This will tend to enhance the greenhouse effect, though the situation is complicated by the difficulty in both projecting changes in cloud formation and determining the radiative
forcing effect of clouds.
I was interested not so much in
the forcing effect of clouds themselves so much as the change in albedo which might result from a change in the overall extent of global cloud cover.
In effect he is saying that it is almost impossible to differentiate
the forcing effect of cloud cover from the feedback effect — and without being able to do this you can not quantify the feedback sensitvity of the climate using cloud cover data.
In effect he is saying that it is almost impossible to differentiate
the forcing effect of cloud cover from the feedback effect» ===============
Not exact matches
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It is rather surprising that adding
cloud lifetime
effect forcing makes any difference, insofar as Aldrin is estimating indirect and direct aerosol
forcings as part
of his Bayesian procedure.
The total
of -0.7 W / m ^ 2 is the same as the best observational (satellite) total aerosol adjusted
forcing estimate given in the leaked Second Order Draft
of AR5 WG1, which includes
cloud lifetime (2nd indirect) and other
effects.
When Aldrin adds a fixed
cloud lifetime
effect of -0.25 W / m ^ 2
forcing on top
of his variable parameter direct and (1st) indirect aerosol
forcing, the mode
of the sensitivity PDF increases from 1.6 to 1.8.
Earth's measured energy imbalance has been used to infer the climate
forcing by aerosols, with two independent analyses yielding a
forcing in the past decade
of about − 1.5 W / m2 [64], [72], including the direct aerosol
forcing and indirect
effects via induced
cloud changes.
In addition, since the global surface temperature records are a measure that responds to albedo changes (volcanic aerosols,
cloud cover, land use, snow and ice cover) solar output, and differences in partition
of various
forcings into the oceans / atmosphere / land / cryosphere, teasing out just the
effect of CO2 + water vapor over the short term is difficult to impossible.
Could the climate
forcing itself, such as increasing GHGs, affect parameterizations independently
of the larger scale climate changes (for example, by changing thermal damping
of various kinds
of waves, or by changing the differences
of radiative
effects between different amounts and kinds
of clouds)?
Even if the total
effect of clouds has not been nailed down yet, it is obviously a small
effect compared to the rest
of the
forcings and feedbacks in the system.
«By comparing the response
of clouds and water vapor to ENSO
forcing in nature with that in AMIP simulations by some leading climate models, an earlier evaluation
of tropical
cloud and water vapor feedbacks has revealed two common biases in the models: (1) an underestimate
of the strength
of the negative
cloud albedo feedback and (2) an overestimate
of the positive feedback from the greenhouse
effect of water vapor.
He goes so far as to say that the IPCC is biased against «internal radiative
forcing,» in favor
of treating
cloud effects as feedback.
Critics
of this result might argue that the solar
forcing in these experiments is only based on the estimated change in total irradiance, which might be an underestimate, or that does not include potential indirect amplifying
effects (via an ozone response to UV changes, or galactic cosmic rays affecting
clouds).
It is my understanding that the uncertainties regarding climate sensitivity to a nominal 2XCO2
forcing is primarily a function
of the uncertainties in (1) future atmospheric aerosol concentrations; both sulfate - type (cooling) and black carbon - type (warming), (2) feedbacks associated with aerosol
effects on the properties
of clouds (e.g. will
cloud droplets become more reflective?)
The top panel shows the direct
effects of the individual components, while the second panel attributes various indirect factors (associated with atmospheric chemistry, aerosol
cloud interactions and albedo
effects) and includes a model estimate
of the «efficacy»
of the
forcing that depends on its spatial distribution.
The details
of the physics
of different
forcings (i.e. ozone
effects due to solar, snow albedo and
cloud effects due to aerosols etc.) do vary the feedbacks slightly differently though.
(Note that radiative
forcing is not necessarily proportional to reduction in atmospheric transparency, because relatively opaque layers in the lower warmer troposphere (water vapor, and for the fractional area they occupy, low level
clouds) can reduce atmospheric transparency a lot on their own while only reducing the net upward LW flux above them by a small amount; colder, higher - level
clouds will have a bigger
effect on the net upward LW flux above them (per fraction
of areal coverage), though they will have a smaller
effect on the net upward LW flux below them.
In fact, if the physics - based understanding
of «equilibrium sensitivity» to any
forcing is too low, then not only will CO2 have a greater
effect, so too will all other
forcings, such as: changes in the sun, in
cloud cover, in albedo, etc..
First, for changing just CO2
forcing (or CH4, etc, or for a non-GHE
forcing, such as a change in incident solar radiation, volcanic aerosols, etc.), there will be other GHE radiative «
forcings» (feedbacks, though in the context
of measuring their radiative
effect, they can be described as having radiative
forcings of x W / m2 per change in surface T), such as water vapor feedback, LW
cloud feedback, and also, because GHE depends on the vertical temperature distribution, the lapse rate feedback (this generally refers to the tropospheric lapse rate, though changes in the position
of the tropopause and changes in the stratospheric temperature could also be considered lapse - rate feedbacks for
forcing at TOA;
forcing at the tropopause with stratospheric adjustment takes some
of that into account; sensitivity to
forcing at the tropopause with stratospheric adjustment will generally be different from sensitivity to
forcing without stratospheric adjustment and both will generally be different from
forcing at TOA before stratospheric adjustment;
forcing at TOA after stratospehric adjustment is identical to
forcing at the tropopause after stratospheric adjustment).
wilt, the paper you cite describes what in their view is a «small but statistically significant
effect of cosmic rays on
cloud formation, which in no way invalidates the large and significant
effects of human emissions on the current anthropogenic radiative
forcing budget
of the atmosphere.
These
forcings are spatially heterogeneous and include the
effect of aerosols on
clouds and associated precipitation [e.g., Rosenfeld et al., 2008], the influence
of aerosol deposition (e.g., black carbon (soot)[Flanner et al. 2007] and reactive nitrogen [Galloway et al., 2004]-RRB-, and the role
of changes in land use / land cover [e.g., Takata et al., 2009].
# 92 Spencer el al 2007 paper doesn't really support the precise mechanism proposed by Lindzen for Iris
effect, but more simply observes a strong TOA negative correction associated with warming events at 20 ° S - 20 ° N (that is: in the 2000 - 2005 period
of observation, the most significative warming episodes
of the surface + low troposphere — 40 days or more — leads to a negative SW+LW
cloud forcing at the top
of the atmosphere).
LOL — Your claims global brightening from reduced
cloud cover is a climate
forcing without considering the
effect of such
cloud cover changes on outgoing IR.
Indirect aerosol
effect - Aerosols may lead to an indirect radiative
forcing of the climate system through acting as
cloud condensation nuclei or modifying the optical properties and lifetime
of clouds.
You claim that what you're doing shows the
effect of cloud forcing uncertainty in the models, but if those results are plainly not really representative
of what would happen in the models, then there's a disconnect.
If, for instance, CO2 concentrations are doubled, then the absorption would increase by 4 W / m2, but once the water vapor and
clouds react, the absorption increases by almost 20 W / m2 — demonstrating that (in the GISS climate model, at least) the «feedbacks» are amplifying the
effects of the initial radiative
forcing from CO2 alone.
The
effect of this mixed dust - pollution plume on the Pacific
cloud systems and the associated radiative
forcing is an outstanding problem for understanding climate change and has not been explored.
If ∆ T = λ ∆ Q is a reasonable approximation
of the (large - scale)
effects of forcing on globally averaged temperature, why does it matter if a few
clouds are banging around locally on a given day?
On the uncertainty
of CO2
forcing, my experience has been that the biggest uncertainy is not in the radiation models themselves, but in the
effect of clouds.
Going forwards CO2
forcing is several times larger than the LIA solar
forcing which was itself measurable in the surface temperature record, so we expect CO2
forcing to be measurable for sure, and yes, it will be accompanied by some
effects of changing
clouds too, but we don't know which direction they would push it.
adding two variables that were requested in the ACCMIP Word document but not explained in the spreadsheet: the longwave and the shortwave
cloud radiative
forcing with reference (fixed) composition, for diagnosis
of aerosol indirect
effect.
Radiative
effects of surface - observed
cloud cover anomalies, called «
cloud cover radiative
forcing (CCRF) anomalies,» are estimated based on a linear relationship to climatological
cloud radiative
forcing per unit
cloud cover.
This led to a nasty scene, when he said I was unable to see what was obvious, ever - accelerating cooling which would lead to a runaway «Neptune
Effect» because of mechanisms of positive feedback (his best examples were clouds which collect over the winter solstice — the «in - law» effect — persisting through to mid-February — the «Cupid» effect — and combining forces to wreck the climate for the entire first half of the
Effect» because
of mechanisms
of positive feedback (his best examples were
clouds which collect over the winter solstice — the «in - law»
effect — persisting through to mid-February — the «Cupid» effect — and combining forces to wreck the climate for the entire first half of the
effect — persisting through to mid-February — the «Cupid»
effect — and combining forces to wreck the climate for the entire first half of the
effect — and combining
forces to wreck the climate for the entire first half
of the year.)
As I have pointed out before, it seems to me that a fair evaluation
of climate models is impossible when there remains vast uncertainty in aerosol
forcing (direct and indirect), and substantial uncertainty in
cloud effects.
«This is the cause - versus -
effect issue I have been harping on for years: You can not measure
cloud FEEDBACK (temperature changes causing
cloud changes) unless you can quantify and remove the
effect of internal radiative
FORCING (
cloud changes causing temperature changes).
«Here, it is sufficient to note that many
of the 20CEN / A1B simulations neglect negative
forcings arising from stratospheric ozone depletion, volcanic dust, and indirect aerosol
effects on
clouds... It is likely that omission
of these negative
forcings contributes to the positive bias in the model average TLT trends in Figure 6F.
Andrew Lacis wrote: (3) Water vapor and
clouds account for about 75 % the strength
of the terrestrial greenhouse
effect, but are feedback
effects that require sustained radiative
forcing to maintain their atmospheric distribution.
As such
cloud variation, independent
of temperature COULD be a significant independent variable, a true cause or
forcing of the climate given the great GHG / albedo
effect they have, perhaps it deserves greater investigation?
Instead, the aim
of our Science paper was to illustrate as clearly and as simply as possible the basic operating principles
of the terrestrial greenhouse
effect in terms
of the sustaining radiative
forcing that is provided by the non-condensing greenhouse gases, which is further augmented by the feedback response
of water vapor and
clouds.
(3) Water vapor and
clouds account for about 75 % the strength
of the terrestrial greenhouse
effect, but are feedback
effects that require sustained radiative
forcing to maintain their atmospheric distribution.
Claiming that the evidence for a particular mechanism
of enhanced solar
forcing (GCR -
cloud) suggests a weak
effect is not a counter to the admission
of substantial evidence that SOME such mechanism does have a powerful
effect.
He thinks GCR -
cloud effects should be weak (a very premature conclusion) and decides on that grounds that the whole idea
of enhanced solar
forcing can be dismissed, despite that added sentence to the contrary.
Clouds are in fact such a strong cooling
force that is has been estimated by several sources (Theodor Landscheidt, 1998) that having
clouds cover 1 % more
of the Earth's surface would cancel the heating
effect of a doubling
of CO2.
Earth's measured energy imbalance has been used to infer the climate
forcing by aerosols, with two independent analyses yielding a
forcing in the past decade
of about − 1.5 W / m2 [64], [72], including the direct aerosol
forcing and indirect
effects via induced
cloud changes.
One aspect
of Roy Spencer's work is that internal random oscillations
of things like surface ocean temperature spatial patterns (affected by winds) which can affect
clouds could have a
forcing effect that could easily be mistaken for climate sensitivity to external
forcing.
Increasing the brightness
of marine stratocumulus
clouds, as proposed by John Latham, would affect about 17 %
of the earth's surface, and the Lenton - Vaughan analysis suggests that the whitening
effect would have to be considerably more marked than previous work has assumed; but if that brightening could be achieved then a negative
forcing that averages more than 3W / m ² should be possible.
«There is nothing inherently wrong with defining aerosol changes to be a
forcing, but it is practically impossible to accurately determine the aerosol
forcing because it depends sensitively on the geographical and altitude distribution
of aerosols, aerosol absorption, and aerosol
cloud effects for each
of several aerosol compositions.
Hartmnn derived an average
cloud radiative
forcing of -27.6 W / m ^ 2 — a net cooling — as the overall average
effect of clouds on global climate.