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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 (DOE Data Explorer). 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

Printable Version  |  Offline PDF Version  |  Link to this page

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Comments 201 to 225 out of 417:

  1. Razo @200:

    "...all the research in global warmimg would not be necessary if this rebutttal was indeed proof"

    First, the rebutal is an attempt at science communication, ie, to present scientific information in a readilly digestible form.  No matter how good it is at that, it can be no substitute for scientific research.

    Second, the evidence summarized in this post establishes a prima facie case that the current warming is anthropogenic.  Scientists are not happy with prima facie cases, and test them rigorously as they should.  The prima facie case was established in a fairly rigourous form by the mid 1960s, and all the testing since then has failed to falsify it.  Indeed, it continues to be tested, because that is what scientists do, but the vast majority of climate research is now focussed on expanding on less well established aspects of climate science.  This is something Raz would know if he knew anything about the scientific method, or climate science.  He is either making a case from his own ignorance, or (at best) being deliberately obtuse for rhetorical advantage.

    It is, however, very kind of him to so prominently flag that his an AGW denier intent on publishing talking points rather than a genuine enquirer or person interested in reasoned debate.

    "The question is 'what impact does man's CO2 producction have' and thus 'emperical evidence of his impact on climate change'."

    Harries (2001) (as shown in the intermediate version of the OP) directly addressed that issue, and showed the following differences in IR brightness temperature: 

    The first thing to note is that the increase in concentration of all the listed gases is anthropogenic in origin, so that even if methane had more effect it would be irrelevant.

    The second thing to note is that the area of reduced emission due to methane is slightlly larger than that of CO2.  That, however, is misleading on two counts.  First, the spectrum shown does not show the full CO2 band, showing, in fact, only one wing (see spectrum below).  With the full CO2 band shown, the impact of CO2 would be approximately double that shown.  Second, the graph shows the "brightness temperature".  The brightness temperature is the emission spectrum so scaled that black body curves are shown as straight lines parallel with the x-axis.  Because the region of the spectrum in which methane is active has much less IR activity at Earth temperatures than does the area in which CO2 is active, that greatly inflates the area in the Methane portion of the spectrum relative to the CO2 portion.  We can see from the spectrum shown below, that approximately doubles the apparent impact of methane.  Combined these factors inflate the apparent effect of methane by a factor of four.  Correcting for this it is very apparent that CO2 has an impact around 4 times that of methane over the time period covered by the chart (27 years).  That short time scale further inflates the apparent effect of methane, which is oxidized to form CO2 plus water over about a thirty year time frame in the atmosphere.  Thus while Harries (2001) shows near the full forcing effect of methane since the preindustrial, it shows only a fraction of the effect of CO2.

    "...methane is heavy, and would stay near the surface."

    Methane (CH4) has a molecular mass of 16, ie, half the molecular mass of oxygen (O2), and 36% of that of CO2.  The claim that it is heavy is the opposite of the truth.  Further it is irrelevant, in that atmospheric motion is sufficient to keep even the heavy CO2 in near constant mixing ratios (within 10-20 ppmv) up to the meso-sphere.

    "It also been all over the news now that temperatures have not risen in the last 15 years."

    The HadCRUT4 OLS for the last 15 years (Jan 1999-Dec 2013) was 0.66 +/-0.13 per decade.  That is, it was positive, but not statistically significant.  It is similar if we take it from May 1999 to April 2014.  Indeed, all major global temperature series are positive (but not stastically significant) over that period.  Clearly Razo has accidentally cherry picked the wrong interval.

    Perhaps he really meant the last 16 years.  That would have included the 2nd largest (SOI) or largest (temperature based ENSO indices) El Nino as the start year, but alas the trend remains positive but not statistically significant if you do.

    To get a negative trend, you have to reduce the trend to 13 years, starting in Jan 2001, which gives you a HadCRUT4 trend of -0.011 +/- 0.145 C per decade, though it remains stubornly positive in temperature series that actually include the entire globe such as Gistemp.  Even then, and cherry picking our temperature indice to get a negative, trend it is misleading to say "the temperature has not risen" in the last thirteen years.  The trends to Dec 2007, or Dec 2010, are both positive.  Ergo, the temperature has risen, then fallen back.  Specifically, it has fallen back in 2008 (due to a strong La Nina and a solar minimum some solar experts consider to have been as low as the Maunder Minimum), and in 2011-2012 (due to the strongest La Nina on record based on the SOI index).  It appears not to be as usefull to Razo to say that two recent short term cooling events have temporarilly wiped out a decades worth of global warming, so he chooses a less accurate form of expression. 

  2. Sorry, I mistyped the HadCRUT4 trend for the last 15 years as 0.66 C/decade rather than the correct 0.066 C per decade.

  3. Hey Tom,

    You're just putting words in my mouth. You wanna critisize me for not being exact, just Relax. FYI I do have a degree in a scientific field, I have bben published, and I didn't know what prima facie means.

    Anyway, this is the article I was reffering to

    http://www.nature.com/nclimate/journal/v4/n3/full/nclimate2106.html

    They say they found a cooling trend. And is was in all the papers around February 10, 2014, such as

    http://www.nature.com/nclimate/journal/v4/n3/full/nclimate2106.html


    Thank you for the information about methane.

    Response:

    [JH] Pease tone down the rhetoric. 

    Please note that posting comments here at SkS is a privilege, not a right.  This privilege can be rescinded if the posting individual treats adherence to the Comments Policy as optional, rather than the mandatory condition of participating in this online forum.

    Please take the time to review the policy and ensure future comments are in full compliance with it.  Thanks for your understanding and compliance in this matter.

    [PS] fixed links

     

  4. Razo @203:

    1)  I did not put words into your mouth.  I quoted you verbatim.

    2)  I am astonished that you do not know the meaning of "prima facie".  As you do not, you need to learn it as it is a useful concept in understanding the practise of science.  Of course, your intention was a rhetorical trick to allow you to criticize the OP without substance, so it may not help you.

    3) Your precise words were:

    "It also been all over the news now that temperatures have not risen in the last 15 years."

    The paper for which you provide a link discusses the so-called "hiatus" since 2001, ie, the last 13 years.  Thank you for indirectly confirming that you were exagerating the length of time involved.  Further, to that, it is irrelevant how frequently a paper is echoed in the press.  

  5. Razo, did you actually read the England et al papers that you quote? How come you have changed a slowing in the rate of warming into a cooling trend?

    From the first "Here we show that a pronounced strengthening in Pacific trade winds over the past two decades—unprecedented in observations/reanalysis data and not captured by climate models—is sufficient to account for the cooling of the tropical Pacific and a substantial slowdown in surface warming through increased subsurface ocean heat uptake."

    and the second...

    "A variety of mechanisms have been proposed to account for this slowdown in surface warming" and "This hiatus could persist for much of the present decade if the trade wind trends continue, however rapid warming is expected to resume once the anomalous wind trends abate."

    The papers conclusions do not appear to match your perception.

  6. scaddenp, I must confess to not reading it thouroghly enough. I seem to remember it differently, or was relying on journalists interpretations too much. For that I apologize. But nevertheless Fig 1 does describe cooling over part of the last decade

    "Observations of global average surface air temperature (SAT)
    show an unequivocal warming over the twentieth century1,
    however the overall trend has been interrupted by periods
    of weak warming or even cooling (Fig. 1)."

    I also do criticize global models for not capturing decade long cooling intervals very well, and not predicting trade winds. I am not in the climate field, but I do have experience with numerical modelling. I simply think GCM should be able to predict trade winds and ocean warming.

    Response:

    [JH] Your "experience with numerical modeling" is nor a substitute for doing your homeowork on GCMs before proceeding to critique them. Please stop flying blind and look before you leap.

  7. Razo wrote "I also do criticize global models for not capturing decade long cooling intervals very well"

    Criticising models for not being good at something they are not designed to do and for which they do not claim a high degree of skill suggests that you have not put much effort into finding out what models do and how they work.  I criticise them for not being able to predict volcanic eruptions.  This is about as meaningful a criticism as Razo's ;o)

  8. I have posted this link elsewhere, but I post it here to show that others share my critism of climate modeling not predicting recent stagnation in global warming. Also he considers the stagnation to be a 15 year period from 1998 to 1012.

    http://www.academia.edu/4210419/Can_climate_models_explain_the_recent_stagnation_in_global_warming

  9. Razo can models be reasonably expected to predict the stagnation of temperatures over a 15 year period?  The answer is essentially "no, but hey can be expected to predict that such stagnations will happen evey now and again (but not when)" and indeed they do, see Easterling and Wehner.

  10. Razo @208:

    1)  von Storch et al (unpublished*) shows a temperature increase over the 15 year interval at 40% of what they claim to be the preceding 30 year trend in the only fully global temperature series used (GISS).  They state:

    "Estimates of the observed global warming for the recent 15-year period 1998-2012 vary between 0.0037 C/year (NCDC), 0.0041 C/year (HadCRUT4) and 0.008 C/year (GISS).  These valuesare significantly lower than the average warming of 0.02 C/year observed in the previous thirty years1970-2000."

    We immediately face problems in that 1970-2000 inclusive is a 31 year period so we do not know which trend they used.  However, the Jan 1971 - Dec 2000 (Jan 1970- Dec 1999) trends are:

    GISS: 0.166 +/- 0.058 (0.164 +/- 0.58) C/decade

    NOAA: 0.167 +/- 0.054 (0.165 +/- 0.54) C/decade

    HadCRUT4: 0.174 +/- 0.056 (0.168 +/-0.057) C/decade

    Which ever trend you choose, von Storch et al have exagerated the preceding thirty year trends by 15-20%, thereby exagerating the extent of the slow down in temperature increase.

    Further, they give incorrect values for the 15 year trends as well.  The actual values are:

    GISS: 0.073 +/- 0.147 C/decade

    NOAA: 0.04 +/- 0.137 C/decade

    HadCRUT4: 0.047 +/- 0.14 C/decade

    Consequently the actual (reported by von Storch et al) ratio of trends using 1971-2000 for the 30 year trends are:

    GISS: 0.44 (0.4)

    NOAA: 0.24 (0.185)

    HadCRUT4: 0.27 (0.205)

    They therefore exagerate the slowdown by 10 or more percent.

    2)  von Storch et al avoid mentioning ENSO events to an extraordinary extent.  There only reference is a casual mention that models have difficulty modelling ENSO events.  He nowhere mentions the fact that 1998 was one of the largest El Nino events on record which, coming at the end of the thirty year trend and the start of the 15 year treand, exagerates the former while depressing the later.  Nor does he mention the strong La Nina in 2008, nor the record La Nina (SOI Index) of 2011/2012.  Nor does he mention the strong La Nina in 1974/75 (second strongest on record in the SOI).  These La Ninas exagerate the 30 year trend, and supress the 15 year trend.

    As a side note, von Storch et al's claims about the inability of models to model ENSO events are not strictly true.  They were true of about half of models used in the CMIP3 intermodel comparison and the IPCC AR4; but it is not longer true of those used in CMIP5 and AR5.  What models cannot do is generate ENSO events with the same timing as real ENSO events for the simple reason that that timing is essentially random.

    3)  von Storch et al make no allowance for the fact that 1998 was well above the temperature trend, or that 2011/12 by virtue of the La Nina were presumably well below it.

    This is extraordinary.  It means his entire argument is analogical to a person trying to prove that water does not settle to the same level because lines drawn from a point at the crest of a wave to other parts of the water surface have, on average, a negative slope.

    Of course trends drawn from a peak well above the trend do not have the same statistical distribution as trends drawn from points on the long term trend line.  For them to have the same statistical distributions, the series of data points (temperature records) must be a random walk.  That the twentieth and early twentieth temperature record constitutes a random walk is a flat contradiction of the predictions of the models and climate scientists - yet that is the implicit assumption in von Storch et al's criticism.  This flaw is made worse by both the fact that von Storch et al use a trend not only from a "peak", but to a "trough", and by the fact that they eschew any discussion of this issue.

    IMO the statistical analysis in von Storch et al falls to the level of pseudo-science.  I was greatly disappointed to see that von Storch had sunk that low.

     

     

    * The article by von Storch et al was never published in any journal, but merely distributed on the internet.  It follows, of course, that it is not peer reviewed.

  11. Razo: Here are some more facts about GCMs for you to ponder.

    Climate Models Show Potential 21st Century Temperature, Precipitation Changes
    Posted Sep. 27, 2013, NASA/GISS

    "New data visualizations from the NASA Center for Climate Simulation and NASA's Scientific Visualization Studio at Goddard Space Flight Center, Greenbelt, Md., show how climate models used in the new report from the United Nations' Intergovernmental Panel on Climate Change (IPCC) estimate possible temperature and precipitation pattern changes throughout the 21st century.

    "For the IPCC's Physical Science Basis and Summary for Policymakers reports, scientists referenced an international climate modeling effort to study how the Earth might respond to four different scenarios of carbon dioxide and other greenhouse gas emissions throughout the 21st century. The Summary for Policymakers, the first official piece of the group's Fifth Assessment Report, was released Fri., Sept. 27.

    "This modeling effort, called the Coupled Model Intercomparison Project Phase 5 (CMIP5), includes dozens of climate models from institutions around the world, including from NASA's Goddard Institute for Space Studies."

  12. Razo - WRT Von Storch and the avoidance of ENSO effects on trends, it is notable that: if you select as an endpoint an extrema value from a time series, the statistical significance of anything terminating there is much much lower. 

    There's a good discussion of this over on Tamino, under Cherry-p. Von Storch followed in the trail of many a pseudo-skeptic, and selected the 1998 El Nino (3-sigma in scale) as one of his trend endpoints. Without noting the fact that it was indeed a time series variation extrema.

    In the presence of such selection of an extrema, the required p-value for statistical signifcance can be 10x normal!! That's because in any system with noise you can find short trends up and down, meaning once you start selecting extrema endpoints, you need far more supporting data to make your claim(s). Supporting data that simply doesn't exist in the temperature record.

    1998 trend claims are the essence of cherry-picking, of selecting a subset of data that appears to support a claim while ignoring the remainder of the data that contradicts that claim. It's a "fallacy of selective attention, the most common example of which is the confirmation bias", and such claims are logical fallacies.

  13. Just to add to KR's comment, if you look at a comparison of the AR4 SRESA1B model ensemble with the observations (courtesy of RealCLimate):

    you can see that the observations were further into the upper tail of the envelope of model runs than they are into the lower tail of the distribution in recent years.


    Now, ask yourself why the skeptics were not interested in pointing out the model observation "inconsistency" in 1998.  Cherry picking indeed, the 1998 one clearly wasn't ripe. ;o)

  14. Note: I am not stating that Von Storch is a pseudo-skeptic, just that the selection of 1998 is statistically ill-considered, and that claims of trends from that time point are not supported by the data. 

    Further discussion on this topic (i.e. no warming since...) should probably move to this thread, as it is somewhat off-topic here.

  15. The Earth's tempurature is 33 degree lower than if no atomosphere and all evidence suggested that CO2 the primary element to create green house blanket. Arround the time of industrial revolution, avarage tempurature is less than 1 degree lower than now. Also the amount of CO2 was 280 ppm and it is almost 400 ppm now.  One thing I  struggle to understand is why temprature raised only less than 1 degree since industrial revolution. If the green house blanket has warmed the Earth by 33 degree in 280 ppm, would 120 ppm increases of CO2 attribute larger temprature variation ? If not what is factors to supress a large margine of warming ? 

  16. Souichi Tsujimoto @215, Schmidt et al (2010) showed that with CO2 concentrations at 339 ppmv (1980 levels), CO2 contributes 20% of the 155 W/m^2 total greenhouse effect, or 31 W/m^2.  The increase in CO2 forcing from preindustrial to 1980 levels is 1 W/m^2, resulting in a net increase in total CO2 forcing from 30 to 31 W/m^2 over that period.  The further increase to the current date is another 0.9 W/m^2, meaning the total increase from the preindustrial to the current date is from 30 to 31.9 W/m^2.  This small increase in forcing as a result of a large increase in CO2 concentration is a result of the fact that you need to double CO2 concentration to obtain a 3.7 W/m^2 forcing.  As a result of that, we know that the increase in temperature is in the right ball park to have been caused by the increase in CO2 levels.

    Of course, there are further complications.  The expected increase in temperature at equilibrium from an increase in CO2 from 280 to 400 ppmv (pre-industrial to current) is 1.55 C.  That has not occurred as yet primarilly because the ocean acts as a thermal fly wheel, slowing the changes in temperature due to changes in forcing.  Of course, that expected increase includes feedbacks, which are partly uncertain, which is another complication.  But the largest cause of the apparent disparity is a failure to allow for the fact that CO2 forcing increases by a constant amount for each doubling of CO2. 

  17. Here is what I believe you are missing. You claim: "Humans are emitting more than twice as much CO2 as what ends up staying there. Nature is reducing our impact on climate by absorbing more than half of our CO2 emissions." It's true. But we have also degraded the ecosystem services by ~1/2 as well...with modern factory farming style agriculture. The hocky stick isn't fossil fuel emissions, it's agricultural degradation of the soils, particularly carbon. Sure emissions also help somewhat, but even without a single fossil fuel drop, degrade the ecosystem services and we get global warming. It is us doing the harm, so it is AGW. But you guys are looking at the wrong source. Here is your evidence:

    http://news.nationalgeographic.com/news/2005/12/1209_051209_crops_map.html

  18. Change in Land use is accounted for - see the IPCC report. Your thesis is not compatible drop in O2 and isotope ratio of CO2 in atmosphere. Some discussion of that here. I think you may be underestimating the role of oceans in CO2 cycling compared to land. You can get references to studies doing the maths of CO2 accounting from the IPCC WG1 chapter 6.

  19. RedBaron @217, adding to scaddenp's response, here is the graphic showing reservoirs and fluxes of CO2 from the IPCC (Fig 6.01):

    Fluxes are shown in by the arrows, reservours by the boxes.  "Natural" (ie, preindustrial) values are shown in black, changes since the preindustrial in red.  Units are in terms of Petagrams of Carbon per year for fluxes, and Petagrams of Carbon for reservoirs, with a Petagram equalling 10^15 grams, or a billion tonnes of Carbon (Gigatonnes).

    So, looking at the reservoirs, we see that the combined atmosphere/ocean reservoir has increased by 395 Gigatonnes of Carbon, while vegetation has decreased by 30 gigatonnes of carbon, and fossil fuel and cement stocks have decreased by 365 gigatonnes of carbon.  That is, the combined effect of land use changes and the CO2 fertilization effect has resulted in only 8.2% of the total increase, with fossil fuels accounting for the rest.

    The total emissions from fossil fuels and cement manufacture is well known.  For it to be even matched by emissions from LUC, you need a new, and very large reservoir to store the excess CO2.

    There is additional evidence that the primary source of the increased CO2 comes from fossil sources.  Of these the most important is the decline in C14 concentrations.  Another is that there is a very strong correlation between cumulative fossil fuel emissions and CO2 concentrations:

     

    Over the period of observations at Mauna Loa, that correlation is 0.9995 with an r squared of 0.999.  That correlation actually decreases slightly when emissions from LUC are included, probably because estimates of those emissions are not as accurate as those for fossil fuels.

  20. @ scaddenp & Tom Curtis,

     I am well aware of the IPCC report and the charts. I even think most of it is relatively good. There are however several flaws that change the overall picture. This for example is potentially quite flawed.

    "It is very likely, based on new experimental results {6.4.6.3} and
    modelling, that nutrient shortage will limit the effect of rising
    atmospheric CO2 on future land carbon sinks, for the four RCP
    scenarios. There is high confidence that low nitrogen availability will
    limit carbon storage on land, even when considering anthropogenic
    nitrogen deposition. The role of phosphorus limitation is more uncertain.
    Models that combine nitrogen limitations with rising CO2 and
    changes in temperature and precipitation thus produce a systematically
    larger increase in projected future atmospheric CO2, for a given fossil
    fuel emissions trajectory."

     

    another flaw is the fixation with forests. The primary historical carbon fixation is not forests. It is grasslands. The fixation is not in vegetative material, but rather exudates. Forests do have a moderating effect, especially as seen now with a new balance being made as fossil fuels emissions increase. But ultimately the long term effect of forests is near neutral, as a much higher % of the products of photosynthesis are above ground. A relatively small % is sequestered, because ultimately above ground and near surface carbon compounds are released in the short term carbon cycle by way of the processes of decay. So you get a net effect of maybe 2% +/-? Depending on how long a time frame you look? Grassland sequestration is completely different. Those grasses and forbs sequesture as much as 37% directly deep in the soil by direct exudate production. The carbon is sequestered far longer than near surface and above surface carbon. In the thousands of years if undisturbed. That's why historically molisols have far deeper A horizons with much higher SOC than alfisols (even old growth forst alfisols).

    But, while only about 1/2 the land suface is under agriculture and there are still forests, the grassland/savannas of the world (primary terrestrial carbon sequetration of the Earth) are largely either extirpated like the tallgrass prairie, or under poor management and no longer functioning as a carbon pump. Pretty much all of it is gone. So the secondary buffers (forests) are helping to take away 1/2 the excess carbon from fossil fuels. But the primary terrestrial buffer to the carbon cycle is nearly completely gone or disfunctional due to poor management.

  21. Redbaron - your quote applies to potential scenarios in the future, not to current source of CO2 in the atmosphere. I am not sure why you think there is a fixation with forest in the carbon budgets given the soil carbon storage in grassland is well known. The change in grassland is explicitly calculated. While land use change is part of AGW, the evidence to date is that is small compared to fossil fuel burning. The check on the calculation is the carbon isotopic concentration in the atmosphere. You need a massive change in carbon fluxes for this to be significant compared to FF.

  22. RedBaron @220, with respect, your anonymous, non peer reviewed analysis consisted of a map showing the proportion of the land surface currently under agricultural production.  But now you want us to give a pass on that analysis, and question the expert, public and peer reviewed analysis of the IPCC based on your say so?  I think you have radically disparate standards of evidence depending on whether or not you agree with a theory.

    Further, you simply neglect the force of the case as presented by the IPCC.  The IPCC shows changes in reservoirs with 90% uncertainty intervals.  Specifically, changes are as follows:

    Atmosphere + 240 +/- 10 GtC

    Ocean  + 155 +/- 30 GtC

    Fossil Fuels - 365 +/- 10 GtC

    It follows that the change of all other reservoirs combined (ie, vegetation plus soils) is 30 +/- 33 GtC from that information alone (assuming the data is independent).  Calling into questin the partition between soils and vegetation in no way allows the sum of change in soils plus vegetation to exceed those limits.  So, until you find the evidence that the ocean is absorbing CO2 at several times its rate as reported by the IPCC, you do not have a case.  Indeed, looking at the uncertainties, it is more likely that vegetation plus soils have increased in CO2 content than that they account for even 20% of the atmospheric and ocean increase, let alone most of it.

  23. Just one more point, one of the factors showing it is the consumption of fossil fuels leading to the increase in atmospheric CO2 has been the reduction in the O2 content:

    As can be seen, given known emmissions from fossil fuels, measured delines in O2 and increases in CO2 concentration, the equations only balance if the combined effect of LUC plus natural uptake by the land (vegetation plus soils) decreases the CO2 concentration over the period of measurement.  That is consistent with total anthropogenic emissions from LUC being positive, but only if they are less than natural sequestration by vegetation and soils.  That is again inconsistent with RedBaron's thesis.

  24. Red Baron, the factor you describe is already taken into account by the IPCC (and all other carbon cycle researchers) and it is described as "land use change emissions" (as pointed out above by scaddenp).  You can get data on on this from the Carbon Dioxide Information and Analysis Centre (CDIADC).  One of the most surprising things I found out about climate change when I first looked into it just how late cumulative anthropogenic emissions from fossil fuel use finally overtook those from land use change.  The answer turns out to be about 1965. 

  25. I'll try to address you guys points one by one. First scaddencamp, you said: "Your thesis is not compatible drop in O2 and isotope ratio of CO2 in atmosphere." Actually it is compatable, even the IPCC report says as much. C12 isotope ratios are consistent vegetative sources, whether fossil, or in the biosphere. "With a very high confidence, the increase in CO2 emissions from fossil fuel burning and those arising from land use change are the dominant cause of the observed increase in atmospheric CO2 concentration." p 493

    But what is lacking in the IPCC report is the Land Use data is far too crude. There is little analysis of land use changes within agriculture. In other words IPCC says this:

    "With a very high level of confidence1, the increase in CO2 emissions from fossil fuel burning and those arising from land use change are the dominant cause of the observed increase in atmospheric CO2 concentration. About half of the emissions remained in the atmosphere (240 ± 10 PgC) since 1750. The rest was removed from the atmosphere by sinks and stored in the natural carbon cycle reservoirs. The ocean reservoir stored 155 ± 30 PgC. Vegetation biomass and soils not affected by land use change stored 160 ± 90 PgC. {6.1, 6.3, 6.3.2.3, Table 6.1, Figure 6.8}"

    But not factored was the "land use change" that was a result of the green revolution. The Green Revolution refers to a series of research, and development, and technology transfer initiatives, occurring between the 1940s and the late 1960s that radically changed how agriculture is practised world wide. That's the same flaw in the graph posted by Dikran Marsupial. Agricultural land that changed methodology but was prior agricultural land and is afterwards agricultural land is no counted as "land use change". However, there is a radical change in the carbon cycle that accompanies that change in methodolgy. Specifically the most radical change is in soil health, primarily carbon. If you change that graph to include changes within agriculture, I believe you'll find that instead of crossing in 1965 you'll see it continuing to be the primary cumulative anthropogenic emissions.

    Further confirmation of this flaw can be seen in this quote from the IPCC report. "Since 1750, anthropogenic land use change have resulted into about 50 million km2 being used for cropland and pasture, corresponding to about 38% of the total ice-free land area (Foley et al., 2007, 2011), in contrast to an estimated cropland and pasture area of 7.5 to 9 million km2 about 1750 (Ramankutty and Foley, 1999; Goldewijk, 2001). The cumulative net CO2 emissions from land use changes between 1750 and 2011 are estimated at approximately 180 ± 80 PgC (see Section 6.3 and Table 6.1)" They have the numbers right for the land use change to agriculture, but are missing the land use changes within agriculture as methodologies change.

    Response:

    [JH] Formatting glitch fixed.

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