Carbon Pollution: If We Don’t Change Our Direction, We’ll End Up Where We’re Headed

By Dr. Jonathan G. Koomey, via

If we don’t change our direction, we’ll end up where we’re headed

Climate Progress did a great service for climate communications on March 8th, 2013 by publishing this graph of historical and projected global temperatures:

Figure 1: Historical and projected global average surface temperatures on our current trajectory for fossil fuel emissions

The historical data in the graph came from a recently published article in Science, and the projected data came from the “no-policy” case developed by the folks at MIT back in 2009. The MIT case showed about a 5 Celsius degree increase in global average surface temperatures by 2100, equivalent to about a 9 Fahrenheit degree increase.

I like this graph because it combines what we know about historical temperatures with what is our most likely future — one where we continue to consume fossil fuels at increasing rates. I realized after seeing Joe’s graph that I could easily add additional context to it, because I have both historical data on carbon dioxide concentrations in the atmosphere, as well as the detailed projections from the MIT researchers (which I obtained from them while working on my most recent book, Cold Cash, Cool Climate: Science-based Advice for Ecological Entrepreneurs).

Here’s Figure 2-3 from Cold Cash, Cool Climate, updated to include CO2 concentrations through 2012. It shows historical carbon dioxide concentrations for the past 450,000 years, including the strikingly rapid increase since the 1800s. The early historical data come from the Vostok and Lawdome ice cores, while the more recent data (post 1959) come from direct measurements. We’ve pushed carbon dioxide concentrations well outside the range that has prevailed over the past 450 millennia.

Figure 2: Carbon dioxide concentrations for the past 450,000 years

The data for the past 12,000 years, the period over which human civilization developed, shows a picture similar to Romm’s graph of temperatures. Carbon dioxide concentrations were relatively stable for the entirety of this period, slightly increasing over time, with the most rapid increase only happening as the industrial revolution accelerated in the 1800s:

Figure 3: Carbon dioxide concentrations for the past 12,000 years

Of course, carbon dioxide concentrations are not the only determinant of global surface temperatures, so the concentrations graph won’t exactly match Romm’s temperature graph, but the fact that concentrations didn’t change much over 10,000 years is consistent with that graph.

The issue of most concern to people thinking sensibly about climate is not the historical change in carbon dioxide concentrations, but the likely trajectory of those concentrations if we continue on the path we’re on now. I’ve modified Figure 3 to include the MIT projections to 2100 to show just how big the change in carbon dioxide concentrations is likely to be (note that the y-axis in Figure 4 starts at 100 ppm, not 0 ppm). We’re on track for a threefold increase in the concentration of carbon dioxide by 2100 if our emissions proceed along the path expected by MIT’s no policy case.

Figure 4: Carbon dioxide concentrations for the past 12,000 years and projected to 2100 assuming no change in policies

The picture is even more striking when compared to the past 450,000 years (Figure 5), showing that we’re moving the earth well out of the comfortable range in which humanity evolved and civilization developed.

Figure 5: Carbon dioxide concentrations for the past 450,000 years and projected to 2100 assuming no change in policies

Of course, it’s not just carbon dioxide that matters. If you include the other important warming agents (like methane, nitrous oxides, CFCs and others) the MIT no policy case shows even bigger changes. Figure 6 modifies Figure 4 to include these other agents in the projection, expressed as carbon dioxide equivalent concentrations. Such conversions are complex and imperfect, but they’re good enough to get an order of magnitude estimate of the total potential impact of the path we’re now on.

Figure 6: Carbon dioxide concentrations for the past 12,000 years and projected to 2100 assuming no change in policies, including other warming gases

Here’s the same graph going back 450,000 years (Figure 7).

Figure 7: Carbon dioxide concentrations for the past 450,000 years and projected to 2100 assuming no change in policies, including other warming gases

The critical takeaway from Figures 6 and 7 is that we’re on track for more than two doublings of greenhouse gas concentrations by 2100 if we continue on our current path (greenhouse gas equivalent concentrations rise by a factor of 4.8 by 2100). Many in the media and elsewhere mistakenly focus only on the climate sensitivity, which is the expected increase in global average surface temperatures for a doubling of greenhouse gas equivalent concentrations (best estimate now is about 3 Celsius degrees, or 5.4 Fahrenheit degrees, per doubling). But it’s not just the temperature increase from a doubling of concentrations that matters, you also need to know how many doublings we’re in for.

I’ve been frustrated for many years by the way numbers about projected greenhouse gas concentrations have been presented, even by some folks who ought to know better. The most common approach has been to focus just on carbon dioxide, and make some hand-waving statements about the effects of the other warming agents, but that never satisfied me. As a comparison of Figure 4 and Figure 6 show, the other warming agents are significant contributors to warming, increasing the effective greenhouse gas concentration from about 900 ppm (for carbon dioxide alone) to about 1350 ppm when all warming agents are included.

The MIT researchers deserve great credit for their work. They appropriately defined a “no-policy” case to clearly show the effect of the current path we’re on (avoiding the confusion among policy makers engendered by the “multiple baselines” approach embodied in the IPCC Fourth Assessment report). They also conducted a comprehensive analysis of all warming agents, and made their data available to other researchers who could summarize the results in effective ways. It was quite a relief to discover their work, and it made writing the first few chapters of Cold Cash, Cool Climate a lot easier.

The last part of the puzzle is to understand whether the MIT no-policy case is a plausible representation of a world in which we initiate no constraints on greenhouse gas emissions. One way to do that is to compare the history for various drivers of emissions (like population, energy efficiency, and economic growth) to the projections, a task that I undertook in Chapter 2 of Cold Cash, Cool Climate. In virtually every case, the projected trends looked a lot like the previous 50 years, and in some cases, the projections showed more modest growth than one might expect from recent history.

Another way to assess the projection is to examine just how many fossil fuel resources exist, to see if it’s plausible that the world could burn the amount of fossil fuels embodied in the MIT no policy case. I conducted this exercise in Chapter 2 and Appendix A of Cold Cash, Cool Climate. I also summarized the results in my blog post titled “Why fossil fuel abundance is an illusion” (see Figure 8).

Figure 8: Lower bound estimates of fossil fuel reserves compared to fossil carbon emissions in the MIT’s no-policy case

The key conclusion from this analysis (which is based on lower-bound resource estimates taken from the most recent Global Energy Assessment) is that fossil fuel resource constraints are unlikely to constrain carbon emissions in the twenty first century. If we just burn the conventional oil and gas resource base plus the coal proven reserves, we’d only need to burn about 10% of the remaining coal in the “resource base” to hit the MIT no-policy case emissions by 2100. In a world where the true cost of fossil fuels is masked by subsidies and unpriced pollution costs, it is clear to me that we’d easily burn enough fossil fuels to match the no-policy case totals.


The case for concern about rising greenhouse gas (GHG) concentrations is ironclad, and the graphics above show one compelling way to describe that case. We’re on track for more than two doublings of greenhouse gas concentrations by 2100 when all warming agents are included. Combined with an expected warming of about 3 Celsius degrees per doubling of GHG concentrations (the climate sensitivity) that implies about a 6 Celsius degree warming commitment on our current path (the 5 Celsius degree warming calculated by MIT for 2100 is lower because it takes many centuries for the climate to equilibrate to fully account for the effects of changes in concentrations).

The graphs above show a dramatic shift in the climate system caused by human activity, one that has no precedent in human history. We need to leave more than three-quarters of proven fossil fuel reserves in the ground if we’re to stabilize the climate (for more technical backup on this point, see this classic paper by Meinshausen et al. and the technical details provided in Cold Cash, Cool Climate). It’s hard to imagine a starker challenge for humanity, but it’s one that we must confront if we’re to leave a livable world for our descendants.

Jonathan Koomey is a Professor at Stanford University and an expert on the economics of reducing greenhouse gas emissions and the effects of information technology on resource use. This piece was originally published on his blog and was reprinted with permission.

32 Responses to Carbon Pollution: If We Don’t Change Our Direction, We’ll End Up Where We’re Headed

  1. prokaryotes says:

    Two notes, first it might be worthwhile to add a graph with extremes, since for the average people 2 degree does not sounds like a big deal.

    Secondly there is a new hockey stick, based on δ18O isotopes…

    “results are unequivocal: there’s about 5 times the fraction of melt layers in the core as there has been on average over previous decades, and at least twice the maximum of any time before about the 1950s. The amount of melting occurring now is greater than at any time in the past 1000 years. If there has ever been a question about whether the “hockey stick” shape of Northern Hemisphere temperatures extends to at least some areas of the Southern Hemisphere, this record provides a decisive and positive answer.”

    “Oxygen isotope ratios (δ18O) in polar snow are well known to be correlated with temperature, and the underlying physics of the relationship is very well understood.”

    “The average of the records for the last 50 years looks very much like temperature records from the last 50 years, with scaling of about 0.5‰/°C, exactly as expected, providing yet another piece of evidence that recent warming in West Antarctica has been both rapid and widespread (see the figure below). A critical point, though, is that it isn’t necessary to use the δ18O data as a proxy for temperature. Because the physics controlling δ18O is well understood, and we are able to implement δ18O in climate models, we can actually just use δ18O as a proxy for, well, δ18O. This simplifies the problem from “how significant is the recent warming?” to “how significant is the recent rise in δ18O”? We’ve shown previously, and show again in this paper, that

    δ18O in West Antarctic precipitation reflects the relevant changes in atmospheric circulation just as well (if not better) than temperature or other conventional climate variables do.”

  2. Paul Price says:

    To give an annotated form of Hagelaars’ Figure 1 above I have added temperature bands and emissions choices in this graphic:

    and in this large format poster:

  3. Joan Savage says:

    This is really useful.

    I’m so grateful for your key points about number of doublings and the need to consider aggregate GHGs.

    What sources would you suggest for the what went into Fig 6’s pre-industrial CO2 equivalent?

    An EPA graph for three major pre-industrial GHGs kept them separate:

  4. BobbyL says:

    I assume these graphs do not take into account potential positive feedbacks such as thawing permafrost. I would imagine that with the feedbacks that the projected values for CO2 equivalent and temperature would be even higher. What about black carbon? That is supposed to be the second biggest contributor to global warming after carbon dioxide. Is it included in CO2 equivalent?

  5. rollin says:

    This sounds bad and when one considers that natural feedbacks were not included, it sounds horrifying.

  6. Jack Burton says:

    I assume the graphs also miss the loss of carbon sinks that have done a wonderful job, up to now, of taking huge amounts of CO2 out of the atmosphere. I think of the oceans in particular. But you can also consider the problem of Boreal forests are now having, due to insect and climate. The Boreal forest is one big climate sink.
    Take into account these three and you see where we are headed for unprecedented disaster.
    1. continued increase in CO2 emissions from the economic expansion across the globe. More power plants, more cars, etc. etc.
    2. The beginning of positive feed backs, thawing permafrost giving back CO2 to the atmosphere, or dieing Boreal forests giving back carbon. As two examples.
    3. The loss of carbon sinks as their ability to soak up carbon decreases due to saturation. I think the oceans are expected to lose carbon sink properties fairly rapidly from their present state. As one big example.
    If you add up numbers 1,2,3 you get a potential for unprecedented warming as CO2 spikes.
    And beyond CO2, there is the methane bomb sitting in our oceans. Some new releases like the arctic methane plumes off of Siberia’s north east coast that were discovered last year to be expanding from meters across to over a kilometer across, and their numbers expanding in lock step with the size increase.
    The 2C goal that all are saying we can manage with a little action on CO2, like a carbon tax, seems to me to be the worst form of wishful thinking and delusional thought.
    The factors that go into the vast equation that produces global climate are spinning out of control. Exponential results could spin the climate out of control is a very short time. I am looking at the speed of the arctic ice decline as an example. Nobody, I mean nobody, even a couple years ago would have dared predict what we see today. The most radical predictions were for what we see this year happening at the earliest in 2050, most said possibly 2100. Now in my book, that is a miss if such staggering proportions that it ought to serve as a warning that climate has shifted to a new state, it could continue to spin out of control.
    Just look at the graphs, exponential is what we see, why should not climate then change in an exponential fashion? The laws of physics do not show me any iron clad law that climate can not follow these exponential changes in chemistry at the same rate. Systems like climate seem prone to changes of state, and that can happen in a matter of years, not decades or centuries.

  7. Mulga Mumblebrain says:

    Jack, I hate to sound like a ‘smart-arse’ as we say here, but I’ve discussed just such catastrophic scenarios with people for decades. A lot of people have seen this coming for a long, long time, knowing that the Right would fight to the death to avert remedial action. And they are still feverishly fighting against such measures. And you omitted oceanic acidification, which is the real killer blow, in my gloomy estimation.

  8. Jack Burton says:

    The Climate Change deniers are too smart by half. In a few years their screed and their lies will stand out as criminal in nature.

    As for our future. If one looks at the whole picture and not one slice of it at a time, there is no reason for optimism at all. The constant repeating of how we need only take action at some point soon, and we can hold this to a manageable 2C change. This seems like a bit behind the times. The Arctic melting is just screaming at people that we are already in a changed state, it just will take a few years for it to become apparent to us all.

  9. Mark Haag says:

    You might be right-but we should not leave any cards on the table-lets hit the streets this summer. If we can prevent the merely terrible from becoming catastrophic, we should at least try.

  10. Paul Klinkman says:

    Feedback is my concern also. When I see the death spiral of Arctic Ocean ice volume, I know that the Arctic Ocean is flipping over to a massive heat absorption mode. Right next door to the Arctic Ocean are millions of square miles of tundra that will no longer be as snow covered as before. Heat in the Arctic equals many gigatons toward teratons of carbon and methane release. Dead forests full of termites and grubs all over much of the Eaarth equals many gigatons of carbon soot and even more methane releases.

    If we know that we have positive feedback loops now, what will the loops be like in 2100? One low-confidence forecast is better than any number of terribly off-base forecasts, so somebody extrapolate the currently observable feedback loops, please.

  11. Paul Klinkman says:

    Peat bogs are real carbon sinks. We know that peat bogs eventually become coal seams. Some people dig down and mine peat bogs for their stored carbon. Bog depths create an anaerobic environment that sequesters hydrocarbons essentially forever.

    I suspect that most if not all boreal forest carbon will wind up back in the atmosphere some day soon. After trees die, termites, grubs and mushrooms take their cellulose hydrocarbons. Some of the hydrocarbons are burned as energy. Then the bugs and mushrooms die or are eaten, and the hydrocarbons continue to cycle until they are nearly all processed into either carbon dioxide or methane.

    If you dig 100 feet deep in a forested area, do you find great deposits of carbon left by forests 100,000 years ago?

  12. Robert In New Orleans says:

    Maybe this is why DARPA and NASA are thinking forward to a time when a select few will escape Earth on a faster than light starship and the sudden interest in potentially habitable worlds.

  13. Bernd says:

    Well above the comfort zone?

    Lets approach the issue not scientific, lets approach it simple bearing in mind the dots on the graphs.

    Pre industrial concentration was about 280ppmv?

    Now we are having 400ppmv?

    How do we want to get CO2 levels ever back to be in the “comfort zone”, which was over thousand of years between 200 and 300 ppmv before 1850, with no industry at all?

    And, how long will any effort back take?

    Seeing the flotation in the CO2 level (up and down) over thousands of years, without any industry influence and only the “normal live” of the planet (volcano’s, natural fires, etc.), it is hard to imagine that we can ever get back to normal state. Even if “somebody” could stop immediately any industrial CO2 output today.
    Lets imagine back to get levels before 1850, how long would it take that mother earth will recover? Hundreds of years or several thousand of years? Or even, would the earth not recover at all, because the level is already today to high? We never had a high level like this during humans life.
    Bear in mind, that my thoughts are on the basis that there is a sudden CO2 output like in the days before 1850.

    Well, it does not look good for all the following generations with even more growing population levels!

  14. fj says:

    The social trend has to catch up with the scientific trend and it will; and it seems like it will take two years at most; maybe any minute now.

    The Army is trying to craft a net zero model for rapid action and broad emulation.

    The World Bank and International Monetary Fund seem to be trying to come on board . . . There seems to be recognition that we will be bludgeoned by the worst of all financial storms caused by the collapse of fossil fuel prices on top of the devastation of accelerating climate change . . .

    The action must be now and decisive.

    Bring emissions to zero as quick as inhumanly possible.

    Restore the environment: Rebuild our planetary home.

    Smarten up. Smarten up . . . Smarten up.

    And prepare to weather the most perfect storm of our own creation. We must learn anew how to live with and within creation.

    Smarten up and learn to survive and prevail despite ourselves as never before.

  15. The asymptotes in these graphs are the very depiction of unsustainable.

    Rather than carbon accumulation in the graphs, mentally substitute pressure accumulation, as in a vice tightening on your finger. Long before you get to the high numbers, something’s gotta give.

  16. Ed Leaver says:

    I looked around a bit last summer for the prehistoric CO2 data. Best I found was the NOAA video Timescale Matters: 800,000 years of CO2. A png still of the last frame may be found as Figure 9: Atmospheric C02 during the Pleistocene Ice Age. The updated full-rez 2012 version is­acker/movies/pumphandle.m­p4 and is available via anonymous ftp if your browser wont load it directly.

    Doesn’t help much with the raw numbers, though. They’re at the above NOAA ftp site in the carbontracker/molefractions subdirectory, but in netCDF data format that your spreadsheet might not recognize

  17. Ed Leaver says:

    Ah. Here is the Pumphandle 2012 video on YouTube. Perhaps Dr. Koomey can help with the raw data.

  18. Ed Leaver says:

    And Noaa’s Carbon Tracker home page. The “Pump Handle” video is under “Additional Products” -> “Other CO2 Movies”.

  19. For those concerned about feedbacks, the MIT modeling effort was very sophisticated and did include the feedbacks that were well known back in 2009 when the study was done. Of course, it couldn’t have included the additional information we’ve gathered since then, which (as several commenters have pointed out) has made the situation even more worrisome than we thought a few years ago.

  20. Mike Roddy says:

    Excellent, Jonathan, thanks.

    I’m working on a magazine article about how utility scale solar was shelved in the Mojave Desert. The villains of the story? False flag environmental organizations, often with financial ties to land speculators and fossil fuel companies. It’s a dark, scary story. Email me if you want to hear more at

  21. SecularAnimist says:

    Mike Roddy wrote: “… utility scale solar was shelved in the Mojave Desert. The villains of the story? False flag environmental organizations …”

    With all due respect, it is not accurate to say that utility scale solar has been “shelved” in the Mojave Desert, given that multiple solar power plants are already online there (including SEGS, the largest solar thermal energy generating facility in the world). More are under construction, and even more are planned.

    Neither is that an accurate characterization of the opposition to building utility-scale solar on certain environmentally sensitive areas of the Mojave, given that space sufficient to power the whole country with solar is available in other, less sensitive or already degraded public lands. The fact is that legitimate environmental concerns were raised by legitimate environmental groups, both national and local, and those concerns improved the process by which the Obama administration identified very large areas of public lands which have been made available for expedited deployment of large-scale solar.


  22. fj says:

    The extreme slope of that red line shooting for the sky is awfully reminiscent of the divergences typical of phase changes; perhaps of life on earth or the future of life; the kind of stuff James Lovelock’s Giai Theory excels in.

    Not good!

    Someone got to grab The President by the collar and shake him and wake him out of his stupor and yell at him that we got to get moving.

    This is no time have one of those Hamlet moments.

    This “To be or not to be” stuff is bull hooey.

  23. Solar Jim says:

    Please notice generally the pervasive euphemisms of “carbon pollution” and “carbon dioxide” (description of a formula) in our discussions of this substance, which could be described more meaningfully for citizens as: Carbonic Acid Gas, as well as the associated Carbonic Acid.

    One might say we have an Acidic Economy, or a Sick Economy. Thanks for the post.

  24. Mulga Mumblebrain says:

    We could do it, even now, but only with sane, rational and moral people in charge. The elites thrown up by neo-liberal capitalism in the West are the antitheses of the type we need. And it must be a global effort, so no bulldust about ‘America leading’ or ‘exceptionalism’ or any other jingoistic balderdash. One earth, one humanity, one shared future- or none.

  25. Bernd says:

    Your comment is so right. ALL must do it, as a global effort!

    This has nothing to do with America, Europe, Asia or any state.

    It is quite common praxis not to dump any waste and rubbish on our neighbors doorsteps, but I really dont understand why this is common praxis and accepted with emission and CO2!

  26. Mulga Mumblebrain says:

    I prefer Macbeth in this context,
    ‘… an idiot, Full of sound and fury, signifying nothing’.

  27. Dennis Tomlinson says:

    Mulga, witness the assymetry of our (‘Merikans’) recent response to the Boston Marathon bombing versus the near disinterest in violence elsewhere in the world – particularly the Middle East, a healthy measure of it our own doing – casues me to wonder how “Merikans’ could ever not be the ‘Xeptional Ones’.

    Meanwhile, we few gathered at the secret, secluded Party Headquarters, publishing by the light of a lone flickering candle, keep putting out the same message: “I think I can.” “I think I can.” “I think I can.” …

  28. The preindustrial CO2 equivalent concentration is just the CO2 concentration in the 1700s. The definition of CO2 equivalent concentration is the level of CO2 in the atmosphere that would result in the same climate forcing as calculated for all the forcings together in some future year. The appropriate reference point in this case is the CO2 concentration in preindustrial times.

    There are additional complexities, which are explored here:

  29. Mike Roddy says:

    I stand by my statements, Secular. In 2009, there were over a dozen large plants planned, with identified sites. Four years later, only three are being built in California, and several companies went broke. Investors got spooked, greatly raising the cost of capital, and killing feasibility. Your information about lots of plants being under ways is the same dream we heard in 2009.

    Brightsource, which is finally building their Ivanpah project, lost $400 million due to the delays, and reorganized and built out of pure stubbornness. The oil and gas companies won this round, but it’s not over yet.

    Catellus is the main force behind sabotage of solar, through a fake green outfit called Wildlands Conservancy. Catellus is a commercial real estate and desert land speculation company. With Feinstein’s help, they made a major score by swapping desert land for a $20 billion gold vein in the Chocolate Mountains. They want solar on their land, and their commercial rooftops, and have been eliminating competition.

  30. Joan Savage says:

    Thanks, It’s useful to know and make clear that the convention is to ignore pre-industrial methane and NOx levels.

    Adding them in, your graph would show a higher pre-industrial baseline, yet the impact of the soaring doublings would undoubtedly be still detectable.

  31. J4Zonian says:

    Maybe I missed it but nowhere did I see an attribution of your title quote. I don’t know the source but the author is Native American activist Ruben Snake.

  32. J4Zonian says:

    I nominate Michelle.