Environmental Engineering Reference
In-Depth Information
Ourjudgmentastotheprobablevaluesoftransientclimateresponse
andequilibriumclimatesensitivityissummarizedinTable3.1.Thevalues
giveninthistable,usedtogetherwiththepattern-scalingforregionalclimate
discussedinChapter4,willformthebasisforourevaluationoftheimpacts
ofclimatechange.Thereasoningleadingtotheseestimates,andanexposi-
tionofthephysicalprocessesinvolved,aregiveninSections3.2and3.3.
At the opposite end of the spectrum of time scales, the third kind of
climatesensitivity,called
Earth System Sensitivity
,incorporatesarangeof
slowerfeedbackprocessesthatcansetinduringthemillenniaoverwhich
anthropogenic CO
2
emissions are expected to continue to affect the cli-
mate.Theseincludelong-termcarboncyclefeedbacksandpartialortotal
deglaciationofGreenlandandAntarctica.Thehumanimprintonclimate
willoutlastthefossilfuelerabymillennia,becauseofthelongatmospheric
lifetimeofCO
2
,andperhapsbecauseoftheadditionalfeedbackstheresult-
ing warming may entrain. To future geologists, the fossil fuel era will ap-
pearasaboundarybetweentheHoloceneepochandasubstantiallyhotter
epoch dubbed the
Anthropocene
(Crutzen and Stoermer, 2000)—which
willbedrivenbydifferentfactors(humanfactors)thananyclimatestates
observedatanytimeinmorethanamillionyears.Willthegreaticesheets
ofGreenlandandAntarcticasurvivetheAnthropocene?Howmuchofthe
world'spresentbiodiversitywillsurvivetheAnthropocene?Howwillagri-
cultureinanAnthropoceneclimatefeedwhateverpopulationmayprevail
TABLE 3.1 Transient and Equilibrium Global Mean Warming as a Function of the Atmospheric
CO
2
Concentration
CO
2
(ppm)
Trans.
Low
Trans.
Prob L
Trans.
Med
Trans.
Prob H
Trans.
High
Eq.
Low
Eq.
Med
Eq.
High
350
0.4
0.4
0.5
0.7
0.8
0.7
1.0
1.4
450
0.8
0.9
1.1
1.5
1.8
1.4
2.2
3.0
550
1.1
1.3
1.6
2.1
2.5
2.1
3.1
4.3
650
1.3
1.6
2.0
2.7
3.2
2.6
3.9
5.4
1000
2.0
2.4
3.0
4.0
4.8
3.9
5.9
8.1
2000
3.1
3.7
4.7
6.2
7.4
6.0
9.1
12.5
NOTE: Warming is given in degrees C relative to a pre-industrial climate with a CO
2
concentration of 280 ppm.
The equilibrium values were extrapolated logarithmically from data given in Table 8.2 of IPCC, Working Group
I, The Physical Science Basis (IPCC, 2007a). The “Eq. Low” column is based on the minimum sensitivity in the
ensemble of models, the “Eq. High” is based on the maximum, and the “Eq. Med” is based on the median. The
transient climate response estimates are discussed in Section 3.3; the “Prob. Low” column represents the low
end of the probable range, the “Prob. High” column the high end of the probable range, and the “Med” column
the median value of transient climate response. The stated warming reflects only the influence of CO
2
on the
climate, but the table can be used to estimate the effect of other greenhouse gases by using the radiative-
equivalent CO
2
e in place of CO
2
.
