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Summary for Policymakers
21
• The high latitudes and the equatorial Pacific Ocean are likely to experience an increase in annual mean precipitation by
the end of this century under the RCP8.5 scenario. In many mid-latitude and subtropical dry regions, mean precipitation
will likely decrease, while in many mid-latitude wet regions, mean precipitation will likely increase by the end of this
century under the RCP8.5 scenario (see Figure SPM.8). {7.6, 12.4, 14.3}
• Extreme precipitation events over most of the mid-latitude land masses and over wet tropical regions will very likely
become more intense and more frequent by the end of this century, as global mean surface temperature increases (see
Table SPM.1). {7.6, 12.4}
• Globally, it is likely that the area encompassed by monsoon systems will increase over the 21st century. While monsoon
winds are likely to weaken, monsoon precipitation is likely to intensify due to the increase in atmospheric moisture.
Monsoon onset dates are likely to become earlier or not to change much. Monsoon retreat dates will likely be delayed,
resulting in lengthening of the monsoon season in many regions. {14.2}
• There is high confidence that the El Niño-Southern Oscillation (ENSO) will remain the dominant mode of interannual
variability in the tropical Pacific, with global effects in the 21st century. Due to the increase in moisture availability, ENSO-
related precipitation variability on regional scales will likely intensify. Natural variations of the amplitude and spatial
pattern of ENSO are large and thus confidence in any specific projected change in ENSO and related regional phenomena
for the 21st century remains low. {5.4, 14.4}
Table SPM.2 | Projected change in global mean surface air temperature and global mean sea level rise for the mid- and late 21st century relative to the
reference period of 1986–2005. {12.4; Table 12.2, Table 13.5}
2046–2065
2081–2100
Scenario
Mean
Likely rangec
Mean
Likely rangec
Global Mean Surface
Temperature Change (°C)
a
RCP2.6
1.0
0.4 to 1.6
1.0
0.3 to 1.7
RCP4.5
1.4
0.9 to 2.0
1.8
1.1 to 2.6
RCP6.0
1.3
0.8 to 1.8
2.2
1.4 to 3.1
RCP8.5
2.0
1.4 to 2.6
3.7
2.6 to 4.8
Scenario
Mean
Likely ranged
Mean
Likely ranged
Global Mean Sea Level
Rise (m)
b
RCP2.6
0.24
0.17 to 0.32
0.40
0.26 to 0.55
RCP4.5
0.26
0.19 to 0.33
0.47
0.32 to 0.63
RCP6.0
0.25
0.18 to 0.32
0.48
0.33 to 0.63
RCP8.5
0.30
0.22 to 0.38
0.63
0.45 to 0.82
Notes:
a
Based on the CMIP5 ensemble; anomalies calculated with respect to 1986–2005. Using HadCRUT4 and its uncertainty estimate (5−95% confidence interval), the
observed warming to the reference period 1986−2005 is 0.61 [0.55 to 0.67] °C from 1850−1900, and 0.11 [0.09 to 0.13] °C from 1980−1999, the reference period
for projections used in AR4. Likely ranges have not been assessed here with respect to earlier reference periods because methods are not generally available in the
literature for combining the uncertainties in models and observations. Adding projected and observed changes does not account for potential effects of model biases
compared to observations, and for natural internal variability during the observational reference period {2.4; 11.2; Tables 12.2 and 12.3}
b Based on 21 CMIP5 models; anomalies calculated with respect to 1986–2005. Where CMIP5 results were not available for a particular AOGCM and scenario, they
were estimated as explained in Chapter 13, Table 13.5. The contributions from ice sheet rapid dynamical change and anthropogenic land water storage are treated as
having uniform probability distributions, and as largely independent of scenario. This treatment does not imply that the contributions concerned will not depend on the
scenario followed, only that the current state of knowledge does not permit a quantitative assessment of the dependence. Based on current understanding, only the
collapse of marine-based sectors of the Antarctic ice sheet, if initiated, could cause global mean sea level to rise substantially above the likely range during the 21st
century. There is medium confidence that this additional contribution would not exceed several tenths of a meter of sea level rise during the 21st century.
c Calculated from projections as 5−95% model ranges. These ranges are then assessed to be likely ranges after accounting for additional uncertainties or different levels
of confidence in models. For projections of global mean surface temperature change in 2046−2065 confidence is medium, because the relative importance of natural
internal variability, and uncertainty in non-greenhouse gas forcing and response, are larger than for 2081−2100. The likely ranges for 2046−2065 do not take into
account the possible influence of factors that lead to the assessed range for near-term (2016−2035) global mean surface temperature change that is lower than the
5−95% model range, because the influence of these factors on longer term projections has not been quantified due to insufficient scientific understanding. {11.3}
d Calculated from projections as 5−95% model ranges. These ranges are then assessed to be likely ranges after accounting for additional uncertainties or different levels
of confidence in models. For projections of global mean sea level rise confidence is medium for both time horizons.
SPM
