Summary for policymakers Technical summary 1. The climate system - an overview 2. Observed climate variability and change 3. The carbon cycle and atmospheric CO2 4. Atmospheric chemistry and greenhouse gases 5. Aerosols, their direct and indirect effects 6. Radiative forcing of climate change 7. Physical climate processes and feedbacks 8. Model evaluation 9. Projections of future climate change 10. Regional climate simulation - evaluation and projections 11. Changes in sea level 12. Detection of climate change and attribution of causes 13. Climate scenario development 14. Advancing our understanding Glossary Index Appendix.

Climate change 2001: the scientific basis

Black carbon aerosol plays a unique and important role in Earth's climate system. Black carbon is a type of carbonaceous material with a unique combination of physical properties. This assessment provides an evaluation of black-carbon climate forcing that is comprehensive in its inclusion of all known and relevant processes and that is quantitative in providing best estimates and uncertainties of the main forcing terms: direct solar absorption; influence on liquid, mixed phase, and ice clouds; and deposition on snow and ice. These effects are calculated with climate models, but when possible, they are evaluated with both microphysical measurements and field observations. Predominant sources are combustion related, namely, fossil fuels for transportation, solid fuels for industrial and residential uses, and open burning of biomass. Total global emissions of black carbon using bottom-up inventory methods are 7500 Gg yr−1 in the year 2000 with an uncertainty range of 2000 to 29000. However, global atmospheric absorption attributable to black carbon is too low in many models and should be increased by a factor of almost 3. After this scaling, the best estimate for the industrial-era (1750 to 2005) direct radiative forcing of atmospheric black carbon is +0.71 W m−2 with 90% uncertainty bounds of (+0.08, +1.27) W m−2. Total direct forcing by all black carbon sources, without subtracting the preindustrial background, is estimated as +0.88 (+0.17, +1.48) W m−2. Direct radiative forcing alone does not capture important rapid adjustment mechanisms. A framework is described and used for quantifying climate forcings, including rapid adjustments. The best estimate of industrial-era climate forcing of black carbon through all forcing mechanisms, including clouds and cryosphere forcing, is +1.1 W m−2 with 90% uncertainty bounds of +0.17 to +2.1 W m−2. Thus, there is a very high probability that black carbon emissions, independent of co-emitted species, have a positive forcing and warm the climate. We estimate that black carbon, with a total climate forcing of +1.1 W m−2, is the second most important human emission in terms of its climate forcing in the present-day atmosphere; only carbon dioxide is estimated to have a greater forcing. Sources that emit black carbon also emit other short-lived species that may either cool or warm climate. Climate forcings from co-emitted species are estimated and used in the framework described herein. When the principal effects of short-lived co-emissions, including cooling agents such as sulfur dioxide, are included in net forcing, energy-related sources (fossil fuel and biofuel) have an industrial-era climate forcing of +0.22 (−0.50 to +1.08) W m−2 during the first year after emission. For a few of these sources, such as diesel engines and possibly residential biofuels, warming is strong enough that eliminating all short-lived emissions from these sources would reduce net climate forcing (i.e., produce cooling). When open burning emissions, which emit high levels of organic matter, are included in the total, the best estimate of net industrial-era climate forcing by all short-lived species from black-carbon-rich sources becomes slightly negative (−0.06 W m−2 with 90% uncertainty bounds of −1.45 to +1.29 W m−2). The uncertainties in net climate forcing from black-carbon-rich sources are substantial, largely due to lack of knowledge about cloud interactions with both black carbon and co-emitted organic carbon. In prioritizing potential black-carbon mitigation actions, non-science factors, such as technical feasibility, costs, policy design, and implementation feasibility play important roles. The major sources of black carbon are presently in different stages with regard to the feasibility for near-term mitigation. This assessment, by evaluating the large number and complexity of the associated physical and radiative processes in black-carbon climate forcing, sets a baseline from which to improve future climate forcing estimates.

/pdf/bounding-the-role-of-black-carbon-in-the-climate-system-a-1fc3novd9r.pdf

Bounding the role of black carbon in the climate system: A scientific assessment

The major source of cloud-condensation nuclei (CCN) over the oceans appears to be dimethylsulphide, which is produced by planktonic algae in sea water and oxidizes in the atmosphere to form a sulphate aerosol Because the reflectance (albedo) of clouds (and thus the Earth's radiation budget) is sensitive to CCN density, biological regulation of the climate is possible through the effects of temperature and sunlight on phytoplankton population and dimethylsulphide production. To counteract the warming due to doubling of atmospheric CO2, an approximate doubling of CCN would be needed.

Oceanic phytoplankton, atmospheric sulphur, cloud albedo and climate

The transfer of monochromatic radiation in a scattering, absorbing, and emitting plane-parallel medium with a specified bidirectional reflectivity at the lower boundary is considered. The equations and boundary conditions are summarized. The numerical implementation of the theory is discussed with attention given to the reliable and efficient computation of eigenvalues and eigenvectors. Ways of avoiding fatal overflows and ill-conditioning in the matrix inversion needed to determine the integration constants are also presented.

Numerically stable algorithm for discrete-ordinate-method radiative transfer in multiple scattering and emitting layered media.

To say that this is the best book on the quantum theory of fields is no praise, since to my knowledge it is the only book on this subject But it is a very good and most useful book The original was written in German and appeared in 1942 This is a translation with some minor changes A few remarks have been added, concerning meson theory and nuclear forces, also footnotes referring to modern work in this field, and finally an appendix on the symmetrization of the energy momentum tensor according to Belinfante Quantum Theory of Fields Prof Gregor Wentzel Translated from the German by Charlotte Houtermans and J M Jauch Pp ix + 224, (New York and London: Interscience Publishers, Inc, 1949) 36s

Quantum Theory of Fields

This paper reviews scattering theory required for analysis of light reflected by planetary atmospheres. Section 1 defines the radiative quantities which are observed. Section 2 demonstrates the dependence of single-scattered radiation on the physical properties of the scatterers. Section 3 describes several methods to compute the effects of multiple scattering on the reflected light.

Light scattering in planetary atmospheres

Preface Acknowledgements Part I. Basic Theory of Electromagnetic Scattering, Absorption, and Emission: 1. Polarization characteristics of electromagnetic radiation 2. Scattering, absorption, and emission of electromagnetic radiation by an arbitrary finite particle 3. Scattering, absorption and emission by collections of independent particles 4. Scattering matrix and macroscopically isotropic and mirror-symmetric scattering media Part II. Calculation and Measurement of Scattering and Absorption Characteristics of Small Particles: 5. T-matrix method and Lorenz-Mie theory 6. Miscellaneous exact techniques 7. Approximations 8. Measurement techniques Part III. Scattering and Absorption Properties of Small Particles and Illustrative Applications: 9. Scattering and absorption properties of spherical particles 10. Scattering and absorption properties of nonspherical particles Appendices References Index.

/pdf/scattering-absorption-and-emission-of-light-by-small-4bn4s9jod3.pdf

Scattering, Absorption, and Emission of Light by Small Particles

We review the current status of Waterman's T-matrix approach which is one of the most powerful and widely used tools for accurately computing light scattering by nonspherical particles, both single and composite, based on directly solving Maxwell's equations. Specifically, we discuss the analytical method for computing orientationally-averaged light-scattering characteristics for ensembles of nonspherical particles, the methods for overcoming the numerical instability in calculating the T matrix for single nonspherical particles with large size parameters and/or extreme geometries, and the superposition approach for computing light scattering by composite/aggregated particles. Our discussion is accompanied by multiple numerical examples demonstrating the capabilities of the T-matrix approach and showing effects of nonsphericity of simple convex particles (spheroids) on light scattering.

T-Matrix Computations of Light Scattering by Nonspherical Particles: A Review

We describe in detail a software implementation of a current version of the ¹-matrix method for computing light scattering by polydisperse, randomly oriented, rotationally symmetric particles. The FORTRAN ¹-matrix codes are publicly available on the World Wide We ba thttp://www.giss.nasa.gov/&crmim .W egiv eal lnecessar yformulas ,describ einpu tand output parameters, discuss numerical aspects of ¹-matrix computations, demonstrate the capabilities and limitations of the codes, and discuss the performance of the codes in comparison with other available numerical approaches. Published by Elsevier Science Ltd. 1. I NTRODUCTION The ¹-matrix method is a powerful exact technique for computing light scattering by nonspherical particles based on numerically solving Maxwell's equations. Although the method is, potentially, applicable to any particle shape, most practical implementations of the technique pertain to bodies of revolution. The method was initially developed by Waterman and has been significantly improved as described in Refs. 2—6. Specifically, Refs. 4 and 6 extend the method to much larger size parameters and aspect ratios, Ref. 2 presents an efficient analytical procedure for computing the scattering properties of randomly oriented particles, Ref. 3 describes an automatic convergence procedure convenient in massive computer calculations for particle polydispersions, and Ref. 5 presents benchmark ¹-matrix computations for particles with non-smooth surfaces (finite circular cylinders). A general review of the ¹-matrix method can be found in Ref. 7. In this paper we provide a detailed description of modern ¹-matrix FORTRAN codes which incorporate all recent developments, are publicly available on the World Wide Web, and are, apparently, the most efficient and powerful tool for accurately computing light scattering by randomly oriented rotationally symmetric particles. For the first time, we collect in one place all necessary formulas, discuss numerical aspects for ¹-matrix computations, describe the input and output parameters, and demonstrate the capabilities and limitations of the codes. The paper is intended to serve as a detailed user guide to a versatile tool suitable for a wide range of practical applications. We specifically target the users who are interested in practical applications of the ¹-matrix method rather than in details of its mathematical formulation.

Capabilities and limitations of a current FORTRAN implementation of the T-matrix method for randomly oriented, rotationally symmetric scatterers

Laboratory and in situ measurements show that scattering properties of natural nonspherical particles can be significantly different from those of volume-or surface-equivalent spheres, thus suggesting that Mie theory may not be suitable for interpreting satellite reflectance measurements for dustlike tropospheric aerosols. In this paper we use the rigorous T-matrix method to extensively compute light scattering by shape distributions of polydisperse, randomly oriented spheroids with refractive indices and size distributions representative of naturally occurring dust aerosols. Our calculations show that even after size and orientation averaging, a single spheroidal shape always produces a unique, shape-specific phase function distinctly different from those produced by other spheroidal shapes. However, phase functions averaged over a wide aspect-ratio distribution of prolate and oblate spheroids are smooth, featureless, and nearly flat at side-scattering angles and closely resemble those measured for natural soil and dust particles. Thus, although natural dust particles are, of course, not perfect spheroids, they are always mixtures of highly variable shapes, and their phase function can be adequately modeled using a wide aspect-ratio distribution of prolate and oblate spheroidal grains. Our comparisons of nonspherical versus projected-area-equivalent spherical particles show that spherical-nonspherical differences in the scattering phase function can be large and therefore can cause significant errors in the retrieved aerosol optical thickness if Mie theory is used to analyze reflectance measurements of nonspherical aerosols. On the other hand, the differences in the total optical cross sections, single-scattering albedo, asymmetry parameter of the phase function, and backscattered fraction are much smaller and in most cases do not exceed 10%. This may suggest that for a given aerosol optical thickness the influence of particle shape on the aerosol radiative forcing is negligibly small. Spherical-nonspherical differences in the extinction-to-backscatter ratio are very large and should be explicitly taken into account in inverting lidar measurements of dustlike aerosols.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/96JD02110

Larry D. Travis

Papers

Light scattering in planetary atmospheres

Scattering, Absorption, and Emission of Light by Small Particles

T-Matrix Computations of Light Scattering by Nonspherical Particles: A Review

Capabilities and limitations of a current FORTRAN implementation of the T-matrix method for randomly oriented, rotationally symmetric scatterers

Modeling phase functions for dustlike tropospheric aerosols using a shape mixture of randomly oriented polydisperse spheroids