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(Fahrenheit) 451 ppm

Posted on 11 December 2011 by Bob Lacatena

A Chilling Thought

The recent Schmittner paper on equilibrium climate sensitivity, estimated by using a simple climate model and a comparison with the Last Glacial Maximum, led me to a new and thought-provoking perspective on exactly what man is doing.  One can use an even simpler model — a simple rule of thumb — to frame exactly what is happening and what we might expect.  One need not even go as far as a simple computer climate model to arrive at an unsettling conclusion. 

Scientists have attempted to define a minimum safe global mean temperature increase, above which we are really taking our chances and rolling the dice.  To stay within this they have computed a threshold of CO2 levels beyond which we should not go.  Based on a best estimate of climate sensitivity of 3˚C per doubling of CO2 and a target temperature increase of 2˚C, the CO2 target level is 450 ppm.

But 451 ppm is just as important a number.

Of Knobs and Levers

CO2 is termed the Earth's biggest control knob.  It hadn't been until now, because a knob implies something that someone can turn to control things.  In a normal, natural world and on relatively short timescales, say tens of thousands of years, carbon dioxide is interlocked with global mean temperature and other variables.  Temperatures can drive carbon dioxide levels up or down, which in turn drive temperatures further up or down.

Carbon dioxide acts as a feedback that enhances temperature changes.

Figure 1: Vostok ice core records for carbon dioxide concentration and temperature change.

Figure 1: Vostok ice core records for carbon dioxide concentration and temperature change.

This is most obvious during the transitions between glacial and interglacial periods, when temperatures rise or drop and CO2 seems to follow along like a happy puppy.  What is not obvious when looking at the readings is that while orbital forcings cause the initial change in temperatures, and CO2 levels rise or fall in accordance with that initial change, the subsequent temperatures themselves also rise and fall in accordance with the changing CO2 levels.

The basic formula behind a glacial termination is that something (orbital forcings) starts the increase in temperature.  Actually, what really starts it is a change in the length and severity of northern hemisphere summers, without changing the overall amount of radiation reaching the planet at all.  That stays fairly constant.  

These seasonal changes in turn cause the ice sheets covering the northern hemisphere land masses to begin to melt.  This reflects less sunlight back into space, and that really does change the amount of energy that the planet receives from the sun, which leads to warming.  It also results in the release of methane, another powerful greenhouse gas, which warms the planet even further.

Then CO2 kicks in.  The oceans warm.  Warmer water cannot hold as much dissolved carbon dioxide and so the oceans release some CO2 into the atmosphere.  CO2 in the atmosphere causes warming.  The increased warming causes the ice sheets to retreat further, and the oceans to warm further, and more CO2 to be released.

This continues, but with limits.  There is (or had been) only so much CO2 that could make its way into the atmosphere.  The system only pushes this cycle so far.   The many previous glacial terminations in the past 2.5 million years (a period known as the Pleistocene Epoch) have seen lows of about 180 ppm of CO2, and highs between 250 ppm and 300 ppm.

The main point is that temperatures and CO2 are interlocked, or at least had been until now.  Temperature changes had to get the ball rolling, so on a graph they will lead the way, but the two work in concert.  One is not pulling a leash to drag the other along.  They each push and pull the other, working their way from low to high, or high to low, as an integrated system.

CO2 does not "lag" temperature.  That's a simplistic, inaccurate and indiscriminate view of a complex interaction.

Turning the Knob

Unfortunately, contrary to recent natural history, man has learned how to remove the regulator and to dial up a far higher level of CO2 in the atmosphere.  CO2 has become the climate's biggest control knob in the last two centuries or so, in the sense that it is in fact a control that mankind can twist, turn, tweak and, sadly, overdo.

A glacial termination happens on very, very long timescales relative to man.  What we have done in the past two centuries, however, applies a change to CO2 levels — implying an equivalent change in climate — that would otherwise take nature 10 to 12 thousand years.

CO2 was once interlocked with temperature.  In the past 200 years we have instead taken 337 gigatonnes of carbon out of the ground and injected it into the atmosphere and the oceans.  Nature spent the better part of several hundred million years converting that carbon into new forms (coal, oil, gas) and sequestering it deep under the surface of the earth.

Figure 2: Human CO2 emissions (blue, left y-axis, Source: IEA) vs. atmospheric CO2 concentration (red, right y-axis, Source: Mauna Loa record)

Figure 2: Human CO2 emissions (blue, left y-axis, Source: IEA) vs. atmospheric CO2 concentration (red, right y-axis, Source: Mauna Loa record)

Man will be able to undo in 200 years what took nature hundreds of millions of years to accomplish, and in so doing, in that same time frame, we are duplicating a feat that normally takes nature 10,000 years to accomplish (i.e. increasing atmospheric CO2 levels by two thirds).

And, as an important point, we have no idea if we are capable of duplicating nature's feat of again sequestering that carbon underground.  We have far too easily turned the knob in one direction, but with no capacity whatsoever to turn it in the other.

An Ice Age

For the past two and a half a million years this planet has been locked in an Ice Age, the Pleistocene Epoch, during which the poles are always covered with ice caps.  During glacial periods those ice caps extend much further down in the northern hemisphere, covering much of the land and oceans above the 34th parallel.  During interglacial periods, such as the one we are in now, the globe warms, the ice retreats and life gleefully expands to fill the space that opens up.

The common man on the street, however, uses the term "ice age" to refer to that glacial period where the permanent (year round) ice sheets extend as far as Michigan, Ohio, and Germany.

The transition out of such an "ice age" to our current world involves an appropriate temperature increase and an interlocked change in carbon dioxide from 180 ppm to 285 ppm.  It took an increase of 105 ppm, or a factor of 1.6, to get us from an "ice age" into the world in which we currently not only live, but thrive.

We have now, as a matter of the natural development of our own civilization and technology, unlocked vast stores of carbon that have been unavailable to the system throughout the Pleistocene Epoch.

By releasing that carbon — by burning fossil fuels and converting the long carbon chains into carbon dioxide — we have dramatically altered the system.  For 2.5 million years it has been seemingly impossible to naturally raise CO2 levels above 285 ppm.  It hasn't happened in dozens of glacial terminations.

We are now at 390 ppm and rising at an average of 2 ppm per year.

Imagine if we were to apply the same change to our world as was required to shift the planet from a glacial to an interglacial period (or in incorrect but layman's terms, from an "ice age" to our current climate). What if we were to raise CO2 levels from 285 ppm by an equivalent factor of 1.6?

That would mean raising CO2 levels to 451 ppm.

We're at 390 ppm now.  Moving from 390 ppm to 451 ppm is a change of a mere 61 ppm.  At the current rate of 2 ppm per year, with no further growth in emissions, that means we will reach 451 ppm in just 31 years.  By 2042 — by the time a 2 year old today turns 33 — we will have released forces equivalent to the transition from glacial period to an interglacial, from an "ice age" to our current "green age."

A Fire Age

What, then, will this new age, the one that follows our "green age," look like?  Various efforts at modeling and climate science attempt to develop a clear picture of the ecosystem, climatic and weather changes that will result, but while it may be important to anticipate the details, the final answer in a more general sense must at the minimum be very different from the world in which we live now.

If, in common parlance, a glacial period is termed an "ice age," while the world we live in today might be termed a "green age," then I would suggest that we are now heading into a "fire age."

Deserts are expected to expand with the growth of the Hadley Cells.  Droughts and wild fires are expected to increase.  Crops will be less productive.  Sea levels will rise as more and more ice melts.

During the Eemian, an interglacial period that began roughly 130,000 years ago and lasted 16,000 years, temperatures in Europe north of the Alps were roughly 1-2˚C higher than today.  Sea levels were 4 to 6 meters higher.  CO2 levels were roughly at 300 ppm.

Going further back, during a warm period 3 million years ago within the Pliocene epoch, temperatures were a mere 2-3˚C warmer than today (see here and here and here).  Sea levels were 25 meters higher.  CO2 levels were between 360 ppm and 400 ppm.

How much will the world change if we increase CO2 levels to 451 ppm?  Time will tell, but one way or the other we may be duplicating in strength in just 200 years what nature itself requires 10,000 years to do.  We are applying that forcing beyond the point at which nature has always stopped.

We are duplicating within that short time period the greatest single force on this planet that nature alone has wielded for the past 2.5 million years.  But nature does so slowly, carefully and predictably.

We are doing so rapidly, erratically, and without awareness or understanding of the consequences, or even taking long enough to recognize that what we are doing does indeed have an irreversible effect.

A Fire Extinguisher

There are some important points to make to temper this realization.

The first is to recognize that in a glacial termination there are forces at work that are not present in today's world.  The retreat of the vast ice sheets account by some estimates for 54% of the global temperature change during glacial termination.  These changes in ice sheets also have huge effects on ocean currents which in turn affect climate.

In today's world, with ice only covering much smaller areas at the poles, that particular influence on climate change is greatly reduced.  As such we should not expect the same response in temperature, and hopefully in overall climate change, with the same relative increase in CO2.

Best Estimates of Climate Sensitivity

Figure 3: Various estimates of climate sensitivity (Knutti and Hegerl 2008).

 On the other hand, this is a new paradigm and one without equal in natural history.  During a glacial termination, the spread of vegetation actually helps to hold CO2 levels down by drawing it out of the atmosphere and using it for plant growth as the forests of the world reclaim the land once covered by glaciers and ice.  In our world, if things get too bad, huge swaths of vegatation may die, for instance if the Amazon rain forests turn in whole or in part into savanna or if the deserts of the world expand due to changes in precipitation patterns and the growth of the Hadley Cells.  This will have the opposite effect, adding even more CO2 to the atmosphere rather than drawing it down.

It's difficult to predict where things will go.  That's what science and climate models and paleo studies are all trying to determine.  There is some reason to hope that the overall temperature and climate change will not be dramatic, but there's also good reason to believe that the effects will be more than strong enough to adversely affect billions of lives.

Ice Age Fauna of Northern Spain

Figure 4: Now extinct fauna from the last glacial period in Northern Spain (image courtesty Wikipedia Commons).

Decades, Centuries or Millenia

Another major difference is that in the case of a glacial termination the changes in both temperatures and CO2 levels are very, very slow, taking more than 10,000 years, and changing continuously in concert.

In our situation we have ratcheted up the CO2 levels in a blink of an eye from nature's perspective.  In 1800 CO2 levels were approximately at 285 ppm.  By 1900 they were closer to 290 ppm.  As of 2010 they were at 390 ppm and rising fast.

So how fast will temperatures rise? This is another area of study and debate in climate science.  There is a lot of variability in the system.  There is a vast amount of water in the oceans capable of absorbing a lot of energy before the planet reaches a new equilibrium temperature.  The ultimate, final equilibrium temperature also depends on feedbacks, and those kick in at different rates.  How quickly will the Amazon transition to savanna, if at all?  How quickly will deserts expand?  How much natural CO2 will be released and add to anthropogenic sources?  How great and how important will the melting of Artic ice become?  How much methane will be released, and how quickly, from the permafrost regions of the Arctic?

We will reach 451 ppm at the current rate by 2042, but that doesn't mean we'll change the planet that quickly. By 2042 we will have "set the thermostat" to the new setting, but it could take anywhere from decades to hundreds to thousands of years for the planet to reach its final, new equilibrium temperature.  No one alive today will live to see what we have utlimately done to planet.

The one thing we do know is that we are turning the thermostat up with no ability to turn it back down.  We are commiting the planet to a 451 ppm scenario with no firm idea of what that is going to mean and absolutely with no ability to draw CO2 levels back down to their natural 285 ppm levels.

450

It is a pure but poignant coincidence that the number discussed here — 451 ppm — is so close to another number that has been bandied about in recent days — 450 ppm.

450 ppm is — given a proposed, best estimate of climate sensitivity of 3˚C — the target level of CO2 that we must not pass if we want to maintain a reasonable chance of restraining climate change to a mere 2˚C increase.  2˚C has been chosen as a maximum "safe" upper bound to avoid truly dangerous climate change.  Any increase beyond that is deemed to be, by mere rule of thumb, unacceptable.

The math is simple, based on the logarithmic relationship between CO2 levels, climate sensitivity and temperature increase:

Ttarget = Tsensitivity • log2 ( CO2-target )
CO2-initial

In English, this means that given a starting level CO2-initial of 285 ppm, a climate sensitivity (Tsensitivity) of 3˚C, and a temperature increase (Ttarget) of 2˚C, we arrive at a CO2-target of 450 ppm.

2 = 3 • log2 ( 450 )
285

Sadly, we may well find that even 2˚C itself is quite far from acceptable.

451 ppm is, as explained here, the forcing that implies a change from our current climate, a "green age," to a new and foreign world, just as it accompanied a change from an "ice age" (i.e. a glacial period) to our current climate.  That forcing caused a change in global mean temperatures of 3˚C to 5˚C, and completely recast the surface of the planet from one of sheets of ice to flourishing green.

One does not need a fantastic education in science or climate science to make a fairly basic, rule of thumb observation of where we may be headed.

One has to look at the similarity in these two numbers, 450 and 451, and wonder if nature isn't, in some small, intelligent-design kind of way, trying to tell us something.

CO2 Targets

Figure 5: Target CO2 levels.

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Comments 1 to 50 out of 106:

  1. Scary!
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  2. "It took an increase of 105 ppm, or a factor of 1.6, to get us from an "ice age" into the world in which we currently not only live, but thrive"

    It took a solar forcing change of roughly 1% (more at higher latitude, less at lower) plus a decrease in albedo from melted ice (and other non GHG feedbacks) and the GHG feedbacks that we have now turned into forcings. Unlike solar and GCR, CO2 was never* a control knob before but it always was an amplifier of other forcings during the glacial periods. *It was a control knob rule once or twice.
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  3. Eric (skeptic) @2, CO2 was the primary control knob at least twice coming out of snowball earth conditions, and again at the PETM, and probably the largest mass extinction the Earth has yet seen, the Permian-Triassic Extinction, in which 96% of marine species went extinct. As can be seen from the following figure, it has also been the control knob for warm periods in the Cambrian (C), Silurian(S), Devonian (D), Triassic (Tr), Jurassic (J), and Cretaceous (K). It's low abundance has been the dominant control knob in glacial periods in the Carboniferous (C) and Neogene (Ng). It is true that within the neogene, and in particular over the last 5 million years CO2 concentrations have been driven temperatures, and have been only the second major driver of temperatures (after the albedo changes due to extensive ice sheets and sea ice). It is, of course, that last period which Sphaerica discusses.



    Richard Alley has a very informative lecture on the subject, and while he is certain that the level of CO2 in the atmosphere has been primarily driven by different rates of volcanism (emitting CO2) and weathering (absorbing it), over the last 5 million years those two factors have been approximately balanced. The Earth has not fiddled with its control knob in the entire time of human existence, until we decided to give it a yank and see what happens.
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  4. Thanks Sphaerica.
    It dismays me that BAU continues unabated when it is so clear that we are off the map, in the sense that we have no record of having been here before. What we are heading into could be as different from what has happened in the past as the difference between receiving a push, and getting hit with a club. The same amount of force is applied, but over a much shorter time frame.

    I've been looking around for a chart/graph of world food production. I'm trying to see what impact recent droughts, floods, and heat waves have had on our ability to feed the world's population. In particular, I'd like to see if the 3-sigma heat waves that Hansen so clearly described show up as some sort of signature when overlaid.

    If they do, then you could almost project forward a range for population and a range for food production, accounting for the expected increase in extreme heat waves (and droughts, and floods, if the data are available). When the population intersects production, the cull starts in earnest. I don't agree with everything that Lovelock says by a long shot, but I am beginning to think he might have gotten the major point correct. (I thought it was almost comical that professors asked him where they should buy land; as though refugees would leave you and your belongings alone because you had a printed title.)

    It will not happen all at once and everywhere. Rich nations or those with a strong military will gather resources to themselves, and be able to preserve their populations for longer than poor nations. But I don't see that lasting indefinitely. Although, it may be that food shortages tend to produce internal wars more than external ones.

    Forgive me; I hate to be a pessimist, but I'm starting to wonder if the survivors would be better off if the cull starts sooner rather than later, in the sense that, whatever environment is left will be more habitable. The damage that, say, 8 billion people can do is surely less than the damage that 9 or 10 can. Also, in non-human populations, there seems to be less over-correction when a sustainability threshold is crossed by less than it is when is crossed by more.
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  5. Chris,

    Do not forget diseases. In the grand experiment of ours, we are going to be shifting the ranges of various tropical and rather scary diseases. Also we will expand the range of many others and allow for the intermixing / genetic enhacement of many virus strains in a way similar to what has happened to the recent swine flu.

    Nature has a way of self-correcting. Does not mean we will be in the plan.

    Hate to be pesimistic too, but I cannot see how we will be able to change our course with the kind of collective burying of heads in the sand.
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  6. Very interesting, Sphaerica. I think you've over-anthropomorphized nature ("carefully and predictably"; "trying to tell us something"). This is all in the interpretation, I might argue. But you make good points in support of your other interpretations, so I shant complain too much.

    I'm left wondering, though, is it better that we're emitting all this CO2 when solar irradiance of high latitudes is declining, or does that make things worse?
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  7. 451 in 2042? with C02 rising at 2.1ppm a year for the next 22 years, I come up with 443ppm- in 2035 now that's with 2.1ppm- what if that increases to an average of 2.5ppm a year-? That brings us to 450 ppm in 2035.
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  8. Is there any evidence of large methane releases at the end of glacials? And if so what is their source?
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  9. Lloyd Flack @8: Yes - methane record in EPICA Dome C ice cores. See http://www.ncdc.noaa.gov/paleo/pubs/spahni2005/
    for measurements. It's thought that the methane is released from northern hemisphere tundra during Dansgaard-Oescher warming events at the end of glacials, then propagates to the Antarctic.
    Methane levels in the ice cores vary from 400-700ppb. Today they are at 1850 ppb.
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  10. "CO2 does not 'lag' temperature. That's a simplistic, inaccurate and indiscriminate view of a complex interaction."

    Analysis of time series data for the last 800,000 years from Antarctic ice cores indicates that the temperature at time t, T(t), is most highly correlated with the atmospheric carbon dioxide concentration at time t+2000 years, [CO2](t+2000). We than therefore say that CO2 does in fact lag temperature for those time series. Certainly, any statistic is "simplistic" in the sense that it is some kind of reduction of data. But you can call it inaccurate only if you can show an error in calculating the statistic. For many purposes, we need "simplistic" information such as "average global temperature" or "mean sea level." How discriminating a person should be depends on the purpose. Statistical relations between variables can only suggest what might be and what probably cannot be. In other words, an adequate model of a complex dynamical system with many variables, with nonlinear interactions, and with variable time lags in feedbacks should produce outcomes with statistics similar to the statistics of the system being modeled.

    If increased CO2 did not initiate historical temperature rises to an interglacial period, then what GHG, if any, was involved? An abrupt increase in the atmospheric CH4 concentration from the region of 350 to 400 ppb to the region of 700 to 800 ppb seems to slightly precede the steep temperature rise on the exit from a deep ice age (glacial period).

    Here is Fig.3 in a paper by Alexey V. Byalko on the paleoclimate published in the journal Priroda [in Russian] (No.12, 2009, pp.18-28). The entire issue is downloadable as a pdf file (5 Mb).


    Cross-correlations (covariances): The blue curve is temperature and CO2, the red curve is temperature and CH4, and the green curve is CO2 and CH4.

    Here is an English translation of Byalko's discussion of that figure in the paper referenced above: "The cross-correlations (covariances) of these variables give even more information. They are presented with a higher time resolution because the shift of the maxima of these functions forward or backward from zero indicates which variable is leading, which is lagging, and with what characteristic time. As Fig. 3 shows, temperature and [CO2] are closely coupled at small times with a maximum covariance equal to 0.88 reached with the temperature leading by about 2 ky relative to [CO2](t). The accuracy of calculating lags and leads, regrettably, is not yet good, being around 0.5 ky. The temperature and methane concentration turned out to be almost synchronous, but their maximum covariance is lower, equal to 0.82. Finally, CO2 concentration lags behind [CН4] with a 1.5 ky average lag; their maximum covariance is equal to 0.74. The logic of this time lag can be explained by the process of oxidizing methane into carbon dioxide."

    Methane release from Arctic permafrost was probably not involved in past major warming episodes, at least not until the Arctic ice sheet had receded. It seems likely to me the significant increase in atmospheric CH4 preceding those warming episodes involved releases from the benthic methane hydrate stores. So now I have the question (which can only be answered speculatively at the present): What if the CO2-induced warming leads to release of CH4 from both benthic and permafrost stores? Would this lead to a major warming episode, of which several have occurred in the past 800,000 years, but starting this time from a warm interglacial plateau and not from the depths of a deep ice age?

    One research project has been involved in trying to find related answers. I quote a couple passges, one long and one short, from their webpage. The long passage: "This effort will develop, for the first time, a tool for the systematic quantification of the potential impact of dissociating marine hydrates on the global climate. The results of this study will be important in testing the validity of the Clathrate Gun hypothesis, and the corollary hypothesis that rapid hydrate dissociation can have a cascading effect resulting in enhanced hydrate dissociation and accelerating global warming, with potentially catastrophic physical and economic consequences."

    The short passage: "Current Status (November 2011): All project research has been placed on hold due to ongoing funding issues."
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  11. BillEverett@10: the Antarctic methane correlates nicely with D-O events. It's been hypothesized that D-O events might have modified the thermohaline circulation, which would have led to Antarctic warming. There's some indication that Caribbean waters warmed too. So it could well be benthic methane.
    It sounds like Byalko is suggesting that oxidation of methane is what causes the CO2 to increase later - explaining the time lag between temp and CO2 (in other words, I read what he says as saying that the methane causes the temp rise, and produces CO2 when it oxidizes, raising the temp still more). That's an interesting idea that I've not seen before. Am I interpreting him correctly?
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  12. Bill, the fact that the cross correlations are so broad means that, as a function of lead and lag in a control system, the effects of CO2 cannot be treated as a simple lag. Whether that qualifies as "inaccurate" or not may fairly be considered a matter of opinion, but it certainly supports Sphaerica's contention that it's "simplistic" and "indiscriminate."

    Running a simple cross-correlation with existing modern CO2 and temperature records and then sweeping it across +/- 20 years or so (using the annual record) produces a similar result - CO2 is leading temperature, but the cross-correlation is high (greater than what could be expected from random noise) across the entire period.
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  13. @ Lloyd Flack @ 8
    "Is there any evidence of large methane releases at the end of glacials? And if so what is their source?"
    I would refer you to Davy et al 2010:
    "Comparison of the history of oxygen isotope variation (Figure 2) with the amplitude variations observed on the “Parasound” sub‐bottom profiler data enables matching of climate cycles over at least the last 0.6 My. We interpret the high‐amplitude reflection horizons to correspond to peak glacial stages and subsequent glacial‐interglacial transitions prior to the resumption of higher carbonate sedimentation in interglacial periods."
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  14. Bill : An abrupt increase in the atmospheric CH4 concentration from the region of 350 to 400 ppb to the region of 700 to 800 ppb seems to slightly precede the steep temperature rise on the exit from a deep ice age (glacial period).

    I used to read that, contrary to this assertion from Byalko 2010, there was a lag too between temperature rise and CH4 rise, for example Delmotte et al 2004 or discussion in Konijnendij et al 2011 . Does Byalko refer to other paleoclimatic works for justifying that CH4 rise precede the temperature change or is synchronous with it ? I do not read Russian but there are probably some publications on this subject referred in his article.
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  15. Sphaerica : your metaphor of 'Fire Age' with mention of Amazonian drought and deserts' extension suggests that a warmer world will not favour vegetation on a global scale. But if vegetation models coupled to AOGCMs do simulate a regression of tropical rainforests, they also obtain an overall increase in net vegetal biomass with increasing CO2 and T, at least in some recent works like for example Notaro et el 2007 , O'ishi et Abe-Ouchi 2010 , Jiang et al 2011 . Or they detail many regional differences in vegetation response as in Levis et 2010 . For Amazonian drought, I mention this special issue of the New Phytologist. Its "whole or part turn into savanna" is at least an uncertain pathway, see Ramming et al on the risk of Amazonian forest dieback.
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  16. 15, skept.fr,

    I don't disagree that in the long run the planet may well be much greener. When a few thousand years have passed and new layers of topsoil are generated in the far north, and plants have shuffled around enough to find the ecosystems in which they do best, then the increase in overall atmopsheric moisture and plant-habitable regions at northern latitudes may well make the planet qualify as "greener."

    From a human perspective, however, places that are green now are going to brown. I'm scared to death of the expansion of the deserts, the loss of the Amazon, and most importantly serious agricultural difficulties in the US Southwest/Midwest and just as importantly Mediterranean Europe.

    I'll stick with the "Fire Age" analogy simply because it's too easy for people to fall into a too simplistic "CO2 is plant food, it must be good, yay, the planet will get greener" mentality.
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  17. Aye, Sphaerica, and while I'm sure that skept.fr understands the following comment, others may not: if the planet stays just as green as it is now but viable areas for agriculture shift hither and fro, massive economic and social disruption will still occur. The bottom line doesn't describe the reality on the ground. In some ways, humanity is in a very good position to tackle the problem (technology). In other ways, we're in the worst possible position (political and economic complexity and fragility).
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  18. lovelock did this simple modelling awhile back and has written a number of books in plain english on what this warming means.
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  19. Surely this should be forwarded for publication in a proper journal. It just might concentrate the minds of those that think we can relax now that we have a global agreement on CO2 reduction and can't hear the deafening clatter of the can being kicked down the road, yet again.
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  20. Sphaerica : the papers I linked did not deal with long term equilibrium sensitivity ("a few thousand years"), but with near term CO2 doubling or 2100 projection in a A family scenario. I've personally no prior assumption about greening or non-greening world, because there so many factors to be considered in plant growth (CO2, T, water, nitrogen, etc.). That's why I rely on vegetation-GCM models as best estimates of our current understanding.

    More broadly, I understand you're scare to death but as Durban COP17 ends, my own reflexion was that 'scary scenario strategy' is quite unable to accelerate political decisions, and will probably be as unable in the near future. First because the more scary are your projections, the more uncertain they (usually) are, so you expose yourself to the suspicion of unbalanced view. Second because India, Brazil, Indonesia and dozen of emerging countries do not basically object the reality of climate change (and the eventuality of huge and fast regional changes). No, they want to escape poverty, so as Western societies did thanks to fossil energy and the 120 ppm added to atmosphere since the 19th century (these 120 ppm are not just radiative forcing, they're also the historical witness of Western access to welfare). Give solutions to do so without relying massively on oil, coal and gas, and scary scenarios will be perfectly useless because climate targets will be fully compatible with development commitment. I think it is the Gordian knot in the new era of climate debate, as denial of basic science looses its (already low) influence except on the right wing of Republicans.

    And conversely, I think excessive metaphor of 'Fire Age' against misleading horizon of 'Green Paradise' is mostly a low-effect rhetoric game. No national representant at Durban denies the 2K / 450ppm target as a necessity from a climatic point of view, and it means all national representants grossly agree with adverse effects of a too fast and huge warming you describe here. That is no more the central point IMO.
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  21. skept.fr#20: "excessive metaphor of 'Fire Age' against misleading horizon of 'Green Paradise' is mostly a low-effect rhetoric game"

    It would be nice if that was only a metaphor. Marlon et al 2009 find paleo correlation between rapid climate change during recent de-glaciation and fire activity in the US:

    Intervals of rapid climate change at 13.9, 13.2, and 11.7 ka are marked by large increases in fire activity. The timing of changes in fire is not coincident with changes in human population density or the timing of the extinction of the megafauna. Although these factors could have contributed to fire-regime changes at individual sites or at specific times, the charcoal data indicate an important role for climate, and particularly rapid climate change, in determining broad-scale levels of fire activity.

    Marshall et al 2008 make a case for increased fire frequency as temperature/precipitation events become more erratic:

    As climate change continues, we can expect increased precipitation variability (ie more frequent wet-and-then-dry periods). In addition, fuels are already being dried by earlier snowpack disappearance, earlier commencement of transpiration, and higher temperatures. Such changes in fire frequency or intensity are almost certain to influence ecosystem structure and function.

    If you've lived through a fire season, you'll agree this is no rhetorical exercise.
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  22. Well I would agree wholeheartedly that "emerging" countries want to escape poverty and need to be more energy intensive to do so. On the other hand, they are the most vulnerable to rapid warming on the whole. The killer in this, is that Western world created the problem but is extremely unwilling to commit to change or to pay for consequences. While the western world won't make meaningful change, the rest of the world wonders why they should be making the sacrifices instead. Worse still, the countries with the highest historical contributions to elevated CO2 are also least affected. It swings on the question of equity. At present, dealing with a generational level problem, the world is committing to go to hell in a handbasket rather than face up to the equity issue. A frankly, I think the major sticking point for a democracy like US, is the denial of science by Republicans. This constrains what any negotiator can sign for and while the US wont make concessions, you can bet your life that China and India wont.
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  23. 20, skept.fr,

    You are missing the point of the "Fire Age" analogy. The planet may well green overall, given enough time. But critical, agriculturally productive and heavily populated areas of the planet are in serious danger of suffering the opposite.

    Consider this prediction of precipitation changes (ensemble average for the Medium A18 emissions scenario) from Climate Wizard:



    I think the odds are stacked very heavily against Texas, Southern California, Mexico, Spain, Italy, the Balkans, Israel, Egypt, South America and others. Large parts of the northern USA, Canada, far northern Europe, Asia and others may well see a greener world. But some very basic parameters look to combine to make those particular changes fairly likely.

    Everyone is going to experience the upheaval of change, however, and that is the main point. The world is going to change, probably more quickly than people expect, and that is going to be both expensive and painful (in a real, personal sense for too many people). It doesn't really take much beyond common sense to look at things at a high level and to say that it is not worth the risk. Not when inexpensive, coordinated, moderate action now is capable of keeping the situation under control with far less expense than is seemingly inevitable given a continuing course of almost inaction.

    From the perspective of actual, living people and today's civilization, the term "Fire Age" may well seem appropriate.
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  24. @newcrusader

    Never heard about exponential functions (e.g. compounded interest)?

    If you add to a solution, the concentration grows exponentially. Actually any kind of growth is exponential => Growth is an Exponential Function
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  25. I think newscrusader's point was that I was actually being generous by hoping that we'll simply hold emissions constant and thus forestall 451 until 2042.

    Obviously continued economic growth in India and Asia could even offset global efforts to reduce emissions in other ways, and hence lead to a higher annual emissions and reaching 451 more quickly.

    Honestly, things are already bad enough. I felt like I was pretty even handed in presenting the possibilities, without even being realistic about things such as increases in annual emissions.

    But for myself, I just didn't want to think about getting to 451 before 2042.
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  26. Wonderful clarity and completeness. Can I have permission to add this to my book as an appendix. It would be a wonderful convenience, rather than just the URL reference.
    My book proposes a solution based on use of the energy of latent heat in the atmosphere to resolve, energy, water, and land problems--- thus all commodities at once.
    Thanks,
    Atanacio Luna
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  27. #21 muoncounter : about fire in this particular sense (non metaphorical), see also this very interesting paper from Withlock et al 2010 .

    #22 scaddenp : I totally agree that the ‘equity issue’ (ie historical responsability of Annex I UNFCCC countries) is a basis for a future international agreement. But for that I read about BRICS’s position in COP or in their national climate plans, it won’t be sufficient : emerging countries are not just searching symbolic rewards, but primarily material developments for their people, the same material developments Western countries has already achieved. I hope non fossil energy will be able so sustain such a quest and I think it’s now a major point of reflexion. But the same is true for US government choices : pipeline from Canadian tar sands, deep offshore GoM, shale gas and oil won’t be given up because of the future (and still uncertain) cost of droughts in 2050s or 2100s, as the present (and certain) cost of their too rapid abandonment would be huge for a heavily fossil-dependent society like the US. Find substitutes (even 10% more costly for a carbon tax compensation) of the same amount, and you’ll find the solution.

    #23 Sphaerica : as your map for 2080s clearly shows, their will probably be winners and losers in precipitation trends. Same is likely true for vegetation growth capacity (precipitation skills of models are still poor, but it is the best we have). That’s why I consider the Fire Age analogy as a good metaphor for regional changes (including probably France ‘sud de la Loire’), but not global changes.

    Anyway and beside the metaphor itself, concerning human choices in the 2010s, I think these two-generations-from-now predictions can not be considered as ‘killer arguments’ in the climate debate. For an example : Spain is a already a semi-arid country who, like others here in Europe, has known a strong warming in the past 30 years (approx 0,5K/dec since the mid-1970s for Spain, if I remember correctly). But in the same time, Spain is a leading exporter of fruits and vegetables and its most productive regions are in the warm South of the country (intensive hydroponics cultures adapt to climate variations, which change mainly the season of growth : in a warmer climate you get the first strawberries in march rather than april, february rather than march, etc.). I think there is a kind of ‘basic instinct’ for such short term adaptations to change and it is very difficult to fight that psychological bias, even with the scariest projections. And for my part, I refuse to endorse particular projections without mentioning their relative level of confidence or the existence of opposite view in the literature (I mean the ‘serious’ view in the 'serious' literature). That’s why IPCC reports are my ultimate reference because it’s their job to check all publications on a subject and to give an informed assessment on what we know.

    But mainly, my basic point is that such long term predictions are no more at stake in climate negotiations. I’m pretty sure nearly all negotiators have these kind of risks in mind, even before Durban COP17. But they have other risks in mind too for their socio-economic pathways, and that’s why they probably refuse a too fast or too constraining treaty (particularly if they benefits of very cheap energy as producers of coal, gas or oil, of course).

    But of course, our discussions have their own interest, as we can compare and evaluate our views on climatic change.
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  28. Well presented Sphaerica with much to consider. I personally am most intrigued by the paleoclimate studies focusing on the mid-Pliocene around 3 mya to see what sort of climate we may be in for. In determining the overall impact on humanity three key issues are of course paramount:

    1) The effect on the food grains. How will wheat, corn, etc. do in a warmer world? Might they survive but their prime growing regions be shifted? What about genetic modifications to these crops to make them more successful in a warmer world?

    2) How will the world respond to and accommodate climate refugees? Mass migrations are possible, and this could lead to conflict if not managed well.

    3) The biggest unknown is the response of the oceans. Rising oceans may play some role, though I think accommodations can be made to mitigate the worst, but more importantly is the overall health of the oceans in terms of the biological and ecological parameters. The ocean has this far buffered us from the greatest impacts from the large scale dumping of CO2 into the atmosphere. This buffering has taken place on two levels: the retention of excess heat and the direct uptake of CO2. So the big question is-- how will the the ecosystems of the oceans respond to being warmer and more acidic? The answer to this question is important, perhaps even key to the overall health of the rest of the planet.
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  29. skept.fr#27: Other than the word 'fire' in the title, is there any relevance in the Withlock reference to this discussion?

    "their will probably be winners and losers in precipitation trends."

    I love that kind of thinking.

    Tweaking sphaerica's climate wizard settings a tad, look at the change in precipitation in summer for a few of the other ensemble percentiles. The growing season across a wide range of southern Europe, the middle east and west/central Asia, South America, western North America, southern Africa and much of Australia is at risk. In that scenario, there are no 'winners and losers.' Displaced populations and pressure on world food supplies will show no favorites; it's naive in the extreme to think that 'it will be greener where I live' makes one a 'winner.'
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  30. "But the same is true for US government choices "

    Yes, there is broad agreement that there is pain in the future but we dont know how much. Even when we are confident that future pain will be worse than taking action now, however, there is an extreme reluctance to do so. The west has no concept of the idea that since we caused a problem, then it behoves us to take responsibility for it, even if it causes us pain. In short, we want the rights but not the responsibility. For all the lip service to equity, there is no intention of giving it, unless a way is found to do so without reducing standards of living and growth in the west. Now I am all for maintaining my standard of living if a way can possibly be found to do so. I am not however prepared to compromise the future of my children and grandchildren to maintain that. Those pushing anti-science are. We need precautionary measures first and then see if we can find a way to prosper within those constraints. Instead negotiators are settling for wild hopes, and a refusal to accept constraints unless there is a way to do so without causing any rich person some pain.
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  31. Sphaerica, this is the skeptic sight so I imagine one would be skeptical of post 26, but I have spent 40 years on it, and have a masters from UCI, so please consider it. May contact me at p*******y@gmail.com. I hope this is not breaking spam rules, if so please forgive me.
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    Moderator Response: [Sph] E-mail address edited for privacy.
  32. @28 muoncounter : "Other than the word 'fire' in the title, is there any relevance in the Withlock reference to this discussion?"

    Quite surprising, did you read the paper? In #21, you speak of climate change and fire correlation. Withlock et al 2010 have developments on weather/climate conditions of fire in climatic archives, but also on all factors influencing fire, including vegetation change. If you consider that as OT, then your #21 wat OT too.

    For 'winners' and 'losers', replace these undue notions by there will be 'regions with more/less precipitation and greening'. That was my initial point in #15, the idea that vegetation will regress globally does not seem to be supported by vegetation models coupled to AOGCMs.

    Don't understand what you mean by 'tweaking climate wizard settings a tad' and how you get summer (or any particular season) precipitation on this site. (For extreme events, I guess the recent SREX is the most updated reference of the expert view. There is just the SPM for the moment, where I read : "There is medium confidence that droughts will intensify in the 21 st century in some seasons and areas, due to reduced precipitation and/or increased evapotranspiration. This applies to regions including southern Europe and the Mediterranean region, central Europe, central North America, Central America and Mexico, northeast Brazil, and southern Africa. Elsewhere there is overall low confidence because of inconsistent projections of drought changes (dependent both on model and dryness index). Definitional issues, lack of observational data, and the inability of models to include all the factors that influence droughts preclude stronger confidence than medium in drought projections.").

    If feeding the world is "at risk" (for change in precipitation), I suppose the global primary productivity conditions in 2050 and 2100 is the most wanted information. Because even today there are deserts, droughts, etc. so agriculture adapts to changing conditions and moves if necessary, many countries depend on regional and global trade rather than sel-sufficiency. At least, it is not unthinkable to imagine that there are adaptative capacities in two or three generations (agriculture was different from now in 1970 or 1930). Conversely, feeding the world without directly or indirectly fossil-assisted technologies that sustained current productivity (mechanical engines, fertilizers, construction of irrigation and stockge systems, R&D biotechnology, etc.) is a challenge, and I'm quite surprised that nobody considers that there are some "risks" here too...
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  33. #30 scaddenp : I globally agree with you. AFIAK, UE negotiators accept the principle of 'common but differential responsibility' in AGW diplomacy. That's why the Kyoto Protocol or the 20-20-20 European climate plan are not bound to commitment by other parties, from Annex I or non-Annex I. And that's why the first, second and third world will not have the same reduction targets in an (hypothetical) 2015 agreement.
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  34. skept.fr#32: Withlock deals with fire's role as an ecological process; re-defining fire-regime triangles has nothing to do with this discussion.

    Customizing the settings on climatewizard.org is straightforward. One of the options in a drop-down menu under 'Measurement' near the top is seasonal, monthly or annual.

    "For 'winners' and 'losers', replace these undue notions by there will be 'regions with more/less precipitation and greening'."

    'Winners' and 'losers' were your choice of words; their replacement with gentler sounding euphemisms is mere semantics.

    "many countries depend on regional and global trade rather than sel-sufficiency."

    That's the point - the global interdependency of the world food supply is exactly why there can be no winners.

    "it is not unthinkable to imagine that there are adaptative capacities"

    Imagine the cost when those 'capacities' need to be developed and brought online at short notice because we sat around, pacified by those who claim 'its not bad,' and did nothing.

    Seems like we've had this conversation before.
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  35. skept.fr @20, no national representative at Durban may deny the 2 degree C, 450 ppmv target, yet they have all just signed of on a deal that almost guarantees that we will exceed that target.
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  36. For me, the biggest fear has been that we're duplicating the conditions that led to the Permian Extinction Event:

    Smoking Gun: Greatest Extinction in History was a Volcanic, Coal fired, Greenhouse Event

    Sphaerica, how would that fit in with your analysis here? Are the Siberian Traps eruptions the closest natural analogy to modern fossil fuel combustion? If so, assuming worst-case scenarios (human CO2 emissions continuing to grow, Arctic belching methane at an ever-increasing rate, natural carbon sinks overwhelmed or turning to carbon source, etc), how soon could a new, Permian-esque mass extinction start?

    Apologies for lack of scientific precision in my question; I'm coming at this issue from a layperson's perspective
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  37. I hate to add to the gloom but given that we are staying on a very high emissions schedule so far and given that we can't change everything in less than decades even when we really decide we must, CO2 may go to 600 ppm or more. This could start serious carbon feedbacks and bring PETM-like instability for a few million years.
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  38. skept.fr @ 27 "...winners and losers in precipitation trends."

    That Climate Wizard map looks rather mild compared to this.
    Whatever the extent of drought in coming decades, considering drought alone overlooks global bunched precipitation. A few paper are linked here and there are more. The weather that seems to be coming at us is floods some places, (some keys to floods and excessive rain are here) drought some places and bunched precipitation (also not good for agriculture) in between. Winners may be scarce.
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  39. 36, PixelDust,

    I wouldn't go nearly that far. Again, to some extent it is apples and oranges. The world was a vastly different place back then, with one giant land mass, different ocean circulation patterns, a sun that was slightly weaker, etc.

    But I don't think we could ever reach 2000 ppm. Civilization wouldn't last that long, even if we found enough coal and gas to burn.

    The one thing I do find interesting is that CO2 in the Triassic was basically 275 ppm (from what I've found... I'm not that familiar with the period). CO2 for that event seemingly increased to 2000 ppm. That's a factor or 7.78 times. The temperature increase was estimated at 8˚C.

    8=Tsensitivitylog2(2000/275)

    gives a climate sensitivity of 2.79˚C... or roughly 3˚C.

    Funny how that number keeps coming up over and over again.
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  40. This new study looks at bunched precipitation on a very fine scale. This one is broad scaled. The bunched precipitation pattern seems to repeat itself from the global scale down to very small events, almost analogous to a fractal.
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  41. Pixeldust - the Permian-Triassic Extinction is ill-suited as an analogue for our future, because it happened so much slower (1-2 billion tons of CO2 per year, versus over 30 billion tons today from fossil fuel-burning). So the current rate of CO2 release is 15 to 30 times faster than the Great Dying. See: Ocean Acidification in Deep Time -Kump (2010)

    But that's not quite an apples-to-apples comparison, because even though the rate of change was slower, it carried on for a very long time, and we don't have enough fossil fuels to replicate that experiment. The greatest problem is the speed of change is so great, that many plants and animals we depend upon for our survival will probably become extinct, before have they chance to adapt.

    Certainly that's what the paleo record tells us, rapid injections of atmospheric CO2 (and by rapid I mean slower than today's rate) lead to widespread extinction.
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  42. Sphaerica: you're absolutely right that the world was a different place; I was thinking conditions that existed back then (e.g. weaker sun as you pointed out, plus no mass deforestation) would mean CO2 feedbacks weren't as strong as they are now. As if permafrost melting wasn't bad enough, we have ozone damage to worry about too:
    High ozone concentrations can affect not only plant growth, but soil fertility. Plants exposed to low ozone concentrations normally metabolize a certain amount of carbon dioxide. They send carbon to their roots, and then to the surrounding soil. Microbes in the soil make use of this carbon. Plants that are exposed to high ozone concentrations metabolize less carbon dioxide, so less carbon is available in the soil, and fewer soil microbes grow and thrive. Microbial activities that result in soil enrichment and carbon processing decrease, with the result that soil fertility diminishes.

    Pretty obvious vicious circle there :( More fossil fuel burning = more smog/ozone = damaged plant life that can't scrub as much CO2 = even worse positive feedbacks

    That's what I'm trying to figure out; are we on a course where all the natural carbon sinks might very well get killed off, thus leading to a Venus-style runaway greenhouse effect.
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  43. skeptic.fr:

    "it is not unthinkable to imagine that there are adaptative capacities"

    Yeah. Foresight and planning, for instance. Unfortunately, these capacities tend to require accurate risk assessment, which is lacking on the "skeptical" side of the argument.
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  44. Sphaerica @39, being somewhat pessimistic after the Durban result, I'll point out that there are sufficient reserves of fossil fuels to raise the CO2 content of the atmosphere to 4600 ppmv, or about four doublings over pre-industrial levels. It is unrealistic to expect all that coal (primarily) to be mined in under a century, but atmospheric concentrations of 1000 ppmv are certainly on the cards by the end of this century. Current policy is relying on their being no tipping point on natural carbon emissions to avoid going from the disasterous (which current policy seems intent on locking in) to the catastrophic.
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  45. 44, Tom,

    As frustrating as current times are, and as both malignant and foolish as I know people have historically been, I am confident that we'll hold CO2 levels well below 1000 ppm. The evidence will not only be incontrovertible, but down right painful in about 20 years. At that time, the effort to get off of fossil fuels will then cause as much harm as anything else, because we'll have to get off of it fast.

    And we'll have pushed things way too far, and we won't be able to get off of it fast enough. Transitioning far enough away from fossil fuels is going to take a half a century, at least. But I do believe events will conspire to prevent us from being so abysmally stupid that we get anywhere near quadruple digit CO2.

    Unfortunately, I also believe that much lower levels are every bit as dangerous. Perhaps not Great Dying dangerous, but too dangerous to think about for too long.
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  46. Jsquared@11: "Byalko is suggesting that oxidation of methane is what causes the CO2 to increase...methane causes the temp rise, and produces CO2 when it oxidizes, raising the temp still more... Am I interpreting him correctly?"

    First a caveat: I am not any kind of scientist. Therefore, if I incorrectly state some physics or chemistry, etc., I sincerely hope a more knowledgeable person will correct me.

    Basically, I think Byalko suggests that oxidation of methane contributes to the CO2 increase. Thinking about it, if I take 400 ppb of CH4, assume an approximate mass value of CH4 to be 16, oxidize it in a chemical reaction CH4 + 2 O2 => CO2 + 2 H20, and assume an approximate mass value of CO2 to be 44, then I find that 400 ppb of CH4 oxidizes to 1100 ppb of CO2 or 1.1 ppm CO2. This is obviously much less than the 100 to 200 ppm increase that ultimately occurs. Because I have seen estimates that CH4 is a more powerful GHG than CO2, ranging from 20 to 30 times more powerful, I would expect that conversion of CH4 to CO2 would reduce the warming effect. On the other hand, I have seen estimates of the half-life of CH4 in the atmosphere on the order of a decade and estimates of the half-life of CO2 in the atmosphere on the order of a century or more. The picture I have is that for some time on the order of thousands of years CH4 was added to the atmosphere faster than it was oxidized to CO2 and the CO2 resulting from this oxidation accumulated in the atmosphere because CO2 was being "scrubbed" by photosynthesis, etc., more slowly than it was being added. Moreover, rising temperatures resulted in release of CO2 from the oceans (the equilibrium concentration of CO2 in water is higher at lower temperatures -- I think this is why I cool the champagne in the refrigerator before midnight on 31 December). Altogether, we have a complex dynamic system.

    I googled for the English translation of Byalko's paper (I knew such a translation existed but didn't know if it was available) and found it on the web. I also found that there is also a German translation.
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  47. BillEveret.

    Traditionally gas concentration ppm are volume or mole based. Therefore 400 ppb of CH4 give 400 ppb CO2. At the initial stages methane is equivalent to multiples of CO2 (x10?) and then it oxidizes to CO2 via several radical pathways reaacting with O2 and other oxidizers.
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  48. BillEverett@46:
    Thanks for translating that paper and making it available.
    He does think that the methane is mostly benthic. According to Byalko, its release starts the warming (it could be a D-O event that starts the methane release, though he also mentions the speculation about the Clovis 'comet'). Oxidation of the methane doesn't produce enough CO2 by itself, so the CO2 comes from elsewhere - ocean warming, maybe.

    But he does seem to be taking the time lags he gets seriously.
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  49. skept.fr@14 "...there was a lag too between temperature rise and CH4 rise... Does Byalko refer to other paleoclimatic works for justifying that CH4 rise precede the temperature or is synchronous with it?"

    No, Byalko does not refer to other paleoclimatic to justify CH4 leading temperature. This was a result of a statistical analysis of the time series data, for which he cites two works (also cited by Konijnendijk et al. 2011):

    Loulergue, L., Parrenin, F., Blunier, T., Barnola, J.-M., Spahni, R., Schilt, A., Raisbeck, G., 25 and Chappellaz, J.: Orbital and millennial-scale features of atmospheric CH4 over the past 800,000 years, Nature, 453, 383–386, 2008.

    Luthi, D., Floch, M. L., Bereiter, B., Blunier, T., Barnola, J. M., Siegenthaler, U., Raynaud, D., Jouzel, J., Fischer, H., Kawamura, K., and Stocker, T. F.: High-resolution carbon dioxide concentration record 650 000–800 000 years before present, Nature, 453, 379–382, 2008.

    Byalko does propose a hypothesis concerning benthic methane hydrates as the source of the initial CH4 increase. I won't go into details of the mechanism he proposes to account for the statistical results. Links to English and German translations of Byalko's 2009 paper are given in #46 above.

    Regarding Delmotte et al. 2004, I think the time series data available to Byalko are more recent, have a higher precision, and cover a longer period of time.

    Regarding Konijnendijk et al. 2011, which is more recent than Byalko's 2009 paper, it seems to me that they were concerned primarily with developing and testing a model. From a cursory review of their paper, it seems to me that they speak about accounting for an observed lag of CH4 concentration behind the orbital forcing (not an observed lag of CH4 behind global temperature). I quote from their abstract: "Tropical temperature and global vegetation are found to be the dominant controls for global CH4 emissions and thus atmospheric concentrations." It should be noted this finding is in terms of their model and is not a conclusion about the statistical properties of the ice core data.

    In the summary, they write: "We have simulated wetland CH4 emissions over the last 650 000 yrs using a simple wetland distribution and CH4 emissions model coupled off-line to the atmosphere-ocean-vegetation climate model CLIMBER-2. The resulting simulated global emissions show a close similarity to the measured EDC-3 timeseries of atmospheric CH4 concentrations, both in spectra and in lags with respect to the orbital forcing."

    Finally, I note that in Fig. 4 (p. 71 in Konijnendijk et al. 2011), GHG concentration is shown in the red curve without distinguishing CO2 (in ppm) and CH4 (in ppb). It appears to my eye that this red (forcing) curve indeed lags the resulting emission temperature curve at the bottom. Although CH4 is a more powerful GHG than CO2, the three orders of magnitude difference in the unit of measure means that CO2 predominates in the green house effect with the values found in the ice core data.
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  50. Thank you, DrTsk@47. Now I know and will try to remember.
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