al 2012 on increasing total OHC, and the SkS discussion on heat sequestration here.
The current period appears to be one of increased deep sequestration of ocean heat, resulting in rather slower warming of the atmosphere - but when that sequestration returns to normal (or lesser) rates we can expect rather fast atmospheric warming in response.
Thanks for the responses. Enough reading to keep me going for a while there! Shame there does not seem to be any direct measurement of the TOA energy balance at the Top of the Atmosphere rather than being inferred indirectly from ocean heat content numbers - but you obviously just have to work with the tools available.
No comment on my points about the divergence between the models and the tropics - which (as you will know) is a hot topic on many blogs at the moment.
Re your comment:
"The tropical hot spot is not an indicator unique to human-caused global warming"
Is anything an indicator "unique to human-caused global warming" other than the TOA energy balance and its link to greenhouse gases? Everything else is an indicator of "warming". I have to say the argument regarding the lack of a troposphere hot spot being likely due to "data errors" sounds mighty like a cop-out to me. There are plenty of measurements, both Radiosonde and Satellite, none of which show evidence of the hot spot. I would be very surprised if they were all wrong.
I would be more impressed with the scientists if they accepted the evidence on face value and tried to hypothesise why the hot spot is not there rather than trying to find excuses as to why it might be there just, somehow, hidden.
Moderator:
"but that very difficulty is evidence that the net effect is not strongly one way or the other"
How so? My reading of "that very difficulty" is that the modellers don't know how to model clouds. Until they know how to model them they won't know whether the net effect is strong, weak, negative or positive.
The fact that they only tentatively suggest that it might be slightly positive or slightly negative suggest that they simply don't know and don't want to get it too wrong (or is that just me being cynical?).
In the absence of decent results from the models it might be useful to measure the clouds albedo / greenhouse effect directly. Is anybody doing that? Surely it is necessary anyway in order to find out if the models are right or wrong.
In my (very humble) opinion, this is the least convincing aspect of the current crop of climate models. The two fundamental forces in our weather are the wind and the clouds. To not be able to accurately model the effect from clouds has to be a prime suspect at the root of the current divergence between the model outputs and the measured temperatures.
[TD] As I already instructed, please put this further discussion of clouds on the thread I pointed you to. I will give you a little while to copy this comment over there, then I will delete this comment here.
Sigh... I don't want to orphan the excellent replies to your comment here, so I will let this comment stay. But no more off-topic comments; I will delete them.
Matthew L - "It has turned out to be difficult to measure or model the overall net effect, but that very difficulty is evidence that the net effect is not strongly one way or the other..."
Simply put, strong signals are easier to detect. If cloud feedbacks were (positive or negative) on the order of magnitude of observed direct forcings or the observed water vapor response, we would have significant evidence for it. And... we don't.
Personally, I consider cloud forcing primarily an issue on transient climate sensitivity, the speed with which the climate responds - longer term responses are fairly well constrained by the paleo data to the 2-4.5C range, and that includes any cloud response.
Matthew L:
Quite the contrary:
In addition, you state:
Your claim here appears to be directly contradicted by the papers discussed in the link you were provided by a moderator. Some choice quotes (emphasis mine in all cases):
I should like to see what sources, and in particular what papers in the literature, form the basis of your claim that "There are plenty of measurements, both Radiosonde and Satellite, none of which show evidence of the hot spot."
Specifically with regards to the accusations of "cop-out[s]", there have been two important cases in the past where apparent data contradicted model predictions - and the data were found to be wrong (vindicating the models):
(See discussions here, here, or perhaps elsewhere on Skeptical Science.)
Finally, your final paragraph in #88 states:
is, quite simply, uncalled for. Frankly it is at best very close to accusing scientists of either incompetence or malfeasance, either way without any good evidence of your own to support such a claim. What is more, it is directly contradicted by the discussion in the tropospheric hot spot thread.
In keeping with the comments policy here if you wish to go into detail in discussing the tropospheric hot spot I recommend posting in the thread linked by the moderator in response to your post #85. I also recommend desisting from any insinuations of ill intent on the part of scientists in future; persevering in such behaviour will very quickly see you ousted from participating at this site.
[TD] Thank you for supporting my frustrating (for me) attempts to keep discussions on the right threads. Everybody, continue discussion of the tropospheric hot spot on the tropospheric hot spot thread, not here. I will delete anybody's further discussion of the hot spot from this thread. Sorry to all you well-meaning responders, but you are just encouraging Matthew L to continue misbehaving.
Matthew L @89:
Your assertion that modelers don't know how to model clouds is totally unfounded.
See SkS post, New tool clears the air on cloud simulations
Matthew L
"Is anything an indicator "unique to human-caused global warming" other than the TOA energy balance and its link to greenhouse gases? "
Several things are strong indicators that narrow the possibilities for the cause of the observed warming radically.
Cooling of the Stratosphere at the same time as the Troposphere is warming is a powerful piece of evidence. If the warming was due to some other source such as increased sunlight we wouldn't see this pattern, we would see a general change increase in the atmospheric temperature at all altitudes. Stratospheric cooling is caused by the fact that more energy is being radiated to space from higher in the atmosphere than from lower down, shifting the balance of where in the atmosphere radiation to space is occurring. Only a change in the optical properties of the atmosphere could cause this.
Heat accumulation in the oceans is at least 5 times greater than the largest available heat source here on Earth. Therefore, that additional heat cannot be coming from anywhere here on Earth. That leaves as the only possible source as being a change in the Earth's radiative balance with space.
That nighttime and winter temperatures are warming as fast, in fact somewhat faster, than daytime or summer temperatures rules out heating from the sun - directly or indirectly due to changes in cloud cover for example - as heating from the sun would cause more heating when the sun shines.
With terrestial heat sources, the sun and cloud changes ruled out, that only leaves a change in the GH Effect as the remaining possible cause. And the primary change that is expected from a change in the GH Effect - Stratospheric cooling - is being observed.
[TD] For more see the counterargument "It's Not Us," including the Basic, Intermediate, and Advanced tabbed panes.
Moderator: I think the following is on-topic. My second post was written before I saw your first post directing me to other threads, so my apologies if it seemed off topic.
Composer99
Your link under the word "here" is to an article on the fact that the increase in CO2 in the atmosphere is "human-caused". That is something well proven and I do not argue with. My contention is that warming itself cannot directly be linked to human causation only indirectly if one assumes that all warming is due to the increase in CO2.
Yes, CO2 has increased caused by human emissions and yes, over the last century there has been warming. However, correlation is not proof of causation.
The global average surface (and Troposphere) temperature is currently pretty stable year to year within a ~ +/- 0.5c range up and down and has been for at least 10 years (depending on the data set). At some point the correlation will break down as the models' predicted increase in temperature moves further and further away from the actual measured temperature.
And the same could be said of numerous 10 years periods in the historical record, even the trend is what it is. Matthew is going down the up escalator, and ignoring that there is a very clear and inescapable physical mechanism for warming from increased atmospheric CO2. Same old...
Matthew L wrote "The global average surface (and Troposphere) temperature is currently pretty stable year to year within a ~ +/- 0.5c range up and down and has been for at least 10 years (depending on the data set)."
Given that the projected rise in GMST for the two decades following the last IPCC report was 0.2c per decade, stating that temperatures are stable to within +/- 0.5c for at least 10 years is pretty much what you would expect if the projection were correct!
I have to say I get a bit tetchy when people write "correlation is not proof of causation" in conjunction with GMSTs and AGW. It is as if this correllation were mainstream sciences only source of evidence regarding the causal relationship, essentially ignoring a couple of centuries of physics and a multitude of other lines of evidence (e.g. OHC).
We also wouldn't expect to see a good correlation over a period of a decade as CO2 is not the only forcing, and as well as forcings, GMSTs are also affected by internal climate variability (e.g. things such as ENSO). This means it is a bit of a red-herring anyway!
Matthew L:
You'll have to put up with some asperity from me, but trying to argue
in 2013 is like trying to argue against the germ theory of disease.
Thus:
“We know from physics theory and lab experiment that adding greenhouse gases to the atmosphere must cause warming (or at least be counteracted by cooling forcings such as reduced solar irradiance or increased concentration of reflective aerosols).”
We know from physics that, all other things being equal and in the absence of feedbacks, that adding extra CO2 to the atmosphere must cause warming.
But of course all things are never equal in a dynamic, chaotic, system such as the Earth’s atmosphere and oceans. There are feedbacks both positive and negative and the deep ocean is capable of absorbing mind bogglingly huge amounts of “excess heat” without rising very much in either temperature or height. If the deep oceans absorb that heat and barely rise in temperature then they cannot heat the atmosphere by any more than they have risen in temperature themselves (an ocean at a temperature of, say, 14c cannot heat the atmosphere to a temperature any higher than 14c) so if the deep oceans really are capable of absorbing most of the excess heat from the last 10 – 15 years as Trenberth and others have hypothesised, then they are clearly capable of acting as a huge heat / energy sink and atmospheric temperatures are likely to be almost entirely “buffered” by the oceans capacity to absorb that heat.
There is no way that the extra heat in the oceans can “come back to bite us” as in some kind of sudden rise in temperature caused by heat coming from the oceans. The oceans may vary in the amount of heat they absorb at various points in time but how much and over what time periods clearly nobody knows or we would have been able to predict the current hiatus in the warming.
“We know by process of elimination that the current global warming must be the result of an enhanced greenhouse effect: no other phenomenon we can observe can account for the behaviour of the Earth climate system.”
Well as you state earlier in your post, the greenhouse effect is what keeps our climate warm. However, the tiny changes in temperature trends we have seen over the last few decades are well within the magnitude of natural variation and/or possible feedbacks to earlier changes in temperature.
For instance we have no way of telling whether the increase in temperature 1979 - 2000 is due directly to the rise in human emissions of CO2 or is a negative feedback to the cooling that took place in the 1950’s and 1960’s (possibly long term changes in ocean currents causing changes in cloud cover) or even a negative feedback to the cooling during the LIA.
“We know, also by process of elimination and by other supporting observations (e.g. declining O2 content in atmosphere), that the only source of greenhouse gases sufficient to account for the observed increase is from human combustion of fossil fuels.”
As stated in my prior comment I do not argue with that. There is no need to rebut arguments I have not made.
Generally my problem with the current climate models is that they do not appear to account sufficiently for natural variability, either in magnitude or duration (particularly in the deep oceans’ ability to absorb heat), nor do they envisage that there can be long-acting negative feedbacks such as long acting changes in cloud cover caused by changes in wind patterns and ocean circulation.
The one niggle in all this that keeps coming back is the question “How far and for how long does the actual temperature record have to diverge from the predictions of the models before the models are falsified?”. This seems to be a continually moving goal post. 15 years ago it was 10 years. 5 years ago it was 15 years and now it seems to be 20+ years. Is there any statistical test? Maybe that is one for Grant Foster!
Matthew L @99.
Concerning that one recurrent "niggle" of yours; the question of how divergent a 'prediction' may become yet still remain valid. I do wonder if you are overlooking the true cause of your "niggle."
@85 you wrote that there has been "little visible trend (in global average temperature) either up or down for some years." What do you mean by "some years"?