Low Carbon City: A Guidebook for City Planners and Practitioners Table 2: Properties of Emissions Pathways for Alternative Ranges of CO 2 and CO 2 e Stabilisation Targets Anthropogenic
addition to radiative
forcing at stabilisation
Multi gas
concentration level
(CO
2
e)
Global Mean
Temperature
increase*
Change in global
emissions in 2050 (%
of 2000 emissions)
2.5-3.0
445-490
2.0-2.4
-85 to -50
3.0-3.5
490-535
2.4-2.8
-60 to -30
3.5-4.0
535-590
2.8-3.2
-30 to +5
4.0-5.0
590-710
3.2-4.0
+10 to +60
5.0-6.0
710-855
4.0-4.9
+25 to +85
6.0-7.5
855-1,130
4.9-6.1
+90 to +140
*at equilibrium using the best estimate of climate sensitivity
Source: IPCC Fourth Assessment Report WG III Table 3.10
Table 2 shows the likely temperature increase with corresponding GHG stabilisation levels. If emissions
continue to rise at their current pace and are allowed to double (i.e., reach 560 ppmv) from their pre-
industrial level, the world will face an average temperature rise of 3.5°C. Serious impacts are associated
with this scenario (IPCC FAR, WG II 2007), including rise in sea-levels, shifts in growing seasons, and an
increasing frequency and intensity of extreme events such as storms, floods and droughts. According to
the IPCC report: i) even a temperature rise to 2°C would exacerbate already observed impacts including
human mortality, loss of glaciers, and increase in extreme events; ii) a warming of 2–4°C would lead
to worsening impacts on all scales, such as a decrease in global agriculture production and the loss of
biodiversity, and iii) a warming beyond 4°C would lead to a significant increase in vulnerability, and exceed
the adaptive capacity of many systems.