It's a well known "dirty" secret that aerosols drive (short lived) cooling effects and that this effect is very significant [0]. In fact, the climate models used in the OP nature paper would not be useful if they didn't account for these aerosols in a meaningful way. Scientists measure aerosols using a mix of different tricks (optical density sensors - AERONET, satellites with hyperspectal sensors, local air pollution sensors, etc).
In my work in industrial air quality we occasionally joke that we are doing a good job if we exacerbate global warming.
In my work in industrial air quality we occasionally joke that we are doing a good job if we exacerbate global warming.
0. https://skepticalscience.com/images/Radiative_Forcing_Summar...