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Climate Hustle

Empirical evidence that humans are causing global warming

What the science says...

Select a level... Basic Intermediate

Less energy is escaping to space: Carbon dioxide (CO2) acts like a blanket; adding more CO2 makes the 'blanket' thicker, and humans are adding more CO2 all the time.

Climate Myth...

There's no empirical evidence
"There is no actual evidence that carbon dioxide emissions are causing global warming. Note that computer models are just concatenations of calculations you could do on a hand-held calculator, so they are theoretical and cannot be part of any evidence." (David Evans)

The proof that man-made CO2 is causing global warming is like the chain of evidence in a court case. CO2 keeps the Earth warmer than it would be without it. Humans are adding CO2 to the atmosphere, mainly by burning fossil fuels. And there is empirical evidence that the rising temperatures are being caused by the increased CO2.

The Earth is wrapped in an invisible blanket

It is the Earth’s atmosphere that makes most life possible. To understand this, we can look at the moon. On the surface, the moon’s temperature during daytime can reach 100°C (212°F). At night, it can plunge to minus 173°C, or -279.4°F. In comparison, the coldest temperature on Earth was recorded in Antarctica: −89.2°C (−128.6°F). According to the WMO, the hottest was 56.7°C (134°F), measured on 10 July 1913 at Greenland Ranch (Death Valley).

Man could not survive in the temperatures on the moon, even if there was air to breathe. Humans, plants and animals can’t tolerate the extremes of temperature on Earth unless they evolve special ways to deal with the heat or the cold. Nearly all life on Earth lives in areas that are more hospitable, where temperatures are far less extreme.

Yet the Earth and the moon are virtually the same distance from the sun, so why do we experience much less heat and cold than the moon? The answer is because of our atmosphere. The moon doesn’t have one, so it is exposed to the full strength of energy coming from the sun. At night, temperatures plunge because there is no atmosphere to keep the heat in, as there is on Earth.

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 the increase is from burning fossil fuels.

And finally, the smoking gun, the evidence that proves ‘whodunit’: energy being trapped in the atmosphere corresponds exactly to the wavelengths of energy captured by CO2.

The last point is what places CO2 at the scene of the crime. The investigation by science builds up empirical evidence that proves, step by step, that man-made carbon dioxide is causing the Earth to warm up.

Basic rebuttal written by GPWayne

Addendum: the opening paragraph was added on 24th October 2013 in response to a criticism by Graeme, a participant on the Coursera Climate Literacy course. He pointed out that the rebuttal did not make explicit that it was man-made CO2 causing the warming, which the new paragraph makes clear. The statement "...and humans are adding more CO2 all the time" was also added to the 'what the science says section. 

Update July 2015:

Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial



Last updated on 12 July 2015 by MichaelK. View Archives

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Comments 351 to 351 out of 351:

  1. JH @ 348

    Thanks. I was working through this thread when I saw the ongoing discussion with Gail and could not resist putting in my two cents.

    Bob Loblaw @ 349

    I appreciate that the future increases may not be linear but it seems to me to be a good baseline with which to start. As soon as you extrapolate beyond a linear analysis my sense is that your are into the validity of the models. I personally do not have sufficient science background to understand the issues regarding their ability to predict the future.

    I was hoping to see a Red Team Blue Team debate this but I do not think that is going to happen given the information I passed on from Climatewire regarding the Trump administration having second thoughts about same.

    Earlier on in this thread there was a fascinating high level exchange going on between riccardo and PaulK who both clearly are physicists which unfortunately petered out.  But it was fascinating to see these two go head to head.  Although I could not understand the physics I did see the two of them being very honest with each other and I could get a sense of what was happening.  It is this "give and take" that would be so fascinating to watch on a Red Team Blue Team discussion. 

  2. Global warming is a fact, but the title of this article is misleading and unhelpful to the cause. It's typical in any debate that both sides overstate their claims. I regularly see and hear the claim that humans are causing global warming, but that doesn't recognize the fact that the earth has been warming for the past 20K years. What is true is that humans are CONTRIBUTING to a climate change that is already underway. In some respects that is even more scary. 


    [TD] Your claim is incorrect. See the post on the wheelchair, and then the post on PAGES 2K. Then read Zeke Hausfather's post including a graph of natural versus human influences. And the Advanced tabbed pane on the post about the human fingerprint.

    [JH] The use of all-caps constitutes shouting and is prohibited the the SkS Comments Policy.

  3. "the fact that the earth has been warming for the past 20K years"

    As the mod's note, that claim is incorrect.  The facts are, increasing carbon pollution has ended the era of stable climate.

    Per Marsicek et al 2018:

    "amplified warming in recent decades increased temperatures above the mean of any century during the past 11,000 years"

    Fig 2

    Fig 2 Legend


    And, per the discussion at Think Progress:

    during the last 5,000 years, the Earth on average cooled about 1.3 degrees Fahrenheit — until the last 100 years, when it warmed about 1.3 degrees F.


  4. gwtalbott @352 links to the composite 500 million year Temperature of Planet Earth from Wikipedia. This plainly shows the last 20ky as warming to 11.7ky bp but then-after zero warming until recent times.

    The graph does get a bit busy when it come up to the present day. The projections for RCP8.5 are about right but for some reason the Berkeley Earth Land&Ocean temperatures which somebody has added are rather misplaced. Although inexpertly applied, it is difficult not to interpret them as showing recent temperature as rising to just +0.4ºC (1960-90=0). The Berkely Earth annual anomalies (duly adjusted to 1960-90) have been knocking on +0.8ºC/+0.9ºC in recent years (the two figures dependant on the treatment of sea ice) and even decadal values are running at +0.6ºC. One wonders if the Berkely Earth additions were misplaced to discredit the RCP8.5 projections which are indeed scary - they suggest a protential global temperature for 2100 that hasn't been seen in over 10 millon years.

  5. Could someone please help me make sense of this graph in this Greg Braden video? I believe a big part is that he is leaving out post-2000 data. Any help is appreciated 

    (At the 7:40 mark of this video)

  6. funkmystic @355,

    It isn't just the post-2000 data that is missing from the graph shown by this Greg Braden character.


    The data (and graph) is from Loehle and McCulloch (2008) 'Correction to: A 2000-Year Global Temperature Reconstruction Based on Non-Tree Ring Proxies'. It has thus corrected criticisms of an earlier paper (see this RealClimate critique) but not all criticisms.

    Additional to that, the data actually ends at AD1935. (There's an ASCII file of the poltted data linked HERE.) Using a modern global surface record to fill in recent decades (BEST was to hand) and aligning it with the tag end of the Loehle and McCulloch data (1850-1935), the temperature for 2016 would be plotted at +1.2ºC which is plainly off the graph. In Greg-Braden-speak, that would be "two-times above the peak of the MWP." (In the video linked @355, good old Greg tells us this 9th-century MWP peak temperature was "three-times above where the anomaly is right now." )

  7. Funkymystic @355 , alas nobody can help you make sense of Gregg Braden's explanation of the graph he shows in his video.

    That's because Gregg Braden's ideas are way beyond California Crackpot.

    The average climate-denialist grudgingly admits [well, most days of the week] that at least some of the modern rapid global warming is caused by higher level of CO2 in the atmosphere.  But Braden is on another planet — he (in his video) claims that as CO2 goes up, it causes temperature to go down.  That the CO2 causes cooling !!   Marvellous how he can suggest that concept, while keeping a straight face.

    Braden's past history also includes other beyond-crazy ideas.  Which he tries to flesh out by displaying actual genuine scientific graphs . . . which he fails to interpret in a sane scientific way.

    For instance, the ice-core temperature/CO2 charts he displays, are stated by him to apply to the whole Earth's climate, rather than just the local regions from which the cores were taken.  Hence his nonsense about the so-called Medieval Warm Period (MWP) being hotter than today's worldwide climate.  And he is obsessed by "natural cycles" (which cannot explain the recent rocketing planetary temperature).   He gazes at cycles (whether regular or irregular, whether Milankovitch-related or not) and he seems oblivious to the basic physical fact that changes in planetary climate must be caused by actual physical effects — they don't just happen because "it's time for them to happen".

    Funkymystic, please have good read through Climate Myth Number 12 "CO2 Lags Temperature" [which you will find via the Home Page here, top left portion].   That will explain the complex feedback link between global atmospheric CO2 and the advance & recession of "ice ages" & interglacials.  You will soon see how Braden has made a colossal error in understanding things.  Doubtless Mr Braden has had these things pointed out to him on various occasions — but it seems he is not interested in scientific truth.

  8. Thanks so much MA Rodger and Eclectic!! Very helpful. Also, I think Braden should be added to the list of “Climate Misinformers” on this site. I hate to say it, but several people in my extended network of artists and musicians listen to him and think he’s telling the truth :/

  9. There are a lot of dead links here that need to be fixed (e.g. Wang 2009, for which an archived copy can be found here:

  10. The NOAA published record of global temperature change since 1880 shows two thirty year periods where global mean temperature did not rise beginning in around 1880 and around 1945.  The recent record shows that another period of probable pause in global warming began shortly after 2000.  There has been argument over the existence of a current pause, however, if a horizontal line is drawn forward from the mean temperature for 2002 it can be seen that there is about as much temperature activity below that line as above it to the present.  The obvious question is why a pause in temperature rise during the continual rise in atmospheric CO2 level?  Another point: have there been any experiments that measure the heat retention capability of the atmospheric level of CO2 rather than CO2 at a 100 percent level?  

  11. billev @360.

    I think you need to explain what you mean by "If a horizontal line is drawn forward from the mean temperature for 2002 it can be seen that there is about as much temperature activity below that line as above it to the present."

    If a horizontal line is drawn from 2002 through the NOAA data, only three of the fifteen following years lie below the 2002 average. So the "activity" is surely pretty-much all above that line. Of course, you may have a different definition for what you mean by "activity", or you could have drawn your line less than accurately.

    Your other point about CO2 "heat retention capability", the radiative forcing of CO2 is well understood and evidentially based, experiments including atmospheric measurement (eg Feldman et al 2015).

  12. Drawing a line between any arbitrarily chosen points will likely show exactly wat you want to see and is useless for figuring out what is happening in reality. Flat lines can be drawn at multiple time periods in the record, yet the overall trend is painfully obvious. There is not and there never was a pause, only variations around a trend that is resolutely up. Temperatures after the 1998 El Nino did not settle back to the pre-Nino level, the same thing is happening now following the 2016 El-Nino. The current US heat wave is showing us what the new normal is, as have all the extreme weather events accumulating everywhere in the world. The radiative properties of CO2 are very well known and the measured values for all altitudes match MODTRAN as well as one could wish for. Look it up.

  13. Indeed. Billev's non-scientific "draw a line where I want to" approach does not replace proper statistical analysis. Tamino has recently posted yet another examination of the zombie "pause" meme.

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