116 Climate changein the twenty-firstcenturyand beyond2000 2020 2040 2060 2080 2100510152025COemissions (Gt C) 2A1BScenarios
A1T
A1FI
A2
B1
B2
IS92a2000 2020 2040 2060 2080 21006008001000CHemissions (Tg CH 4) 4A1B
A1T
A1FI
A2
B1
B2
IS92a2000 2020 2040 2060 2080 2100161820222426N^2O emissions (Tg N)A1B
A1T
A1FI
A2
B1
B2
IS92a2000 2020 2040 2060 2080 2100
Year Year50100150SOemissions (Tg S) 2A1B
A1TA1FI
A2
B1B2
IS92aScenariosScenariosScenariosFigure 6.1Anthropogenic
emissions of carbon dioxide,
methane, nitrous oxide and
sulphur dioxide for the six
illustrative SRES scenarios,
A1B, A2, B1 and B2, A1F1 and
A1T. For comparison the IS
92a scenario is also shown.
A wide range of scenarios was developed by the IPCC in a Special Report
on Emission Scenarios (SRES)^1 in preparation for its 2001 Report (see
box below). It is these scenarios that have been used in developingthe
projections of future climate presented in this chapter. In addition, be-
cause it has been widely used in modelling studies, results are also pre-
sented using a scenario (IS 92a) taken from a set developed by the IPCC
in 1992 and widely described as representative of ‘business-as-usual’.^2
Details of these scenarios are presented in Figure 6.1.
The SRES scenarios include estimates of greenhouse gas emissions
resulting from all sources including land-use change. Estimates in the
different scenarios begin from the current values for land-use change in-
cluding deforestation (see Table 3.1). Assumptions in different scenarios
vary, from continued deforestation, although reducing as less forest re-
mains available for clearance, to substantial afforestation leading to an
increased carbon sink.