I was alerted to this new paper by M. Andreae. It presents evidence of yet another climate forcing which has not been adequately examined in the IPCC reports. It makes understanding climate processes even more difficult. The new paper is
Després, V. R., Huffman, J. A., Burrows, S. M., Hoose, C., Safatov, A. S., Buryak, G., Fröhlich-Nowoisky, J., Elbert, W., Andreae, M. O., Pöschl, U., and Jaenicke, R., Primary biological aerosol particles in the atmosphere: a review: Tellus, 64, 1-58, 2012.
The abstract reads [highlight added]
Atmospheric aerosol particles of biological origin are a very diverse group of biological materials and structures, including microorganisms, dispersal units, fragments and excretions of biological organisms. In recent years, the impact of biological aerosol particles on atmospheric processes has been studied with increasing intensity, and a wealth of new information and insights has been gained. This review outlines the current knowledge on major categories of primary biological aerosol particles (PBAP): bacteria and archaea, fungal spores and fragments, pollen, viruses, algae and cyanobacteria, biological crusts and lichens and others like plant or animal fragments and detritus. We give an overview of sampling methods and physical, chemical and biological techniques for PBAP analysis (cultivation, microscopy, DNA/RNA analysis, chemical tracers, optical and mass spectrometry, etc.). Moreover, we address and summarise the current understanding and open questions concerning the influence of PBAP on the atmosphere and climate, i.e. their optical properties and their ability to act as ice nuclei (IN) or cloud condensation nuclei (CCN). We suggest that the following research activities should be pursued in future studies of atmospheric biological aerosol particles: (1) develop efficient and reliable analytical techniques for the identification and quantification of PBAP; (2) apply advanced and standardised techniques to determine the abundance and diversity of PBAP and their seasonal variation at regional and global scales (atmospheric biogeography); (3) determine the emission rates, optical properties, IN and CCN activity of PBAP in field measurements and laboratory experiments; (4) use field and laboratory data to constrain numerical models of atmospheric transport, transformation and climate effects of PBAP.”
Key extracts from this paper include
“[the] global average number concentrations of biological particles have often been assumed to be insignificant compared to non-biological material and have thus not typically been considered for widespread measurements or included in global climate models. The Third Assessment Report (TAR) of the Intergovernmental Panel on Climate Change (IPCC) in 2001, for example, listed the global source strength of primary biological aerosol particles to be only 56 Tg/yr, in contrast to 3340 Tg/yr for sea salt and 2150 Tg/yr for mineral dust listed in the same report (Penner et al., 2001). Furthermore, the Fourth Assessment Report of the IPCC in 2007 stated that these estimates had not been refined, and primary biological particles were not mentioned in the contribution of Working Group I (Physical Science Basis) to the overall report (IPCC 2007b). PBAP concentrations have been estimated by other researchers (e.g. Matthias- Maser and Jaenicke, 1995) as comprising a much higher percentage of total atmospheric aerosol volume, however, and so important discrepancies exist.”
“Recently, several investigations have suggested that biological particles can have a substantial influence on clouds and precipitation and thus may influence the hydrological cycle and climate at least on regional scales (e.g. Andreae and Rosenfeld, 2008; Prenni et al., 2009; Poschl et al., 2010).”
“The absorption and scattering of radiation by aerosol particles are important physical properties that influence regional and global radiation budgets. Better understanding of the effect that natural aerosols have on the atmosphere is necessary to constrain effects that anthropogenic influence may have on global climate. Because PBAP can be a major fraction of aerosol number and surface area in certain locations, it is possible that they may also affect climate forcing both directly (by absorbing or scattering radiation) and indirectly (through cloud processes). Certain fungal spores and other PBAP classes can be highly coloured and absorbing, which may increase their direct influence on the surrounding atmosphere (e.g. Adams et al., 1968; Troutt and Levetin, 2001). However, there have been very few studies estimating the direct effect of PBAP on climate, in part because geographically or temporally comprehensive PBAP measurements are not yet available. A theoretical description of the interaction between electromagnetic radiation and PBAP is difficult because the Mie theory is only valid for spheres, and thus many biological aerosol particles cannot be well described (Bohren and Huffman, 1983).”
“One of the main influences of PBAP on climate and atmosphere is through the capability of certain PBAP to function as excellent ice nuclei. Future research should thus concentrate on the determination of actual emission rates and optical properties of PBAP and to link results from laboratory experiments concerning the IN ability of PBAP to atmospheric measurements.”
Climate Science: Roger Pielke Sr. 
