Soil and Climate - Soil: Reflections on the Basis of our Existence - page 124

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Leaking soils . Cloudberry and crowberry bushes cover palsas at Stormyren marsh near Abisko
research station in northernmost Sweden. The palsas are raised peat mounds with a permanently
frozen core and with grass, sedges and cotton grass growing in the wetter parts
Global warming is causing the palsas' frozen core to thaw, a process that cracks the peat (see
photo), accelerates its decomposition and releases more carbon dioxide into the atmosphere.
Ground methane also seeps out, fuelling the greenhouse effect. As the climate warms, increasing
amounts of methane will leak from large areas of permafrost in northern Siberia

penetrate. The oxygen level in these aggregates is often low, further retarding the
decomposition process. There is still a long way to go before we will be able to
describe all soil components and how climate change will affect them. Models of
soil carbon inflow and outflow are integral to the larger models used by scientists
to project how global climate patterns will change in future. However, these mod-
els assume that decomposition of all substances in the soil will have the same tem-
perature dependence. Researchers know that this does not reflect reality but lack
the knowledge needed to make the models more accurate.
Temperature is not the only factor that affects soil carbon decomposition.
Changes in rainfall can have a major impact on the flow of carbon from soil to
air. Mediterranean soils, for example, are likely to become even drier in future,
potentially disrupting the decomposition process there and resulting in lower car-
bon dioxide emissions. On the other hand, decomposition rates in damp areas
may accelerate due to reduced rainfall or if marshes or bogs dry out due to higher
temperatures. Lower precipitation would enable oxygen to penetrate deeper into
the soil and hasten decomposition. In northern latitudes, rainfall is expected to
increase—and this ought to lead to an increase in soil carbon as additional precipi-
tation would make wet areas even wetter and less oxygenated, slowing the decom-
position process.
It is clear that substantial difficulties must be overcome to improve the mod-
els for predicting global flows of soil and atmospheric carbon. Still, a number of
empirical studies have been carried out in recent decades tracking changes in soil
carbon. In Sweden, soil carbon volume has risen by one third since 1926, equiva-
lent to an increase of three million tonnes per year. This corresponds to almost half
of Sweden's total carbon dioxide emissions during the period. The main reason is
an increase in forest biomass, which means more dead roots and leaves that even-
tually enter the soil and raise its carbon content. The increase has been most pro-
nounced in the south of the country.
By contrast, Britain's soil has lost thirteen million tonnes of carbon to the
atmosphere in the last 25 years, equivalent to around a tenth of the country's car-
bon dioxide emissions during this period and roughly the same figure as the total
reduction in carbon emissions achieved by energy efficiency and other measures
during the same timeframe. Carbon loss is greatest in peatlands, probably due
to surface drying brought about by a warmer climate and the knock-on effect of
added aeration accelerating the decomposition process.
Parched soil can lead the organisms in it to change behaviour. In acidic
soil, centimetre-long white worms known as enchytraeids generally replace