Discussions on climate sensitivity at Ringberg

[Michael Hauber]

I thought the recent discussions on climate sensitivity at Ringberg were quite interesting.  I have summarised each one to the best of my understanding.  Note that these presentation are not peer reviewed science, but more the working hypothesis of researchers currently on the frontline, so a solid peer review may spot errors and issues with any of these claims.  I have tried to represent each presenters view as faithfully as I can and noted as a comment anything that is my opinion about these presentations:

Andrews
   - feedbacks within most models become stronger over time, from about year 21 onward
   - different patterns of regional sea temperature change cause different feedbacks
   - for the 'slow pattern' equilibrium climate sensitivity is 5 degrees,
   - For the 1900-2012 observational pattern climate sensitivity is 2.3 degrees
Comment:  The slow pattern looks similar to El Nino.  The observed pattern looks more La Nina like.  The question is whether the observed pattern is due to natural variability occurring on a century timeframe to slow down warming , or whether this pattern represents a significant negative feedback.  If the pattern has been a response to Co2 it may continue and be a substantial negative feedback.  However the pattern may change over time.  In particular it could be a response to the rate of warming (eg related to the temperature difference between surface and deep ocean),  in that case the patterns would induce a negative feedback while warming is fast, but as we approach equilibrium and the rate slows the feedback may disappear, with the net result that sensitivity is still high but it takes a lot longer to reach.

Annan I
   - Compares model results with paleoclimate observations, particularly for the last glacial maximum. 
   - Earth System Sensitivity likely beteween 1.1 and 2 times Equilibrium Sensitivity, best estimate of 1.5.  Most likely Equilibrium Sensitivity is 3, Earth System Sensitivity 4.5
   - Modesl good at broad scale, poor at regional scale, no improvement from CMIP3 to CMIP5
   - Doubts that sensitivity outside CMIP range (say 1.5 to 5) could reproduce changes observed in LGM and other paleo epochs

Annan II
   - Discusses model independance and bayesian analysis. 
   - True independance would give a range of 2.9 to 3.5 for sensitivity (with a 95% confidence interval)
   - No one thinks the models are independant.
   - Although some have tried, no one has produced a useful definition of independance.

Armour
   - models show feedbacks that increase over time.  Energy balance models assume constant feedbacks. 
   - Therefore energy balance models may underestimate sensitivity should be considered a lower constraint

Armour Efficacy
   - Discusses energy balance calculations

Bellouin
   - Discusses 'fast adjustments'

Bengtsson
   - discusses the usability of various sources of temperature data for estimating sensitivity

Bony
   - Finds observational evidence for an IRIS effect. 
   - But finds no negative feedback associated with this effect
   - Short wave effects from low clouds seem to oppose this effect
   - Sensitivity unlikely to be below 3 degrees

Caballero
   - Discusses paleo, primarily PETM.  Sensitivity about 3K
   - higher sensitivity at warmer temperature due to tropical cloud feedbacks
Comment:  The model output looks to me like a stronger MJO, and an increased convective aggregation (IRIS effect)
   - no compelling reason to think that modern ECS is outside "canonical" 2.5-4.5 K

Church
   - Discusses heat uptake of oceans

Crucifix   
  - discusses energy balance modelling from paleo data
  - finds effective (transient?) sensitivity of 2.33 K

Dessler
  - equilibrium sensitivity is 1.8-2.2 without considering cloud effects (comment: and excluding earth system issues such as changes in Co2 via vegetation, permafrost etc)
  - Once clouds are included it is 1.9 to 5.1

Edwards
  - Based on paleo evidence equilibrium climate sensitivity is between 1.6 and 5.4

Fasullo
  - As the energy balance was unchanged during the hiatus there is no evidence for weaker +ve feedbacks
  - sea level rise during the "grand" hiatus 1945 - 1975 continued with no slowdown
  - Therefore the slow down was not externally forced, implying a greater role for PDO, smaller role for aerosol cooling. 
  - Comment: less aerosol cooling tends to imply a lower climate sensitivity as less current warming has been offset by this cooling effect

Geoffroy
  - Describes cloud changes for higher sensitivity models

Golaz
   - to some extent climate sensitivity can be 'tuned'
comment:  It is a favorite denier meme that the climate models can be tuned to get any result wanted.  Note that Golaz says 'to some extent'.  If they can be tuned to give any result wanted then why has no skeptical scientist tuned a climate model to produce a low sensitivity?

Gregory
   - climate feedbacks increase over time.
   - therefore energy balance estimates may be low

Hegerl
   - Discusses diagnosis sensitivity from observations
   - good lower bound, not so good upper bound due to potential non-linearities (comment:  increasing over time is a non linearity)

Knutti
   - Feedbacks change over time
   - Comment: The presentation here makes it look more like a fast feedback vs slow feedback issue

Kosaka
   - Energy accumulation during the hiatus has continued without slowdown, however energy balance model suggests that 'natural variability' would cause an increase in heat accumulation
   - Therefore current hiatus is internal variability not externally forced
   - Comment:  while this would be the case if natural variability involves moving heat from the ocean surface to the depths, it would not be the case if natural variability causes a change in the radiative balance.  Natural variability could affect the radiative balance through changes in clouds, or increasing warmth in snow covered areas resulting in an albedo shift.

Latif
   - Southern ocean obs suggests a 100 year cycle, modelling can produce a 400 year cycle.

Lewis
   - Many observational estimates of climate sensitivity are flawed (AMO, bad priors too high aerosol forcing).  (comment: that is all the higher ones)
   - Paleo estimates are generally uncertain
   - models warm 3 times faster than obs for 1988 to 2012
   - therefore the lower estimates of climate sensitivity from obs are the only good estimates and ECs < 2.2
 Comment:  while the criticisms he makes of other estimates may be (at least in part) genuine he ignores weaknesses in the estimates that he prefers.  It is not very useful or even particularly clever in science to point out that particular methods have weaknesses or uncertainties (particularly in a field like climate science). 
 It is more interesting to point out how these weaknesses may be corrected and what happens when you do.  As an example models overestimate recent warming.  What happens if you try to correct for this by selecting model runs that match the recent slow warming?  You get almost exactly the same warming rate.

Schmidt
   - not all forcings have the same effect.
   - adjusting for this effect on observational studies results in an increase in ECS as calculated from energy balance methods from 1.9 to 3.1

Sexton
   - General discussion on issues around climate sensitivity

Sherwood
   - Slower warming in SH since 1979 which is not explained by models
   - Possible mechanism is that ozone reduction has caused an increase in Southern Ocean winds.  This has increasing aerosols, leading to an increase in cloud that has caused regional cooling

Stephens
   - discussion on cloud feedback issues (both +ve and -ve).  Seems incomplete.

Stevens
   - some (not yet entirely convincing) reasons why Equilibrium climate sensitivity is between 2.0 and 3.5
   - cloud feedbacks are positive, but not strongly positive
   - aerosol forcing is not likely to be high
   - no strong negative feedbacks to push ECS under 2.0

Sutton Hawkins
   - Constraining CMIP models based on observations results in a 10-20% reduction in 21 century projections
   - using a different reference period for climate projections changes the result

Vial
  - Discussion on detailed modelling of convection to investigate low cloud feedbacks.  No results.

Webb
   - Discussion on a variety of mechanisms for cloud feedback

Zelinka
  - cloud feedbacks are not likely to be strongly negative.

[oren]

Thank you MH

[AbruptSLR]

Thank you MH

I find MH's summaries to be of limited value (if you are interested in this topic I recommend that you look at the presentations yourself); and I find that the comments are at best wishful thinking, and at worse to be manipulative.

Since the Kyoto Protocol was drafted the canonical range for ECS has been between 2 and 5C, and it is still cited as being in this range (by Schmidt and others).  In actuality, at any given time ECS can only be one value and cannot be a range.  The canonical range is either an expression of scientific ignorance, or of an expression of scientific radiances (i.e. an expression of the scientific consensus to err on the side of least drama; which means to discount the probability of higher climate sensitivities).

The Earth does not care at all about man's desire to err on the side of least drama; therefore, I am concerned that by the time that a reasonably reliable state-of-the-art Earth Systems Model (like ACME) provides a reasonable estimate of ECS, that modern society will already committed to unnecessary level of climate change induced damage in the decades to come.

[TeaPotty]

Michael's posts here shows a clear attempt to mislead forum readers.

Furthermore, the length & complexity of deceptions in this thread and many others lend credibility to theory that Michael is not one person, but a paid organization pushing misinformation.

[Neven]

Michael's posts here shows a clear attempt to mislead forum readers.

Furthermore, the length & complexity of deceptions in this thread and many others lend credibility to theory that Michael is not one person, but a paid organization pushing misinformation.

In that case the Michaels would be swarming all over the threads on Arctic sea ice, as these are most dangerous to paid organizations pushing misinformation. This forum is not going to sway minds with regards to climate sensitivity, so there is no danger in engaging with Michael Hauber and emphasizing your arguments.

Could you please stop making threads about Michael Hauber, and return to the subject at hand, or go to some other part of the forum where you don't get agitated? I mean, the melting season has started! This is all so boring.   

[TeaPotty]

Michael's posts here shows a clear attempt to mislead forum readers.

Furthermore, the length & complexity of deceptions in this thread and many others lend credibility to theory that Michael is not one person, but a paid organization pushing misinformation.

In that case the Michaels would be swarming all over the threads on Arctic sea ice, as these are most dangerous to paid organizations pushing misinformation. This forum is not going to sway minds with regards to climate sensitivity, so there is no danger in engaging with Michael Hauber and emphasizing your arguments.

Could you please stop making threads about Michael Hauber, and return to the subject at hand, or go to some other part of the forum where you don't get agitated? I mean, the melting season has started! This is all so boring.   

Neven, this is Michael's thread, not mine. His first post is highly misleading, and his argument has been thoroughly discredited by other valued members of this forum.

Also, I never made any threads about Michael, so not sure where this accusation comes from.

I, like many others here, enjoy reading science, not propaganda. So long as he is allowed to post his propaganda, we should all be equally free to call him out on his nonsense based on the science.

[Neven]

Also, I never made any threads about Michael, so not sure where this accusation comes from.

I'm sorry, TP, I wasn't addressing you specifically, but I did have this comment of yours in mind.

His first post is highly misleading, and his argument has been thoroughly discredited by other valued members of this forum.

I think his argument has been refuted by Jai and ASLR (and others), so that was useful. That's what a discussion forum is for.

I, like many others here, enjoy reading science, not propaganda. So long as he is allowed to post his propaganda, we should all be equally free to call him out on his nonsense based on the science.

Yes, but try to not make it personal, and don't try to force me into banning other members. I will do what's necessary, but in my own time, when I think it's necessary. Besides, if there's not a bit of non-alarmist 'propaganda', there will be nothing left to rebut. I think there is plenty of room for Michael Hauber on this forum.

Okay, that's it. I don't want any more metaforum talk in threads about Michael Hauber or other non-alarmists. Take a deep breath and feel the love of the Cosmos flow through you. 

[Michael Hauber]

The simple fact is that the majority of the assessments of climate sensitivity at this conference find that climate sensitivity finds that sensitivity is about the same as what the IPCC state.  A small but significant number estimate a possible small reduction.  None make a claim for a higher sensitivity. 

I encourage anyone interested to read these assessments and see that I have not been misleading.

[jai mitchell]

 

Dessler says that it is likely that the lower limit of 2.0 is too low.

http://www.mpimet.mpg.de/fileadmin/atmosphaere/WCRP_Grand_Challenge_Workshop/Ringberg_2015/Talks/Dessler_24032015.pdf

[Neven]

I've given weatherdude88 permission to discuss climate sensitivity some more here (rather than on the melting season thread). I've warned him not to wander off too far into climate risk denial territory, because it's simply annoying and we already have the rest of the Internet for that kind of bullshit.

If commenters are annoyed by something weatherdude88 says, and I'm not (yet), then just ignore it. There's room on the forum for devil's advocacy.

[weatherdude88]

http://link.springer.com/article/10.1007/s00382-014-2342-y


"Using 1859–1882 for the base period and 1995–2011 for the final period, thus avoiding major volcanic activity, median estimates are derived for ECS of 1.64 K and for TCR of 1.33 K. ECS 17–83 and 5–95 % uncertainty ranges are 1.25–2.45 and 1.05–4.05 K; the corresponding TCR ranges are 1.05–1.80 and 0.90–2.50 K."

I see a general reduction in climate sensitivity estimates first in journals and then the IPCC assessments over the coming years. I would make a strong argument that climate sensitivity is most definitely on the lower end of the range (or less) given we are in a inter glacial and temperatures are suppose to rise. (This start of the years for the base period falls towards the end of the little ice age which corresponded with low solar activity) Temperatures where already rising due to an increase in solar activity.

[sedziobs]

I don't think anyone on this forum will be surprised that there are papers out there positing an ECS under 2, or that the climate is in an interglacial and a couple centuries removed from the LIA.  If you limit yourself to these pieces of information, then of course you will believe climate sensitivity is low.  The full breadth of current observations, paleo evidence and physical models tell us a lot more than that.   

[Neven]

Just curious: Where does a low climate sensitivity get us temperature-wise at the end of 2100 under a business-as-usual scenario? That means a doubling around 2050, right? And then it continues, so that by 2100 we're at around 600 ppm.

[weatherdude88]

Just curious: Where does a low climate sensitivity get us temperature-wise at the end of 2100 under a business-as-usual scenario? That means a doubling around 2050, right? And then it continues, so that by 2100 we're at around 600 ppm.

Neven,

Here is a link to a climate sensitivity calculator. (However the climate sensitivity range is only from 2-5 C)

http://scied.ucar.edu/climate-sensitivity-calculator

[AbruptSLR]

Just curious: Where does a low climate sensitivity get us temperature-wise at the end of 2100 under a business-as-usual scenario? That means a doubling around 2050, right? And then it continues, so that by 2100 we're at around 600 ppm.

Neven,

That depends on how much air pollution you want to clean-up.  Per the attached plot by Michael Mann (if you down-load it you can magnify it electronically) for a BAU case, if we clean-up all air pollution (aerosols) then for ECS of 2C by 2100 we would have a global mean temperature rise of about 2.5C.  If you make different assumptions about air pollution then by interpolating on the graph we would well below a 2C global mean temperature rise.

Best,
ASLR

[AbruptSLR]

Neven,

If you want to use the calculator and RCP 8.5 then you could use the accompanying plots; however, if you want to be correct you would need to covert the non-CO2 greenhouse gases into a CO2 equivalent concentration; which would put you well over 1,000ppm by 2100.  Also, after you use the calculator you would need to correct for aerosols.

Best,
ASLR

[Michael Hauber]

http://link.springer.com/article/10.1007/s00382-014-2342-y


"Using 1859–1882 for the base period and 1995–2011 for the final period, thus avoiding major volcanic activity, median estimates are derived for ECS of 1.64 K and for TCR of 1.33 K. ECS 17–83 and 5–95 % uncertainty ranges are 1.25–2.45 and 1.05–4.05 K; the corresponding TCR ranges are 1.05–1.80 and 0.90–2.50 K."

I see a general reduction in climate sensitivity estimates first in journals and then the IPCC assessments over the coming years. I would make a strong argument that climate sensitivity is most definitely on the lower end of the range (or less) given we are in a inter glacial and temperatures are suppose to rise. (This start of the years for the base period falls towards the end of the little ice age which corresponded with low solar activity) Temperatures where already rising due to an increase in solar activity.

The IPCC estimate a range of climate sensitivity based on a wide variety of research, some of which suggests a higher sensitivity, some a lower.  Picking one paper out of all this research, and using it to justify either an estimate at the low end or high range is basically cherry picking.

This estimate is effectively discussed in the first post of this thread, as it is by the same author, and uses the same energy balance model method as one of the presentations that is discussed.  There are a variety of papers that use an energy balance model, and they get a variety of answers.  They are all generally towards the low end of the IPCC range, and Nic's is one of the lowest.  There are problems with using an energy balance model, (as discussed in first post) which mean the real sensitivity is probably higher.

[Michael Hauber]

Just curious: Where does a low climate sensitivity get us temperature-wise at the end of 2100 under a business-as-usual scenario? That means a doubling around 2050, right? And then it continues, so that by 2100 we're at around 600 ppm.

If you mean RCP8.5 as business-as-usual, then we get a Co2 equivalent of 1250 ppm.  Currently we are at about 400 ppm equivelant, so this gives 1.6 doublings.  Equilibrium climate sensitivity is only achieved after centuries, and although a higher ECS is likely to mean a higher warming by 2100, it is more accurate to use the transient climate sensitivity.  Nic's transient response has a central estimate of 1.3, and the resulting warming would be about 2.1 above current temperatures, or about 3 degrees above pre-industrial.  If aerosols could be significantly reduced whilst still maintaining Co2 emissions then the warming would be even higher, but I doubt this is likely.

[anotheramethyst]

i'm confused, i've been encountering some ambiguous language.  so climate sensitivity is measured as the temperature response to our atmosphere with double the co2 levels (or co2 equivalent minus aerosols) of preindustrial times. 

global surface temp = climate sensitivity x radiative forcing

ok i'm not sure if it's my language skills or my math skills suffering here, but that looks to me like a linear equation, and to me, that does not imply that any additional doublings of co2 would yield the same amount of temperature increase as that first doubling.  ok what am i missing?

[Wipneus]

i'm confused, i've been encountering some ambiguous language.  so climate sensitivity is measured as the temperature response to our atmosphere with double the co2 levels (or co2 equivalent minus aerosols) of preindustrial times. 

global surface temp = climate sensitivity x radiative forcing

ok i'm not sure if it's my language skills or my math skills suffering here, but that looks to me like a linear equation, and to me, that does not imply that any additional doublings of co2 would yield the same amount of temperature increase as that first doubling.  ok what am i missing?

radiative forcing approximately increases with equal amount for each doubling. In formula : RF ~ log( CO₂p)

[anotheramethyst]

thanks wipneus!!!!! that was the missing piece of the puzzle for me