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Climate Hustle

What does past climate change tell us?

Posted on 21 October 2009 by John Cook

If there's one thing that all sides of the climate debate can agree on, it's that climate has changed naturally in the past. Long before industrial times, the planet underwent many warming and cooling periods. This has led some to conclude that if global temperatures changed naturally in the past, long before SUVs and plasma TVs, nature must be the cause of current global warming. Ironically, this conclusion is the opposite to what peer reviewed science has found.

Our climate is governed by a simple principle. When the planet has an energy imbalance, global temperature changes. Say the planet is in positive energy imbalance. More energy is coming in than going out. The planet accumulates heat and global temperature gradually rises (not monotonically, of course, internal variability will add noise to the signal). Eventually, the planet returns to equilibrium at a higher temperature. The key question is how much does temperature change for a given change in heat content. This is determined by the planet's climate sensitivity. The change in global temperature can be expressed by the following equation:

DT is the change in global temperature. RF is the radiative forcing, the change in net energy flow at the top of the atmosphere. This might be due to the sun getting brighter. Or a volcanic eruption spewing sulfate aerosols into the atmosphere, reflecting sunlight and letting less energy in. When radiative forcing RF is positive, it means the planet is accumulating heat. Lastly, l is the climate sensitivity parameter. This is a measure of how sensitive our climate is to changes in our climate's heat content.

The most common way of describing climate sensitivity is how much global temperature would change if CO2 is doubled. What does this mean? This is not to say CO2 is the only driver of climate. The amount of energy absorbed by the extra CO2 is calculated using line-by-line radiative transfer codes. These results have been experimentally confirmed by satellite and surface measurements. The radiative forcing from a doubling of CO2 is 3.7 Wm-2 (IPCC AR4 Section 2.3.1). So when we talk about the climate sensitivity to doubled CO2, specifically, we're talking about how much global temperatures would change when the climate experiences a radiative forcing of 3.7 Wm-2.

What is the result from a radiative forcing of 3.7 Wm-2? If we lived in a climate with no feedbacks, global temperatures would rise 1.2°C (Lorius 1990). However, our climate has feedbacks, both positive and negative. The most dominant positive feedback is water vapour - as temperature rises, so too does the amount of water vapour in the atmosphere. However, water vapour is a greenhouse gas which causes more warming which leads to more water vapour and so on. There are also negative feedbacks - more water vapour in the air can cause more clouds which reflects incoming sunlight, resulting in a cooling effect.

So what is the net feedback? We can calculate climate sensitivity from empirical measurements. One needs to find a period where we have temperature records and determinations of the various climate forcings that drove the climate change. If we can measure the change in temperature DT and the radiative forcing RF, climate sensitivity l can be calculated.

Hansen 1993 is one of the earlier determinations of climate sensitivity, examining the period when the Earth fell into the last major ice age. They calculated the change in Earth's albedo due to growing ice sheets. Ice core measurements yielded falling levels of greenhouse gases and increased atmospheric aerosols. From the surface and atmospheric changes, they were able to calculate a net radiative forcing. Coupling this with the temperature record, they found climate sensitivity to be 3 ± 1°C for a doubling of CO2. This means our climate has net positive feedback.

Over the last 1000 years, we've experienced climate change such as the Medieval Warm Period around AD 800-1300. This was followed by the Little Ice Age, roughly spanning the 16th century to the mid 19th century. Hegerl 2006 looks at Northern Hemisphere temperatures spanning both periods, using 4 different temperature reconstructions.


Figure 1: 4 different palaeoclimatic records over the past 1000 years (Hegerl 2006).

They calculate forcing from solar variations, volcanic activity and greenhouse gas forcing. They find a climate sensitivity range of 1.5 to 6.2°C, with the most likely value around 2.6°C. Again, confirmation of net positive feedback.


Figure 2: Probability density functions (PDFs) for equilibrium climate sensitivity to CO2 doubling (in K). Combined estimate using a result from instrumental data as prior distribution.

Hegerl found the temperature record with the most variety yielded the greatest climate sensitivity. And thus we come to the great irony in the argument that past climate change proves humans can't change global temperatures now.

CO2 has caused an accumulation of heat in our climate. We know the radiative forcing from CO2, confirmed by empirical observations. The effect of this heat build-up on global temperatures is determined by climate sensitivity. The greater climate has changed in the past, the greater the climate sensitivity.

Ironically, when skeptics cite past climate change, they're in fact invoking evidence for climate sensitivity and net positive feedback. Higher climate sensitivity means a larger climate response to CO2 forcing. Past climate change is actually evidence that humans can affect climate now.

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Comments

Comments 1 to 32:

  1. "The greater climate has changed in the past, the greater the climate sensitivity."

    I have a problem with this statement. If T is a function of two variables, then a change in either variable causes T to change.
    Thus T is affected by changes in solar radiation ( from whatever effect) and by the way the planet system as a whole responds to/ influences such changes. In other words, climate sensitivity is never a fixed multiplier, but varies according to various physical, chemical and biological responses.
    Past climate change shows more colder than warmer phases, indicating climate sensitivity is historically less than unity; so should we not accept this as a reason to maintain ( or even enhance) CO2 levels?
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  2. The statement you have a problem with is really a no-brainer Mizimi. If the climate didn’t respond historically to changes in forcings it would have a very low sensitivity…..if it changed a lot it would have a high sensitivity. There’s nothing controversial about that.

    Of course that doesn’t mean that the climate sensitivity is “a fixed multiplier”. It likely varies a bit according to the position of the continents, ocean currents, whether or not the world has significant ice sheets etc. But we expect that the essential factors involving water vapour feedbacks to be rather constant and so don’t expect the climate sensitivity to vary that much between different epochs. The fact that climate sensitivity determined by analysis of temperature changrs involved in ice age cycles of the last several 100s of 1000’s of years, and that determined from analyzing the relationship between paleoCO2 and paleotemp proxies during the last several hundred millions of years, yields a similar climate sensitivity (around 3 oC of temperature rise per doubling of atmospheric CO2), tends towards that conclusion. In fact the long term climate sensitivity in our present world with lots of polar ice is likely somewhat larger (large albedo amplification) than during ice-free periods in the past.

    Past climate surely “shows” more warmer than colder phases. In any case your statement is a logical non sequitur….and what is a climate sensitivity “historically less than unity”??? The reason that the Earth had cold periods in the past is because the climate has a moderate to high sensitivity to changes in forcings. For example, the extended glacial periods of the Carboniferous were due to the sensitivity of the climate system to drops in atmospheric CO2. Climate sensitivity works in both the warming and cooling directions!

    A very significant reason why enhanced CO2 levels are particularly problematic now (apart from the fact that they’re racing upwards at a rapid rate), is that solar constant is much greater now than in the past (the sun shines around 4% more strongly now than 400 million years ago). So the absolute surface temperature with CO2 levels now are considerably greater than the surface temperature at the same CO2 levels then.
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  3. "Ironically, when skeptics cite past climate change, they're in fact invoking evidence for climate sensitivity and net positive feedback. Higher climate sensitivity means a larger climate response to CO2 forcing."

    In fact, "it's the Sun" skeptics tend to support the idea of a positive climate feedback because it's required to boost the impact of relatively weak solar forcing. Skeptics of the "Hockey Stick", claiming larger variance than all multi-proxy studies indicate, need an even stronger positive feedback to explain such variances with natural factors. Here is an example from Willie Soon, who believes reduced solar output will result in substantial global cooling (which hasn't happened yet despite a decade of solar activity trending down):

    "1. A reduced energy input from a dimmer sun will result in less heating of the oceans' surface, which would lead to less evaporation from the ocean surface. The result of this would be a decrease in water vapor, which is by far the earth's major greenhouse gas."

    Positive water vapor feedback - check

    "2. Less water vapor would result in a decrease in high cirrus clouds, which trap more heat than they reflect."

    Positive cloud feedback - check

    "3. A reduced energy input from the sun would equal less energy to bring water vapor high into the atmosphere, so more would end up collecting a few kilometers from the surface, resulting in more low clouds. Low clouds are much more effective at reflecting sunlight, which would produce a net cooling effect."

    Positive cloud feedback - check

    http://global-warming.accuweather.com/2009/04/plausible_scenarios_of_a_dimme.html

    Willie Soon is essentially supporting the idea of not only positive water vapor feedback but positive cloud feedback as well, with negative forcing leading to more reflective low clouds and less heat-trapping high clouds. One has to wonder, then, what Soon's complaint with the scientific consensus is? It seems then that he must then be disputing the direct forcing component of CO2, rather than the feedback that other skeptics generally dispute. Soon and Lindzen should debate the issue, perhaps at the "contrarian-only" Heartland Institute political conference. But that would violate their doctrine "speak no evil of other contrarians". Still, it would be nice to see two contrarians take turns calling each other "alarmists".
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  4. Just for the record, I think here is a contrary view, where solar activity is amplified(it is not increased by a positive feedback).

    http://www.friendsofscience.org/assets/documents/Shaviv-Ocean%20as%20calorimeter-solar%20forcing.pdf

    Using the oceans as a calorimeter to quantify the solar
    radiative forcing
    Nir J. Shaviv

    Over the 11-year solar cycle, small changes in the total solar irradiance (TSI) give riseto small variations in the global energy budget. It was suggested, however, that different mechanisms could amplify solar activity variations to give large climatic effects, a possibility which is still a subject of debate. With this in mind, we use the oceans as a calorimeter to measure the radiative forcing variations associated with the solar cycle. This is achieved through the study of three independent records, the net heat flux into the
    oceans over 5 decades, the sea-level change rate based on tide gauge records over the 20th century, and the sea-surface temperature variations. Each of the records can be used to consistently derive the same oceanic heat flux. We find that the total radiative forcing associated with solar cycles variations is about 5 to 7 times larger than just those associated with the TSI variations, thus implying the necessary existence of an
    amplification mechanism, although without pointing to which one.

    Cheers, :)
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  5. The climate sensitivity has been introduced to allow comparison between different forcing. Given a starting condition, it can be considered the same for all forcings essentially because you average both anomaly and forcing over space and time. The only exception i'm aware of is the Galactic Cosmic Rays feedback that works only for the sun forcing. (Incidentally, this explains why many sceptics are stuck to the beloved GCR).
    The logical consequence is that if you try to explain the trend with just one forcing you need a larger sensitivity (amplification factor). But if you put back all the forcings, everything's screwed up; this last step is too often missing.
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  6. re #4

    Whether or not the warming effect of solar activity is "amplified" or is "increased by a positive feedback" is immaterial to the question of climate sensitivity, unless one considers that there is something "special" about the forcing from solar activity that doesn't apply to other forcings. We’ve already seen, for example, that there is evidence for a positive cloud feedback (call it an “amplification” if you like!) as a result of radiative-forcing-induced ocean warming:

    A. C. Clement et al. (2009) Observational and Model Evidence for Positive Low-Level Cloud Feedback Science 325, 460 – 464

    And one has to be a little careful in taking Shaviv's analysis at face value, due, amongst other things, to his selection of data sets. For example much of his analysis is based on a set of tide guage records of Douglas (1997), which shows a marked cyclic variation of local sea level that matches the solar cycle. However, this doesn't match the globally averaged sea level variation, especially the satellite-derived record which doesn’t show a marked variation with the solar cycle; e.g.:

    Church JA, White NJ, Aarup T, et al. (2008) Understanding global sea levels: past, present and future Sustainability Sci. 3, 9-22.

    It’s proposed that the tide guage measures, many of which are close to continental margins, have solar forcings magnified by more rapid warming/cooling in shallow waters, and that this amplifies the amplitudes of responses to forcings by a factor of 2-3 relative to the globally averaged response. So Shaviv’s use of this data to determine a radiative forcing from sea level response may well be erroneous (greatly overestimated) by that sort of factor. Whatever the origin of the discrepancy between tide guage measures and satellite measures with respect to amplitudes of response to solar cycles, I suspect that Shaviv’s analysis will be found to be a rather marked overestimation of the solar cycle response and his required “amplification”.
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  7. I am dizzy.
    So the logic goes that since climate is demonstrably susceptible to change, it is easy for humans to affect change. Furthermore, by correlating the recent temperature rise with a doubling of CO2, it is possible to deduce the leverage and scale of this influence.

    ''''''''''''''''''''''
    Getting practical
    How productive is it to be focussing on a symptom, when the real cause and problem is overpopulation? You wouldnt have as much CO2 to begin with if there were simply less people around. Anyone bother to correlate CO2 with population growth? Curbing population will not only lower CO2 emissions, it will also give people a chance for surviving (and with less pain) the fall out of global warming. I'm sure the CO2 proponents admit that CO2 is not the only man-made factor that is contributing to global warming. And again, even if GW were completely caused by nature, the remedy for humans would be the same. Decrease population.
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    Response: To answer your first section:
    1. "since climate is demonstrably susceptible to change, it is easy for humans to affect change" - well, I don't know if it's easy, we have to work pretty hard to send 29 gigatonnes of CO2 into the atmosphere every year. But the basic point is true - past climate change shows how sensitive climate is to radiative forcing - therefore it will be sensitive to the radiative forcing from CO2
    2. "by correlating the recent temperature rise with a doubling of CO2, it is possible to deduce the leverage and scale of this influence" - no, not the case. We deduce the scale of CO2 influence by calculating the radiative forcing from CO2. This is worked out using line-by-line radiative transfer codes. This result is then verified by direct observations of satellites and surface measurements which quantify the amount of longwave radiation that CO2 has sent back to the Earth's surface.
    "Has anyone bothered to correlate CO2 with population growth?" Yes, in fact, to quote Monbiot: "A paper published yesterday in the journal Environment and Urbanization shows that the places where population has been growing fastest are those in which carbon dioxide has been growing most slowly, and vice versa. Between 1980 and 2005, for example, Sub-Saharan Africa produced 18.5% of the world’s population growth and just 2.4% of the growth in CO2. North America turned out 4% of the extra people, but 14% of the extra emissions."
  8. At the risk of moving a bit off-topic, I'll respond to RSVP:

    I think you are right that in the long term, human population is a huge concern regarding all sorts of environmental abuse and resource consumption. But for now, let's put the blame firmly where it belongs: in the hands of the industrialized societies, whose extreme per capita consumption has led to the current situation with greenhouse gases and the measured temperature increases to date and the potential increases to come. An interesting, if perhaps overwrought, discussion of this issue can be found on George Monbiot's site at http://www.monbiot.com/archives/2009/09/29/the-population-myth/. While most population increases are occurring in the less-developed nations, it is the industrialized nations, and the growth-at-all-costs economic model that we have espoused, that have led to the current levels of greenhouse gases in the atmosphere.
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  9. cbrock
    I just read Monbiot's essay. It is a bit off topic because I was not focussing on CO2. I was implying that the negative effects of Global Warming or and Ice Age (whether man-made or not, and whether the time scale for disaster is 100, 1000, or 10,000 years) seem to indicate that there is less habitable space than one might initially suppose. In other words, even if mankind were able to supress absolutely all forms of pollution (which is nearly impossible), the natural fluctuations of global temperatures would at some point catch up with us and eat away many of the areas of the Earth that are now inhabited. It is easier to imagine (although maybe I am too optimistic here) human migrations on a less populated planet than one that is maxed-out as is the current situation. Please see:
    http://en.wikipedia.org/wiki/Waterworld for further reference.
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  10. Chris:"Whether or not the warming effect of solar activity is "amplified" or is "increased by a positive feedback" is immaterial to the question of climate sensitivity, unless one considers that there is something "special" about the forcing from solar activity that doesn't apply to other forcings."

    Well, clearly there is a lot different about solar activity than other sorts of forcings. Solar energy heats the oceans directly, it is composed of many different wavelengths of energy and it is correlated with other phenomena. IAC, in this context an amplification means an increased forcing.

    "And one has to be a little careful in taking Shaviv's analysis at face value, due, amongst other things, to his selection of data sets. For example much of his analysis is based on a set of tide guage records of Douglas (1997), which shows a marked cyclic variation of local sea level that matches the solar cycle. However, this doesn't match the globally averaged sea level variation, especially the satellite-derived record which doesn’t show a marked variation with the solar cycle"

    Well, given that the tide guage data set is only one of three that demonstrate the same basic magnitude of solar cycle response, the totality of the date is fairly suggestive. IAC, do you have a reference for your claim that the satellite measurements don't show a marked solar cycle response? It does not appear to be the Church reference. and regardless, satellite measurements of sea level seem much too short to reach such a conclusion(less than two complete solar cycles along with a likely PDO regime shift since satellite measurement began).

    You potentially make a good point about placement of the tide guages though.

    Cheers, :)
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  11. Yes there's a number of reasons for being skeptical of Shaviv's study that you cite, shawnet:

    1. The sub-set of tide guage measurements he used show a marked modulation with the solar cycle that isn't seen in the globally averaged sea level analysis. The fact that the satellite measure is short doesn’t discount the fact that it doesn’t show the marked solar cycle modulation; after all one only needs the satellite measures through one solar cycle to assess whether the globally averaged sea level shows the marked solar cycle modulation seen in the sub-set of continental margin-biased records…it doesn’t. The data is in the Church et al. reference I cited above – see their Figure 3.

    2. This obviously leads to a problem with this measure of apparent “amplification”, and has a knock on effect with the rest of the analyses, since if this part of the analysis is likely wrong due to the bias described in (1), the agreement with the other analyses suggests that the others might also be spurious. This is particularly the case considering the fact that Shaviv’s apparent “correlations” between ocean heat content (OHC) and solar cycle is poor. So in fact the tide guage analysis actually plays a dominant role in Shaviv’s paper. As Shaviv states (see section 3.2):

    “Given the relatively small correlation coefficient and modest significance, it is worthwhile to corroborate the existence of the large heat flux variations using an independent data set. We thus turn to analyze tide gauge data measuring sea-level variations.”

    And:

    “Note that the relatively low correlation coefficient between the OHC and solar signals may seem somewhat suspicious” (page 10)


    3. The third problem also relates to the OHC (ocean heat content) measures. Shaviv has to apply a number of corrections to remove “noise” like ENSO modulation of upper OHC, and after all of the corrections are made the correlation with the solar cycle is low as he states (see (2) above). What Shaviv doesn’t seem to have done is to remove the influence of volcanic eruptions, which is important in analyzing solar cycle related effects on OHC since for two of the 5 cycles (or 6; it’s not clear from Shaviv’s paper) analyzed, the volcanic forcing happens to be in phase with the solar cycle. This will produce a spurious “amplification” of any apparent solar effects that is not, in fact, related to solar effects. This has been pointed out by Lean and Rind in their recent analysis of attributions to 20th century warming (see section 4 on page 4 of their paper):

    J. L. Lean and D. H. Rind (2008) How natural and anthropogenic influences alter global and regional surface temperatures: 1889 to 2006 Geophys. Res. Lett. 35, L18701
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  12. Chris:"1. The sub-set of tide guage measurements he used show a marked modulation with the solar cycle that isn't seen in the globally averaged sea level analysis. The fact that the satellite measure is short doesn’t discount the fact that it doesn’t show the marked solar cycle modulation; after all one only needs the satellite measures through one solar cycle to assess whether the globally averaged sea level shows the marked solar cycle modulation seen in the sub-set of continental margin-biased records…it doesn’t. The data is in the Church et al. reference I cited above – see their Figure 3."

    Ok, well I haven't read the original Douglas paper, so I can't really comment here at the moment, perhaps you are right and they are improperly chosen for the purpose.

    As to the Church paper and the lack of solar cycle trend: Are you just eyeballing it and guess-timating or do you have an actual reference here? I think drawing this conclusion is much more complicated than that.

    3. The third problem also relates to the OHC (ocean heat content) measures. Shaviv has to apply a number of corrections to remove “noise” like ENSO modulation of upper OHC, and after all of the corrections are made the correlation with the solar cycle is low as he states (see (2) above). What Shaviv doesn’t seem to have done is to remove the influence of volcanic eruptions, which is important in analyzing solar cycle related effects on OHC since for two of the 5 cycles (or 6; it’s not clear from Shaviv’s paper) analyzed, the volcanic forcing happens to be in phase with the solar cycle. This will produce a spurious “amplification” of any apparent solar effects that is not, in fact, related to solar effects. This has been pointed out by Lean and Rind in their recent analysis of attributions to 20th century warming (see section 4 on page 4 of their paper):

    Thanks for this. It does appear to be a flaw in Shaviv's paper. It would be interesting to see it redone with volcanic corrections made(if in fact they weren't done).

    IAC, I still tend to think that the amplification factor will still be there when appropriate adjustments were made. It is pretty clear the solar signal has been much more strongly evident in its climate effects than its raw forcing value might suggest. It is pretty hard to imagine Herschel in 1801 being able to detect 0.1% change in solar radiation if that's all there was to it.

    Cheers, :)
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  13. There seems to be a leap in this article that is unexplained and leaving me confused.

    Many things can absorb the suns energy and many things can reflect the suns energy and maybe the amount of energy from the sun can vary. And maybe the way processes (currents, continents, winds) move that energy around the global alters things.

    You show an equation, very sciencey. Then make the comment "The most common way of describing climate sensitivity is how much global temperature would change if CO2 is doubled."

    and from then on it seems everything is explainable by CO2 levels.

    I don't get that last jump. Just because some people simplify the process down to CO2 levels doesn't mean that CO2 is the main cause. Or have other factors been corrected for? How would you know albedo, volcanic activity, cloud cover, ocean currents etc for this whole period?

    Few other things.

    1) So there was a Medieval Warm Period? Because I thought this was expunged from history by Mann as an inconvinient truth.
    2) "Hegerl 2006 looks at global temperatures spanning both periods, using 4 different temperature reconstructions." Isn't it northern semishpere temperature not global temperature in that publication?
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    Response: In its most fundamental terms, climate sensitivity means "if climate experienced a radiative forcing of 3.7 Wm-2, global temperatures would rise 3°C". This is the case whether the radiative forcing came from CO2, methane, solar variations, changes in albedo, etc. Or more accurately, all those factors added together.

    CO2 is not the only driver of climate. When you add them all together, then you have the net radiative forcing that is driving climate. I've gone back and tweaked the wording of that paragraph, hopefully clarifying the language somewhat. In fact, I'm currently working on a post coincidentally titled "CO2 is not the only driver of climate" :-)

    The main controversy with the Medieval Warming Period is whether it was global or a regional phenomenon. However, bickering over how widespread the MWP was underlies the irony of arguing about past climate change. If, as skeptics say, the MWP was a global phenomenon and temperature change was greater than currently thought, that would mean climate is more sensitive than previously thought. Hence the climate reaction to current CO2 radiative forcing would be even larger.

    Re Hergerl 2006, you're right, it did use NH reconstructions, not global. Thanks for spotting that, I've updated the post.
  14. @ RSVP

    You include this

    "Monbiot: "A paper published yesterday in the journal Environment and Urbanization shows that the places where population has been growing fastest are those in which carbon dioxide has been growing most slowly, and vice versa. Between 1980 and 2005, for example, Sub-Saharan Africa produced 18.5% of the world’s population growth and just 2.4% of the growth in CO2. North America turned out 4% of the extra people, but 14% of the extra emissions."

    I'm not sure what point you are trying to make. That population can expand ith limited impact on CO2 levels?

    Sub-Saharan Africa has just about the worst living condition for human being than any place on earth. Life expectancy, child mortality, education, infrastructure I could go on and on and on.

    It seems you (or more accurately Monbiot) are holding these people up as examples to us all. You want all of us to have quality of life similar to sub-saharan africans?

    I'd prefer to fight for an improvement in their quality of life and the inevitable increase in their carbon footprint than champion extreme poverty as some way forward.

    Unpleasant decadence from privileged western liberals
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    Response: The point is to address the argument that it's increasing population that is causing increasing CO2 emissions. On the contrary, the cause is over-consumption more than over-population. If we're going to hit CO2 emissions, best to be pointing in the right direction.
  15. Reply to HumanityRules
    I am in agreement with you, which I will explain, however, you have confused my point with content added by "Response". In fact it was "cbrock" who originally cites Monbiot.

    I agree with you in that I do not see Monbiot as being correct in, as you imply, holding up some of the worst living conditions as the way forward. On the contrary, my assessment is that the only viable solution is to work on curbing population.

    What I dont understand is how the "non-skeptics" somehow think it is possible to lower CO2 contamination without addressing population growth and the other sources of global warming?? What do they think got the CO2 contamination to these levels in the first place? And to be quibbling about who exactly is responsible is hypocritical when you consider the extended influence of the globalized economy.

    Aside from CO2, isnt it clear that there is no energy delivery system that does not pollute heat directly in some form or another, starting with nuclear energy???
    Example
    http://en.wikipedia.org/wiki/Heat_engine

    And getting real... behind every solar cell, there is a automobile in a chip plant parking lot used everyday for a 25 mile commute. Behind every wind farm, there are trucks (as you read this) used in transport and maintenance burning diesel. ETC.

    Getting back to my original point. I wasnt addressing man-made global warming. I was referring to the historical data that indicates potential for global warming or cooling whether man-made or not. And the fact that so many people live on the fringes of habitable terrain.

    ------------------------
    By the way, in the news yesterday, an AP article terms greenhouse gasses as "global-warming gases"... fait accompli.

    http://www.google.com/hostednews/ap/article/ALeqM5jZFyOvC-Hn8ZRKlbw2eJKukIRmHAD9BFKLT00
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  16. @RSVP

    "What I dont understand is how the "non-skeptics" somehow think it is possible to lower CO2 contamination without addressing population growth and the other sources of global warming?"

    If i get your thoght right, i think you should focus a little bit more. Given that poor people emit enormously less CO2 than rich, the question should be how can they improve their condition without a catastrophic increase of GHGs?
    This point is made clear and addressed in the UNDP Human Development Report 2008. This little step will change the view that the problem is population by itself, the raw number. And also again underline that the problem is global as global has to be the solution.
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  17. Response: The point is to address the argument that it's increasing population that is causing increasing CO2 emissions. On the contrary, the cause is over-consumption more than over-population. If we're going to hit CO2 emissions, best to be pointing in the right direction.

    You didn't answer the point I made you you hold up the Sub-saharan life as the way forward for humanity.

    Along with empty bellies, disease, illiteracy and wasted potential they also have a small carbon footprints. Well done the sub-saharan africans.

    Humanity isn't just about a head count its about a quality of life which requires consumption.

    Briefly forget about emission and think about the life of the people you are talking about.
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  18. "we have to work pretty hard to send 29 gigatonnes of CO2 into the atmosphere every year."

    Only by breathing humans releases approximately 2 gigatonnes of CO2 every year into the atmosphere. (The calculation is based on that one(1) human release about 1 kg of CO2 per day)
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  19. "...poor people emit enormously less CO2 than rich"

    You probably will find your "poor" closer to template climates for starters. And for however closer they may be, they tend to burn and destroy more forests per capita than anyone on the planet. This does not make industrialized nations any less guilty, however, if anything is going to help us get through this it is science and technology.
    And to contrast human values, historically, one of the strongest incentives to having more children in these "poorer" countries is tied to a desire for more hands in the fields, while "global ecology" (if it even registers on the mental radar) is some strange luxury of the rich. Monboit's thesis is kin to the concept of the "nobel savage" of the 18 and 19 centuries.
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  20. As a non scientist I read your comments with great interest and would like to ask what many of you would consider rather basic question I'm sure.

    Another article I read on Skeptical Science dealt with Milankovitch cycles - how increased temperature causes CO2 rise.

    http://www.skepticalscience.com/co2-lags-temperature.htm

    So relative to this blogs emphasis of past change I would like to propose a hypothetical and hear your thoughts.

    The question: If we humans were not here, thus not pumping out C02, and when considering the Milankovitch cycles, would temperatures still be rising, albeit at a bit slower rate?

    As a non scientist I'm having a hard time quantifying what I've read, that warming started again in the late 19th century following the little ice age. Did the earth basically shrug off the short term effects of the little ice age during this period to begin its relentless march towards warming because of the Milankovitch cycle? If so, I would assume we humans are just juicing this effect now, but that it started before we contributed much C02? If this is the case, I would be curious hearing a hypothesis looking into the future of the difference where sea levels would be without humans versus with humans. Excuse my layman thinking!
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  21. RSVP,
    i'm sure you know the per capita emissions in poor country, what you say has not been confronted with reality. And it's worse than that, in what even in poor countries there are rich and the industrial system is much less efficient than ours (compare emission per unit GDP).
    And yes, global ecology is definitely a luxury as well as the possibility to plan a relatively far future.
    But this points in the very same direction, it's not over-population but over-consumption.
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  22. batsvensson,
    luckly the CO2 we release with respiration does not come from fossile carbon ;)
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  23. Kevin, if anything the Earth would be cooling, if left only Milankovitch cycles. That would be a slow process though, leading to cold conditions within 25 to 50000 years.
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  24. Thanks Philippe,

    So we're now moving into the cooling phase of the Milankovitch cycle correct?
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  25. HumanityRules, there's a strong dose of false logic combined with crocodile tears in the sorts of argument you are presenting. I’m not saying they necessarily apply to yours specifically, but they hint in that direction!

    1. False logic.
    Large parts of sub-Saharan Africa are (and will continue to be) regions of the world that are most susceptible to the effects of global warming. It's established that the effects of global warming has produced increasing drought in these regions, and as warming progresses the region of reduced precipitation will spread Northwards and Southwards from the mid latitude bands already suffering from drought [*]. The global areas classified as "severely dry" by the Palmer Drought Severity Index (PDSI) more than doubled from 12% to 30% in the period 1970-2002 with surface warming as the dominant cause post-1980 [**]. This is the major cause of current, and near and medium-term food limitation that is the source of much of the problems in these and other areas in the middle latitude bands of the earth. The notion that this situation can be eased by beefing up the carbon footprint of these populations (and similarly low-carbon footprint populations elsewhere) is simply fallacious. What these increasingly drought-ridden regions need is a reduction in global warming.

    The obvious means of addressing this problem is to make a large investment in providing sustainable energy for these people, while we do the same for ourselves. This has to happen sometime (our civilizations are untenable into the future on the centennial timescale without this), and it should be happening with increasing urgency now (it is to some extent).

    [*] Zhang XB, Zwiers FW, Hegerl GC, et al. (2007) Detection of human influence on twentieth-century precipitation trends Nature 448, 461-465

    [**] Dai AG, Trenberth KE, Qian TT (2004) A global dataset of Palmer Drought Severity Index for 1870-2002: Relationship with soil moisture and effects of surface warming J. Hydrometeorology 5, 1117-1130

    2. Crocodile Tears
    One wonders where the concern for sub-Saharan Africa has suddenly sprung from! During the past 40-odd years this part of the world has suffered enormously from economic mismanagement a large extent of which was perpetrated by Western governments in support of their own economic advantage, largely in relation to extraction of raw materials. This encompassed major political interference in support of despotic or otherwise compliant leaders, and imposition of severely unfavourable trade and social conditions by the IMF/World Bank in which economic assistance was built around a system of enforced restructuring involving easing access of Western corporations to commodities and infrastructure, and dismantling of social structures. The World Bank ultimately admitted that it had caused huge social damage through these policies.

    That's happened and it can't be easily undone. However if we are truly concerned about those people (rather than using them for convenient hand-wringing in fallacious arguments to avoid doing anything about global warming), then we should address the problem directly. For example, cheap solar panels of the sort that China can producing in large amounts could be distributed, so villages could power fridges to keep medicines and run basic systems to power educational facilities and peripherals and so on. Major efforts to make local use of the abundant solar power in the central latitudes for more widespread industrial and social applications could be promoted. Properly planned programmes for sustainable biofuel generation in the so-far drought-free regions south of the equator could be developed…and so on. The notion that the well-being of populations can only be improved through burning fossil fuels is not only wrong...it's an admission of an essential futility of future progress.
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  26. I'd like to respond to Humanity Rules. First, I don't think we need cheerleaders on a science blog. That's a comment on your net name, but it's also a comment on your attack on John Cook. You say that in 17, John "hold up the Sub-saharan life as the way forward for humanity". I don't think he does any such thing. I think he merely points out that human population by itself doesn't increase CO2 content of the atmosphere -- that requires liberation of fossil carbon (as Ricardo makes clearer in 22).

    It's really very simple:
    CO2 added to the biosphere = (human population) x (environmental consumption per capita) x (CO2 emissions per unit of environmental consumption). So you could say that CO2 added to the biosphere = (N x E x C).
    To limit increases in atmospheric CO2, it doesn't matter if you manage to reduce population (N) by 20%, per capita consumption (E) by 20%, or CO2 required to provide that consumption (C) by 20%. If you hold the other two components constant, then you end up with a 20% overall reduction. But, one must be aware that these components interact in a complex manner, and focusing on one of them (especially a difficult one, like population) will likely not result in the CO2 limitation one might have simply imagined (China's population didn't stop growing via one-child policy; their CO2 production went up greatly at the same time).

    Nobody here is advocating "back to the stone age" policies, so please leave that rhetoric at home.
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  27. @Chris #25
    In response

    1. False Logic
    Medical clinics are meagre and have no drugs not because of global warning. Infrastructure is poor not because of global warning. People earning next to nothing not because of global warming. Child mortality is not because of global warming. These are the real problems I am concerned with now. There is no false logic in worrying about real issues rather than being alarmist about future problems.
    I thought it was a fact that that region of the world does produce sufficient food to feed itself and has the potential to produce more it's the complicated (and screwed) relationship it has with the global economy that has kept that region in the state its in. Nothing about it's past, present or future climate.

    2Crocidile tears
    I have no problem with your first paragraph, I totally agree. I've been an active anti-imperialist most of my adult life.
    But I don't see the jump of going from blaming the west and it's institutions to giving them cheap solar panels.

    Imperialism has thru the ages changed but it has always been morally justified. The civilizing of the savage argument came to look out-dated and racist after the war but during the 19th centuary was absolutely mainstream, as you say the more recent IMF/world bank form of fiscal imperialism played on the protection of the african people from their corrupt leaders. My worry is the next moral reasoning for western control of the poor will be environmental protection.

    It does appear one country is breaking the mould in Africa. China is doing what has never really been done investing in infrastructure. It's big, dirty and has a high carbon footprint but it has the potentially of shifting some african countries into the industrialized world. Many african commentators see this as preferrable to either western conservative fiscal control or western liberal charity.

    You can give african villages free solar panels. I aspire to see them have everything we have, and more.
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  28. "Ironically, when skeptics cite past climate change, they're in fact invoking evidence for climate sensitivity and net positive feedback. Higher climate sensitivity means a larger climate response to CO2 forcing. Past climate change is actually evidence that humans can affect climate now".

    No, large climate response to CO2 doesnt necessarily follow from higher climate sensitivity. Note that skeptics agree with high climate sensitivity (eg ice ages as a result of small solar/orbital changes etc), they just think that c02/greenhouse gases are not a major part/factor in it, ie they think greenhouse gases are being articifially enhanced in past (and present) climate analyses(largely as part of an agenda).

    EG. Please explain how c02 was up to 5000ppm in the Jurassic and there was no significant change in earth temperatures/runaway greenhouse?. (the argument on this site earlier of c02 'thresholding' for various periods in earth climate history is weak, because you could just as well say the earth has 'c02-thresholded' now in its current climate state).
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    Response: To answer your question re higher CO2 levels in the Jurassic, during this period, solar activity was also lower than current solar levels. The combined effect of sun and CO2 matches well with climate.
  29. re #27:

    HumanityRules, let me go back to my vision for a future and compare it with yours, since we seem to share the ideal of economic and societal advance in poor countries. I suggested that a huge investment in sustainable energy sources (especially solar power, with some carefully considered biofuel production etc.) is the likely way that economic advance might be realised in these countries. You consider that unworthy of comment.

    So let’s be a little more specific. Solar power is a truly massive potential source of power. Despite the fact that it’s in relative infancy, it produces around 16 GW of power worldwide. This is a tiny proportion of the total human energy use (~15 TW), but the potential for expansion, especially in regions of the world with high surface solar flux, is huge (the solar flux at the surface is equal to ~10,000 x the total world energy use, so we need to tap a tiny proportion of this to make massive inroads into replacing fossil fuels with solar, not to mention other sustainables). There are already solar power plants in the US, Spain (lots), Germany, Portugal, Korea….when completed the solar thermal power station in Gujarat in India will be the largest in the world…a 2GW solar plant is being built in Mongolia; there are major projects approved for large solar plant in Egypt, Mexico, Morocco….etc. etc. I’d like to know why you consider that these technologies should be left out of the equation for sub-Saharan Africa.

    Likewise, careful approaches to biofuel production has considerable potential. Brazil gets nearly 20% of its automotive fuel from (bio)ethanol…the production of ethanol in the US is now a large industry employing many hundreds of thousands of people. Again I’d like to know your reasons for dismissing this (and geothermal, wind, hydroelectric where this is still untapped, wave …) from your future for economic expansion in sub-Saharan Africa. The countries in this region are starting from a very, very low base in terms of current energy use – expanding this with a strong focus on sustainable energy is an obvious means of economic advance.

    On the other hand, your vision is seemingly based on a truly massive expansion of fossil fuel use. Speaking of the poor regions of the world you say you “aspire to see them have everything we have, and more”. Fine, but what specifically do you mean by that? At present each US citizen releases 19 metric tons (mt) of CO2 into the atmosphere each year. Is that level of fossil fuel consumption in your aspiration for the world? If so, CO2 emissions will rise to around 5 times current emissions, and our civilizations will be committed to a hellish short future with extremely rapid warming and sea level rise, unstoppable destruction of the tropical rainforests, until we run out of oil (in around 10 years), gas (30 years) and eventually even coal (~80 years). Then we’re pretty much back to the stone age…

    Or might your aspirations be more along the lines of Switzerland (5.6 mt CO2 per person per year). Then CO2 emissions would only double, the rate of adverse consequences would be slowed somewhat, and we’d have a rather larger number of decades before the fossil fuels were used up and the populations return to the stone age…

    So you have to be a bit clearer about your vision. I don’t think yours (massive expansion of fossil fuel use to promote industrialisation such that everyone has “everything we have, and more”) can avoid apocalyptic scenarios. On the other hand we know without any doubt whatsoever that the only long term future for mankind is one based on sustainable energy production. I’d like to know why you don’t consider it appropriate to consider the latter.
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  30. Re #28 thingadonta

    Yes there’s good evidence of a couple of “rapid” excursions of atmospheric CO2 levels well above the background CO2 levels during the Jurassic; see, for example, Figure 3 of:

    http://droyer.web.wesleyan.edu/PhanCO2(GCA).pdf

    However it’s wrong to state that there was no significant change in earth temperature. At least the earlier event has been studied in some detail and is associated with marked global warming, ocean anoxia, extinctions, and a carbon isotope excursion consistent with a massive release of C13-depleted carbon back into the atmosphere. This is similar to events at the PaleoEocene Thermal Maximum, and is indicative of extreme burning of biomass-derived carbon (coal seams, terrestrial wildfires) and/or release of methane into the atmosphere (e.g. [*]).

    The earth does have a ” 'c02-thresholded' now in its current climate state”. This refers to the concentration of CO2 and other greenhouse gases above which cool states, or states with permanent land ice, is not possible (this also depends on the location of continents since build up of ice at the poles is promoted if there are polar land masses like Antarctica and Greenland). For example it’s considered that polar ice caps are unsustainable at atmospheric CO2 equivalents above around 750 ppm under present conditions, and the Greenland ice cap is likely committed to melt at atmospheric CO2 equivalents above around 280 ppm (i.e. we expect to lose the Greenland ice cap in the future, although, unless there are some catastrophic mechanisms involving breakup that accelerate the process, it will take a long time to melt); (e.g. [**]).

    The reason that these greenhouse gas thresholds are considerably lower now than in the past is because the sun is quite a bit brighter now than in the past. During the Jurassic the solar constant was around 2% lower than now (it remorselessly increases as time advances), and so greenhouse gas concentrations had to be higher in order to sustain any particular surface temperature.

    [*]
    Cohen AS, Coe AL and Kemp DB (2007) The late Palaeocene-Early Eocene and Toarcian (Early Jurassic) carbon isotope excursions: a comparison of their time scales, associated environmental changes, causes and consequences J. Geol. Soc. 164, 1093-1108

    http://jgs.lyellcollection.org/cgi/content/abstract/164/6/1093

    [**]
    DeConto, RM et al (2008) Thresholds for Cenozoic bipolar glaciations Nature 652-655.

    http://www.nature.com/nature/journal/v455/n7213/abs/nature07337.html
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  31. Chris# I think you may have typo'd here...
    "and the Greenland ice cap is likely committed to melt at atmospheric CO2 equivalents above around 280 ppm"

    or are you really letting us off the hook?
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  32. Riccardo,
    "luckly the CO2 we release with respiration does not come from fossile carbon ;) "

    You with drawing attention from the real point I made. The point was to show that the claim that it demands "hard work" to release 29 giggatonnes of CO2 in the atmosphere is at best a misleading, and at worst a false, claim.
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