New Paper “Improved Constraints On 21st-Century Warming Derived Using 160 Years Of Temperature Observations” By Gillet Et Al 2012

Dan Hughes alerted us to this new paper. It is

Gillett, N. P., V. K. Arora, G. M. Flato, J. F. Scinocca, and K. von Salzen  (2012), Improved constraints on 21st-century warming derived using 160 years of temperature observations, Geophys. Res. Lett.,39, L01704, doi:10.1029/2011GL050226.

The abstract reads [highlight added]

Projections of 21st century warming may be derived by using regression-based methods to scale a model’s projected warming  up or down according to whether it under- or over-predicts the response to anthropogenic forcings over the historical period.Here we apply such a method using near surface air temperature observations over the 1851–2010 period, historical simulations  of the response to changing greenhouse gases, aerosols and natural forcings, and simulations of future climate change under  the Representative Concentration Pathways from the second generation Canadian Earth System Model (CanESM2). Consistent with previous studies, we detect the influence of greenhouse gases, aerosols and natural forcings in the observed temperature record. Our estimate of greenhouse-gas-attributable warming is lower than that derived using only 1900–1999 observations. Our analysis  also leads to a relatively low and tightly-constrained estimate of Transient Climate Response of 1.3–1.8°C, and relatively  low projections of 21st-century warming under the Representative Concentration Pathways. Repeating our attribution analysis with a second model (CNRM-CM5) gives consistent results, albeit with somewhat larger uncertainties.

I have just two comments. First, while some will be pleased with the smaller global average temperature increase predicted for the 21st century, the assessment is based on:

i) a surface temperature record back to 1851 which not spatially representative and has unknown biases with respect to the changes in local conditions where the temperature measurements were made during this time period (e.g. see Fall, 2011),

and

ii) a model is used for the attribution study of the forcings, yet these models do not have all of the first order climate forcings and feedbacks accurately represented (e.g. see NRC, 2005).

When they write

 “……we detect the influence of greenhouse gases, aerosols and natural forcings in the observed temperature record”

they more accurately should state

“…….we detect IN THE MODEL the influence of greenhouse gases, aerosols and natural forcings WHEN COMPARED WITH the observed temperature record.

At some point, the entire climate science community is going to realize that models are just hypotheses; e.g. see

Short Circuiting The Scientific Process – A Serious Problem In The Climate Science Community

 Scientific rigor requires that real world observations be used to test the models, not the other way around! It is inappropriate to use multi-decadal climate model predictions (even in a hindcast mode) to make conclusions on real world attributions without such an observational validation. They are only a guide as to how we should set up observational studies in order to perform scientifically robust attribution studies.  

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