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Comments 39601 to 39650:

39601. tcflood at 11:32 AM on 11 January 2014
       New Study Suggests Future Global Warming at the Higher End of Estimates: 4°C Possible by 2100
       

       Tom Curtis @ 13

       If nearly all of the ECS response is attained at a couple hundred years, then one could use the TCS and ECS pretty much interchangeably.  This was the impression that I had because of the apparent lack of distinction in common use in discussions. 

       But the reason I focused on the hydrosphere @ 8 is because of the “pause” in SAT over the last 15 years being explained by supposing that periodic oscillations in ocean-atmosphere thermal coupling can lead to faster than usual heat transfer from the lower troposphere into the oceans below 700 m or so. 

       Does periodic slowing of SAT increase by periodically enhanced AO coupling imply that those models that don’t do the AO coupling especially well could significantly overestimate the rate of SAT increase over, say, a 50-100 year period?  So could the TCS in fact be significantly smaller than the ECS?  Could this have led to an over-estimation of likely rate of SAT heating in the 21^st century?  

39602. chriskoz at 11:09 AM on 11 January 2014
       Global warming is being caused by humans, not the sun, and is highly sensitive to CO2, new research shows
       

       Climate Agnostic@12,

       I am simply stating that a negative trend in solar activity could be consistent with solar driven global warming, if the starting point before the decline is high enough to cause warming in the first place

       Can you please elaborate a little bit on that "theory", i.e. explain (or even speculate on) some physical processes that might be responsible for such outcome?

       The first part of that sentence contradicts the energy preservation law: the only known source of energy in the climate system - sun - weakens, and everything else (uncluding geothermal that looks remarkably stable) remains the same or its influence is marginal by comparison; but the result ia an overall increase of the energy in the system? That's pure nonsense.

       The second part of that sentence is baseless trolling because it does not explain the apparent nonsense, i.e. how the energy in the system is balanced.

       If you want to come up with a new theory, the onset is on yourself to provide the realistic basis for it, grounded in our understanding of the physical world. That's how science progresses. If you don't and your "theory" contradicts the known physical world, it remains you imaginary world only, but for everyone else, it remains baseless nonsense.

39603. Tom Dayton at 10:58 AM on 11 January 2014
       New Study Suggests Future Global Warming at the Higher End of Estimates: 4°C Possible by 2100
       

       macoles, there is one estimate of consequences of cutting back CO2 emissions summarized on RealClimate.

39604. macoles at 10:42 AM on 11 January 2014
       New Study Suggests Future Global Warming at the Higher End of Estimates: 4°C Possible by 2100
       

       Sorry Tom, didn't see your reply to Willi @20. I'll take my question as answered :)

39605. macoles at 10:38 AM on 11 January 2014
       New Study Suggests Future Global Warming at the Higher End of Estimates: 4°C Possible by 2100
       

       Tom Curtis @13

       Layperson's question, where did you get the 9% of CO2 emissions = no ppm increase from?

       I was under the impression that around 45% of our CO2 emissions are absorbed by the natural carbon cycle, so I always figured if we cut back to that level then ppm will stop increasing.

39606. Rob Honeycutt at 10:08 AM on 11 January 2014
       Global warming is being caused by humans, not the sun, and is highly sensitive to CO2, new research shows
       

       Climate Agnostic...  Even assuming your speculation is correct, the change in radiative forcing from the sun is still 1/10th that of man-made sources. What you're suggesting doesn't present that much of a change in the overall picture we're looking at.

39607. Andy Skuce at 09:01 AM on 11 January 2014
       Talking Trash on Emissions
       

       Tom@17

       See graph #4 in this link. It shows the extent to which rich countries are outsourcing emissions. 

39608. Tom Dayton at 08:10 AM on 11 January 2014
       Global warming is being caused by humans, not the sun, and is highly sensitive to CO2, new research shows
       

       Climate Agnostic, Tom Curtis addressed your objection in his reply:  "global temperatures would increase at an increasingly slow rate after insolation ceased increasing, as the difference between incoming insolation and OLR fell with rising temperature. That is not what we see."  That increasingly slow rate would be due to the decreasing energy imbalance that the moderator's reply referenced.

39609. Climate Agnostic at 07:47 AM on 11 January 2014
       Global warming is being caused by humans, not the sun, and is highly sensitive to CO2, new research shows
       

       Tom Curtis - Sorry to veer "off-thread" but neither your repsonse nor the moderator's is reponsive to my point. I am not talking about time lags, though they no doubt play a role in deciphering the climate equation. I am simply stating that a negative trend in solar activity could be consistent with solar driven global warming, if the starting point before the decline is high enough to cause warming in the first place. This is a simple mathematical fact. Yes, other factors are at work, including CO2 and other GHGs, and time lags and feedbacks make it difficult to "tease out" the relative effects, but to assert, as the summary of the article above clearly does, that declining solar activity absolutely rules out the sun as a possible driver of late 20th century warming, is simply wrong.

39610. funglestrumpet at 07:44 AM on 11 January 2014
       Global warming is being caused by humans, not the sun, and is highly sensitive to CO2, new research shows
       

       What I find confusing about the skeptics' position is that they seem to be saying that global warming is not anthropogenic in origin so there is nothing that we can do about it. That has to be nonsense, surely? Icebergs and asteroids are not anthropogenic in origin, but it would be strange behavour indeed if we did not try to avoid the former and get the latter to avoid us.

       Even if the warming we are currently experiencing were due in large part to an increase in solar radiation, are the skeptics really saying we shouldn't try to reduce our contribution to global warming in order to mitigate the sun's effect? I would have thought that such a situation would call for an even greater reduction of our generation of CO² even if I did not believe in its effect. The fact that there is such argument about it can only mean that the only choice is to act and hope that it has an effect. The question of whether I was right or wrong would be answered either way. To not act is irresponsible. Especially so when one considers the weight of scientific opinion that is calling for action. Indeed, to not act is akin to giving the finger to future generations.

       (In addition to the above, anyone who follows financial matters will know how silly the argument is that we should save up so that we have sufficient funds to enable us to adapt to the increased warmth. The way things are going, the survivors of the coming collapse will probably all be living in caves, chasing wild animals for food and bartering for their daily needs, oh, and commenting on how hot it has become.)

39611. Tom Curtis at 07:35 AM on 11 January 2014
       Global warming is being caused by humans, not the sun, and is highly sensitive to CO2, new research shows
       

       Climate Agnostic @9, as you say, if solar insolation increases, it will continue to lead to warmer global temperatures for as long as the increase in insolation excedes the increase in top of atmosphere Outgoing Longwave Radiaton (OLR).  However, global temperatures would increase at an increasingly slow rate after insolation ceased increasing, as the difference between incoming insolation and OLR fell with rising temperature.  That is not what we see:

        

       Further, if the increase in insolation were sufficient to account for the twentieth century warmth, then the early twentieth century increase in temperature would have resulted in an increase in OLR falling well behind the increase in insolation.  It, therefore, should have shown an acceleration which is absent from the record.

       Finally, they theory you propose implies a the long delay between increase in forcing and temperature response to that forcing.  Such a long delay means that in increase in insolation and temperature in the early twentieth century are coincidental.  That is, if your theory is correct, the evidence that has been presented that the Sun is responsible for the temperature increase in the early twentieth century is misleading.

       Indeed, had your theory been correct, the initial increase in temperature should have followed the increase in insolation by a decade or more.  The increase in temperature would have then accelerated over time, until about 1950/60, whereupon it should have started decelerating.  No such pattern is evidenct so that theory is falsified.

       Finally, this discussion is strictly off topic on this thread.  If you wish to continue, please do so on a more appropriate thread.  Once we conclude our discussion on that thread, you can then cite that conclusion on this thread, and discuss the implications for the topic above. 

39612. Tom Curtis at 07:15 AM on 11 January 2014
       New Study Suggests Future Global Warming at the Higher End of Estimates: 4°C Possible by 2100
       

       wili @20, Bob @21 is correct.  You will find that my quotations of other people are always enclosed in inverted commas, and typically indented unless they are quotations of less than a full sententence.  Consequently my quotations should be easy to distinguish from my own comments.

       With regard to the 9% emissions comments, that comes from reflection on implications of various models of the carbon cycle, as for example, the geocarb model placed online by David Archer.  

       Using that model, if you set the "transition CO2 spike" to 5000 Gt C, and the simulation "CO2 degassing rate" to 70 x 10^12 mol/yr *, leaving all other values at the default values, you will see that the initial peak is 2394 ppmv of CO2, and that it falls to 1326 ppmv at 650 years, before rising to 77,095 ppmv (ie, 7.75 of the atmosphere) at a million years.  70 x 10^12 mol/yr is 9% of current anthropogenic emissions plus ongoing natural emissions.  The curve is not linear indicating the value will stabilize, but it clearly still rising at a million years so has some time to go for stabilization at a million years.

       The Geocarb model dumps its CO2 into the atmosphere as a single pulse, making it hard to model ongoing releases.  You can partially model those releases using the simulation "CO2 degassing rate", but are constrained to a single value rather than an increasing value.  In real life, the gradualy increasing emissions since c1850 has lead to a situation where 55% of emissions if we count industrial emissions only (ie, CO2 from fossil fuels or cement manufacture), or 44% from all anthropogenic emissions including land use changes such as deforestation has been retained in the atmosphere.

       Taking the values above, and the 272.6 ppmv 'natural CO2 concentration' (scare quotes rather than quotation**) we see that the increase in atmospheric concentration  for a 5000 Gt C slug of CO2 is 2120 ppmv.  The increase at minimum concentration is 1055 ppmv, ie, approx 50% of the overall increase.  That is, my estimate over estimates the standard of CO2 not falling.  In actual life it will do worse than that because as we approach 5000 GtC the percentage of CO2 retained in the atmosphere will increase significantly.  On the other hand, it does considerably better than that (and worse for us) at 1000 GtC, the level of emissions we notionally should not exceed to keep the global temperatures increase below 2 C. 

        

        

       (* Note that the units are 10^12 mol/yr, so you only need to type 70 in the box.

       ** The 'natural level of emissions' used in the model in fact includes a significant level of emissions from human agricultural activity and pre-industrial fossil fuel and cement use.)

39613. Climate Agnostic at 06:04 AM on 11 January 2014
       Global warming is being caused by humans, not the sun, and is highly sensitive to CO2, new research shows
       

       Moderator - even a declining "imbalance" can cause continued warming, even after the decline starts. Assume I turn my stove burner up to 190 degrees and place a pot of water at 70 degrees on the stove. Even as I turn the burner down from 190, to 170, 160, 150, 140......, as long as the temperature of the burner is higher than the temperature of the water, the water will warm, albeit at a decreasing rate, until the temperature of the burner falls to the water temperature. Temperature increase in the water is driven primarily by the relative temperatures of the burner and the water, not the rate of change (increase or decrease) in the temperature of the burner. Is it not possible that the hiatus in surface temperature increase reflects the decline in insolation from a net warming level to a neutral or even a cooling level? Of course it is. 

       Moderator Response:

       [TD] That's what I wrote in my previous comment to you.  Please read the links I provided there.  Further, there is no hiatus in surface temperature increase, but surface temperature is not even relevant to your argument--the total energy content of the whole system is.

39614. Climate Agnostic at 05:19 AM on 11 January 2014
       Global warming is being caused by humans, not the sun, and is highly sensitive to CO2, new research shows
       

       I'm not saying this paper is wrong, nor am I trying to take issue with the general concept that CO2, whether from humans or other sources, contributes to general global warming. However, the statement in this article to the effect that "we know that the sun is not the cause of recent warming because solar activity has been declining" cannot be supported. If, for example, solar activity was at a relatively high level over the last 50 years, then a slight decline, or even a substantial decline, in that activity might still be consistent with primarily solar induced warming. For the same reasons, a car can continue to accelerate even if you take your foot off the throttle a bit, as long as you're still giving it enough gas to continue acceleration. Solar warming would be driven not by the rate at which solar activity is declining or increasing but rather by the relative level of solar activity in comparison to earlier periods.

       Moderator Response:

       [TD] Insolation has not continued to increase but just less fast as your gas pedal analogy implies.  Instead, insolation has been flat or even decreased.  You are correct in your implication that there is a lag during which the energy of the Earth's system continues to increase after a forcing such as insolation stabilizes.  However, literally the moment that the insolation stops increasing, the energy imbalance due to the increased insolation starts to decrease.  Even if insolation continues to increase but at a lower rate of increase (as in your gas pedal analogy), the energy imbalance instantly will begin to grow at a lower rate. Because the total energy imbalance continues to grow, that imbalance cannot be due to catchup from the previous rise in insolation. The components of the energy imbalance have been teased apart by several researchers.

39615. Bob Lacatena at 02:32 AM on 11 January 2014
       New Study Suggests Future Global Warming at the Higher End of Estimates: 4°C Possible by 2100
       

       wili,

       Tom was not quoting Sherwood in that comment.  Sherwood does not deal with emissions or the results of different emissions scenarios.  His paper deals solely with models, low cloud cover, and climate sensitivity.

39616. KR at 02:16 AM on 11 January 2014
       Global warming is being caused by humans, not the sun, and is highly sensitive to CO2, new research shows
       

       YubeDude - You are technically correct, as all but a tiny fraction of climate energy (excepting geothermal) comes from the sun. And all of the cooling consists of IR to space. 

       The changes in forcings leading to recent changes in climate, however, are changes primarily caused by anthropogenic emissions. And natural forcings including the sun are not significant causal agents, as they have not changed sufficiently nor in the correct direction for recent warming. 

39617. gws at 00:58 AM on 11 January 2014
       It's aerosols
       

       carbtheory,

       Most atmospheric aerosol is secondary in nature, meaning it is formed in the atmosphere through gas-to-particle conversion, not via direct emissions. Most direct emissions are coarse mode emissions of sizes >2-5µm, which have relatively short atmospheric lifetimes. Accumulation mode particles, which contain most CCN, have longer lifetimes, but are formed through gas-to-particle conversion, mostly involving sulfur dioxide (and resulting sulfuric acid) and ammonia. Thus, their abundance is largely driven by SO₂ and NH₃ emissions. The first is dominating the graph you refer to. SO₂ emissions, dominated from coal combustion, have dropped since the 80s, but have risen again in the 00s due to coal combustion in East Asia.

       The net effect of these aerosols is cooling because they increase Earth's albedo.

       btw, CCN are not defined by size, but, as the name "Cloud Condensation Nuclei" says, they have the ability to take up a lot of water ultimately growing/leading to (cloud) droplets. Their existence (or increase) does not lead to drying in the atmosphere, but to a redistribution of cloud water content from larger to smaller droplets, also known as the Twomey effect, which makes clouds "brighter" (as seen from space), which has a cooling effect (search "ship tracks").

       The emisisons standards induced changes most likely have only a small and regional/local effect. The biggest large-scale changes come from how much coal is burned and what end-of-the-pipe technology is used to clean the stack gas from SO₂.

39618. Jubble at 00:53 AM on 11 January 2014
       Global warming is being caused by humans, not the sun, and is highly sensitive to CO2, new research shows
       

       Thank you for this excellent article.  

       There is one point I would like to make, not on the science, but on the message.

       People advocating doing something to counteract anthropogenic climate change are sometimes accused of being pleased when there is some extreme weather or such.

       The line in the article "Clouds, whose responses in a warming world have been difficult to pin down, were the contrarians' last and best hope." could look the same.  

       In fact, clouds may have been all of our last and best hope.  If they are a positive feedback, that is bad news.

39619. YubeDude at 00:33 AM on 11 January 2014
       Global warming is being caused by humans, not the sun, and is highly sensitive to CO2, new research shows
       

       This may stir up a hornets’ nest...

       I have a slight problem with the title of this article because the wording is low hanging fruit for the denial-istas to focus on the title and not the message.

       
       All warming is caused by the sun.

       
       The fact that recent increases and the temporal rate of increase has, as the one of the authors is quoted as saying, a robust and significant anthropogenic signal does not change the fact that all heat is derived from the sun. If anything our impact is effecting what should be the natural release of this energy back from whence it came.

       Our impact is what this article is about and the research helps to further establish that fact.
       I have no issue with the central article just the awkward choice of title and how it could easily be manipulated to discredit the message inside

        

39620. wili at 23:10 PM on 10 January 2014
       New Study Suggests Future Global Warming at the Higher End of Estimates: 4°C Possible by 2100
       

       Tom, so your paragraph at #13 that goes:

       "For practical purposes, if we cease all emissions, then temperatures will not rise much above the TCR to the peak CO2 concentration - but will not fall much below it for thousands of years either. However, if we retain emissions at just 9% of current levels, CO2 concentrations will not fall and we will face the equilibrium climate response within two centuries, and temperatures will keep on rising slowly for thousands of years to come. It follows that the relevance of the ECS depends on our future policies, and therefore it is at least relevant in helping us determine those policies."

       
       is a direct quote from the Sherwood paper?

39621. wili at 23:07 PM on 10 January 2014
       New Study Suggests Future Global Warming at the Higher End of Estimates: 4°C Possible by 2100
       

       Bob at #16 wrote: "the moisture precipitates out or is distributed (based on whatever criteria/profile the model may use) throughout the atmospheric column, leaving some for low clouds, some for middle clouds, and some for high clouds."
          Thanks tons. That helps a lot. As usual, these things are more complex than what can easily be squeezed into a two minute video.

39622. carbtheory at 18:20 PM on 10 January 2014
       It's aerosols
       

       @ 7, first graph. To get a better picture of how changes in emissions between the 70's and more recent years would require a profile of the changing emissions particle size over that period. Below CCN size, smaller average particle size would result in longer residence time in the atmosphere, while they grow in size, raising the opportunity for the particles to bypass water vapour to higher altitudes leaving a higher WV content at lower altitudes. An examle of how raising emission standards can affect particle size can be seen in the following study " Measurement of Engine Exhaust Particle Size" by David B. Kittleson, ( pages 7 and 8 in particular ) where they describe the effect of new standards ( introduced in 1990 ) on deisel emissions.

39623. davidnewell at 17:56 PM on 10 January 2014
       2013 SkS Weekly News Roundup #52
       

       Right on!  This "worrying about the future" is not joyful!

        

       Happy New Year!

39624. carbtheory at 17:31 PM on 10 January 2014
       Water vapor is the most powerful greenhouse gas
       

       @ 174, " Biotic Regulation Theory ", good read btv123, nice explanation of how changes in land use can lead to a change in weather patterns. This in turn can lead to so called 'erratic weather'. Interestingly there are claims on the web of global forest cover halving over the 20th century.

39625. Tom Curtis at 16:52 PM on 10 January 2014
       New Study Suggests Future Global Warming at the Higher End of Estimates: 4°C Possible by 2100
       

       willi @15, other than the first quote, which is a transcript from the video, all my quotes were from the actual paper.  I think the most important one is that first one, ie, the transcript, as it gives the clearest statement of the mechanism involved, which appears to have been giving some people (including myself) difficulty understanding.  However, the paper deals with the issue in more detail than the does Sherwood's discussion on the video.

       With regard to your first question, I have nothing to add to Bob Lacatena's answer. 

39626. Bob Lacatena at 14:34 PM on 10 January 2014
       New Study Suggests Future Global Warming at the Higher End of Estimates: 4°C Possible by 2100
       

       Additional note... some air (and moisture) will obviously also be transported horizontally, which is a major mechanism in the climate system for transporting moisture from the equator poleward.  So again, it's not as simple as more clouds or less clouds in a column.

39627. Bob Lacatena at 14:29 PM on 10 January 2014
       New Study Suggests Future Global Warming at the Higher End of Estimates: 4°C Possible by 2100
       

       Wili, re high clouds... No, because it's not an all or nothing thing, and it's not discrete.  We're not talking about a "block of moist air" that either rises 10km up, taking all of it's moisture with it, or not.  What is involved instead is the parameterized estimation of how much moisture rises to what altitude at what temperature, how much remains as vapor, how much condenses into cloud, and how much precipitates out.

       The models in which air predominently rises 10km and higher does not take all of the moisture with it (remember, the ability of air to hold moisture drops with temperature, which in turn drops wih altittude).  In those models, instead, the moisture precipitates out or is distributed (based on whatever criteria/profile the model may use) throughout the atmospheric column, leaving some for low clouds, some for middle clouds, and some for high clouds.  More moisture (in a warmer climate) will then increase clouds at all levels, a positive feedback for high and middle clouds, but a negative (reflecting more sunlight) for low level clouds.

       In contrast, a model which better simulates up and down drafts will leave the lower levels of air in the boundary layer (2km) dryer, leading to more cloud formation at middle and high levels (a positive feedback) and less low cloud formation (another positive feedback).

39628. wili at 13:54 PM on 10 January 2014
       New Study Suggests Future Global Warming at the Higher End of Estimates: 4°C Possible by 2100
       

       Thanks, Tom; those quotes really help. The one I am still left puzzled by is from the second quoted paragraph in your #12: "The air allways rises up to 10 or 15 kms, and so these models have been predicting a lower climate sensitivity..."
         If the air in these models always rises to this height bringing moisture up that high to form high clouds, shouldn't that bias those models toward a higher climate sensitivity, since it is the high clouds that do more heating, while the low clouds reflect sun more effectively and keep in less heat?

          Thanks again for your continued efforts in helping us undestand this important paper. What is your source for the second paragraph in 13. I'd like to point this out to people at other sites, but it would be nice to be able to site somthing more convincing than "a poster named Tom on another site."

39629. Tom Curtis at 12:03 PM on 10 January 2014
       2013 SkS Weekly News Roundup #52
       

       Further to my comments @14 above:

       As he says at the end, John Green says at the end, "... much of this progress is unsutainable with current technology, but it is real and it is worth celebrating."

39630. tcflood at 11:32 AM on 10 January 2014
       New Study Suggests Future Global Warming at the Higher End of Estimates: 4°C Possible by 2100
       

       Bob Lacatena @10 and 11:  

       Thanks for your responses.

       I must say, though, that I found rather perplexing your introduction of the concept whose generation we care about into an answer to what I thought was a fairly straightforward technical question.    

       Tom Curtis @13: 

       Thanks for your helpful response.

       Just to clarify my question, let’s assume some arbitrary, hypothetical numbers. Suppose the globally averaged surface air temperature in 1850 were 286 K, and [CO2] were 280 ppm. Then in, say, 2050 the [CO2] were 560 ppm and that [CO2] were to remain constant at that value until year 3000 (preposterous, I know).  If one postulates an ECS (primary effects and all feedbacks, fast and slow) of, say, 4 degrees, what does this imply for the likely global SAT in, say, 2100?   I suppose that one might react differently if models projected an SAT of 290 K in 2100 versus in 3000. Whenever I read papers or discussions about the ECS, I am always left with this lack of clarity.  Perhaps it’s just me.

39631. dana1981 at 10:21 AM on 10 January 2014
       Global warming is being caused by humans, not the sun, and is highly sensitive to CO2, new research shows
       

       Thanks Composer, fixed.

39632. Tom Curtis at 09:05 AM on 10 January 2014
       Climate's changed before
       

       pheidius @376, I am unable to comment further unless you do in fact cite the two papers, ie, either list their names, authors, date and journal of publication; or provide a link to the abstract including those details.

39633. Tom Curtis at 09:02 AM on 10 January 2014
       New Study Suggests Future Global Warming at the Higher End of Estimates: 4°C Possible by 2100
       

       tcflood @8, strictly speaking it does take thousands of years to reach ECS, but in practise nearly all of the Equilibrium Climate Response is achieved in about 200 years.  To confuse things, however, by two hundred years you are starting to feel some of the effects of slow feedbacks, such as melting ice sheets and changes in vegetation.  Arguably we are already feeling some of those effects.  Consequently it is not safe to assume the change in temperature in human time scales is limited by the ECS.

       For practical purposes, if we cease all emissions, then temperatures will not rise much above the TCR to the peak CO2 concentration - but will not fall much below it for thousands of years either.  However, if we retain emissions at just 9% of current levels, CO2 concentrations will not fall and we will face the equilibrium climate response within two centuries, and temperatures will keep on rising slowly for thousands of years to come.  It follows that the relevance of the ECS depends on our future policies, and therefore it is at least relevant in helping us determine those policies.  

39634. Tom Curtis at 08:51 AM on 10 January 2014
       New Study Suggests Future Global Warming at the Higher End of Estimates: 4°C Possible by 2100
       

       Some of the questions about the mechanism described in the paper are answered by Sherwood in the video (1:08):

       "What we see in the observations is that when air picks up water from the oceans surface and rises up, it often only rises a few km before it begins its descent back to the surface.  Other times it might go up 10 or 15 km.  And those shorter trajectories turn out to be crucial to giving us a higher climate sensitivity, because of what they do to pull water vapour away from the surface and cause clouds to dissipate as the climate warms up.  

       In many of the models this doesn't happen.  The air allways rises up to 10 or 15 kms, and so these models have been predicting a lower climate sensitivity, but we believe they're incorrect.

       What these shallower overturning circulations do is they pull the water vapour away from the part of the atmosphere where clouds form that cool the climate.  If these things are strong, and if they do this more in a normal climate, which is what all the models agree is what happens, then you loose your low clouds and the Earth absorbs more sunlight.

       The question for many years has been what's going to happen to the amount of low cloud.  Does it decrease when the Earth warms up, or does it stay the same, and maybe even increase; and what we found is that it should be decreasing because of this mixing process which pulls water vapour away from the layers were these clouds form, and causes there to be fewer of them in the wamer atmosphere." 

       So, the increased warming is definitely due to the reduction of low cloud.  

       However, Sherwoods account is simplified relative to the paper.  Specifically, in the video, where he refers to the circulation that "only rises a few km", the video shows a circulation rising to 5 km.  In fact the paper mentions two forms of low circulation:

       "As discussed above, air there is either transported directly from the boundary layer with minimal precipitation via lower-tropospheric mixing, or indirectly by ascending in deeper, raining clouds and then descending. The air would arrive cool and humid in the former case, but warmer and drier in the latter case owing to the extra condensation, allowing us to evaluate which pathway dominates by observing mean-state air properties."

       That is, in the lower tropospheric circulation, sometimes air (with its attendant water vapour) is carried only as high as the level of formation of low clouds (around 2 km); but sometimes it is carried higher - precipitating out some of the water vapour, before descending back to the level of low clouds. 

       Sherwood et al measure the different rates of these two types of circulation with the index S:

       "To do this we use an index S, proportional to the differences DT_700–850 and DR_700–850 of temperature and relative humidity between 700 hPa and 850 hPa (S taken as a linear combination; see Methods Summary) averaged within a broad ascending region which roughly coincides with the region of highest Indo-Pacific ocean temperatures (the Indo-Pacific Warm Pool; Fig. 1)." 

         To help make sense of that, 850 hPa corresponds to an altitude of 1.5 km, and 700 hPa corresponds to an altitude of 3 km.

       In addition to these two forms of low level circulation, Sherwood et al describe a higher level circulation:

       "We next turn to the large-scale lower-tropospheric mixing, which we associate with shallow ascent or flows of air upward through the top of the boundary layer that diverge horizontally before reaching the upper troposphere. Although air ascending on large scales over warm tropical oceans typically passes through nearly the whole troposphere, over cooler oceans its ascent often wanes with altitude, showing that this type of mixing indeed occurs in the Earth’s atmosphere (Fig. 3). The associated mid-level outflows are well documented for the central and eastern Pacific and Atlantic Intertropical Convergence Zone and some monsoon circulations13,14. Although these are indeed the regions where shallow ascent is steadiest, and hence clearest in monthly-mean data (Fig. 3), in daily reanalysis data, shallow ascent is equally strong outside the tropics owing largely to contributions from extratropical storms."

       Clearly this form of circulation will also dry the region around 2 km altitude where low level cloud forms.

       Sherwood et al define an indice of the ratio of large circulation to low level circulation:

       "We quantify the large-scale lower-tropospheric mixing more thoroughly by calculating the ratio D of shallow to deep overturning (see Methods Summary) in a broad region encompassing most of the persistent shallow ascent (see Fig. 3). This index D varies by a factor of four across 43 GCMs (see below). Interestingly, however, D and S are uncorrelated (r50.01), confirming that the two scales of mixing are controlled by different aspects of model design."

       Because low circulation provides the numerator, and high circulation the denominator, D will be larger when low circulation dominates over the high circulation.

       It turns out that the differences in low circulation (indexed by S) and the ratio of low to high circulation (indexed by D) equally contribute to reduced low cloud.  However, the model spread relative to S is not biased relative to observations.  In contrast, the model spread relative to D is, with models consistently underestimating D, that is, the ratio of low to high circulation.  Consequently it is differences in D that explain why low climate sensitivity models are probably inaccurate (according to Sherwood et al).  That is probably why Sherwood in the video concentrates on explaining the factors relevant to D, essentially ignoring S.  If you find all this confusing, it is probably better to also ignore S, and simply rely on Sherwood's description as transcribed above.

39635. Bob Lacatena at 08:36 AM on 10 January 2014
       New Study Suggests Future Global Warming at the Higher End of Estimates: 4°C Possible by 2100
       

       But yes, ECS concerns longer time frames than TCS.  We can't actually say "thousands of years," though, because we can't really know at this time how quickly the slowest feedbacks will take effect, of how much of the total climate sensitivity they will represent.

39636. Bob Lacatena at 08:26 AM on 10 January 2014
       New Study Suggests Future Global Warming at the Higher End of Estimates: 4°C Possible by 2100
       

       tcflood,

       On choosing between ECS vs. TCS:

       Only if we can presume to know the temporal difference between the two, but given that humidity and low cloud changes should be fast feedbacks, i.e. ones which occur very rapidly as a direct consequence of changes in land surface, ocean surface and atmospheric temperatures, then my immediate reaction would be that this is a very big problem, and there is no reason to think that we should ignore the results because final ECS is a thousand years in the future.

       But the distinction has little to do with this paper.  It's more of a general question of "well, do I care about TCS, because I could care less about anyone but my own generation and maybe the next, or do I care about ECS, because I care about future generations, even after I'm gone."

       With that said, if you want to know what difference this makes in the model runs, you'd have to look at the selected and excluded ensembles, and compare their TCS period results.

39637. Bob Lacatena at 08:23 AM on 10 January 2014
       New Study Suggests Future Global Warming at the Higher End of Estimates: 4°C Possible by 2100
       

       Clouds:

       The paper specifically addresses moisture levels in the 2km to 3km range, meaning low clouds, i.e. those that have a primarily cooling effect by reflecting incoming sunlight (so less such clouds would be a positive feedback).  The paper did not re-run model simulations, but rather examined existing models, and various parameters, to identify those models whose temperature and humidity changes in the 2km to 3km range more accurately reflected actual observations, taking these models to be more accurate in that respect.

       What they found was a very, very strong correlation between how well a model matched observations in that respect, and therefore had fewer low level clouds, and climate sensitivity.

       Those that more closely matched observations consistently had a higher climate sensitivity.

       Those that were less of a match for observations consistently had a lower climate sensitivity.

       Restricting estimates to include only those models whose ensembles more closely match observations leads to the ECS given.

39638. tcflood at 07:09 AM on 10 January 2014
       New Study Suggests Future Global Warming at the Higher End of Estimates: 4°C Possible by 2100
       

       Sorry, I think I put this question under the wrong topic, so I'll put it here where I think it belongs.

       Does equilibrium climate sensitivity include complete equilibration with the hydrosphere? Does this imply a time span of a thousand or so years? Would a transient CS be more appropriate coefficient to discuss for a century timescale?

39639. bibasir at 05:11 AM on 10 January 2014
       The Weekly Standard's Lindzen puff piece exemplifies the conservative media's climate failures
       

       I read the link in 12 giving the Catholic Church's view of the Galileo inquisition, and I think it is somewhat self serving. From wikipedia, " On February 24 the Qualifiers delivered their unanimous report: the idea that the Sun is stationary is "foolish and absurd in philosophy, and formally heretical since it explicitly contradicts in many places the sense of Holy Scripture..."; At a meeting of the cardinals of the Inquisition on the following day, Pope Paul V instructed Bellarmine to deliver this result to Galileo, and to order him to abandon the Copernican opinions; should Galileo resist the decree, stronger action would be taken. On February 26, Galileo was called to Bellarmine's residence and ordered, "to abstain completely from teaching or defending this doctrine and opinion or from discussing it... to abandon completely... the opinion that the sun stands still at the center of the world and the earth moves, and henceforth not to hold, teach, or defend it in any way whatever, either orally or in writing."

       In addition, the January Scientific American has an article titled "The case against Copernicus." There was substantial scientific controversy about Copernicus' heliocentric theory well after both Copernicus and Galileo. Below are the final paragraphs. The full article requires a subscription.

       " The acceptance of Copernicanism was thus held back by a lack of hard scientific evidence to confirm its almost incredible claims about cosmic and stellar magnitudes. In 1674 Robert Hooke, curator of experiments for the British Royal Society, admitted, “Whether the Earth move or stand still hath been a problem, that since Copernicus revived it, hath much exercised the wits of our best modern astronomers and philosophers, amongst which notwithstanding there hath not been any one who hath found out a certain manifestation either of the one or the other.”

       By Hooke’s time a growing majority of scientists accepted Copernicanism, although, to a degree, they still did so in the face of scientific difficulties. Nobody convincingly recorded the annual stellar parallax until Friedrich Bessel did it in 1838. Around that same time, George Airy produced the first full theoretical explanation for why stars appear to be wider than they are, and Ferdinand Reich first successfully detected the deflection of falling bodies induced by Earth’s rotation. Also, of course, Isaac Newton’s physics—which did not work with Brahe’s system—had long since provided an explanation of how Brahe’s “hulking, lazy” Earth could move.

       Back in Galileo’s and Riccioli’s day, however, those opposed to Copernicanism had some quite respectable, coherent, observationally based science on their side. They were eventually proved wrong, but that did not make them bad scientists. In fact, rigorously disproving the strong arguments of others was and is part of the challenge, as well as part of the fun, of doing science."

        

       Moderator Response:

       [PS] Interesting as this may be, can we please not have this topic derailed by historical discussions.

39640. ubrew12 at 03:19 AM on 10 January 2014
       New Study Suggests Future Global Warming at the Higher End of Estimates: 4°C Possible by 2100
       

       I'm no expert, but I think what they're saying is if the atmosphere heats up due to CO2, where does it heat up?  In heats up in the lower troposphere, mostly.  Hence, where is additional H2O going to make its home?  In the lower troposphere, below cloud-formation level.  This has the unfortunate effect of increasing the lower troposphere further, making it a better home for even MORE H2O.  If much of the additional H2O never makes it high enough to form clouds, its a positive feedback (or at least less of a negative feedback than it would be if you assumed most of it WAS making it up that high).

39641. gws at 02:44 AM on 10 January 2014
       Methane emissions from oil & gas development
       

       check, e.g., here, here, or more detailed here (Fig. 5).

39642. martin3818 at 23:47 PM on 9 January 2014
       New Study Suggests Future Global Warming at the Higher End of Estimates: 4°C Possible by 2100
       

       @Rob

       If you could find the time to explain in detail (diagrams and all) where high and low clouds form, where mixing takes place, how mixing influences cloud formation and why mixing will increase when the temperatures go up - this would probably answer many of the questions being asked in this comment section.

       I must admit, I'm still confused.

39643. Composer99 at 22:54 PM on 9 January 2014
       Global warming is being caused by humans, not the sun, and is highly sensitive to CO2, new research shows
       

       FYI the block-quoted text from Jara Imbers, likely because it is cut off before being completed, is affecting the formatting on the main page. At least, that is how it appears to me.

39644. pheidius at 22:43 PM on 9 January 2014
       Climate's changed before
       

       I also read the second figure in question to be natural output. He phrased it as "the modern mean annual rate of Mantle co2." So I have the concepts but got led astray by dividing by 12 in my attempt to get to the modern atomic weight and then try to convert that when all I had to do was multiply by 12.  So 6,000 GT divided by 2.13 would mean a theoretical atmospheric input of 2817 ppmv over that (plus minus) 1,000,000 million year time period  less whatever the Earth's carbon sinks could then reabsorb. Mclean strongly implied a weaker feedback mechanism in describing the ocean's of the day as being warm, deep and with slugish circulation. So a conservative number might be closer to 40%. That would imply the the ppmv towards the end of the period was around 2012 ppmv.   The other author'(s) paper, however, stated that the ppmv was pretty consistant at around 350-500 ppmv until, right at the KT mark, it shot up to 2300 ppmv. Darn: it would seem both of these sources can't be right.   I was looking, in all of this, for an aproximation of the tipping point when the ocean's heatsink mechanism just shuts down. It would seem all the author's numbers agree about ppvm being roughly in the  2000-23000 range indicating dead oceans below at the end of the sequence. The Ma period numbers preceding are wildy divergent. The second paper looked for 4600 Gt to be thrown up by an impact to get to 2300 ppmv.

       4600Gt divided by  the current anthrogenic number of 8.2 is 560 years to dead oceans.  That is worrysome indeed, but I wish there was more consensus on the background data as there seems to be on current data. In both of the papers I cite, the ppmv figures in the long term neatly support each author's hypothesis but both can't be correct. One would think peer review would catch major discrepencies such as these. Thanks for the help. I am just a laymen who can read fairly technical data but strugeles a bit with the math.

        

39645. Tom Curtis at 20:48 PM on 9 January 2014
       Climate's changed before
       

       pheidius, 1 mole of CO2 contains 12 grammes of carbon.  Thus, 5 x 10^17 moles of CO2 equals 60 x 10^17 grammes, or 6,000 petagrammes of Carbon.  A petagramme is also a Gigatonne, so 6,000 petagrammes of Carbon is 6,000 Gigatonnes of Carbon.  4.1 x 10^12 moles equals 49.2 x 10^12 grammes, or 0.0492 Gigatonnes Carbon.  In contrast, the IPCC cites a value of 9.5 Petagrammes of Carbon (or Gigatonnes of Carbon) in 2011.  Given the large discrepancy, it is likely the figure you cite from McLean is an estimate of natural emissions only.

       The unit, ppm does not stand for a given mass of CO2, but for part per million, ie, a concentration of the gas within the atmosphere.  Strictly what is called ppm in climate science is actually ppmv, ie, parts per million by volume - ie, the ratio of numbers of molecules in the atmosphere rather than the ratio of the total mass of each component of the atmosphere.   Given the mass of the atmosphere, 2.13 Gigatonnes of Carbon = 1 ppmv of CO2.  However, about half of all emissions are taken up by the ocean or biosphere rather than staying in the atmosphere.

39646. Jonas at 20:17 PM on 9 January 2014
       Talking Trash on Emissions
       

       Wunderful idea to make the numbers less abstract! 

       I reposted it with the numbers for germany:

       597 kg waste per year ( http://de.wikipedia.org/wiki/Abfall )
       11,2 tons of CO2 per year ( http://de.wikipedia.org/wiki/Länderliste_CO2-Emission )
       11200kg / 597g = ca 18.76 kg CO2 per kg of waste ...

39647. pheidius at 19:02 PM on 9 January 2014
       Climate's changed before
       

       As a footnote to the above, I am reading another paper, "An Atmospheric pco2 Reconstruction across the Cretaceous_Tertiary Boundary from Leaf Megafosils."  This paper compromises the usual bolide vrs. outgassing argument by accepting the linear increase from the Daccan traps but postulates a bolide colision as well that threw 4,600 GT c into the air rasing the ppm from 500 PPM to 2,300 ppm in only 10,000 additional years. I think were the two authors to duke it out in person, Mclean would argue that 500 PPM was the tipping point where the carbon sinks failed causing the rapid rise and consequent extinction while the author(s) of this other paper argue that another cause was neccssary for such a quick and dramatic increase.

        

39648. chriskoz at 18:45 PM on 9 January 2014
       Global warming is being caused by humans, not the sun, and is highly sensitive to CO2, new research shows
       

       If Sherwood 2014 ECS of 4°C is correct, then the actual equilibrium deltaT will be incidentally equal to the W/m2 forcing, which is the RPC number. That makes it very easy to calculate, e.g. RCP6.5 - 6.5°C.

       That does not mean that I like the larger deltaT; but the simplicity is my favourite aspect of any knowledge according to KISS paradigm especially important while talking to denialists.

39649. pheidius at 18:29 PM on 9 January 2014
       Climate's changed before
       

       I admit to some difficulty with Mclean's math as he was using moles as a measurement while current measurements use ppm(petagrams). I could not find any online calculator as moles and metric measurements are apples and oranges. He cites the figure of 5 x 10 to the 17th moles of co2 as the total Deccan release. I made that out to be 500,000,000,000,000,000(500 quadrillion moles). He gave a current mean figure of 4.1 x 10 to the 12th moles as the annual realease from all sources. (410,000,000,000 410 billion moles) At first, I thought I would try to convert from moles to the modern atomic unit by dividing by 12 and then trying to convert to ppm but then got muddled into thinking I could just multiply the moles by 1,000,000 to get PPM. Then I got tired and decided to post in the forum before going further. So how does Maclean's  1985 math fare against more recent calculations?

39650. Bernard J. at 17:05 PM on 9 January 2014
       Global warming is being caused by humans, not the sun, and is highly sensitive to CO2, new research shows
       

       On the matter of the climate sensitivity side of things Steven Sherwood says:

       Rises in global average temperatures of [at least 4C by 2100] will have profound impacts on the world and the economies of many countries if we don't urgently start to curb our emissions.

       One of the foremost denialist mantras at the moment is the notion that climate scientists are "extremist" - an yet Sherwood's words are simply "profound impacts"...  This is hardly an extremist statement, so I struggle to understand why there is such venomous antipathy to the warnings of the professional scientists.  Even Dana refers to "potentially catastrophic" results - I'm happy to go out on a limb and say that the adverb is unnecessary and that 4+ °C will be catastrophic if we allow the planet to warm to that extent.

       It's worth noting that we're tracking close to the RCP8 pathway, although I think that over the course of the century the RCP6.5 pathway is likely to be closer to what eventuates.  Taking this latter emissions trajectory into consideration and using Sherwood's et al results we are heading for somewhere between a tad under 5 °C and a smidgin over 7 °C of warming since the beginning of the Industrial Revolution.  And this is only for 2100 - not for the eventual plateauing of the trajectory...

       My money's currently on the the lower end of Sherwood's et al estimate for equilibrium climate sensitivity (for a couple of years now I've punted for 3.4 ± 0.2 °C for ECS) but this is still in "catastrophic" territory with a respond of just over 5 °C by 2100 is we continue with business as usual for the rest of the century.  Even half of that amount of warming would be "catastrophic" for hundreds of millions (at least) of people and for >20% of the planet's biodiversity, and given that we're just about locked into that lower temperature plateau already, based on an assumption of a (now apparently conservative) 3 °C ECS and the emissions intentions of the international community for the forseeable future, there seems to be no way to avoid a bad end. And despite all this we continue to conduct out business such that we track at the higher end of emissions.

       It's really a choice of a 'little' catastrophe in the future, or a big one.  How long before we finally stop shovelling coal into the boiler?

        

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