I thought this post on clouds and climate modeling below from Steve McIntyre’s Climate Audit was interesting, because it highlights the dreaded “negative feedbacks” that many climate modelers say don’t exist. Dr. Richard Lindzen highlighted the importance of negative feedback in a recent WUWT post.
One of the comments to the CA article shows the simplicity and obviousness of the existence of negative feedback in one of our most common weather events. Willis Eschenbach writes:
Cloud positive feedback is one of the most foolish and anti-common sense claims of the models.
This is particularly true of cumulus and cumulonimbus, which increase with the temperature during the day, move huge amounts of energy from the surface aloft, reflect huge amounts of energy to space, and fade away and disappear at night.
Spot on Willis, I couldn’t agree more. This is especially well demonstrated in the Inter Tropical Convergence Zone (ITCZ) The ITCZ has been in the news recently because early analysis of the flight path of Air France 447 suggests flying through an intense thunderstorm cell in the ITCZ may have been the fatal mistake. There is a huge amount of energy being transported into the upper atmosphere by these storms.
Here are some diagrams and photographs to help visualize the ITCZ heat transport process. First, here is what the ITCZ looks like from space. Note the bright band of cumulonimbus clouds from left to right.
Here is a pictorial showing a cross section of the ITCZ with a cumulonimbus cloud in the center.
And finally, a 3D pictorial showing ITCZ circulation and heat transport. Note the cloud tops produce a bright albedo, reflecting solar radiation.
And here is the post on Climate Audit
Cloud Super-Parameterization and Low Climate Sensitivity
“Superparameterization” is described by the Climate Process Team on Low-Latitude Cloud Feedbacks on Climate Sensitivity in an online meeting report (Bretherton, 2006) as:
a recently developed form of global modeling in which the parameterized moist physics in each grid column of an AGCM is replaced by a small cloud-resolving model (CRM). It holds the promise of much more realistic simulations of cloud fields associated with moist convection and turbulence.
Clouds have, of course, been the primary source of uncertainty in climate models since the 1970s. Some of the conclusions from cloud parameterization studies are quite startling.
The Climate Process Team on Low-Latitude Cloud Feedbacks on Climate Sensitivity reported that:
The world’s first superparameterization climate sensitivity results show strong negative cloud feedbacks driven by enhancement of boundary layer clouds in a warmer climate.
These strong negative cloud feedbacks resulted in a low climate sensitivity of only 0.41 K/(W m-2), described as being at the “low end” of traditional GCMS (i.e. around 1.5 deg C/doubled CO2.):
The CAM-SP shows strongly negative net cloud feedback in both the tropics and in the extratropics, resulting in a global climate sensitivity of only 0.41 K/(W m-2), at the low end of traditional AGCMs (e.g. Cess et al. 1996), but in accord with an analysis of 30-day SST/SST+2K climatologies from a global aquaplanet CRM run on the Earth Simulator (Miura et al. 2005). The conventional AGCMs differ greatly from each other but all have less negative net cloud forcings and correspondingly larger climate sensitivities than the superparameterization
They analyzed the generation of clouds in a few leading GCMs, finding that a GCM’s mean behavior can “reflect unanticipated and unphysical interactions between its component parameterizations”:
A diagnosis of the CAM3 SCM showed the cloud layer was maintained by a complex cycle with a few hour period in which different moist physics parameterizations take over at different times in ways unintended by their developers. A surprise was the unexpectedly large role of parameterized deep convection parameterization even though the cloud layer does not extend above 800 hPa. This emphasizes that an AGCM is a system whose mean behavior can reflect unanticipated and unphysical interactions between its component parameterizations.
Wyant et al (GRL 2006) reported some of these findings. Its abstract stated:
The model has weaker climate sensitivity than most GCMs, but comparable climate sensitivity to recent aqua-planet simulations of a global cloud-resolving model. The weak sensitivity is primarily due to an increase in low cloud fraction and liquid water in tropical regions of moderate subsidence as well as substantial increases in high-latitude cloud fraction.
They report the low end sensitivities noted in the workshop as follows:
We have performed similar +2 K perturbation experiments with CAM 3.0 with a semi-Lagrangian dynamical core, CAM 3.0 with an Eulerian dynamical core, and with the GFDL AM2.12b. These have λ’s of 0.41, 0.54, and 0.65 respectively; SP-CAM is about as sensitive or less sensitive than these GCMs. In fact, SPCAM has only slightly higher climate sensitivity than the least sensitive of the models presented in C89 (The C89 values are based on July simulations)…
The global annual mean changes in shortwave cloud forcing (SWCF) and longwave cloud forcing (LWCF) and net cloud forcing for SP-CAM are _1.94 W m_2, 0.17 W m_2, and _1.77 W m_2, respectively. The negative change in net cloud forcing increases G and makes λ smaller than it would be in the absence of cloud changes.
Wyant et al (GRL 2006) is not cited in IPCC AR4 chapter 8, though a companion study (Wyant et al Clim Dyn 2006) is, but only in the most general terms, no mention being made of low sensitivity being associated with superparameterization:
Recent analyses suggest that the response of boundary-layer clouds constitutes the largest contributor to the range of climate change cloud feedbacks among current GCMs (Bony and Dufresne, 2005; Webb et al., 2006; Wyant et al., 2006). It is due both to large discrepancies in the radiative response simulated by models in regions dominated by lowlevel cloud cover (Figure 8.15), and to the large areas of the globe covered by these regions…
the evaluation of simulated cloud fi elds is increasingly done in terms of cloud types and cloud optical properties (Klein and Jakob, 1999; Webb et al., 2001; Williams et al., 2003; Lin and Zhang, 2004; Weare, 2004; Zhang et al., 2005; Wyant et al., 2006).
(Bretherton 2006)
Dessler et al (GRL 2008) made no mention of strong negative cloud feedbacks under superparamterization, stating that sensitivity is “virtually guaranteed” to be at least several degrees C, unless “a strong, negative, and currently unknown feedback is discovered somewhere in our climate system”:
The existence of a strong and positive water-vapor feedback means that projected business-as-usual greenhouse gas emissions over the next century are virtually guaranteed to produce warming of several degrees Celsius. The only way that will not happen is if a strong, negative, and currently unknown feedback is discovered somewhere in our climate system.
There are a limited number of possibilities for such a possibility, but it is interesting that cloud super-parameterizations indicate a strong negative cloud feedback (contra the standard Soden and Held results.)
This is not an area that I’ve studied at length and I do have no personal views or opinions on the matters discussed in this thread.
References:
Bretherton, C.S., 2006. Low-Latitude Cloud Feedbacks on Climate Sensitivity. Available at: www.usclivar.org/Newsletter/VariationsV4N1/BrethertonCPT.pdf [Accessed June 12, 2009].
Wyant, M.C., Khairoutdinov, M. & Bretherton, C.S., 2006. Climate sensitivity and cloud response of a GCM with a superparameterization. Geophys. Res. Lett, 33, L06714. eos.atmos.washington.edu/pub/breth/papers/2006/SPGRL.pdf
Bretherton, C.S., 2006. Low-Latitude Cloud Feedbacks on Climate Sensitivity. Available at: www.usclivar.org/Newsletter/VariationsV4N1/BrethertonCPT.pdf [Accessed June 12, 2009].
Wyant, M.C., Khairoutdinov, M. & Bretherton, C.S., 2006. Climate sensitivity and cloud response of a GCM with a superparameterization. Geophys. Res. Lett, 33, L06714.
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Well several people raised issues with elements of one of my posts.
Ric Werme introduced the 4:1 ratio of a sphere surface are a to a circle of the same diameter. That has little to do with the issue I raised. When the sun comes up over San Jose California; it doesn nto radiate at 342 W/m^2 less atmospheric absorption; we are used to getting the full 1366 W/m^2 less atmospheric absorption which brings it down to aorund 1000 W/m^2 which is a far cry from the 168 +30 reflected, that NOAA claims. Now we also have a latitude obliquity factor to get actual ground area insolation; but the point is that when we get sun, we get it at a level that is about 5 times what NOAA figures suggest.
This does two things; first of all our surface temperatures warm up much faster than they would under the NOAA sun, and because of the greater flux; the surface temperatures get very much higher than the 15 deg c that corresponds to NOAA’s budget. That means that our surfaces radiate infra red energy at a much higher rate than the NOAA model would lead to, and when the sun goes down in the evenings which it doesn’t in the NOAA budget, our suface temperatures drop very rapidly.
My whole point is that the real planet earth responds completely differently to the real energy and temperature variations than some fictitious planet would to NOAAs global average fictional model.
Harold Ambler says that his surfing temperatures go down evn though no hurricane comes within 300 miles.
Well then that has nothing to do with my post; because what I talked about was what happened to the water surface temperatures AFTER a real live hurricane had already passed over those waters. So NO Harold, if the hurricane didn’t come within 300 miles of you then what I said would not apply to your surfing waters. The astronomical thermal energy in a hurricane can only come from the waters that the hurricane passed over; it won”t transport enegy from the sourth pole or any other place that the hurricane didn’t pass over.
Bill Illis mentioned that a photon escapes from the atmosphere on average within 18 hours. I would venture that it doesn’t last here for more than 18 milliseconds.
An incoming solar photon can traverse 300 km of the atmosphere in a single millisecond. If it encounters elastic scattering on the way, it may meander for a bit, somewhat like Brownian motion or a random walk problem; and something tells me that doesn’t increase the travel time by more than a factor of pi on average, or maybe it is sqrt (pi). So solar photons are all dead in less than 5 milliseconds; having hit something fatal to their existance; like the waters of the ocean mostly; where their energy becomes thermalized as waste “heat energy”, or else they get capture by some clorphyl or other biologicvally active molecule and energise some life form.
Outgoing thermal radiation photons have a more bizarre life since they can escape in one msec or else get captured; and at high altitudes coud re-radiate; but at lower altitudes they get lost to thermalization by collisions with atmospheric gases. This will result in thermal emission at some other energy level and wavelength; only to run the gauntlet again.
But once agfain I don’t see any photon surviving for 18 msec, let alone 18 hours.
Photons are not like high energy neutrons that can get thermalized down to a few eV, and then wander around aimlessly; but they too suffer oblivion; since free neutrons have a half life of 14 minutes
So nearly 99% fo thermal neutrons would be gone in just one hour.
Most of the time, when I post something here; I specify the conditions I am talking about rather carefully. You can introduce arbitrary variation like surfing wet suits if you want to; but that makes it a diffeent problem from the one I was talking about.
I once wrote in Physics Today, in commenting on a review of Spencer Weart’s book; “The Discovery of Global Warming”, that when the floating se ice melts, the latent heat to melt it comes out of the ocean water it is floating on which thereby cools, and shrinks so the sea level will go down when the floating sea ice melts.
Weart scoffed at that suggestion, in his response to my letter; and affirmed that whent he ocean waters heat up; they expand so the sea level will rise.
I couldn’t agree more; but what the blazes does that have to do with the melting of the floating sea ice; which is what I was talking about.
So if you want to change the problem conditions then don’t expect to come up with the same conclusion I reach for my set of conditions.
George