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Comments 39601 to 39650:

39601. KR at 16:12 PM on 11 January 2014
       Global warming is being caused by humans, not the sun, and is highly sensitive to CO2, new research shows
       

       davidsanger - There would be a short-term dip in forcings until the stratospheric aerosols came down, much as we saw with the 1991 Pinatubo eruption - see the stratospheric aerosols below:

       

       [Source]

       After that warming would simply resume. At most warming might be delayed 5-10 years, resuming on much the same track after that. And no, no permanent amelioration, just a short delay reaching radiative balance at the same temperature we would reach without such a volcano.

39602. Glenn Tamblyn at 16:12 PM on 11 January 2014
       Global warming is being caused by humans, not the sun, and is highly sensitive to CO2, new research shows
       

       davidsanger

       Generally speaking the cooling impact of volcanic aerosols will dissipate within a few years. Then the full warming effect of the CO2 emerges. As long as the CO2 concentrations remain the same no persistent amelioration can occur. The only remotely conceivable way that amelioration could occur is if it resulted in increased carbon sequestration somewhere, pulling it out of the atmosphere. If volcanic cooling persisted for a  long time then it might lower ocean temperatures and allow greater uptake of CO2 by the ocean. However when the volcanic cooling ended the system rewarms and the oceans outgas the CO2 again and result is zip.

       The only type of volcanic impact I can imagine have a long term effect would require continuous vulcanism for centuries to millenia, long enough for the increased uptake of CO2 into the ocean to be transferred down to the depths and possibly deposited on the sea floor. If the extra CO2 absorbed is still near the surface when the volcanic cooling ends it will outgas again; it needs to be removed from contact with the surface for any long term impact.

39603. KR at 16:04 PM on 11 January 2014
       Hockey sticks to huge methane burps: Five papers that shaped climate science in 2013
       

       Hank_Stoney - Regarding Marcott et al 2013, Tamino tested a theoretic 0.9 spike (100 years up, 100 years down) against their Monte Carlo testing, and found they were clearly visible in the resulting analysis. I personally repeated that with a separate technique, using the frequency transform Marcott et al described in their supplemental data, and found that such a spike would leave a 0.2-0.3C spike in the final data. 

       No such spike appears anywhere in the Holocene data Marcott et al analyzed. And that doesn't even include the physics indicating a CO2-driven spike of the kind we are currently experiencing cannot just vanish over 100 years - rather, 1-10Ky would be required (Archer et al 2008); there is just no physical mechanism for such a spike. 

       The entire 'dust-up' you mention arose from fantasy hypotheticals created by 'skeptics', hypotheticals which simply do not hold up under analysis. Hypotheticals, I'll note, which are certainly not peer-reviewed...

39604. chriskoz at 15:43 PM on 11 January 2014
       2013 was Australia's Hottest Year, Warm for Much of the World
       

       It's worth adding that last year's rainfall anomaly in the East (coastal floods on QLD & NSW due to Oswald while extreme drought inland) happens to be consistent with the CSIRO model predictions in this part of the world due to climate change: the East Coast will become generally wetter and inland drier and rain will be falling in more sporadic and more intense events.

39605. davidsanger at 15:28 PM on 11 January 2014
       Global warming is being caused by humans, not the sun, and is highly sensitive to CO2, new research shows
       

       A question on volcanoes: Hypothetically, if there were to be a major volcano in the near future, and a subsequent increase in aerosols and reduction in temperature for a while, and at the same time CO2 levels continued to follow the same pattern as before, would the net result centuries later be the same or would some of the effects of the increased CO2 levels be permanently ameliorated?

39606. Hank_Stoney at 15:10 PM on 11 January 2014
       Hockey sticks to huge methane burps: Five papers that shaped climate science in 2013
       

       Not trying to be make any waves but wasn't there a big dust-up at the time of publication regarding statements similar to the following (quoted from above):

       1. What hockey stick graphs tell us about recent climate change

       . . . Shaun Marcott and colleagues showed global temperature rose faster in the past century than it has since the end of the last ice age, more than 11,000 years ago. . .

       And the actual language in the paper that was expanded upon in the FAQ at realclimate.org (my emphasis):

       Q: Is the rate of global temperature rise over the last 100 years faster than at any time during the past 11,300 years?

       A: Our study did not directly address this question because the paleotemperature records used in our study have a temporal resolution of ~120 years on average, which precludes us from examining variations in rates of change occurring within a century. Other factors also contribute to smoothing the proxy temperature signals contained in many of the records we used, such as organisms burrowing through deep-sea mud, and chronological uncertainties in the proxy records that tend to smooth the signals when compositing them into a globally averaged reconstruction. We showed that no temperature variability is preserved in our reconstruction at cycles shorter than 300 years, 50% is preserved at 1000-year time scales, and nearly all is preserved at 2000-year periods and longer. Our Monte-Carlo analysis accounts for these sources of uncertainty to yield a robust (albeit smoothed) global record. Any small “upticks” or “downticks” in temperature that last less than several hundred years in our compilation of paleoclimate data are probably not robust, as stated in the paper. (link)

        

       In my mind, that's a pretty clear contradiction. Maybe others disagree?

       If not, I think we should offer proper caveats about the results of the study rather than open ourselves up to such easy criticisms.

       Just my $.02.

       P.S. I know that Tamino made a blog post defending those types of claims so maybe reference that as well even though it was neither peer-reviewed nor included in the Marcott analysis.

39607. Bob Lacatena at 14:55 PM on 11 January 2014
       New Study Suggests Future Global Warming at the Higher End of Estimates: 4°C Possible by 2100
       

       Macoles, 24,

       Your understanding is incorrect.  The "natural carbon cycle" is just that, a cycle, not a reservoir.  About half of human emissions go into the ocean, causing acidification which may turn out to be as or more dangerous than climate change.  A big chunk goes into the atmosphere.  Most of the rest goes into expanded vegetation.

       It can't and doesn't just disappear.  It took nature hundreds of millions of years to bury it in the ground.  That won't happen easily, or quickly.  There are some mechanisms by which carbon will be deposited in the deep oceans, but that will happen very slowly.

       worse yet, we can't even count on it continuing to go into either the ocean or vegetation.  As the ocean warms, it's capacity to absorb CO2 is reduced.  Eventually, if it warms enough, it may release some of that absorbed CO2 -- a positive feedback.  The same goes for vegetation.  While for a while, it may show more growth due to mildly warmer temperatures, increased precipitation, and higher CO2 levels, that's hardly a permanent trajectory.  Eventually, expansion of the deserts and droughts, especially if it happens too quickly, will reverse some or much of that growth (worst case would be, for example, the transition of major parts of the Amazon to savanna).  The subsequent release of carbon is yet another positive feedback.

       If we reduce emissions, there is no reason to think one particular sink (atmosphere, ocean, vegetation) to absorb more than another, and as the planet will continue to warm until it reaches a new equilibrium temperature, any of those positive feedbacks listed above could still come into play.

       Interestingly, even if we found a magical, technological way to suck CO2 out of the atmosphere, the ocean would still replace some of it, and those positive feedbacks might still kick in.  It's a very dangerous game that we're playing... Carbon Roulette.

39608. Tom Curtis at 13:35 PM on 11 January 2014
       New Study Suggests Future Global Warming at the Higher End of Estimates: 4°C Possible by 2100
       

       As an addendum to my @28, and Chriskoz's @27, increasing background emission rates by 1.51 x 10^12 mol per year (2.4% of the current increase of emissons over background levels) with a 0 Gt C spike results in a CO2 concentration of 400 ppmv after 1 million years.  That is an excess emissions rate of 0.02 Gt C, and represents a reasonable estimate of the maximum safe emissions in the very long term.  For all intents and purposes, that means we need to target 0 net emissions in the long run.  An intermediate target less than 5 - 9% of current emissions will be necessary to ensure we avoid the full ECS response to increased CO2.  I am sure Chriskoz and I will agree that above that is madness, and the closer to 0 net emissions the better.  

39609. Tom Curtis at 13:21 PM on 11 January 2014
       New Study Suggests Future Global Warming at the Higher End of Estimates: 4°C Possible by 2100
       

       chriskoz @27, I quite agree, and am happy to see your expansion on my point that:

       "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."

       My original point was that for any reasonable estimate of cumulative emissions by 2100, ongoing emissions after 2100 of just 9% of current emissions will be sufficient to prevent CO2 levels from falling.  I did not claim they would not rise.  As also noted @22, that level is sufficient for an effectively indefinite rise in CO2 levels in the very long term (by human time scales).

39610. chriskoz at 12:59 PM on 11 January 2014
       New Study Suggests Future Global Warming at the Higher End of Estimates: 4°C Possible by 2100
       

       Tom Curtis@22,

       You modelled your scenario in GEOCARB model a little bit inaccurately. Originally, you said @13:

       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

       (emphasis yours)
       It mean that your scenario is to cease the CO2 emissions now but keep the 9% residue of CO2 emissions (70E12 mol/yr as "degassing simulation") forever. Such scenario translates to the Transition CO2 Spike of sth like 500GtC (cumulative emissions to 2011) in GEOCARB. Yours 5000GtC input is unrealistic.

       So, with 500GtC spike input and degassing simulation of  70E12 mol/yr, the GEOCARB output is 505ppm CO2 spike (obviouly higher than today's real value because of shorter timeframe - 50y - of release in GEOCARB) but the minimum CO2 reached is 455ppm (in 400y), therefore somr than 50ppm higher than today. So I think, according to your argument, the residual degasing rate does not need to be as high as 9% of the current rate, so that CO2 concentrations "will not fall". In fact, I modified the degassing simulation of 40E12 mol/yr (5% of current levels) and I got the minimum CO2 of 398ppm in 700y, which is incidentally the current level.

       So I argue that CO2 degasing of just 5% of current levels, if kept indefinitely, will ensure that the current 400ppm "will not fall". Further, please note that this 40E12 mol/yr degassing includes the volcano output (7.5E12 mol/yr spinup parameter) estimated from the current geo configuration. Therefore, the "human C residual outpout" in this scenario is only 32E12 mol/yr, or 4% of current levels.

       For those who want to understand how the numbers are spun by GEOCARB on a shorte and long timescale, check out the rock weathering simulation by choosing "Silicate Thermostat" as an output graph. Before the simulation (years -100 to -50), the silicate weathering rate (WeatS) is in balance with volcano degassing (Degas), which is equal to the spinup value of 7.5. That equilibrium results in 272ppmCO2. If you show "Silicate Thermostat" for 1 million years, you sea that WeatS still would not catch up with Degas (33.7 vs. 40 in my simulation), therefore CO2 in the A would still be rising causing T rise and slowly speeding up WeatS. Such scenario (CO2 degassing at 5 times the natural level for 1My) has nothing to do with AGW and I'm not a geologist to judge how likely it is (i.e. if enough C and the mechanisms of its elevated level of release) exist in the system. It is just to show how miniscule CCycle changes are in the long-term natural system, as opposed to the "disaster-like", abrupt anthropo disturbance.

39611. Tom Curtis at 12:39 PM on 11 January 2014
       Global warming is being caused by humans, not the sun, and is highly sensitive to CO2, new research shows
       

       chriskoz @15, the situation he implies is implicit in the fact that the temperature response lags the forcing.  Because of that, the temperature response can be below the equilibrium temperature response for a value less than the peak insolation long after the peak insolation has passed.  So long as the decline in insolation has not fallen below that lower value, temperatures will continue to rise, albeit at a slower and slower rate.  I discuss this @10.  

       As mentioned @16, this situation occurs annually.  In fact, the peak insolation annually is in December, coinciding with the peak SH insolation.  The peak SH temperature, however, lags the peak SH insolation by about a month, and occurs in January.  Likewise the peak NH insolation is in July, but the peak NH temperature is in August.  Because air over land heats faster than air over sea, the NH has a larger response to changes in insolation than the SH, resulting in the peak global temperature also occuring in August.

       Indeed, this situation also occurs daily on a local level, with peak insolation at noon, but peak temperatures around 1 or 2 pm.

       It is, however, important to note that this situation can only occur when there is a lag in the temperature response to forcing.  Absent that lag, peak temperature will always occur at the time of peak forcing.

39612. Tom Curtis at 12:30 PM 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, if your point is the very narrow and technical point that it is theoretically possible that global temperatures could continue to rise after the forcing that caused that rise had started to fall, then I have already conceded that point.  As it happens, that happens every year when the seasonal peak temperature occurs in August though the relevant forcing (NH summer insolation) peaks in July, and falls thereafter.  

       However, as I have pointed out @10, the merely theoretical possibility that the increase in insolation to 1950 was the cause of the increase in temperature to 2014 is inconsistent with observations.  As a candidate scientific theory, it has been falsified.  Therefore that merely theoretical, but in fact falsified possibility is irrelevant to this discussion.  At most your point is that the statement:

       "we know the sun can't be causing the current global warming because solar activity has declined slightly over the past 50 years"

       represents a contingent (inductive) argument ie, one that is not guaranteed to be valid under all circumstances.  But unless you wish to argue that all inductive arguments should be avoided, that is irrelevant.  The number of circumstances under which the argument is valid far exceeds those under which it is invalid, including the current circumstances as shown @10.  Therefore the only 'flaw' in the argument is that it provides less certainty than can be obtained by a more detailed argument.

       Now, either you know that the Sun is not the cause of the continuing increase in global warming after approx 1960, in which case you are arguing a mere technicality; or you do not, in which case you are massively confused.  The later appears likely in that you appear to think the possibility of ongoing warming from a declining forcing is independent of the lag in the forcing.  That is false.  If there is no lag, then the increase in temperature at any time will exactly correspond to the increase in forcing, so that at the peak of forcing, you will also be at the peak in temperature. 

39613. 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?  

39614. 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.

39615. 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.

39616. 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 :)

39617. 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.

39618. 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.

39619. 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. 

39620. 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.

39621. 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.

39622. 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.)

39623. 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. 

39624. 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.)

39625. 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.

39626. 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.

39627. 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.

39628. 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. 

39629. 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.

39630. 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.

39631. 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

        

39632. 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?

39633. 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.

39634. 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.

39635. 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!

39636. 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.

39637. 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. 

39638. 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.

39639. 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).

39640. 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."

39641. 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."

39642. 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.

39643. 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.

39644. 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.

39645. 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.  

39646. 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.

39647. 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.

39648. 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.

39649. 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.

39650. 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?

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