P. R. Shukla Indian Institute of Management Ahmedabad

2. The Science of Global Climate Change

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6
Promoting low carbon transPort in india
Low Carbon City: 
A Guidebook for City Planners and Practitioners
Emissions of greenhouse gases (Figures 1 and 2) mainly include those from energy use, as well as non-
energy emissions. Energy related emissions include CO
2
, which predominantly arise from energy supply, 
residential and commercial buildings, transport and industrial energy use, and methane (CH
4
) that is 
emitted in the natural gas supply-chain. Non-energy sector emissions mainly include CH
4
, N
2
O and CO
2
from land-use change and forestry. CO
2
emissions primarily from fossil fuel use occupy the largest share 
of global anthropogenic GHG emissions. The CO
2
concentration in the atmosphere, which was 280 ppmv 
during the early industrial revolution period two centuries ago, has risen significantly, and in May 2013 
passed the 400 ppmv level (UNFCCC, 2013).
Figures 1 and 2: Global Anthropogenic GHG Emissions in 2004 (by Type and Sector)
Source: IPCC Fourth Assessment Report, Working Group III
The IPCC Fourth Assessment Report (IPCC WGI AR4, 2007) noted that “changes in atmospheric 
concentrations of greenhouse gases and aerosols, land cover and solar radiation alter the energy 
balance of the climate system”, and concluded that “most of the observed increase in globally averaged 
temperatures since the mid-20th century are very likely (greater than 90% probability) due to observed 
increase in anthropogenic greenhouse gas concentrations”. 
Information on future changes in the concentration of greenhouse gases, associated temperature rise and 
impacts on various systems are studied with the help of climate models. Climate models compute these 
future climatic changes by incorporating several complex scientific phenomena, including air circulation 
patterns, ocean atmospheric interactions, radiative forcing of different greenhouse gases and interactions 
with other climate influencing agents like aerosols. There is a level of uncertainty associated with the 
climate projections due to the complexity of the interactions within the climate system. Hence, for every 
given path of global emissions, there is an associated probability distribution of temperature changes 
(Table 2).
Figure 1: Global anthropogenic greenhouse gas 
emissions in 2004 in terms of CO
2
-eq
CO
2
(fossil
fuel use), 56.6%
CO
2
(other),
2.8%
CO
2
(deforestation, 
decay of biomass,
etc.), 17.3%
F-gases,
1.1%
N
2
O,
7.9%
CH
4
,
14.3%
Figure 2: GHG emissions by sector 
in 2004
Energy supply,
25.9%
Transport,
13.1%
Buildings,
7.9%
Forestry,
17.4%
Agriculture,
13.5%
Industry,
19.4%
Water and wastewater,
2.8%

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Promoting low carbon transPort in india