Many Phycists are Climate Change Skeptics

https://www.aps.org/policy/statements/climate/

Here are some questions that can’t be answered or talked about in dinosaur media.

http://motls.blogspot.com/2008/03/lindzen-vs-rahmstorf-exchange.html

Lindzen vs Rahmstorf: an exchange the points in this epic battle are not talked about either.

What do you consider to be the greatest advances in our understanding of the physical basis of climate change since AR4 in 2007?
What do you consider to be the most important gaps in current understanding?
How are the IPCC confidence levels determined?
What has caused the 5% increase in IPCC confidence from 2007 to 2013
What gives rise to the large uncertainties in this fundamental parameter of the
climate system?
How is the IPCC’s expression of increasing confidence in the detection/ attribution/ projection of anthropogenic influences consistent with this persistent uncertainty? Wouldn’t detection of an anthropogenic signal necessarily improve es
timates of the response to anthropogenic
perturbations
The last column of the table above [see Nature Geosciences 1, 735 (2008)] shows successive IPCC estimates of the Equilibrium Climate Sensitivity
4
, following first estimates more than a century ago. A
factorof-three uncertainty in the global surface temperature response to increased atm
ospheric CO2 as expressed by ECS has persisted through the last three decades of research despite the significant intellectual effort that has been devoted to climate science.
What gives rise to the large uncertainties in this fundamental parameter of the
climate system?
How is the IPCC’s expression of increasing confidence in the detection/ attribution/ projection of anthropogenic influences consistent with this persistent uncertainty? Wouldn’t detection of an anthropogenic signal necessarily improve es
timates of the response to anthropogenic perturbations?
Equilibrium Climate Sensitivity (ECS) is the change in equilibrium global mean surface temperature induced by a doubling of the atmospheric CO2 concentration.
If the atmospheric concentration of CO2 were to rise to 550 ppm with all other anthropogenic effects unchanged, this perturbation would rise to be 3.9 W/ m2
.
The radiative forcing associated with atmospheric CO2 varies
logarithmically with the concentration due the shape of the relevant absorption band and the strong saturation of the band center.
The left-hand figure on the following page [AR5 WG1 Figure 2.11] shows the global radiative balance, with the total downward flux on the Earth’s surface
estimated as 503 ± 7 W/m2 (161 W/m2 solar + 342W/m2thermal). The right
-hand figure on the following page [AR5 Figure SPM.4] shows the total
anthropogenic direct perturbation of this balance to be some 2.3 ± 1 W/ m2
, less than 0.5% of the downward flux.
The earth’s climate stems from a multi-component, driven, noisy, non

-linear system that shows temporal variability from minutes to millennia. Instrumental observations of key physical climate variables have sufficient coverage and precision only over the past 150 years at best (and usually much less than that). Many different processes and phenomena will be relevant and each needs to be “gotten right” with high precision if the response to anthropogenic perturbations is to be attributed correctly and quantified accurately.

Moreover, there areexpected feedbacks (water vapor-temperature, ice
-albedo, …) that would amplify the perturbative response by factors of several. How can one understand the IPCC’s expressed confidence in identifying and project
ing the effects of such small anthropogenic perturbations in view of such difficult circumstances
The present moment is clearly a very special time in the geological context (well into an
interglacial). How well do we understand the climate and climate variability expected duringsuch a time, especially at the currently high atmospheric CO2 concentration? For example, what would be the precursors of an end to the interglacial (beyond the obvious “it will get colder”)?
For example, a change in the earth’s average shortwave albedo from 0.30 to 0.29 due changing clouds, snow/ice,aerosols, or land character would induce a 3.4 W/m2 direct perturbation in the downward flux, 50% larger than the present anthropogenic perturbation.
While the Global Mean Surface Termperature (GMST) rose strongly from 1980 –
1998, it has shown no significant rise for the past 15 years, as shown in the upper panel of Figure SPM.1 below.
That behavior does not track the CMIP3 model projections of AR4,as shown in the figure below, where the observations are overplotted on the AR4 projections http://climateaudit.org/2013/09/30/ipcc-disappears-the
-discrepancy/

 

Nor is the stasis reproduced by the CMIP5 ensemble projections of AR5 WG1 under any of the emissions scenarios considered, as shown in the upper panel of that report’s Figure 11.25 below. [See AR5 WG1 report page 11-120 for complete figure and caption.]
Synthesis of near-term projections of global mean surface air temperature (GMST). a) Projections of annual mean GMST 1986–2050 (anomalies relative to 1986
–2005) under all RCPs from CMIP5 models (grey and coloured lines, one ensemble member per model), with four observational estimates (HadCRUT4:(Morice et al., 2012); ERA
-Interim: (Simmons et al., 2010); GISTEMP: (Hansen et al., 2010); NOAA: (Smith et al.,
2008)) for the period 1986–2012 (black lines).
Section D.1 of the AR5 WG1 SPM discusses this shortfall (greater detail can be found in the citations to the WG1 report):                                                                                                         The observed reduction in surface warming trend over the period 1998–2012 as
compared to the period 1951–2012, is due in roughly equal measure to a reduced
trend in radiative forcing and a cooling contribution from internal variability,
which includes a possible redistribution of heat within the ocean (medium confidence
).
The reduced trend in radiative forcing is primarily due to volcanic
eruptions and the timing of the downwar
d phase of the 11-year solar cycle.
However, there is low confidence in quantifying the role of changes in radiative
forcing in causing the reduced warming trend. There is
medium confidence that internal decadal variability causes to a substantial degree t
he difference between observations and the simulations; the latter are not expected to reproduce the timing of internal variability. There may also be a contribution from forcing inadequacies and, in some models, an overestimate of the response to increasing
 greenhouse gas and other anthropogenic forcing (dominated by the effects of
aerosols). {9.4, Box 9.2, 10.3, Box 10.2, 11.3}
This IPCC text lists internal variability, forcing inadequacies, and model over
-responsiveness as all possibly contributing to the stasis, but without a quantitative resolution. To what would you attribute the stasis?
If non-anthropogenic influences are strong enough to counteract the expected effects of
increased CO2, why wouldn’t they be strong enough to sometimes enhance warmin
g trends, and in so doing lead to an over-estimate of CO2 influence?
What are the implications of this stasis for confidence in the models and their projections?
Some analyses attempt to fit the GMST over almost a century by a linear combination of
aerosol, ENSO, CO2, and TSI 7. As the natural aerosol and ENSO forcings are coherent only over a few years, only anthropogenic aerosols, CO2
, and perhaps TSI are responsible for interdecadal climate change. As the anthropogenic aerosols and CO2 were present only after about 1850, this picture implies that only variations in TSI are responsible for centennial-scale climate change prior to the 20th Century. [See AR5 WG1 Figure 5.7 below.]

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