Global Warming Potential (GWP) and
Global greenhouse gas emissions since 1970
CO
2
equivalence
Gigatonnes of CO
2
-eq
Each of the greenhouse gases affects the atmos-
phere to a different degree, and survives for a dif-
50
F-gases
N
Agriculture ferent length of time. The extent to which a given
2
O
and other
GHG is estimated to contribute to global warming
CH
4
Agriculture,
40 waste, energy
is described as its Global Warming Potential (GWP).
To make the effects of different gases comparable,
Deforestation
the GWP expresses the factor by which the gas in
30
CO
question is more (or less) damaging than the same
2
mass of CO
2
over a given period of time, so the GWP
of CO
2
is always 1. Gases which cause much more
20 warming than CO2 may in turn decay faster than it
does, so they may pose a considerable problem for
Fossil fuels a few years but a smaller one later. Equally, others
10 may decay slower and pose a greater problem over a
long period of time.
0
1970 1980 1990 2000 2004
To talk of CO
2
-equivalent emissions is to take carbon
dioxide as a benchmark and to describe the amount
Source: IPCC, 2007.
of CO
2
that would cause the same amount of warming
over a specified timespan as would be caused by one
that commonly marks the beginning of industrial activi- of the other GHGs.
ties – and are now far higher than pre-industrial levels,
as shown by ice cores spanning many thousands of For example, the GWP for methane over 100 years is
years. Levels of the first two gases are far above their 25 and for nitrous oxide 298. This means that emis-
natural range over the last 650,000 years. The global sions of one metric tonne of methane or of nitrous ox-
atmospheric concentration of CO
2
before the start of ide are equivalent to emissions of 25 and 298 metric
the Industrial Revolution was around 280 parts per mil- tonnes of carbon dioxide respectively. One of the F-
lion (ppm). By 2005 it had reached 379 ppm. And the gases, HFC
23
, is 12,000 times more potent than CO
2
increase is accelerating: The annual growth rate was over 20 years, becoming even more potent (and thus
larger from 1995 to 2005 than at any time since contin- “dangerous” for the climate) over 100 years, the pe-
uous atmospheric measurements began in the 1950s. riod in which its GWP reaches 14,800.
Present changes, causes and observed impacts 21
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60