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3 Questions about Greenhouse Gasses

  1. Jul 9, 2009 #1
    I like to think that I'm pretty good at sorting out the BS from the actual facts, but with global warming, I'm having a hard time determining what is actual science, and what is politicized pseudo-science. Just for reference, I have generally accepted that human actions have been responsible for the current changes in the Earth's climate.

    However, I recently heard a statistic that put a small seed of doubt in my mind. The statistic stated that out of the total greenhouse gas output per year, humans are only responsible for 3% of that amount. The rest is due to natural processes.

    Question 1. Is this true? Like I said, it's hard to know what information out there is reliable

    Question 2. If this is true, how much of an effect does that 3% have? By extension, our efforts to reduce our carbon output can only affect that 3%, so what effect can that have on correcting the problem?

    I realize that the ecosystem and climate are ridiculously complex, and that a 3% change could very well have a profound impact, but I don't personally have any concept of how sensitive the climate would be to such a change. That's basically what I'm asking.

    Question 3. This is a bit more hypothetical. We are currently making efforts to reduce emissions and burn cleaner fuels, but the likelihood is that we humans will eventually burn all of the fossil fuel we can get our hands on. The emission problem will probably only go away when we run out of fuel.

    With this in mind, has anyone ever tried to calculate the total amount of fossil fuel available on earth, and what the effect would be if we simply burned all of it? Wouldn't that give us the answer we're really looking for? If we could answer that question, we'd have a pretty good idea if we're going to kill ourselves off or not.

    So yeah, how much fossil fuel is there, and if we simply burn all of it, do we survive?

    Again, I have no idea what information to believe at this point, so any answer based on (gasp) actual scientific fact would be a breath of fresh air.
  2. jcsd
  3. Jul 9, 2009 #2


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    Where did you read this statistic and in what context was it presented? Anyone can make up a number and bend the facts to fit it.
  4. Jul 9, 2009 #3
    The statistic was presented in an episode of "Penn and Teller's BullSh!t", which is admittedly not a scientific journal. However, there was no real spin to this number. They basically had the same reaction I did, which was, "How are we supposed to know what any of this means without being climate scientists in our own right?"

    Based purely on their record of dealing with subjects that I do know about, they appear to have a healthy skeptical attitude towards the subjects they broach. By no means was the theme of the show that climate change is not true. If it had been, I would have dismissed it out of hand.

    That's why I'm trying to verify what I heard by asking the only people I can think of that usually know what they're talking about.
  5. Jul 9, 2009 #4


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    No one here is a climate scientist and is qualified to answer. Not even climate scientists agree.
  6. Jul 9, 2009 #5

    Ivan Seeking

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    From a thread below, this report was just released and touted to be the most comprehensive report to date.

  7. Jul 9, 2009 #6

    Ivan Seeking

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    This seems to address your question.

    Figure 3. Global Carbon Cycle (Billion Metric Tons Carbon)

    The IPCC report is found here
    http://www.ipcc.ch/ipccreports/ar4-syr.htm [Broken]

    I remember the anti-warming crowd crying "What about volcanoes?!?!?"

    So while it appears that indeed, humans are only responsible for about 3% of the gross release [~ 7.2/210] of CO2, the net release is a far different story. It would appear that the natural systems are a net negative system.
    Last edited by a moderator: May 4, 2017
  8. Jul 18, 2009 #7


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    Here are my answers:

    1) The 3% value is roughly correct.
    2) It results in atmospheric CO2 levels gradually increasing. 3% may not sound like much, but the problem is that CO2 levels have increasing for a while and will continue to do so for a while.
    3) There are several hundred years (possibly over 1000) worth of fossil fuels. The problem is that we have been buring mostly gas and oil which don't have as much carbon as does Coal. So, the prospects of actually reducing CO2 emissions any time soon are unlikely. This doesn't mean a lot of people are going to die, but the earth will become a warmer and wetter planet. Short term, this isn't all that bad, but long term (200 years), there are going to be significant problems. I'm sure that we as a civilization will adapt, but after we run out of fossils fuels people are sure to wonder why we had to burn them all so fast.
  9. Jul 18, 2009 #8


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    On who is qualified to answer

    I disagree with Evo that "no-one is qualified to answer". That's the primary message I want to make here.

    Just as in other areas of science, it is perfectly possible to learn about the subject and be able to answer basic questions. This question is not a complex one for which there is any credible dispute, except possibly in some fine details on nailing down a precise number as well as we can. The magnitude you've got is correct... depending on how terms are defined.

    Nearly all the public dispute on climate change is not a scientific dispute in the conventional sense. This is not a tricky topic where the basics are beyond you and where you can't hope to resolve such issues. It's a lot like relativity and cosmology, in some respects (another topic I engage here). It's a complex subject with a hell of a lot to learn; but you CAN learn it. It's always good to get more detail and background from experts, but an amateur is well able to get to the point of giving useful and accurate answers to basic questions.

    And like relativity and cosmology, there are a lot of cranks around, and if you haven't yet learned about it you can go badly off the rails by listening to the wrong people. But if you are serious about learning, sooner or later you'll get to the point of identifying the cranks. They are shown up in the end as you progress in the basic background theory used by the vast majority of the scientific community. You also get to learn about the genuinely open questions and unresolved issues. It's the same in climate science. The major difference is not a scientific one, but a political one. Climate is an issue with major political implications and that means more cranks and more public support for politically convenient but scientifically nonsensical ideas.

    People will tell you different things about which "side" is the one politically motivated to support ideas with no good scientific basis... and if you really can't tell then the solution is simply to forget the political implications yourself and get serious about learning the basic background. It takes time, but it works.

    The role of emissions

    The diagram by Ivan Seeking is a good one to explain the nature of ambiguities. It's even more subtle than the diagram suggests, because fluxes changes with seasons. Basically, there's a lot of carbon dioxide cycling in and out of the atmosphere. The human emissions are comparatively small, seen on a single year, by comparison with other fluxes in the carbon cycle.

    What is special about fossil fuel emissions is that they are added into the dynamic cycle from an external source -- geological reserves. Hence there's a continuous increase, which has raised atmospheric carbon levels by over 30% in the last hundred years.

    Furthermore, studies of the isotopes of carbon demonstrate that this increase really is from geological reserves. There's a difference in the relative amount of C12 and C13 in fossil fuels, and in the active carbon cycle, and fossil fuel emissions have imposed a clear signature.

    There's another good diagram that shows that emissions are small in magnitude compared with other fluxes over a year, and at the same time are the major driver for change over several decades. This is from the NOAA monitoring station at Mauna Loa.
    This is a measurement of atmospheric carbon dioxide. You can see a clear annual cycle, due to seasonal changes in the large natural fluxes in and out of the atmosphere. On top of this, there is a steady trend, most of which is due to fossil fuel emissions. The large fluxes redistribute carbon between ocean and vegetation and atmosphere. The small but cummulative emissions flux adds more carbon into the carbon cycle, without replacement.

    So yes, the number you've quoted makes sense, and it is completely consistent with the fact that anthropogenic emissions are the major driver of a changing climate in the present.

    Cheers -- sylas
  10. Jul 19, 2009 #9
    OB 50, by extention of the comments by sylas and Ivan, the 3% number is roughly correct but it is also irrelevant. About 100% of the *change* in CO2 *concentration* (i.e., from 280 to 385 ppm) is due to human activities, as can be clearly seen from the isotopic signature of fossil fuel carbon, as well as the fact that carbon content in the oceans and terrestrial biosphere has both increased (if the change in concentration in the atmosphere was natural, you'd expect a decrease in these carbon reservoirs as it would be mined into the atmosphere). It is the concentrations that matter for radiative transfer (and hence warming of the surface-troposphere system), and human activitity is clearly why CO2 is changing today.

    This is a fundamentally different question that how anthropogenic CO2 *emissions* compare with natural fluxes. In fact the carbon exchange between the oceans/biosphere and the atmsophere is much higher than the anthropogenic exchange, but the natural fluxes in pre-industrial times were roughly in balance (i.e., what went in also goes out) such that the absolute CO2 concentration in the atmosphere was nearly stable over the whole Holocene.

    By analogy, suppose you had a sink with a faucet and drain. The faucet pumped out 30 units of water and the drain got rid of 30 units of water over the same time frame, such that the water level in the sink was roughly stable. Now suppose someone comes in and dumps about 1 unit of water in without changing the efficiency of the drain. Now you have 31 units going in and 30 going out. It is true that "1" is probably small compared to "30" but now the much more important point is that your equilibrium system is now thrown into a state where the water level can only rise, despite the fact that it will take some time to be overpowering. As this imbalance persists over extended periods of time, the water level change will eventually become significant, and probably reach a new equilibrium eventually (say as increased downward pressure makes the drain more efficient) although the water level will stabilize at a higher point in the sink. Right now though we're putting CO2 in much faster than the oceans can possibly keep up with (see some of David Archer's work on the millennial-scale lifetime of our extra impulse of carbon) and therefore concentrations can only rise. The other thing is that natural sinks are probably in significant decline, which makes natural removal processes less efficient and is contributing to the near-exponential rise in CO2 levels.

    The reason why fossil fuels are so unique (as compared to, say, the CO2 we admit breathing) is that it has been buried underground for millions of years and is those no longer part of the immediate exchange between the oceans, biosphere, and atmosphere. In contrast, the CO2 we breath came from something (plants or animals) that interacted with the atmosphere and the short-term carbon cycle and therefore releasing it back into the atmsophere had no net effect on concentration. This should all make sense when you realize CO2 levels are usually very stable over timescales of decades to hundreds or thousands of years. They start changing very slowly on glacial-interglacial timeframes, usually because changes in the ocean and biosphere conditions cause changes in atmsopheric chemistry. In contrast, the CO2 change today is very rapid (at least an order of magnitude faster) and total concentration levels are higher than during the whole ice core record (close to a million years now) and probably much longer.

    Hope that helps
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