A review of natural aerosol interactions and feedbacks within the Earth system

Abstract

Abstract.The natural environment is a major source of atmospheric aerosols, including dust, secondary organic material from terrestrial biogenic emissions, carbonaceous particles from wildfires, and sulphate from marine phytoplankton dimethyl sulphide emissions. These aerosols also have a significant effect on many components of the Earth system such as the atmospheric radiative balance and photosynthetically available radiation entering the biosphere, the supply of nutrients to the ocean, and the albedo of snow and ice. The physical and biological systems that produce these aerosols can be highly susceptible to modification due to climate change so there is the potential for important climate feedbacks. We review the impact of these natural systems on atmospheric aerosol based on observations and models, including the potential for long term changes in emissions and the feedbacks on climate. The number of drivers of change is very large and the various systems are strongly coupled. There have therefore been very few studies that integrate the various effects to estimate climate feedback factors. Nevertheless, available observations and model studies suggest that the regional radiative perturbations are potentially several Watts per square metre due to changes in these natural aerosol emissions in a future climate. Taking into account only the direct radiative effect of changes in the atmospheric burden of natural aerosols, and neglecting potentially large effects on other parts of the Earth system, a global mean radiative perturbation approaching 1 W m −2 is possible by the end of the century. The level of scientific understanding of the climate drivers, interactions and impacts is very low.

Climate Feedback on Aerosol Emission and Atmospheric Concentrations

“…Human-induced land use changes by, e.g., deforestation or agriculture influence BVOC emissions, as do variations in natural vegetation due to climate change impacts like droughts causing alterations in vegetation types and cover. Carslaw et al [3] summarize several earlier publications that show that projections of future changes in isoprene emissions from climate effects (i.e., increasing temperatures) from year 2000 to 2100 range from an increase by 20 to 55%, increasing up to 90% when dynamic vegetation is included [30]. The response to land use changes ranged in different studies from − 20 to + 30%, while a decrease of 8% was predicted in response to increasing CO 2 concentrations [31].…”

“…However, in addition to the aerosol effects on climate, climate variables in turn also influence processes that control atmospheric aerosol distributions, including emissions, transport, transformation, and deposition of aerosol particles. The various impacts of climate on aerosol distributions were summarized in several reviews in recent years [2][3][4]. While those reviews were mainly motivated by surveying the role of climate variability on air quality changes and concentrations of cloud condensation nuclei (CCN), variability and trends in aerosol optical depth (AOD) ( [5], Fig.…”

A steady-state analysis of the temperature responses of water vapor and aerosol lifetimes

“…We conclude that the influence of the ALTR on aerosol forcing may be significant, but it is probably small compared to other influences. Particularly important in this respect are changing spatial distributions of aerosol (precursor) emissions and transport routes (Bellouin et al, 2011;Zhang et al, 2007;Carslaw et al, 2010;Zhou et al, 2011), and changes in the aerosol activation efficiency. We present suggestions for model experiments involving idealized aerosol-like tracers that may help to quantify the separate influences on aerosol lifetime and assess their relevance for aerosol-climate simulations.…”

“…The first term on the right-hand side of Eq. (12) describes changing aerosol emissions; these may be associated with anthropogenic activities but also with temperature-dependent processes such as climate-biosphere feedbacks and chemical transformation rates (Carslaw et al, 2010). The last term refers to a change in the processing of the atmosphere by clouds as discussed above, and in the aerosol activation efficiency and the fraction of the dissolved aerosol mass that is transferred to precipitation.…”

Photochemical oxidation of dimethylsulphide to dimethylsulphoxide in estuarine and coastal waters

“…A marine DMS-climate feedback loop was first proposed by Charlson et al (1987), in which gas to particle conversion of phytoplankton-derived DMS in the marine boundary layer produces sulphate aerosols that act as cloud condensation nuclei, thereby impacting Earth's radiation balance via changes to cloud albedo. While some recent modelling studies imply a rather weak marine DMS-climate feedback (Carslaw et al, 2010;Quinn and Bates, 2011), others support the notion that cloud condensation nuclei abundance may be controlled by DMS-derived and other secondary aerosols (Lana et al, 2012). Considerable uncertainty regarding the contribution of DMS to indirect aerosol forcing Woodhouse et al, 2013) illustrates the need for further studies of biogeochemical DMS cycling.…”