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that were either deliberately lit or triggered by lightning strikes towards the end of the
dry season. The total amount of carbon released from all sources of biomass burning
up until 1990 was estimated as 500-1,000 Tg of carbon/year (Crutzen and Andreae,
1990 ), of which more than one-tenth came from Asia, one-quarter came from South
America and two-fifths came from Africa (Andreae, 1993 ). (One tera-gram is 10 12 g.)
Fine particulate emissions from Asia amounted to 1.7-5.6
10 12 g/year, soot emis-
×
10 12 g/year (Ghan
and Penner, 1992 ). All of these figures have increased since then. Ghan and Penner
( 1992 ) estimated that total global fine particulate emissions from fossil fuel com-
bustion amounted to 22.5-24.0
10 12 g/year and the total biomass burned 351
sions equalled 0.4
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×
10 12 g/year
from biomass burning. If droughts become more frequent even beyond the presently
drier parts of Asia, as they are predicted to do (IPCC, 2007a ), the health hazards from
smoke inhalation will increase in the region centred on Indonesia-Papua New Guinea-
Malaysia and Singapore, which shows that the effects of desertification processes can
have repercussions well beyond the source area.
One important but often overlooked consequence of increased biomass burning in
the seasonally wet tropics is the loss of the protective surface layer of vegetation,
which reduces the impact of falling raindrops at the beginning of the wet season,
leading to an order of magnitude increase in soil loss on even very gentle slopes
( Chapter 10 ). The loss of soil will further reduce plant growth, leading to the onset
of desertification. In fact, the French forester Aubreville ( 1949 ) first coined the term
'desertification' after many years of observing that biomass burning in tropical Africa
was rapidly destroying the original forest cover and was creating desert-like conditions
in areas with a mean annual rainfall of 750-1,500 mm/year. Needless to say, many
savannas are not the result of the destruction of forest and woodland through the
repeated and indiscriminate use of fire, since they reflect the primary impact of a
seasonal rainfall regime and have been in existence for many millions of years before
ancestral fire-using humans first appeared on the planet (see Chapter 3 ).
We now turn to examples of desertification in Australia, Africa and Asia in order to
illustrate some of the general propositions outlined earlier. Australia is a fitting place
to begin, because unlike every other inhabited continent, it evaded the impact of ten
thousand years of Neolithic herding and farming until a mere two centuries ago, and
has suffered from the resulting culture shock ever since.
10 12 g/year, compared to 25.0-79.0
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24.8 Desertification in Australia
The Neolithic revolution (see Chapter 17 ) came late to Australia, but when it did
come some 200 years ago, it had an impact that resonates to this day. Occupied for
more than 40,000 years by small bands of hunter-gatherers, Australia had escaped
the early impact of herds of sheep, goats and cattle, with their hard hooves and
occasional destructive grazing habits. The first non-Aboriginal settlers, whether they
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