Home/BlogThis is the first paper in a long time that made my brain hurt to read.
“Spread in Model Climate Sensitivity Traced to Atmospheric Convective Mixing“, by Sherwood, Bony, and Dufresne is actually quite well written (Nature editors help to make sure scientists don’t publish bad prose in their magazine). But the concepts involved are pretty complicated, which is what happens when you try to understand atmospheric convection.
Basically, the authors claim to show that a significant amount of the spread in the climate sensitivity across dozens of climate models is due to how the models partition tropical convection between deep versus shallow convective mixing.
Although I don’t yet fully understand their reasoning, they claim these differences impact low cloud amounts, and thus low cloud feedback in the models. Low cloud feedback is arguably the least certain feedback in models, capable of either greatly amplifying or reducing the small direct warming from more CO2 in the atmosphere.
The authors present evidence that those models which have the strongest shallow mixing are the closest to the observations. Furthermore, since those models also exhibit the strongest positive low cloud feedback, we should believe the predictions of the models that predict the most warming for the future.
(What’s that you say? You thought the models with the most warming were also the ones which have failed most miserably in their temperature predictions over the last 30+ years? Ha! You silly mortal! The Climate Modelers now have a new, complex diagnostic quantity to test models with…not that silly old temperature metric.)
The paper does seem to provide some new and important insight into why different climate models have different strengths of low cloud feedback. But I suspect their “observational evidence” of just how strong shallow mixing in the real tropical atmosphere is (the MERRA reanalysis model) is, in this case, more model than it is observation. We don’t really have direct observations of the average strength of tropical lower tropospheric mixing. And even if it is true that the most sensitive models have the most realistic lower tropospheric mixing, there are so many different compensating (and highly parameterized!) processes in models, I don’t think we can use such model diagnostics as reliable tests for climate sensitivity. At least not yet.
So, for the time being, I’m sticking with the simpler tests…such as simple energy conservation and just how much the ocean/atmosphere system has warmed in the last 50 years.
The paper thus represents a bold prediction in the face of contrary evidence. So I give Sherwood et al. 5 stars out of 5 in the much-coveted cojones category.
Roy,
There was a decent discussion of related issues on the climatedialogue.net “hotspot” thread that John Christy participated in. There is a comment from Carl Mears that I will copy here (I’ll link any further references) that I think might be relevant. Steve Sherwood was on this thread….
“Carl Mears
July 24, 2013 at 12:33 amLog in to Reply
If we calculated the amplification starting at 850 hPa, instead of the surface (1000 hPa), the trend ratios from Johns figures 2 and 4 would be much more in line with the expectations of moist adiabatic lapse rate theory….What I think is more likely is that the models are getting something wrong about the boundary layer response to global warming. The boundary layer is much more complicated than the free atmosphere above it, so if the models are wrong, it seems more likely to be in this region.
It is indeed surprising that the trend is less at 850 hPa than the surface. Here is one way that it might be happening. Assuming that the lapse rate is determined by the moist adiabatic rate from the surface to the tropopause might be too simplistic. Under most convecting clouds, there is a sub-cloud region where the air is not saturated, and the lapse rate is closer to the dry adiabatic lapse rate, which is much larger. (You can read about this in Kerry Emanuels book Atmospheric Convection) If the thickness of this layer increased over time fast enough, then the temperature at 850 hPa (above this layer) would have a smaller trend than the surface, and we would get the observed temperature trends. This (I think) would require that the relative humidity at the surface trend downward, and I am not sure how this might occur.”
Or-maybe-the warming of the surface is actually exaggerated. Due to various urbanization/landuse/surface process effects. To my knowledge it does not appear to be the case that near surface relative humidity is decreasing.
And, let’s keep in mind, Mears is suggesting models are in error *in the layer they match best in absolute terms*. Because they have been tuned to do so. If he is right, then models get roughly the right surface temperature trend in the last about 30 years, *for the wrong reasons*.
Which, wow, would be kind of a big indictment of the models in any case, don’t you think?
For example, I am under the impression that the NCEP reanalysis is thought to systematically overestimate humidity in the earlier years of the record, but even it has a positive trend in surface relative humidity since 1979. Which probably means the reality is a fairly strong relative humidity upward trend near the surface.
I think we’re mostly talking about over the ocean here.
Well, those might be biased, too. As I recall, if you use Marine Air Temperature, you get lower trends over the tropics in particular.
Maybe I’m confused, but isn’t it a major contention now that much of the missing excess energy in the atmosphere is going into the oceans? If more energy goes into the oceans, but the air over these oceans is becoming drier, then the necessarily evaporated moisture has to be getting transported up to higher levels, doesn’t it? Or have we changed the laws of physics now so that warmer water doesn’t produce more evaporation?
willywolfe – it seems counterintuitive I agree.
Very interesting discussion.
So, apparently, Carl Mears had not the right answer.
About Steven Sherwood, then, he seemed pretty hesitant about sensitivity. In the same place (August 11, 2013 at 2:20 pm) :
“Finally, it may signal a somewhat low climate sensitivitybut a sensitivity low enough to make global warming cease to be a problem is basically ruled out by other evidence, particularly palaeoclimate evidence.”
There are only two ways that the mass of an atmosphere can transfer energy, namely, radiation and conduction.
In order to maintain radiative balance between surface and space the total combined effect of radiation and conduction must be stabilised at a level determined by the need to match energy out with energy in at any given level of insolation from outside the system.
Convection is the process whereby the system corrects itself if there is too much or too little of either radiation or conduction.
Everything flows from that.
Convection (utilising the gas laws) is the global thermostat and it achieves its effect by speeding up or slowing down to ensure that precisely the right amount of thermal (kinetic) energy is delivered to the effective radiating height in the atmosphere wherever that height might be at any given moment.
The phase changes of water, especially evaporation, act as a lubricant for the process because water vapour is lighter than air which makes it easier for convection to do its job.
Convection is not difficult in itself but its complex behaviour within the system certainly is.
I remember a paper for a year or so ago, that made the same claims of models with the highest warming. At that time it was a feature around the tropics. DMI reported about it and made it very important, but the authors where a lot more cautious.
Wonder just why no one ever reports of models of low warming that best show some selected feature?
Are you familiar with Public Choice Theory?
Yawn! Not much point in the “scientific holy rollers” doing this sort of patch job. The developing world is not going to wear hair shirts on THEIR say-so.
“…cojones category.”
My wife says “Wheresoever two cojones are gathered together, there will be found a big…p*tz.”
“Low cloud feedback is arguably the least certain feedback in models, capable of either greatly amplifying or reducing the small direct warming from more CO2 in the atmosphere.”
I and Troy Masters had a paper we submitted to GRL a few years back now, arguing that feedback responses were more accurately calculated by using atmospheric temperatures than surface temperatures. The reviewers rejected it as spurious because TLT has most weight above the altitude of low clouds and low clouds were “expected” to be the most important feedback. I found that remark sort of puzzling at the time, but it makes sense now: because that feedback is so important *in models* (in that it determines the uncertainty in sensitivity of models so much) the reviewers assumed it would be equally important in *reality*.
I suspect the paper got through the peer review process because the reviewers didn’t want to admit that they didn’t understand it.
The authors interested me…
Steven Sherwood works here:
Climate Change Research Centre and ARC Centre of Excellence for Climate System Science
Further down the page you see this:
“The authors declare no competing financial interests”
I suppose if you don’t include their keeping their jobs– future tenure possibilities etc… then they don’t have financial interest.
Just the name of the place tells it all.
This type article reminds me of the days when the universe was thought to be geocentric…they actually had mechanical devices to show the movements of the planets (and sun)….with dozens of nested gears capable of retrograde motion and everything else then Kepler came along and showed that a much simpler mechanical device was all that was needed.
We live in a messed up world…caused mostly by the dumbing down of education…(my theory)…or as Alduous Huxley said education of the masses produces every kind of imbecility–a bit
snobbish for my scruples.
“…Centre of Excellence…”
Any group with the vanity to actually keep that vacuous bit of smug, corporate-speak in its name, has to be stuffed full of humbugs.
We are going to see more of this dead parrot routine:
“Your ‘real expert’ knows that the Mexican Blue likes pretending to be dead. If he’s still not moving in a year, give him a tonic.”
“But… Why is he stuffed?!”
Davey
(” On A Good Day, Mediocre. “)
Or:
“I fixed your oven. It’s working again.”
“But it’s cold!”
“It’s in the small print, see?, “oven AND refrigerator.”
They say shallow convection mixing in the tropics leads to more low clouds which leads to more warming.
Sure, of course. Next joke. First of all there is no hot spot being observed in the lower tropical troposphere which would support shallow convective mixing. Secondly there is really no observational evidence that shallow convective mixing would create more low clouds in the tropics. Third there is no evidence that an increase in low clouds in the tropics or else where would amplify warming. In fact evidence is an increase in low clouds will promote global cooling. Fourth they have no evidence to say shallow convective mixing in the tropics is going to increase.
To sum this up this is more grasping at straws to come up with some wild explanation to say their obsolete climate models are still relevant in the climate projections they predict for the future.
Hi Roy, thought this link from the horses mouth might interest..
http://theconversation.com/how-clouds-can-make-climate-change-worse-than-we-thought-21617
What do you think about the Antarctic ice sheet “anomaly”:
http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/seaice.anomaly.antarctic.png
The Antarctic is a land continent unlike the floating Arctic ice cap (which is over-hyped by ice-propagandarists) and the Antarctic sea ice sheet area has INCREASED by 1,400,000 square km since 1979.
If a new ice age sets in, Al Gore and Mike Mann will another Nobel prize for predicting “climate change”. Newsweek magazine and the scare-mongering media was hyping a rapidly approaching new ice age as a “climate change” fact forty years ago: see the article by Peter Gwynne, The Cooling World, Newsweek, 28 April 1975, page 64 (pollution will cut out sunlight and cause a new ice age, the 1970s “global cooling” scam):
https://www.facebook.com/photo.php?fbid=4348749910095&set=a.4348749870094.2162146.1028004904&type=1&theater
Dr. Spencer, will you be writing a comment to Nature with your objections to this paper? That’s what professional scientists do when they believe a published paper is incorrect.
Presuppositions
Further to Roy’s comments, a foundational issue is what defines science? In turn that requires examination of the underlying presupposition of what science can examine by objective observation or evidence.
Closed Science
One presupposition is materialism/naturalism and the insistence that there is only matter. Those holding this presupposition further demand a closed science which must exclude all hypotheses of an extramaterial intelligent cause. However, logically one cannot prove such a negative. Furthermore, this presupposition requires that one must only entertain hypotheses of abiogenic origin of life influenced by the stochastic processes of the four forces of nature, and consequent atheistic evolution.
Open ScienceThe alternative presupposition is agnosticism where one allows that there may be an intelligent agent behind terrestrial life, whethe4r extraterrestrial or an extramaterial intelligent agent. This allows for an open science in which observational evidence is examined to see if it corresponds to such intelligent agents, or whether it can be inferred from stochastic processes of the four laws, or by order due to natural law. Thus the development of Intelligent Design theorists in contrast to Creation Science which seeks for observational evidence corresponding to the Biblical record. Such allow for terrestrial life could have been caused by intelligent agent.
Ask and explore whether a person’s Your hypothesis infers whether they are holding presupposition restricting hypothesis to closed science. Or are they open to examining observational evidence for intelligent agents? e.g. compare forensic science, archeology, etc.