From Nature Climate Change:
Ill-sooted models by Baird Langenbrunner
Atmospheric black carbon (BC) or soot — formed by the incomplete combustion of fossil fuels, biofuel and biomass — causes warming by absorbing sunlight and enhancing the direct radiative forcing of the climate. As BC ages, it is coated with material due to gas condensation and collisions with other particles. These processes lead to variation in the composition of BC-containing particles and in the arrangement of their internal components — a mixture of BC and other material — though global climate models do not fully account for these heterogeneities. Instead, BC-containing particles are typically modelled as uniformly coated spheres with identical aerosol composition, and these simplifications lead to overestimated absorption.
Full article here
The PNAS paper has this to say:
Absorption by black carbon strongly affects regional and global climate. Yet, large discrepancies between standard model predictions and regionally specific observations—often with observed absorption lower than expected—raise questions about current understanding of black carbon absorption and its atmospheric impacts. Through a combination of measurement and modeling, our analysis resolves the discrepancy by showing that particular laboratory designs or atmospheric conditions engender distinct compositional heterogeneity among particles containing black carbon. Lower-than-expected absorption results largely from increased heterogeneity, although slightly lowered absorption occurs even in a purely homogeneous system. This work provides a framework that explains globally disparate observations and that can be used to improve estimates of black carbon’s global impact.
In a nutshell, in their zeal to model and prove global warming, climate researchers assumed that all carbon black particles ejected into the atmosphere are created equal, and stay equal. In reality, that’s not the case and it is a huge oversimplification of what actually occurs in nature.
It’s equivalent to saying that every grain of sand on the beach is exactly the same size, shape, and composition, or that snowflakes aren’t unique, but all exactly the same. As even a grade-schooler knows, nature doesn’t work like that.
Once again, “climate science” fails the tenets of basic science.
UPDATE: this books talks about the issue.