Environmental Engineering Reference
In-Depth Information
causing global warming of 2 1C or more can be found in Table 1. The limit
takes into account the ability of carbon sinks to absorb some of the CO
2
emitted into the atmosphere and sets aside a proportion of the budget for
non-CO
2
greenhouse gases, providing the gross total CO
2
from fossil fuels
and land-use change that can be released into the atmosphere with a good
chance of avoiding a 2 1C increase. The limit is based on what can be emitted
between the years 2000 and 2050. This timeframe was chosen as it has the
most significance to decision-makers today, however, this does not mean
that after 2050 fossil-fuel burning can resume. In fact, beyond 2050 the
cumulative emissions budget is even lower, and analyses suggest net zero-
CO
2
emissions are necessary by around 2070 to avoid dangerous climate
change.
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3.3 Fossil Fuels in the Context of Emissions Budgets
In summary, to avoid 'dangerous climate change' the most relevant metric is
the cumulative amount of greenhouse gases released during the next cen-
tury, particularly in the next 35 years when decision-makers have the most
immediate influence over emissions. Thus, not only the carbon intensity of a
fuel is important but the quantity of it which is used and, therefore, the
cumulative amount of CO
2
it contributes to the atmosphere.
Table 3 demonstrates that, globally, 40% of the cumulative emissions
budget associated with avoiding more than 2 1C of warming has already been
used up. Global emissions from fossil-fuel burning, cement manufacturing
and land-use change, released between 2000 and 2012, add up to 432 Gt CO
2
.
The International Energy Agency estimate that non-energy-related CO
2
sources (e.g. from chemical processes, land-use change and deforestation)
will release approximately 136 Gt CO
2
in the period to 2050.
34
This leaves
between 322 and 872 Gt CO
2
that can be released into the atmosphere from
2013 to 2050 from the energy sector. The average annual rate of fossil-fuel-
related emissions between 2000 and 2011 is 29 Gt CO
2
yr
1
; continuing
emissions at this rate would mean the remaining CO
2
budget was used up by
2023 (20% probability of exceeding 2 1C temperature increase) or 2042 (50%
Table 3 Comparison of the amount of CO
2
from fossil fuel and land-use change that
can be released into the atmosphere from 2000 to 2050 and emissions to
date.
Global emissions
budget
to avoid a 21C global
temperature increase
890 Gt CO
2
(20% probability
of exceeding 2 1C)
1000 Gt CO
2
(25% probability of
exceeding 2 1C)
31
1440 Gt CO
2
(50% probability
of exceeding 2 1C)
Amount emitted
2000-2012.
30
432 Gt CO
2
432 Gt CO
2
432 Gt CO
2
Predicted non-energy
CO
2
emissions
2012-2050.
34
136 Gt CO
2
136 Gt CO
2
136 Gt CO
2
Remaining CO
2
budget
for energy 2012-2050.
322 Gt CO
2
432 Gt CO
2
872 Gt CO
2
