The main internal variability phenomena include El Niño–Southern Oscillation, Paciﬁc Decadal Variability and Atlantic Multi-decadal Variability through 
their regional influence. The internal variability of global surface temperature in any single year is estimated to be about ±0.25°C (5 to 95% range, high confidence). 
{WGI SPM footnote 29, WGI SPM footnote 37}
150 Based on 2500-year reconstructions, eruptions with a radiative forcing more negative than –1 Wm-2, related to the radiative effect of volcanic stratospheric aerosols in the 
literature assessed in this report, occur on average twice per century. {WGI SPM footnote 38}
land, ocean, and water (high conﬁdence). Several near-term risks can 
be moderated with adaptation (high conﬁdence). {WGI SPM C.2.6; 
WGII SPM B.2, WGII SPM B.2.3, WGII SPM B.2.5, WGII SPM B.3, 
WGII SPM B.3.2, WGII TS.C.5.2} (Section 4.5 and 3.2)
Principal hazards and associated risks expected in the near term 
(at 1.5°C global warming) are:
• Increased intensity and frequency of hot extremes and dangerous 
heat-humidity conditions, with increased human mortality, morbidity, 
and labour productivity loss (high conﬁdence). {WGI SPM B.2.2, 
WGI TS Figure TS.6; WGII SPM B.1.4, WGII SPM B.4.4, 
WGII Figure SPM.2} 
• Increasing frequency of marine heatwaves will increase risks 
of biodiversity loss in the oceans, including from mass mortality 
events (high conﬁdence).