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![](/i/favi32.png) P. R. Shukla Indian Institute of Management AhmedabadEmission levels in 2020, 2030 and 2050 forLow Carbon City Guidebook3.3 Emission levels in 2020, 2030 and 2050 for
the 2°C target
To analyse the least cost scenarios, we bring them into a
common analyical framework and esimate the probability
of each scenario exceeding 2°C and 1.5°C of warming. A
probabilisic approach is important because of the great
uncertainies of climate sensiivity (roughly speaking, the
response of global temperature to addiional greenhouse
gas emissions) (Knui and Hegerl, 2008) and transient
climate response
20
. Temperature ranges are projected
using the probabilisic carbon-cycle and climate model
MAGICC
21
(Meinshausen et al., 2011a) in a setup that closely
simulates the global temperature response to greenhouse
gas emissions of the most complex climate models (Rogelj
et al., 2012) as assessed in the Fourth Assessment Report
20 According to the IPCC, transient climate response is a measure of the
strength and rapidity of the surface temperature response to greenhouse gas
forcing.
21 The setup of the climate model has been updated from the 2011 Bridging
the Emissions Gap Report. Unil now, the setup described in Meinshausen et
al. (2009) was used. Here we use the setup presented in Rogelj et al. (2012),
which is basically an extension of the work described in Meinshausen et al.
(2009), to represent more closely the uncertainies in climate sensiivity in
line with the assessment of the Intergovernmental Panel on Climate Change
(IPCC, 2007b) and take into account the latest historical emission esimates
from the Representaive Concentraion Pathway (RCP) exercise (Meinshausen
et al., 2011b).
<2°C <2.5°C <3°C <3.5°C <4°C <5°C >5°C
25
30
35
40
45
50
55
60
65
70
75
1990 GHG level
2010 GHG level
20
20
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