Present climate and biological change - Climate Change: Biological and Human Aspects - page 252

model. They also used deuterium (isotopic 2 H, sometimes represented by D) analysis
of the hydrogen in methane to further disentangle some of the methane source options.
They concluded that the 13 C observations are consistent with long-term reductions
in agricultural emissions or another microbial source in the northern hemisphere.
Approximately half (51 18%) of the decrease in northern-hemisphere methane

emissions can be explained by reduced emissions from rice agriculture in Asia over
the past three decades associated with increases in fertilizer application and reductions
in water use.
Taken together, these papers suggest that roughly half (or perhaps a little more)
of the decline in methane emissions came from better prevention of methane escape
from fossil fuel refining and storage (notably Russia improved its energy infrastructure
over this period), and half (or perhaps a little less) from improved rice agriculture
that reduced the area of paddy field wetland needed. If this work does interpret
what is going on reasonably accurately, then unless further improvements in fossil
fuel management occur, and as fossil fuel use continues to grow, methane emissions
will rise in the future. Similarly, unless there are continued improvements in rice
agricultural production techniques then as the world population continues to grow,
and demand more rice, and rice production increases, then so methane emissions will
rise. In short, we should expect the atmospheric concentration of methane to rise once
more in coming decades.
At the end of 2011, MethaneNet (an affiliation of British researchers) sponsored a
symposium on methane research, held at the headquarters of the Geological Society.
Various strategies for reducing anthropogenic methane were proposed. First, with
regard to methane from agricultural ruminants (principally cattle), studies show that
kangaroos ( Macropus spp.) emit around 2% of the CO 2 equivalent for methane of
sheep and even less than that for cattle. Could it be, by altering cattle gut microflora
(bacteria) to be more like that of kangaroos, that emissions can be reduced? Progress
is difficult because cultivating pure strains of species in ruminant gut flora is not easy.
However, attempts are being made to create a meta-genome of the whole gut microbial
community. The bad news for prospects of future ruminant methane emissions is that
as countries develop, so their protein consumption per capita increases. The good
news is that the growth in protein consumption in Asia is largely related to chicken
and pork, and consequently less beef.
Second, with regard to rice cultivation, research shows that methane emissions
can be greatly reduced by allowing paddy fields to periodically dry out. In areas
where the water supply is gravity-fed this is easy to do and it also, given appropriate
water-management infrastructure, lowers water consumption. Of course, it should
be noted that the carbon does not just vanish. The methane emissions are partly
compensated for by the mineralisation of carbon, hence the resulting increased carbon
dioxide emissions. But given methane's higher GWP (see Table 1.2) this is a far more
preferable option.
Finally, it should be noted that methane from melting permafrost regions in high
latitudes largely comes from wetlands and frozen lakes. Methane released within
permafrost soils gets converted to carbon dioxide which, as noted, has a lower GWP:
this is still a great concern but a lesser one than would otherwise be.

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