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Are humans too insignificant to affect global climate?

What the science says...

Select a level... Basic Intermediate
Atmospheric CO2 levels are rising by 15 gigatonnes per year. Humans are emitting 26 gigatonnes of CO2 into the atmosphere. Humans are dramatically altering the composition of our climate.

Climate Myth...

Humans are too insignificant to affect global climate
To suggest that humanity is capable of impacting and disturbing forces of such magnitude is reflective of a self-centred arrogance that is mind numbing. Humanity is a subset of Nature. Nature is not a subset of humanity. We have travelled full circle. We are back in the mindset that prevailed when Society’s leaders dictated what people in Copernicus’ days may or may not think. The Earth is once again flat. (source: Financial Sense University)

Are humans too insignificant to affect global climate? After all, our planet is a big place. Isn't it arrogant to claim puny little humans could make a dent in such a huge climate? However, whether human activity might affect climate is not a question of arrogance. It's merely a question of numbers. In particular, there are two numbers to consider.

Atmospheric CO2 is rising by 15 Gigatonnes per year

The first on-site continuous measurements of atmospheric CO2 were implemented by Charles Keeling in 1958 at Mauna Loa, Hawaii. This station provides the longest continuous record of atmospheric CO2. Currently, atmospheric CO2 levels are being measured at hundreds of monitoring stations across the globe. For periods before 1958, levels of atmospheric CO2 are determined from analyses of air bubbles trapped in polar ice cores.

What we observe is that in pre-industrial times over the last 10,000 years, CO2 was relatively stable at around 275 to 285 ppm. Over the last 250 years, atmospheric CO2 levels have increased by about 100ppm. Currently, the amount of CO2 in the atmosphere is increasing by 15 gigatonnes every year.

Figure Figure 1: CO2 levels (parts per million) over the past 10,000 years. Blue line derived from ice cores obtained at Taylor Dome, Antarctica (NOAA). Green line derived from ice cores obtained at Law Dome, East Antarctica (CDIAC). Red line from direct measurements at Mauna Loa, Hawaii (NOAA).

Humans are emitting 26 Gigatonnes of CO2 per year

Global CO2 emissions are derived from international energy statistics, tabulating coal, brown coal, peat, and crude oil production by nation and year. This means we can calculate how much CO2 we're emitting not only in recent years, using United Nations data, but also estimate fossil fuel CO2 emissions back to 1751 using historical energy statistics. What we've found is fossil fuel and cement emissions have continued to increase, climbing to the current rate of 26 Gigatonnes of CO2 per year.


Figure 2: Total Global Carbon Emission Estimates, 1750 to 2006 (CDIAC).

In other words, humans are emitting nearly twice as much CO2 than what ends up staying there. Nature is reducing our impact on climate by absorbing a large chunk of our CO2 emissions. The amount of human CO2 left in the air, called the "airborne fraction", has hovered around 55% since 1958.

Detecting the human signature in atmospheric CO2

Further confirmation that rising CO2 levels are due to human activity come by analysing the types of CO2 found in the air. The carbon atom has several different isotopes (different number of neutrons). Carbon 12 has 6 neutrons, carbon 13 has 7 neutrons. Plants have a lower C13/C12 ratio than in the atmosphere. If rising atmospheric CO2 comes fossil fuels, the C13/C12 should be falling. Indeed this is what is occuring (Ghosh 2003) and the trend correlates with the trend in global emissions.


Figure 3: Annual global CO2 emissions from fossil fuel burning and cement manufacture in GtC yr–1 (black), annual averages of the 13C/12C ratio measured in atmospheric CO2 at Mauna Loa from 1981 to 2002 (red). (IPCC AR4)

So we see that humans have indeed changed the composition of our atmosphere in dramatic ways. If anyone could be accused of arrogance, you might say it's more arrogant to think we can pollute without consequences.

Last updated on 26 June 2010 by John Cook.

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Comments

Comments 1 to 20:

  1. It would be interesting to have atmospheric CO2 and human emitted global carbon emissions plotted in same graph with time scale of last 200 years.
    Response: This is done in Comparing CO2 emissions to CO2 levels.
  2. I’ve always been puzzled as to why people think humans are too puny to have any effect on the planet.
    Far smaller organisms than us have had a significant impact. Just look at the Great Barrier Reef, the White Cliffs of Dover or the Peak District. None of these would be present, or would be substantially different, if the results of the blind unthinking actions of primitive creatures had not accumulated over long periods of time.

    Neither would we be breathing an oxygen-rich atmosphere were it not for the photosynthetic activity of plants over millions of years.

    OK, none of this was deliberate or short-term, but it shows that really insignificant life forms can have an impact on the planet.

    As for humans, we can and have created deserts, made semi-desert more arid and the like by over-grazing of livestock, over-intensification of non-sustainable agricultural practices and deforestation. None of this is necessarily irrecoverable in the long term, given the will, the power and the knowledge of how to undo the damage, but our impact on so much of the biosphere is indisputable. Of itself this does not prove global warming, but it does invalidate any assertions that we are too unimportant to have any effect
  3. John said: "The amount of human CO2 left in the air, called the "airborne fraction", has hovered around 55% since 1958."

    Isn't the Airborne Fraction around 43-44%? Appears that you have it reversed - 55% would be the proportion absorbed by the sinks.

    Or is there a higher AF since 1958 because of the time lag for the sinks to absorb the large, recent emissions?

    A
  4. I have heard this argument (humans are too insignificant to affect climate) more often than any other over the past few years.

    I have been thinking much lately that this attitude is an example of numerical illiteracy. The numbers documenting CO2 emissions do not mean something tangible that many people can imagine. And those who do not, or cannot turn very large numbers into something personally meaningful, simply see that Earth as overwhelmingly larger than mankind. Scientists are trained for years in making sense of large numbers. Very few other people are adept at this ability. It is easy for anyone to see how "small" we are as individuals on the vast Earth. But it is not easy to quantify the true dimensions of the atmosphere, the biosphere, communities, and how human activities add up. There is a failure at a personal level to understand the total global impact from summing every small contribution. This is as true for understanding rising CO2 as for anything that results from the actions of populations that now number in the 'billions'.

    Seems to me that we all could benefit from creative graphical and narrative examples that would illustrate how human sources of CO2 have been increasing the levels in the atmosphere for many years, in sync with economic expansion. Those trying to demonstrate this point need to make the human impact of CO2 emissions tangible.

    One simplistic example I once used as a comment to someone about this topic is night time photos of North America and Europe from space. These show the enormous networks of lights from communities. It makes the human race appear as quite a significantly large presence.

    I am sure that far better quantitatively based examples could be composed to get people (and critics) past this misconception.
  5. woodtom at 12:35 PM on 10 March, 2010

    Or "innumeracy" as I've heard the concept called.

    I think you're quite right, we're adapted to succeed with intuiting small numbers but the quantities and effects we're dealing with here are on a inhuman scale, bigger than their creators.

    I've mentioned here before that on RC a tractable skeptic and I each did back-of-the-envelope calculations to reveal some idea of how much additional instantaneous power was going into the Arctic ocean during late summer as a result of ice loss. If I remember right I came up with ~80TW, my skeptic friend ~40TW. To put that in proportion, the entire world electrical generation capacity is about 16TW.

    My skeptic acquaintance and I found a point of agreement on our inability to predict such staggeringly large numbers from what is after all the loss of "only" about 6% of ice cover. "Only" 6% is of course an enormous surface area, multiply that by an additional few tens of watts per square meter absorption and numbers get very big indeed.

    Our brains don't produce good results dealing with numbers this large, our discrimination becomes mushy, orders of magnitude mix together.

    Our very largest artifact is so big it's almost incomprehensible.
  6. When facing this argument I always like to bring this cartoon.

    (Clue: cyanobacterias)
  7. Damn it, I have ruined the cartoon by giving the clue just in the following line! :P
  8. A Drop in a Bucket

    Volume of the Earth’s Atmosphere:

    How thick is the atmosphere?
    There are many different answers to this question. Everyone agrees that the atmosphere consists of 5 layers. The bottom layer, the troposphere, contains 75% of the gas. The thickness of this layer, depending on who you ask, varies between 8 km and 15km above the surface of the earth. For the purposes of this discussion, I’ll use the lower limit of 8 km. Also, for this discussion, I won’t consider the remaining 4 layers of the atmosphere, as there is very little gas in these layers.
    Volume of a sphere:

    The radius of the earth is 6,360 km
    This makes the radius of the earth plus the troposphere to be 6368 km (6,360 + 8).
    The formula for finding the volume a sphere is: 4/3 X π X r3.
    To determine the volume of the troposphere:
    (1) Plug in the larger number (radius of the earth plus the troposphere) (2) subtract the volume of the earth:

    (4/3) X (3.142) X (6,368km)3 = (4/3) X (3.142) X (258,231,468,032 km3) = 1,081,817,696,742. km3

    For the earth:
    (4/3) X (3.142) X (6,360km)3 = (4/3) X (3.142) X (257,259,456,000 km3) = 1,077,745,614,336 km3

    Subtract the volume of the earth from the volume of the volume of the earth plus the troposphere:
    1,081,817,696,742 km3 – 1,077,745,614,336 km3 = 4,072,082,406 km3 = the volume of the troposphere

    For this discussion, I’m going to use 4.07 billion cubic kilometers as the volume of the troposphere.

    US Gasoline Use in 1 Year

    The U.S. Energy Information Administration says the United States uses 378 million gallons of gasoline, per day, for motor consumption.
    (378,000,000 x 365) = 137,970,000,000 gal/year
    For this discussion, I’m going to use 138 billion as the number of gallons of gasoline, for motor consumption (cars), burned in the U.S. in a single year.

    CO2 Emissions

    The International Carbon Bank and Exchange states that burning a gallon of gasoline produces 4.867m³ of CO2. Multiplying the 138 billion gallons of gasoline burned in the U.S. by the 4.867 m3:
    (138,000,000,000 x 4.867 m3) = 671,646,000,000 m3

    There are 671.6 trillion cubic meters of CO2 produced by gasoline motors in the U.S. in one year. This is equal to 671.646 cubic kilometers. To give this unit a name, I’m calling it an ALGIT (Al Gore’s Inconvenient Truth). One algit = 671.646 cubic kilometers = the volume of CO2 gas produced by all the gasoline motors in the US in one year.

    Percentage of the Atmosphere
    If the volume of the atmosphere is 4.07 billion km3, and an Algit is 671.646 km3, then the atmosphere contains (4.07 billion / 671.646) algits. This equals 6,059,739.80 algits. The CO2 produced by the U.S. (from gasoline burning motors), in a single year is equal to .0000165% of the atmosphere.

    Drops in a Bucket
    One drop of water is a minum. Twenty minums make a milliliter. If we consider a one gallon bucket, there are 3,785.4 milliliters in a gallon, so there are 75,708 minums (drops) in a bucket.
    The number of Algits in the atmosphere is 6,062,039, so there are 80 times (6,059,739.8 / 75,708) as many algits in the atmosphere as there are drops in bucket.
    Another way of looking at this is that it would take 80 years for all the gasoline motors in the U.S. to produce the amount of CO2 that would be the equivalent of a drop in a bucket.
    So if we stopped using all gasoline motors in the U.S. today (impossibility), each year would have the effect of 1/80th of a drop in the bucket of the atmosphere.

    Doesn’t seem worth it.

    The earth is warming up - let's spend our efforts (and $) figuring out what to do as it gets warmer. Buying electric cars and crappy lightbulbs won't do it.
    Response: Another way of looking at it, and I would argue the most appropriate way to look at it, is how much heat is this trace amount of CO2 trapping? This has been accurately determined by line-by-line calculations and confirmed by direct measurements by satellites and surface measurements. Observations in the real world confirm the increased greenhouse effect from more atmospheric CO2.

    But I agree, buying electric cars and more efficient lightbulbs are only a tiny drop, to borrow your metaphor, compared to the effort required to lower and eventually stop CO2 emissions.
  9. PS: This is the best web site I've seen for rational debate. I haven't read one post where someone is called ....ing idiot or ....redneck. Very cool.
  10. I'm not a scientist, so maybe I didn't get my point across: It's not possible for us to make a radical enough change to the amount of CO2 humans are putting into the atmosphere to make a difference. We'll have to live with it.
    Response: The question of whether it's possible to reduce our CO2 sufficiently has been examined in the peer-reviewed literature (Pacala 2004). The verdict:
    Humanity already possesses the fundamental scientific, technical, and industrial know-how to solve the carbon and climate problem for the next half-century. A portfolio of technologies now exists to meet the world's energy needs over the next 50 years and limit atmospheric CO2 to a trajectory that avoids a doubling of the preindustrial concentration. Every element in this portfolio has passed beyond the laboratory bench and demonstration project; many are already implemented somewhere at full industrial scale.
    To borrow from the Bionic Man, "we have the technology!"
  11. jmymac1958, we're going to be forced to make a radical change in the amount of fossil C02 we liberate into the atmosphere not so far down the road, not necessarily because we actually care about the climate but because fossil fuels are a but a blip on our history, here today and gone tomorrow. Now-- while we still have "free" power available from fossil fuels-- is the time to figure out what our long term energy supply will be. We've got a limited amount of resources and time to sort out what our more permanent and reliable energy sources will be.

    Assuming we don't succumb to some sort of disaster, this era of fossil fuel usage we're living in right now will seem to our descendants as quaint and outmoded as do chipped flints to our own modern day chefs.

    Imagining that C02 is the only challenge we're facing w/regard to fossil fuels misses many future chapters of our story.
  12. jmymac1958, you're comparing the quantity of CO2 emitted from burning gasoline to the total atmosphere. But the atmosphere is mostly made up of inert nitrogen and oxygen, which are irrelevant to the radiation balance. Instead, you need to compare the increase in CO2 to the total quantity of CO2.

    The mass of CO2 in the atmosphere is about 3E15 kg. The mass of CO2 produced annually by burning gasoline in the US is 1.2E12 kg. So US gasoline consumption increases CO2 in the atmosphere by about 0.04%.

    That's a small amount. But it accumulates over time, due to the long lifetime of CO2 in the atmosphere, and gasoline in cars is not the only source of CO2 (see coal, natural gas, and petroleum not used in cars), and the US isn't the only country in the world.

    Thus, in a fairly short time, we are doubling the concentration of CO2 in the atmosphere ... even in spite of the fact that some of the CO2 we produce is taken up by the oceans and the biosphere.

    It is sometimes hard to believe that a small quantity of something can have a serious impact. The lethal dose for arsenic is around 13-14 parts per million, for dioxin it's 0.02 parts per million (0.000002%).

    As John points out, it's quite possible to reduce our CO2 emissions with current technology and without destroying the economy. The Socolow and Pacala 2004 paper is a good place to start. And as Doug points out, we're going to have to move away from fossil fuels anyway, so why not start now? Oil is a very valuable substance for manufacturing and industry; it's stupid to just burn it all. Doesn't it seem a bit selfish to take a valuable resource that's accumulated over hundreds of millions of years and burn it all in the course of a century or so? One assumes that human civilization will still be around past 2100; even if you ignore the climate issue our descendants may not appreciate our profligate squandering of their inheritance.

    Finally, I'd politely suggest not making ad-hominem remarks in your posts (e.g., your references to Al Gore). It's much better to make your point without name-calling or insults, no matter how subtle and humorous you think you're being.
  13. Because it's a hobby horse for me, let me amplify Ned's remark about our crude habit of burning our petroleum.

    Not only is petroleum pyromania pathetically primitive, but burning this resource will seriously balloon our future energy requirements while simultaneously throwing sand into the gears of our economy. Using petroleum for liberation of heat via combustion is a wretched waste that is going to come back and haunt us in a bad way.

    We're heavily dependent on polymers made from oil. Nearly all of our daily activities are dependent on products made using petroleum feedstock. That's because the simple molecule of methane and all of its more evolved and advanced cousins are absolutely fabulous structures for rearranging into different configurations, tweaking with the addition of other components and then creating useful things.

    All of that hydrogen and carbon we lean on was jammed together for free, eons ago, over plenty of time when nobody was tapping their foot waiting for their next roll of polyethylene, collection of O-rings, damping bushing, etc. As we burn what could be made into relatively durable and incontrovertibly essential artifacts, we're going to see the prices of nearly every product we use steadily creep upward quite independent of direct impacts of rising motive power costs.

    If we continue to burn petroleum willy-nilly as we do now, our requirement for hydrocarbon feedstock to produce things we need will collide with insufficient supply. At that point, we're going to have to -manufacture- methane and all its more useful cousins, and that's going to require a staggeringly large amount of of energy. Marrying hydrogen and carbon is only possible with a large energy dowry, which of course is why the stuff burns so nicely. That energy demand is going to be stacked on top of what will already be a horrendous challenge, that of substituting for and eliminating hydrocarbons for thermal applications such as heating and motive power.

    We really do need to change our approach to how we use petroleum. We can start by recognizing what rotten stewards of this resource are our petroleum producers, refiners and marketers, how defective is their drive to encourage waste. However, they're not really the primary problem. These entities have commercial considerations compelling them to encourage us to be thoughtless, feckless consumers. At the end of the day, it's up to us to cease our fascination with igniting petroleum and instead consider it irreplaceable, something to be husbanded jealously.
  14. I read the Pacala 2004 paper. I guess my post was too flippant, so I'll be nice.

    I need to state a few things first:

    I believe the scientists have proven the Earth is getting warmer.

    I believe that the additional CO2 from human activity has greatly accelerated the natural cycle of CO2 levels in the atmosphere.

    I know the oil is going to run out.

    I know we must develop new energy sources to replace the oil.

    Now as to the Pacala 2004 paper:

    The statement that technology available today could be used to make the 15 "wedges" called for (in the paper)to keep from doubling the CO2 concentration is most likely true. But, just because the technology is available, doesn't mean the wedges will ever be implemented.

    Some of the wedges seem a little unobtainable to me:

    Using 1/6th of the earth's farmland to produce crops for biofuel, while at the same time reducing deforestation to zero, and planting more trees. Grow more on less land? (Don't yell at me about the rain forest, I'm just questioning the ability to feed everybody, make ethanol and use less land.)

    The green parts of the paper (windmills, solar, geothermal, etc.) won't happen unless some company could prodcue and sell the items at a profit. The reason these technologies have not taken off is they don't fill that requirement.

    Some of the suggestions will never be implemented because people just won't do it. For example: you'll never make everybody on the planet drive only 1/2 as much as they do today.

    This being said, my main point is that we probably can't do the things suggested in the paper, so we need to concentrate on what to do because the earth is warming up. I don't beleive we can stop it so let's not waste time on the unobtainable, and concentrate on what to do once it happens.
  15. "Of course, as CO2 is the most common of greenhouse gasses, the additional concentration is what causes most of the rise in temperature."

    - careful! You mean most common of anthropogenic greenhouse gases.

    Accuracy is key in the fight against misinformation.
  16. "Further confirmation that rising CO2 levels are due to human activity come by analysing the types of CO2 found in the air. The carbon atom has several different isotopes (different number of neutrons). Carbon 12 has 6 neutrons, carbon 13 has 7 neutrons. Plants have a lower C13/C12 ratio than in the atmosphere. If rising atmospheric CO2 comes fossil fuels, the C13/C12 should be falling. Indeed this is what is occuring (Ghosh 2003) and the trend correlates with the trend in global emissions."

    I'm having trouble understanding this statement, but the basic version is a bit too basic and doesn't answer the question, "How can scientists tell the difference between the CO2 from plants and that from fossil fuel consumption?"
  17. They don't. ;-)

    Fossil fuels are made from plants so they have the same C13/C12 ratio. The difference is not between fuel and plants, but between fuel/plants and "natural" CO2 content of the atmosphere.

    The atmosphere is a bit richer in 13C because plants have a slight preference for 12C. So if you burn fossil fuels (made from plants), the 13C/12C ratio drops, and you can calculate which part of the CO2 in the atmosphere comes from fuel.
  18. So, by burning fuel/plants, we add more 12C to the atmosphere. Aha! Thank you!
  19. You're welcome. :)

    Of course there's never much 13C to begin with (only 1.1% of Earth's carbon is 13C), but the preference plants have for 12C makes their 13C/12C ratio about 2% lower, causing (by burning fuel) the atmospheric 13C/12C ratio to drop 0.15% since 1850.

    Now this may not look like much, until you realize this 0.15% drop comes from just a 2% lower ratio of just a 1.1% isotope, and then it's suddenly quite a lot.

    Still, I think it's quite amazing someone actually thought of it. :D
  20. Sure, humans don't have the ability to seriously harm life on earth, and the Cold War was really about the rise of polar bear batallions.

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