**5. Anthropogenic sources of the breaches and exceedances of planetary boundaries**

The major anthropogenic GHGs breaching planetary boundaries and perturbing the global climate system are CO2, CH4, N2O, and F-gases. Their percentage repartitions to the global GHG budget are estimated at 72–76% for CO2, 16–19% for CH4, 6% for N2O, and 2–3% for F-gases [58, 59]. The major aerosols include BC, organic carbon

## *Dialing Back the Doomsday Clock with Circular Bioeconomy DOI: http://dx.doi.org/10.5772/intechopen.113181*

(OC), SO4 2−, and NO3 − . BC and OC are primary aerosols because they are emitted directly from pollution sources, while SO4 2− and NO3 − are secondary aerosols given that they are generated from precursor pollutants. The F-gases are totally anthropogenic, and their industrial applications are highlighted in Section 4.1. Anthropogenic sources of the other GHGs, primary aerosols, and precursor pollutants are intricately tied to humanity's methods of exploitation of fossil and biomass energy resources. Their three main sources are:


Global annual GHG emissions increased by about 57% between 1990 and 2018, from 32.7 to 51.2 Gt CO2 eq, with the increment dominated by CO2 emissions from fossil fuels. Anthropogenic CO2 emissions declined from ≈ 37.7 Gt in 2018 to ≈ 36 Gt in 2020 [37]. Fossil energy CO2 rose to 40.0 ± 2.9 GtCO2 in 2021 [60], and in 2022 was reported to be about 36.8 Gt [61]. Anthropogenic share of global BC aerosol inventory in 2010 was reported as 66%. Those for precursor gases were 64%, 68%, and 83% respectively for nitrogen oxides (NOx = NO + NO2), ammonia (NH3), and sulfur oxides (SOx) [23]. The global percentage contribution of GHG emissions by the economic sector in year 2010 is shown in **Table 3**.
