From The Hockey Schtick:
A paper under discussion for Earth System Dynamics finds the transient climate response [TCR] to CO2 is 1.3°C per doubling of CO2 levels, about 35% less than claimed by the IPCC mean estimate and the same as determined by another recent paper by Otto et al finding a TCR of 1.3°C.
The authors say:
“assess the origin of these differences [between the IPCC high TCR estimates and lower estimates from this paper and others] and highlight the inverse relation between the derived anthropogenic temperature trend of the past 30 years and the weight given to the [natural] Atlantic Multidecadal Oscillation (AMO) as an explanatory factor in the multiple linear regression (MLR) tool that is usually employed. We highlight that robust MLR outcomes require a better understanding of the AMO in general and more specifically its characterization. Our results indicate that both the high- and low end of the anthropogenic trend over the past 30 years found in previous studies are unlikely and that a transient climate response with best estimates centred around 1.3°C per CO2 doubling best captures the historic instrumental temperature record.”
Earth Syst. Dynam. Discuss., 5, 529-544, 2014
www.earth-syst-dynam-discuss.net/5/529/2014/
doi:10.5194/esdd-5-529-2014
G. R. van der Werf and A. J. Dolman
Abstract:
VU University Amsterdam, Faculty of Earth and Life Sciences, Amsterdam, the Netherlands
Abstract. The instrumental surface air temperature record has been used in several statistical studies to assess the relative role of natural and anthropogenic drivers of climate change. The results of those studies varied considerably, with anthropogenic temperature trends over the past 25–30 years suggested to range from 0.07 to 0.20 °C decade−1. In this short communication we assess the origin of these differences and highlight the inverse relation between the derived anthropogenic temperature trend of the past 30 years and the weight given to the [natural] Atlantic Multidecadal Oscillation (AMO) as an explanatory factor in the multiple linear regression (MLR) tool that is usually employed. We highlight that robust MLR outcomes require a better understanding of the AMO in general and more specifically its characterization. Our results indicate that both the high- and low end of the anthropogenic trend over the past 30 years found in previous studies are unlikely and that a transient climate response with best estimates centred around 1.3 °C per CO2 doubling best captures the historic instrumental temperature record.
Just to correct Phil.’s link; it’s http://www.ast.cam.ac.uk/~pettini/Physical%20Cosmology/lecture10.pdf
Somebody: I really don’t know how to respond to a tirade like that. You are merely illustrating how someone will demand impossible levels of evidence to believe something that they are ideologically opposed to. It has nothing to do with science and everything to do with what you want to believe…and so it is useless for me or anybody else to try to convince you.
joelshore says:
Somebody: I really don’t know how to respond to a tirade like that.
That was not a “tirade”. joelshore’s comment was because he has no better response to ‘Somebody’.
“””””…..Phil. says:
May 11, 2014 at 9:49 am
Monckton of Brenchley says:
May 10, 2014 at 6:28 am
Also, Will Happer has recently pointed out that the logarithmic form of the CO2 forcing function is only an approximation. Given the long period of what the imperial Chinese would have called “no-warming”, it may be that the CO2 forcing function is not as well understood as Mr Shore suggests. My own approach is to use the IPCC’s current estimates, because then they can’t argue, but to bear in mind the possibility that in a complex, non-linear, chaotic object in which measurement error is very large we do not understand matters as well as the champions of Thermageddon would have us believe.
I’ve been making that point on here for several years, probably for longer than Will has. It follows from the ‘curve of growth’, where the present-day concentration of CO2 lies in the approximately logarithmic region between the ‘weak’ linear region and the ‘strong’ square root region. …..”””””
I’m quite familiar with real world situations, where events are combinations of two or more different physical processes, each of which has been explained, in terms of well based theoretical terms governed by closed form mathematical equations, but the total effect changes from one regime to another.
An example is the forward current in a semiconductor diode, as a function of forward Voltage; which can be found derived in detail, in Andy Grove’s book. There are at least two components of that current; one due to recombination, and one due to diffusion of carriers. Both components theoretically obey exponential equations, but they have a 2:1 slope ratio on a log current plot.
But those two behaviors, can persist for 3-5 orders of magnitude in current; below or above some crossover point, where one swamps the other. At much higher current densities, the diode characteristic may be dominated by built in series resistance, rather than semiconductor processes.
But each region can be explained by actual physics processes.
So if global surface / lower troposphere / upper atmosphere / whatever Temperature; or the corresponding W/m^2 “forcing” due to CO2 / O3 / H2O / whatever is linearly / logarithmically / square rootedly / whatever, to the atmospheric CO2 volume / mass / molecular relative abundance / whatever; just what is the actual physical process that theoretically would produce that particular mathematical form for that particular regime of CO2 relative abundance.
So far, in the Mauna Loa data record, we have about 25 % of one single octave of CO2 increase.
So for that experimental 25 % range, how much of that range is theoretically shown to be linear; how much of that range has been shown to be theoretically logarithmic, and how much of that 25 % range has been shown to be theoretically square root. ??
So what is wrong with simply saying the Temp / forcing / CO2, in whatever combination you want to relate them, is just …..””” Non- Linear “”” ….. With no known theoretical physical reason.
The ML data and any of the GISS / RSS / HADCRU / UAH fit a perfectly linear graph, at least as well as almost any other mathematical function. You can even reverse the two variables, and jigger an equally good fit to the same equation.
You can even fit it to the form:- y = exp (-1/x^2) with suitable parameters.
So far, nobody has seen a doubling of CO2 in the earth’s atmosphere, and measured either the Temperature, anywhere they want to designate, from the ground on up, or the “forcing”, in whatever language they want to put it.
No laboratory environment, can duplicate the real earth atmosphere environment.
George e. smith says:
You don’t need a laboratory experiment of the full earth atmosphere in order to gain confidence in the sort of radiative transfer calculations that are done to determine the forcing. Radiative transfer in the atmosphere (and radiative transfer in general) is tested in a variety of ways and underlies an entire field of technology (remote sensing).
Granted, the translation of this into a resulting temperature increase involves considerably more uncertainty, but that is not what we are talking about here. Part of doing science is distinguishing what we understand better from what we understand less well. Just throwing one’s hands up and saying, “Woe is us. It is so complex. How can we understand anything” may serve the political purposes of those you who are so strongly ideologically opposed to taking action but it does not really serve the cause of advancing knowledge, or clarifying the true sources of uncertainty from those aspects that are actually very well understood.