Q&A

Here is an extract from the 2015 article:

“Although a systematic, quantitative analysis of interactions among all of the processes for which boundaries are proposed remains beyond the scope of current modeling and observational capacity, the Earth system clearly operates in well-defined states in which these processes and their interactions can create stabilizing or destabilizing feedbacks.”

PB, 2015

Create link between boundaries in not the main goal of the fresco, but it’s not forbidden :-)

An aerosol is a fine liquid or solid particle suspended in the atmosphere. This definition is very broad, and there are several types of aerosol.
Tropospheric aerosols mainly have a cooling effect on climate, via 2 effects: a direct effect, as they reflect part of the sun's energy back into space, and an indirect effect, as they increase cloud reflectance. (IPCC, AR6, WG1, Box TS. 1 and Sect 7.3.3.2)
Conversely, soot carbon ("black carbon"), an aerosol formed during the incomplete combustion of fossil fuels or biomass, has a warming effect. When these particles settle on snow, they reduce its albedo and contribute to its melting (IPCC, AR6, WG1, Sect 7.3.4.3). The radiative forcing associated with soot carbon is therefore positive, and has been estimated at +0.08 [0.00 to 0.18] Wm-2 (IPCC, AR6, WG1, Sect 7.3.4.3). This warming effect is not the dominant one.
The total effect of aerosols on radiative forcing between 1750 and 2019 is negative (the cooling effect dominates) and has been estimated at -1.1 [-1.7 to -0.4] W m-2 (TS & Sect 7.3.3.2, 7.3.5.2). This represents a cooling of -0.50 [-0.22 to -0.96] °C (Sect 7.3.5.2).
The figures above show the contributions of various factors to radiative forcing (right) and temperature (left): tropospheric aerosols have a negative effect on radiative forcing, and a cooling effect on climate.