Land-Use 
Change and 
Forestry 
(LULUCF)
warmest 
multi-century 
period in more 
than 100,000 
years
410 ppm CO2
1866 ppb CH4
332 ppb N2O
200
400 Parts per billion (ppb)
Nitrous oxide
°C
0
0.5
1
1.5
Key
*Other human drivers are predominantly cooling aerosols, but also 
warming aerosols, land-use change (land-use reﬂectance) and ozone.
Figure 2.1: The causal chain from emissions to resulting 
warming of the climate system. Emissions of GHG have 
increased rapidly over recent decades (panel (a)). Global net 
anthropogenic GHG emissions include CO2 from fossil fuel 
combustion and industrial processes (CO2-FFI) (dark green); 
net CO2 from land use, land-use change and forestry (CO2-LULUCF) 
(green); CH4; N2O; and ﬂuorinated gases (HFCs, PFCs, SF6, NF3) 
(light blue). These emissions have led to increases in the atmospheric 
concentrations of several GHGs including the three major well-mixed 
GHGs CO2, CH4 and N2O (panel (b), annual values). To indicate their 
relative importance each subpanel’s vertical extent for CO2, CH4 and 
N2O is scaled to match the assessed individual direct effect (and, 
in the case of CH4 indirect effect via atmospheric chemistry impacts 
on tropospheric ozone) of historical emissions on temperature 
change from 1850–1900 to 2010–2019. This estimate arises from 
an assessment of effective radiative forcing and climate sensitivity. 
The global surface temperature (shown as annual anomalies from 
a 1850–1900 baseline) has increased by around 1.1°C since 
1850–1900 (panel (c)).