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Humans on the verge of causing Earth’s fastest climate change in 50m years

Posted on 17 April 2017 by dana1981

A new study published in Nature Communications looks at changes in solar activity and carbon dioxide levels over the past 420 million years. The authors found that on our current path, by mid-century humans will be causing the fastest climate change in approximately 50 million years, and if we burn all available fossil fuels, we’ll cause the fastest change in the entire 420 million year record.


Changes in atmospheric carbon dioxide and in the combined solar and carbon dioxide forcing over the past 420 million years. Illustration: Foster et al. (2017); Nature Communications.

The study relates to a scientific conundrum known as the “faint young sun paradox” – that early in Earth’s history, solar output was 30% less intense than it is today, and yet the planet was warm enough to have a liquid ocean. A stronger greenhouse effect due to higher carbon dioxide levels in the atmosphere may be one explanation.

Over time, solar output has grown stronger, and atmospheric carbon dioxide levels have fallen due to an effect known as “weathering” of rocks and an increase in plant life. The authors of this study found that over the past 420 million years, the slow heating of the sun and slow decline of the greenhouse effect have roughly offset each other, leading to a fairly stable long-term global climate.

solar co2

Changes in the solar and carbon dioxide forcings over the past 420 million years. Illustration: Foster et al. (2017); Nature Communications.

In particular, as shown in the first chart above, Earth’s climate has been fairly stable over the past several million years. The wiggles in the blue line represent transitions in and out of ice ages, due to wobbles in the Earth’s orbit around the sun, amplified by changes in the amount of carbon dioxide in the atmosphere (these are known as Milankovich cycles).

The bottom frame in the chart shows the change in forcing (global energy imbalance) caused by the combination of changes in solar activity and the greenhouse effect. When the line is flat, the Earth’s energy balance is stable, and thus so is its climate. When there’s a steep change, something is upsetting that balance and causing a rapid climate change. The five colored lines toward the end of the chart show potential pathways we’ll follow, depending on how much fossil fuels humans burn over the coming decades.

In every case the line is already quite steep due to the hundreds of billions of tons of carbon pollution humans have dumped into the atmosphere thus far. The size of the global energy imbalance we’ve caused is already on par with those previous blue wiggles – Earth’s ice age transitions. If we keep burning lots of fossil fuels, we could soon cause higher carbon dioxide levels and faster climate change than the Earth has seen in 50 million years. If we burn all available fossil fuel reserves (the black “Wink12k” line), we’ll see faster climate change than in the entire 420 million year record.

It’s an alarming proposition. Climate deniers will often argue against taking action to curb carbon pollution because climate changed naturally in the past and carbon dioxide levels were higher in the past. One Republican congressman repeated these talking points in the latest House “Science” committee hearing. While both arguments are technically true, they miss several important points.

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Comments 1 to 16:

  1. The " Wink12K scenario" is based on this article, speculating the realease of 10Pg anthropogenic C, is the first such scenario I've seen. Apart from being unrealistic (only 5PgC of recoverable FF reserves have been estimated), I think homo sapiens would be technically unable to burn it before the transit climate change effects wiped off or seriously crippled the whole FF burning infrastructure. Then, it comes the increasing awareness that will put more pressure to curb the burning in the future, with possibly other/renewable energy sources replacing it. So, we can safely cross that Wink12K scenario as impossible.

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  2. chriskoz @1, while the IEA only estimated 728 Gt (=728 Pg) of coal reserves in 2010, they estimated 17,204 Gt of coal resources.  The difference is that while reserves for reserves, they are recoverable given current mining technology, they are also economic to recover at current prices.  Resources in excess of reserves are also recoverable given current technology, but are not economic to recover at current prices.  The transition from resource to reserve can be quite rapid given changes in technology and/or increased demand.  It follows that the Twink12K (ie, 12,000 GtC) is well within the limits of fossil fuel resources, and what is within the limit of fossil fuel reserves is a matter to be proven by future technological and economic developments.

    That leaves aside emissions from LUC and cement manufacture.

    It is unlikely that we would be able to burn that much fossil fuels before the effects of climate change made further burning of fossil fuels politically infeasible (if not necessarilly destroying the infrastructure, which is no more vulnerable than any other part of our civilizations infrastructure).  In a world where Trump is President of the US, however, there are no guaranttees.

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  3. I also don't think that 12000 Ptg of fossil carbon could be liberated, mainly because, even incluiding the Trumps, Putins et al. pro-fossil fuel politicians and regimes, the human devastation would be so huge that humanity will be destroyed much before that happens.

    As an example, most of the Middle East, that has some of the biggest (and cheapest) oil&gas resources would cross the 35°C (wet bulb temperature) boundary of human survival. Most people die of high fever above that temperature. Imagine hunded of millions of Arabs, Indians, Iranians and Africans storming Russia, China and Europe escaping the uninabitable landscapes behind.

    Behind there would be disaster zones surely taken by extremist groups that would not certainly did a good maintenace to the legacy oil&gas facilities, just like has happened in the areas occupied by ISIS/ISIL/DAESH today, specially if bombed by the Putins and Trumps.

    Given that human component, I don't think we can pass 6°C without destroying the fossil fuel infrastructure (either by climate disasters, political violence or global war).

    This is a negative feedback, given some climate change, the planet become deadly for most people, and the following collapse prevents further fossil fuel burning. This is however the worst kind of negative feedback imaginable, because the biosphere is saved by killing us as if we were some kind of deadly virus or bacteria

    There is catch,  unfortuately: given the huge amount of carbon stored in shallow soil, permafrost and gas hydrates that could be destabilised by warming, maybe  once the human emissions (and the human population) approach zero, those "natural" emissions triggered could push the planet to a state not seen since the Snowball Earth meltdown (i.e. Tmean= 50°C) in the Precambrian, killing everything that is not a microorganism.

    If the Sun has warmed enough since the Snowball Earth meltdown, maybe even a moist greenhouse could be triggered, that will end only when the carbon is sequestered by the flash cap-carbonate reaction. If that is not enough to to compensate for the increasing water vapor greenhouse effect, the greenhouse state will last until Earth has lost most of its water to space, leaving a desert planet behind (I however doubt that Earth is vulnerable to runaway greenhouse like Venus).

    I however have strong hope that nothing like that will happen, because "people can be all stupid sometimes, always there is some stupid people, but people cannot be all stupid alltimes" ( I don't remember who wrote that, any idea?).

    After all, hope is what moved a lot of brave people against very adverse events in the past, and hope is badly needed to face this crisis.

    By the way, I hope you have had a nice Easter.

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  4. green tortoise @3, even in a wink12 scenario, GMST will rise by about 10 C (the temperature at which wet bulb temperature emergencies become endemic in the tropics) only around 2200.  By then, the vast majority of the fossil fuels have been burned, and if on that pathway, it would still take several decades to convert to renewable sources.  Further, even then, a nation determined to "Put America First", or "Put Europe First" rather than putting the globe first, and which was determined to adapt to climate change by massively increased energy use powered by fossil fuels could still power on regardless.

    Do I think it likely that governments will be persistently that stupid?  No!  But while a large number of influential think tanks, and several major governments continue to push "Burn, baby, burn", it is a scenario that ought to be included to show the real consequences of their policies.  That is, in addition to scenarios that undershoot BAU (RCP 6) to guide those who want a sensible response to AGW, we need policies that overshoot it as a warning to those who do not (or those who do, but might be tempted by the massive PR campaign for fossil fuels being run by the likes of WUWT).

    As an aside, I suspect you were tongue in cheek, but the quote was:

    "You can fool all of the people some of the time, and some of the people all of the time, but you can't fool all of the people all of the time."  (Quoted from memory.)  The author was Abraham Lincoln, the first Republican President.  To that, pro-fossil fuel lobby and the most recent Republican President has added the addendum, you can fool enough of the people enough of the time that you can sideline those who see through your nonsense.

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  5. Tom@2,

    Appology for my typo @1. I typed 5Pg and 10Pg (peta-grams == giga-ton), but I meant 5Eg and 10Eg (exa-gram) which is 1000 times more.

    Where did you find your number "17,204 Gt of coal resources" and 728 Gt reserves? I searched various IEA publications but cannot find your numbers.

    From the Wikipedia, the world's proven C reserves are 909,064 Mt. Such numbers obviously change as new discoveries are made and extraction methods (e.g. hydraulic fracking) improve.

    The resources number can be very fluid and change depending on definition of "resources". The one from IPCC AR4, e.g. as shown among other C reservoirs in OA not OK series:

    shows only 3700GtC of all fossil fuel resources.

    Archer 2005, 2007 etc, that we both know very well, considers only a 5000PgC slug in their model. Accordingly, David teaches 5000PgC to be the most likely slug if all FF are burned (a version of your "world where Trump is President of the US"). That number is still nowhere near your number of 17Eg+ of coal only.

    So I wonder where these large differences of various estimates of FF reservoir size do come from.

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  6. Is the following a fair summary?

    On the one hand, we have a continuous increase in the burning of fossil fuels.

    On the other hand, we have the increasingly damaging effects of climate change.

    At some time in the future, climate effects will damage human civilization sufficiently to disrupt the burning of fossil fuels, resulting in a rapid decline in such burning.

    If this summary is valid, the obvious question is: When?

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  7. chriskoz @5, the figure is from the IEA's Resources and Reserves 2013.  With regard to different estimates, this pyramid of US resources and reserves from the EIA is helpful:

    Converting from short tons to tonnes (ie, metric tons) we have 232 Gigatonnes of estimated recoverable reserves, 1514 Gt of identified resources, and a total resource base of 3544 Gt of total resources.  They further estimate that the US has 26% of the world's coal reserves, which would indicate a world recoverable reserves at 892 Gt of global recoverable reserves.

    For comparison, IEA 2013 estimates 8,130 Gt as the total resource for hard coals and lignite in North America (ie, the US, Canada and Mexico).  As that is more than double the US estimate, and the US has more coal than either Canada or Mexico, clearly the IEA 2013 estimate is larger - as will happen given that it is in part an estimate.  If we assume all North American coal is in the US, and scale the IEA 2013 global estimate so that the North American estimate matches that by the EIA, then the global resource would be 7,500 Gt.  Alternatively, if we scale the EIA US resource using the percentage of global share of the reserve, we get a total global resource of 13,630 Gt. Even on the low value, once you throw in tar sands, oil shale, deep sea oil and gas resources, arctic oil and gas resources, antarctic oil and coal (not incuded in any of the above) etc, a civilization determined to "burn, baby, burn" regardless of consequences could far exceed the RCP 8.0 scenario; and the Twink12 scenario is a reasonable scenario for such a strategy.

    As to the large differences in estimates, that will be in part because they are estimates when we are talking about the total resource.  More importantly, many estimates of amount of fossil fuels remaining in the ground restrict themselves to reserves, and/or reserves plus identified resources.  I once did a spread sheet of all the publicly available estimates across coal, oil and gas.  Only a few of the estimates included any oil sands, shale oil or unconventional gas (and they not all of it), and a range of criteria were used.  Of 14 estimats across 9 sources, only 3 provided estimates that may have represented the Total Resource, with estimates of 3000 GtC (World Energy Council 2010, "possible"), 11,000 GtC (S&W 2011, "TRB") and 16,000 GtC (IEA 201, "estimated").  (Note, the values quoted are my estimate of the carbon content allowing for amounts not oxidized due to spills, etc, and for carbon content of the fuel, based on the original resource and/or reserve estimates.  I do not think the WEC "possible" estimate is an estimate of the TRB, but rather an estimate of what part of that base could become economically accessible.  The other estimates nearly match (S&W) or significantly exceed the Twink12 requirements - and all with limited examination of unconventional sources, and without allowing for LUC and cement emissions. 

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  8. Good article. It gives a lot of pertinent info about our situation in some fairly simple graphs. I was surprised to see the RCP4.5 and RCP6 lines so close together especially in the forcing graph (second one) so went back to the SKS post below. And fig 4 in this RCP guide shows that the numbers 4.5 and 6 actually refer to the forcing level (no doubt a lot of readers already knew this). So the gap between 4.5 and 6 seems too narrow when compared to the gap between 0 and 4.5, or am I interpreting this wrong. Perhaps of more interest is that fig 4 also gives temperature anomalies 2.4 degC for RCP4.5 and 3.0 degC for RCP6, and the CO2 eq figures are 650 and 850 ppm. These temperature figures, while bad, aren't as high as I expected, and give a glimmer of hope. James Hansen in Storms of My Grandchildren estimates a conversion of .75 when going from forcing to temp which gives 3.4 degC and 4.5 degC, which are more concerning.


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  9. Digby Scorgie @6, nobody knows, and the time will depend on the rate of fossil fuel burning.  Further, to a certain extent, increased energy resources and be used to counter much of the economic effect of AGW, particularly in highly industrialized areas.  A sufficiently irrational person could greatly extend the time before it became impossible to maintain the technological civilization needed to burn fossil fuels by burning fossil fuels faster and faster.  (This strategy requires calous disregard for those whose economic situation isn't so favoured.)

    I do not think the OP argues for so high a benchmark on disruption, ie, that it will significantly impair our ability to burn fossil fuels.  I think it is arguing that at some point the level of economic harm and natural disasters will catastrophic, potentially to the point of negative economic growth and declining population.  Our civilization can survive declines in both of low percentage; and with it our ability to burn fossil fuels will also be preserved should we be mad enough.

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  10. BC @8, the gap appears compressed because of the use of a log scale on the y-axis.  Further, the scenarios are defined for their forcing as at 2100.  RCP 8.5 continues to expand atmospheric concentration long after that so that its final focing is significantly greater than 8.5 W/m^2.  RCP 6.0, in contrast, maintains a near constant forcing after 2100.  Finally, Twink12 is defined by the number of terratonnes of carbon emitted rather than by forcing (as I understand it).

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  11. Thanks Tom. (BTW - I live in Brisbane too)

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  12. Tom@7,

    Thanks for the pointer to the source publication of your claim. It was an interesting read. And it confirms that the amount on FF reserves can be hgher than I thought beforehand and Wink12K scenario of releasing 12EgC anthropogenic CO2 slug is at least theoretically possible, though constrains other than resource limit can make it unrealistic. I would add that with a CO2 slug that big, the natural feedback of thawing permafrost and unknown mechanisms that can turn the ocean into CO2 source, can contribute to even more CO2 release.


    A conversion of .75 when going from forcing to temp is the fact that Equilibrium Climate Sensitivity used by Hansen is 3K/double CO2 while double CO2 creates 4Wm-2 forcing. Hence 3/4=.75.

    But I think not just ECS should be used to determine temp evolution on the timescale in the OP graph. More appropriate is Earth System Sensitivity which takes into account millenial scale feedbacks, such as melting icesheets, permafrost thaw I mentioned above. ESS is larger than ECS. So, having not read the OP study, I don't understand why the temps on fig 4 are smaller than ECS. From your eyeballing, it looks more like Transient Climate Sensitivity figures - 2K/double CO2 wich is 50% of forcing number in Wm-2 - e.g. 3.0 degC for RCP6. Maybe figure h shows just the amount of CO2 released in each scenario and does disregards the ocean CO2 uptake, optimistically assuming the strength of the ocean CO2 sink will not be affected till the end of the period shown and ESS feedback wil not happen. With such assumptions you can say that ocean CO2 uptake will largely counter-balance the warming progressing from TCS to ESS within decadal to a century timescale and postulate TCS only level of warming on that timescale.

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  13. Even if humans don't burn all the fossil fuels, the rapidly thawing permafrost could boost CO2 to that higher level, or to the GHG equivalent since that would add a lot of methane to the mix.

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  14. Tom Curtis @9

    When the "level of economic harm and natural disasters" becomes sufficiently catastrophic, I can't see anything less than a collapsing global civilization, with huge numbers of people dying of starvation and strife (Syria many times over) and economic activity plummeting as a consequence.  Local civilizations will still survive but far less fossil fuel will perforce be burnt.  Anyway, that's my gut-feeling — but then I'm a cynical old man.

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  15. I confess that I cannot say if Dana's article is good or bad.
    My main observation is that the first chart puts together very different kind of data, which are related to different time scales. So when Dana proposes a comparison between the information of the last panel (h) with information from the previous ones, I am afraid he is pushing his hand in the wrong direction.
    In a way, instead of highlighting the uniqueness of changes that are happening right now, the article promotes the sense that anthropogenic climate change can be fitted into the natural history of the planet.
    Would do you guys think?

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  16. RR... The issue of global climate change isn't that we're going to push the system outside of all historical bounds, it's that we're pushing the system faster than at any point in historical bounds. The rate of change very much is the issue and always has been.

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