Guest essay by Larry Hamlin

The new climate model study by Dr. Curry addressed in the February 21 WUWT article provides some very powerful conclusions regarding the unsuitability of using climate models for purposes of projecting future global climate behavior.

In the Executive Summary of this study Dr. Curry delivers the bottom line on the unsuitability of climate models for use in addressing future global climate behavior by noting:

“The climate model simulation results for the 21st century reported by the Intergovernmental Panel on Climate Change (IPCC) do not include key elements of climate variability, and hence are not useful as projections for how the 21st century will actually evolve.”

She further concludes that current climate models:

“are not fit for the purpose of attributing the causes of 20th century warming or for predicting global or regional climate change timescales of decades to centuries, with any high level of confidence.”

“are not fit for the purpose of justifying political policies to fundamentally alter world social, economic and energy systems.”

These are powerful and well supported conclusions which challenge the validity of global governmental political forces which have proposed massively costly, bureaucratically intrusive and economically damaging initiatives to address global CO2 emissions entirely based upon climate model results which Dr. Curry finds to be woefully inadequate and lacking in scientifically supportable evidence.

Dr. Curry’s new study describes global climate models (GMCs), how they are constructed using various schemes and assumptions to try and address the complicated processes of global climate and also assesses their reliability. She provides the following summary of GMC reliability:

“GCM predictions of the impact of increasing carbon dioxide on climate cannot be rigorously evaluated on timescales of the order of a century.”

“There has been insufficient exploration of GCM uncertainties.”

“There are an extremely large number of unconstrained choices in terms of selection model parameters and parameterizations”

“There has been a lack of formal model verification and validation, which is the norm for engineering and regulatory science.”

“GCMs are evaluated against the same observations used for model tuning.”

“There are concerns about a fundamental lack of predicability in a complex non-linear system.”

Additionally she addresses in detail and summarizes the basic failings and inadequacies of climate models in projecting excessively high global temperatures as a function of atmospheric CO2 levels and in dealing with the chaotic nature of the climate system and internal climate variability.

Figure 6 from Dr. Curry’s new study shows an updated IPCC AR5 Fig. 11.25 demonstrating that using temperature observations through 2015 the CMIP5 climate model simulations project warming, on average, about a factor of 2 higher than observed temperatures. She attributes this excessive projected warming to “a combination of inadequate simulations of natural internal variability and oversensitivity of the models to increasing carbon dioxide (ECS).”

Figures 2 and 3 from Dr. Curry’s new study show global surface temperature anomalies since 1850 and climate model simulations for the same period respectively. She notes that the modeled global temperatures match closely for the period 1970 to 2000 but fail to capture the warming period between 1910 and 1940.

The failure of climate models to address the earlier warming period is described by Dr. Curry as follows:

“If the warming since 1950 was caused by humans, then what caused the warming during the period 1910-1940? The period 1910-1940 comprises about 40% of the warming since 1900, but is associated with only 10% of the carbon dioxide increase since 1900. Clearly, human emissions of greenhouse gases played little role in this early warming. The mid-century period of slight cooling from 1945-1975 – referred as the ‘grand hiatus’ – has also not been satisfactorily explained.”

In the study Summary Dr. Curry further notes:

“The 21st century climate model projections do not include:

a range of scenarios for volcanic eruptions

a possible scenario for solar cooling, analogous to the solar minimum being predicted by Russian scientists

the possibility that climate sensitivity is a factor of two lower than that simulated by most climate models

realistic simulations of the phasing and amplitude of decadal – to century- scale natural internal variability”

“Hence we don’t have a good understanding of the relative climate impacts of the above or their potential impacts on the evolution of the 21st century climate.”

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