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.
Matthew L, you wrote the oceans "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."
Yes, almost entirely, as you can see from the first figure in this post. So what? The atmospheric temperature portion not buffered is sufficiently large to cause the atmospheric temperature rise from greenhouse gases that we have seen historically and continue to see. You seem to be implying that the amount of buffering will drastically increase starting now... well, now... well, tomorrow...
Matthew L wrote "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."
This is nonsense. Please can you tell me what is thought to have caused the sudden rise in surface temperatures in 1998?
It is also a blatant straw man, the extra heat in the oceans need not cause a sudden rise in temperatures to cause a problem. Equalising over the course of a couple of decades would be bad enough, the point is that thermodynamics tells us that the oceans and atmosphere will equalise at some point.
As to statistical tests, yes, of course such tests are possible (you need to look at the statistical power of the test).
Have you performed or seen demonstrated a statistical test that establishes that there actually has been a hiatus in GMSTs and what we are seeing is not just an artefact of the noise? If not, perhaps you need to ask yourself how you are in a position to question the statistics of mainstream science when you have not subjected your own position to a rigorous test. Do look into this question, it is likely to resolve your niggle.
Where is this idea coming from?
Do you have a cite or is this idle speculation?
Considering we can quantify the radiative forcings, either through direct measurement or by proxy, affecting the Earth's energy balance, and quantify, to a reasonable first approximation, the effects of feedbacks, over the time frame in question (1970s to present) I would have to say that this claim is simply incorrect.
The climate change Clue(do) post, and other posts here, show that we cannot account for the warming of the past 40 years without the enhanced greenhouse effect. On that basis, of course we can tell that "the increase in temperature 1979 - 2000 is due directly to the rise in human emissions of CO2".
ENSO would appear to be just such a phenomenon.
The point of this paper, as stated here many times, is that the lack of a rise in the temperature of the atmosphere recently is at least partly due to an increase in the heat uptake of the deep oceans. So they clearly believe that the heat uptake of the deep oceans can change and in fact has changed in the last 10 years.
No “drastic”extra buffering needs to occur. Because the heat capacity of the oceans is circa 280x greater than the heat capacity of the atmosphere, only a tiny change in deep ocean heat uptake has been enough to almost completely stall the previously seen rise in global atmospheric temperatures.
So what magnitude of deep ocean temperature change are we talking about that has contributed to this slowdown in the rate of global warming? An increase for the 700-2,000 metre layer of about 0.002 degrees Celsius.
This is natural variability and may well be a natural negative feedback to atmospheric and ocean surface warming (or it could be noise - research needed). This, to date, has not been included in the models and needs to be if we are to make meaningful projections of future climate change. More research needs to go into identifying and quantifying the magnitude and processes driving natural climate variability.
The warm waters below the surface of the western Pacific Ocean accumulated through solar gain because of high winds and low cloud cover in the deep La Nina in 1997 sloshed back east and came to the surface - as always happens in an El Nino. What do you think caused it?
The surface waters concerned were substantially warmer than the atmosphere over them. In the case of the deep oceans the water is somewhere around 5c, considerably colder than the surface temperatures.
As to the warming 1979 - 2000, do we know - to the nearest 0.001C - the change in the global temperature of the deep oceans (700 - 2000m) during that period?
Do we know how it changed in the period 1950 - 1979?
If a tiny change in deep ocean temperature can result in a reduction in warming 2000 - 2013, why is it not possible that variability in the rate of deep ocean heat uptake was at least partially responsible for the cooling 1950 - 1979? Or the warming 1910 - 1950?
Give Mr Trenberth more funding!
When I see an oscillation in temperatures from cooling (LIA) to warming (1850 - 1950) to cooling (1950 - 1980) to warming (1980 - 2000) to (possibly) cooling (2000 - ?) then it puts me in mind of a feedback effect. So, yes, I have used my own brain and had an idea. In your view is all speculation "idle"?
Matthew L - Atmospheric temperatures have a much higher variability than the oceans; not surprising since there is far more thermal mass in water. Attempting (as you have) to draw significance from 10-12 year air temperature trends is just the Escalator fallacy all over again.
Compare and contrast ocean and atmospheric data - while air temperatures vary a lot, they cycle around the changes in ocean energy:
As to oscillations - beyond short term variability (5-20 years or so) the climate tracks forcings, as in:
The climate just doesn't change willy-nilly, and sheer energy constraints rule out 200 year oscillations such as you seem to advocate. Understood forcing changes (including anthropogenic greenhouse gases) appear more than sufficient explanation.
Quite frankly, your post appears to consist primarily of armwaving about possibilities while ignoring evidence. Oh, and claiming models are incomplete, which while unsupportable should be discussed here.
Matthew L, you obviously didn't see the point of my question. The exchange of heat between the atmosphere and oceans is very sensitive to relatively small changes in ocean circulation, in particular ENSO. This means that the oceans can equalise the the extra heat they have taken in really quite quickly. It also means that it is not particularly difficult for small changes in ocean circulation (e.g. ENSO) to give rise to an apparent hiatus in global mean surface temperatures. It is a pity that you can't see that uncertainties apply in both directions.
As to the attribution of previous periods of warming or cooling, try reading chapter 9 of the most recent IPCC WG1 report.
I agree with more funding for Prof. Trenberth though, science in general is rather underfunded.
I also notice that you have ignored my challenge to give details of "a statistical test that establishes that there actually has been a hiatus in GMSTs and what we are seeing is not just an artefact of the noise? ". You ought to ask yourself why it is that you are unable to answer this fairly basic question and yet seem quite confident of your own position on this.
MatthewL:
Since you:
(a) have asserted your speculation as fact ("For instance we have no way of telling whether the increase in temperature 1979 - 2000 is due [...]" - your words), and
(b) have taken into account neither the responses of others in this thread nor the quantified radiative forcings applied to the Earth climate over this time frame (see a globally- and annually-averaged radiative forcing history in Figure 1 of this post, or a comparison of global mean temperature versus solar forcing here, or the inability of natural radiative forcings only to match the 20th-century observational record),
I am comfortable in describing this specific speculation of yours as idle.
Matthew L: Not all speculation is idle. Using your brain and having ideas is a good thing. It is idle speculation when you don't test your assumptions or find out what scientists who have looked into the question have found out, or tested the consequences of their ideas. I can assure you if you can produce a workable model that convincingly explains why mainstream science are mistaken about the causes of 20th century and current warming, academic journals would be keen to publish it and we would all be genuinely keen to read about it. However, that takes a lot of work (on which the climatologists have commanding head start).
"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." Don't misunderstand me---I do think that anthropogenic effects appears to be the dominant factor in global warming--but 33 Celsius is significantly warmer than 59.4 Fahrenheit. A bit over 90 degrees F, actually. Perhaps the author should take another look at his/her calculations.
Jonathon Swift @109, the conversion to differences between centigrade and fahrenheight is accomplished simply by multiplying by 1.8. You only add 32 if you are comparing absolute values, and need to account for the difference in the zero point (ie, the temperature at which ice melts, or -17.8 C degrees.
This would be plainer if instead of saying "approximately 33°C (59.4°F) cooler", the OP had said that the Earth would have had a mean global surface temperature of approximately -18 C (ie, 33 degrees below the current value of approximately 15 C), or -0.4 F (59.4 F below the current value of approximately 59 F).
This document is misleading:
1) Water vapor accounts for 50% of greenhouse "effect" and is counted as a greenhouse gas.
2) Clouds account for 25% of the greenhouse effect
3) CO2 is 20%
The graph is obviously more impressive by leaving out these 2 more significant contributors.
I also find the graph showing ocean heat content increasing to be highly questionable. Since it is 90% of the retained heat and we still know so little about the ocean, in particular the ARGO floats have been in existence for only 15 years and even they do not capture the entire ocean heat content it is impossible to believe the graph as fact. Even if we assume the graph is correct ocean heat content is enormous and obviously contributes as part of the "blanket" that is unmentioned in your blanket analysis. You seem to be implying that the atmosphere provides the full explanation for the slow movement of temperatures on the earth when a large part clearly belongs to the oceans which store 1000 times the heat content of the atmosphere.
You are very good at leading the first parts of the argument, i.e. the greenhouse effect and the increase in co2. However, the conclusion that our temperature increase over the last 50 years is due to co2 is not proven because you exclude 75% of the greenhouse gases and their changing composition, you exclude the ocean which is 99.9% of the heat storage. If 90% of the heat went into the ocean and the ocean did not re-radiate that heat back in some form the oceans would rise negligibly in temperature and the atmosphere would be similarly little affected.
Also a smart student would notice another big hole in the argument. The earth is volcanically active and has a hot magma layer that is leaking into the environment under the ocean and the surface. There are also other concerns as pointed out by the IPCC which include albedo and aerosols which could have major impacts on the heat retained by the earths atmosphere.
Your argument appears oriented to a 3rd grader not a high school student even. A smart science high school student would see the missing pieces or be very upset when told you were excluding more than 75% of greenhouse gases and didn't mention the incredible role of the ocean. I think you can still make the argument but it has to include these complexities.
Something I didn't understand from the beginning was the hubris of climate scientists to speak as if this is so simple even though it is plain even a high school student could see the holes in the argument. The point you make that CO2 contributes heat is fine (with my caveats) but to go beyond that and ascribe it as the sole reason for temperature variation is reaching and weak. You simply rush to the point without explaining the complexity of how the system will respond to the changes. I think you are better off if your purpose is to show the effect of CO2 is proven to leave off the latter part of your argument.
It would also be very important to show a graph of how the radiation at the surface has changed because of the changing CO2. Showing a single graph implies that you could simply leave all the other elements the same and move the co2 contribution up or down exactly based on the movement of co2. Having such a graph of real data would be the "proof" that would complete this argument nicely.
jmath, lets start with the first issue. Water vapour is not a long lived GHG, the amount of water vapour the atmosphere contains depends on temperature (the Clausius–Clapeyron relation). Thus while water vapour may accont for X% of the pre-industrial greenhouse effect, that doesn't mean it accounts for the same percentage of the enhanced greenhouse effect that gives rise to the recent increases in temperature. Thus it seems to me to be correct not to give it a great deal of a mention in a discussion of global warming (i.e. the increase over pre-industrial temperatures).
Now anthropogenic emissions of long-lived GHGs can be expected to result in warming, which will in turn support higher concentrations of water vapour as a positive feedback. However, this additional water vapour is only present in the atmosphere as a result of anthropogenic emissions.
Now if you can provide a calculation that shows how much of the observed global warming has come from the additional water vapour, then do present it here.
jmath... [sigh] It's amazing to me how many times all these issues have to be explained and repeated. If you'll take some time to read through the other materials on this website, you'll actually find answers to everything you've mentioned here.
More interesting to me is your approach. You seem to think you're being "skeptical" of the science, but it's clear that's not the case. You've certaintly identified several areas of climate science which you don't yet understand, and that's good. But what you immediately do is jump to the conclusion that the entire field of research is somehow mistaken and you can somehow, even though you have very limited understanding of the research, see the truth for what it is.
You need to start thinking of those "gaps" in the science as being your shortcoming, and not that of the researchers. There are many 10's of thousands of research papers out there on the subject of climate change. My suggestion is, if you're genuinely interested in understanding the answers to the questions you raise, go read the research. You don't even need to rely on SkS to deliver it to you. Go to google scholar and start searching the published materials on what you don't yet understand.
Get a few hundred of those papers under your belt, then come back and you can discuss these issues a little more intelligently.
jmath, I'll emphasize what Dikran and Rob have said, and I'll add that there's a document that summarizes climate science. It directly references 20,000+ publications, and those directly reference tens of thousands more. It's a well-ordered document, and it was written by ~850 unpaid experts who publish regularly in their respective sub-fields. It was peer-reviewed by several thousands, and the review resulted in 150,000+ comments. You can find this unprecedented "state of the science" document right here.
If you want a historical look at how the science has developed over the last 150 years, you should read Spencer Weart's The Discovery of Global Warming in hypertext at the American Institute of Physics website.
Beyond that, could you provide evidence for this: "The point you make that CO2 contributes heat is fine (with my caveats) but to go beyond that and ascribe it as the sole reason for temperature variation is reaching and weak"?
Jmath's rich inventory of superficially impressive but fundamentally vacuous talking points as well as prickly presentation ("hubris, "third grade" etc.) suggest it's highly unlikely any useful communication will flow in that direction because jmath's dominant subtext here isn't about science but policy implications.
That said and imagining for a moment that jmath were actually here to seek information through dialogue, Rob's basic point is worth repeating:
"I don't understand it" does not equate to "it's wrong."
Regardless of one's willingness to accept what science tells us is happening to Earth systems thanks to CO2, ignorance isn't a substitute for understanding. Stop being ignorant and see where that choice leads.
It shouldn't be necessary to point out such an obvious thing; most of us have struggled in one course or another in school and have probably rarely or never confronted an instructor with news such as "your linear algebra is wrong because I don't understand it." More typically one would seek more information and more skill so as to surmount difficulty and frustration. That of course won't necessarily pertain if passing the course isn't the primary objective.
I think we need to avoid dogpiling here. Jmath's attitude to the correctness of the science will be evident in his response to my question on the first of the issues he raised. We shouldn't expect him to be able to answer it immediately, so lets give him time to perform some background reading.
Jmath, this advice is genuinely well intentioned: You are much more likely to get a hostile response to the issues you raise if you present them in an arrogant and hostile manner. If you think an article is wrong, it could be that this is because you don't understand it rather than because it actully is wrong. If you point out non-existent errors with hubris, you will make yourself look silly. If you ask questions, or ask for explanations, you will make yourself look like a true skeptic and student of science.
JasonB "But pointing it out in this context is like a driver complaining to the cop who just pulled him over for speeding that it's the turbo's fault that he was going so fast and not the position of his foot on the accelerator."
The graph presented was not about what was causing warming. It was about what the relative contributions of the greenhouse gases. It was an effort to demonstrate that CO2 is important. Including water vapor and clouds s necessary just to show the relative contributions.
If you want to talk about what was causing the warming you would need to show how each of those components changed over some time and show that CO2 was the dominant contributor.
[JH] Please explain why you are responding to JasonB.
The period 1910-2014 has 4 epochs of interest. From 1910-1940 was a period of rapid warming without significant increase in CO2. The IPCC also agrees by selecting the period after 1950 that it agrees the pre-1945 time was not a period of rapid greenhouse gas accumulation yet the warming in this period corresponds roughly to the warming with CO2 from 1975-1998. The period 1945-1975 and the period 1998-2014 both had rapid increase in CO2 yet no appreciable temperature change. Therefore 3 of the 4 epochs and 75% of the period from 1910 - 2014 contradict the idea that CO2 is the primary driver of temperature. I have not seen adequate explanations for these variances. Using the period 1975-1998 over and over again as proof is not convincing as the other periods appear to contradict this. The ideal thing would be to show how during the period 1945-1975 CO2 increasing was apparently counteracted by other gases. Oh wait, no gases changed so so I'm confused. You are trying to make it easy for people to understand but you fail to understand that people are also aware of the obvious problems. 1945-1975 was described as a period of high aerosols yet we are recently discovering that it was primarily an ocean current phenomenon previously not understood that caused that period. Neither of these explanations however fits with your tidy little charts. So, if all I knew about the theory was what you wrote above I would be at a complete loss to explain anything outside the period 1975-1998.
[JH] More than one of our regular readers have responded to the issues and questions you posited in you initial post. Please have the courtesy to acknowledge their responses and let them know if their responses have satisfied you. Ignoring responses and proceeding to a new topic suggests that you are not here to learn, but to stir up trouble.
Jmath,
JasonB made his post you are replying to in July 2013. He may not see your comment here. If you answer the recent comments you get more interaction.
All: If he is willing to do so, I suggest that we task Dikran Marsupial with the responsibility to respond to jmath on this comment thread.
Agreed with John Hartz... Let's let Dikran take the lead here.
jmath@118 I have answered the first of the points your raised in your first post on this thread. Scientific discussion requires depth, rather than merely breadth, so please do not raise other issues until the more fundamental ones have been dealt with first and we have reached agreement on those. To do otherwise is essentially a Gish Gallop, which is usually an indication of rhetorical intent.
I have explained why water vapour being responsible for 50% of the pre-industrial greenhouse effect does not imply that it is responsible for 50% of the post-indistrial warming. Please provide the details of your calculation of the proportion that actually is due to water vapour (hint: climate sensitivity is not 1).