Geography Reference
In-Depth Information
Box 2.2
Carbon dioxide released from forest fires
The year 1997 witnessed some of the worst forest and
scrub fires ever recorded. There are no accurate
estimates yet of how much biomass was converted
into CO
2
, but an attempt is made to assess the impact
of the fires of 1997-8. The process of forest burning in
the tropics is an integral part of traditional farming,
known universally as 'slash and burn'. Regional terms
include
ladang
in Indonesia and
roça
in Brazil. Some
governments such as that in Malaysia have attempted
to ban or control the burning, but in neighbouring
Indonesia the practice has gone unchecked. While
research suggests that agroforestry can help carbon
sequestration by converting Imperata grasslands into
more productive tree-based systems, wholesale
burning fails to achieve such an end. There are other
dimensions to the problem apart from the use for
shifting cultivation, such as the actions of logging
companies in allowing or promoting burning, and the
need for more land for rice and food crops, as in the
permitted burning of 40,000 ha southeast of
Palangkaraya (Kalimantan). To these must be added
in 1997-8 the active El Niño phase of ENSO, which
caused almost unprecedented drought across many
parts of equatorial Southeast Asia.
Estimates of C released on burning are based on
the following approximations:
•
1 ha contains 200-5001 (tonnes) of biomass, about
50% of which is carbon.
•
Mature tropical forests in Indonesia average about
365 t ha
-1
.
•
Burning probably releases two-thirds of carbon into
the atmosphere as CO
2
.
•
The intensity of the fires has caused the peat of the
forest floor to ignite, adding to the release of carbon
dioxide into the atmosphere by an unknown amount.
The value of 365 t ha
-1
is taken to include this effect
in the following estimates. The same figure is used
for Brazil.
Comparative data on recent burning and CO2 release:
•
The burning of 40,000 ha would therefore release
about 0.5 Mt as CO
2
.
•
Around 2 million ha were lost to fire in 1997 in
Indonesia alone, releasing about 0.25 Gt of CO
2
(1
Gt=1,000 Mt= 10
9
t) (Dudley 1997).
•
Estimates by the IPCC of CO
2
emissions from
tropical land-use changes—mostly deforestation—
in the late 1980s are about 1.6±0.4 Gt per annum.
As may be seen from Figure 2.6, this may be
compared with 1.75 Gt of CO
2
emissions from fuel
combustion in North America in 1996.
Figure 2.6
Estimated
carbon dioxide emissions
into the atmosphere.
Sources:
Various, mostly from
Nature
and IPCC.
While it is very difficult to obtain estimates of emissions
for a specific year, the fires of 1997-8, the worst of which
were those in Brazil, must cause concern, since the
addition of CO
2
is unlikely to be balanced by
sequestration through afforestation in the near future.
Serious fires were also reported from Papua New
Guinea, Colombia, Peru, Mexico, Australia, parts of
Africa and southern Europe.
