Observed Warming and its Causes
Global surface temperature was around 1.1°C above 1850–1900 in 
2011–2020 (1.09 [0.95 to 1.20]°C)64, with larger increases 
over land (1.59 [1.34 to 1.83]°C) than over the ocean 
(0.88 [0.68 to 1.01]°C)65. Observed warming is human-caused, with 
warming from greenhouse gases (GHG), dominated by CO2 and 
methane (CH4), partly masked by aerosol cooling (Figure 2.1). 
Global surface temperature in the ﬁrst two decades of the 21st century 
(2001–2020) was 0.99 [0.84 to 1.10]°C higher than 1850–1900. Global 
surface temperature has increased faster since 1970 than in any other 
50-year period over at least the last 2000 years (high conﬁdence). The 
likely range of total human-caused global surface temperature increase 
from 1850–1900 to 2010–201966 is 0.8°C to 1.3°C, with a best estimate 
of 1.07°C. It is likely that well-mixed GHGs67 contributed a warming 
of 1.0°C to 2.0°C, and other human drivers (principally aerosols) 
contributed a cooling of 0.0°C to 0.8°C, natural (solar and volcanic) 
drivers changed global surface temperature by ±0.1°C and internal 
variability changed it by ±0.2°C. {WGI SPM A.1, WGI SPM A.1.2, 
WGI SPM A.1.3, WGI SPM A.2.2, WGI Figure SPM.2; SRCCL TS.2}
Observed increases in well-mixed GHG concentrations since around 
1750 are unequivocally caused by GHG emissions from human activities.