Large contribution of natural aerosols to uncertainty in indirect forcing

Abstract

The effect of anthropogenic aerosols on cloud droplet concentrations and radiative properties is the source of one of the largest uncertainties in the radiative forcing of climate over the industrial period. This uncertainty affects our ability to estimate how sensitive the climate is to greenhouse gas emissions. Here we perform a sensitivity analysis on a global model to quantify the uncertainty in cloud radiative forcing over the industrial period caused by uncertainties in aerosol emissions and processes. Our results show that 45 per cent of the variance of aerosol forcing since about 1750 arises from uncertainties in natural emissions of volcanic sulphur dioxide, marine dimethylsulphide, biogenic volatile organic carbon, biomass burning and sea spray. Only 34 per cent of the variance is associated with anthropogenic emissions. The results point to the importance of understanding pristine pre-industrial-like environments, with natural aerosols only, and suggest that improved measurements and evaluation of simulated aerosols in polluted present-day conditions will not necessarily result in commensurate reductions in the uncertainty of forcing estimates.

Injection of iodine to the stratosphere

“…Measurements were made in the Northern Hemisphere (NH) and Southern Hemisphere (SH) tropics during the Tropical Ocean tRoposphere Exchange of Reactive halogen species and Oxygenated VOC (TORERO) project (January/February 2012) [Volkamer et al, 2015] , in an area categorized as preindustrial environment [Carslaw et al, 2013]. All research flights (RF01, RF12, RF14, and RF17) targeted remote pristine marine conditions, cloud free, and aged air in the tropical free troposphere.…”

Aerosol generation by raindrop impact on soil

“…A erosols, which are tiny liquid droplets or solid particles suspended in a gas [1][2][3] , have been investigated because of their significant impact on the environment, human health and industrial applications [4][5][6][7][8][9][10][11][12][13][14] . Aerosol particles, larger than 1 mm, are known to originate from windblown dust and sea salt from sea spray resulting from bursting bubbles 6,[15][16][17][18][19][20] .…”

Reduced cooling following future volcanic eruptions

“…Thus the absolute course of tropospheric aerosols is subject to much uncertainty. The nature of the aerosol-cloud interaction strength is also highly uncertain (Carslaw et al 2013). Although, HadGEM2-ES is one of the best models in CMIP5 [see Fig.…”