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lakes studied. Furthermore, the methane emitted was dated to 35 260-42 900 years
ago. In short, this carbon was not recently (geologically speaking) fixed: the carbon
was not fixed in the Holocene interglacial that began about 11 700 years ago, rather in
the depth of the last glacial. What this means is that this carbon is not part of current
Holocene carbon cycling and it is additional carbon. The release of this carbon due to
warming is acting as a positive feedback to current warming (especially as methane
has a higher global warming potential [GWP] than carbon dioxide; Table 1.2).
How serious this positive feedback is will depend on other carbon cycle factors:
remember, it is the whole climate system that needs to be considered, and this is
made up of many interacting feedback factors (see Figure 1.8). For example, another
peri-polar counteracting factor is Antarctic ice-shelf melt, which can produce new
carbon sinks. In 2009 a report of research by the British Antarctic Survey showed that,
in around the past 50 years, in a large body of new open water (at least 24 000 km 2 ,
the area of Wales or, alternatively, Israel) blooms of phytoplankton are flourishing.
These new areas of high-latitude open water were left exposed by recent and rapid
melting of ice shelves and glaciers around the Antarctic Peninsula. This new natural
carbon sink is taking an estimated 3.5 million t of carbon (equivalent to 12.8 million t
of carbon dioxide) from the ocean and atmosphere each year (Peck et al., 2009). It is
the second largest factor acting against climate change so far discovered (the largest
is new forest growth on land in the peri-Arctic). Having said that, the Arctic thaw-lake
margins are tentatively estimated to be releasing 3.8 Mt of methane year 1 (Walter
et al., 2006), which is equivalent to 2.85 Mt of carbon year 1 . Yet, given that the
Arctic carbon release is in the form of methane (with a larger GWP than carbon
dioxide), the Arctic methane release is likely to have a greater warming effect in the
coming decades than this new Antarctic carbon sink will act to cool.
It is not just near-polar high-latitude ecosystems such as Arctic lakes that depend
on ice. Mountain snowpacks affect the quantity and annual timing of water in streams
supplying ecosystems in the surrounding lowlands. Even in a warm interglacial mode,
nearly all mountains of sufficient height, save those near the equator, have snow caps.
In a warmer world these will be reduced in volume, especially at lower latitudes,
although note that smaller mountain snow caps may be seasonally thicker due to extra
precipitation. This reduction in snowpack volume is something we are seeing already,
not just at lower latitudes but at mid latitudes too, including those in part occupied
by China, North America and Europe. Furthermore, in a warmer world snow-cap
melt run-off will shift away from summer and autumn, when biological, and indeed
human, demand for water is greatest compared to winter and early spring. In short,
the annual cycle of water supply for many terrestrial and human systems will see
reduced temporal buffering. The human ecology dimension is indicative of the likely
biological impact of such a shift, and here this is exemplified by the broad statistic that
one-sixth of the human population relies on glaciers and seasonal snowpacks for their
water supply. In terms of terrestrial ecosystems, in which more than 50% of river flow
is dominated by snow melt, this area includes nearly all of Canada's catchment, the
north-western Rocky Mountain states of the USA, nearly all of Scandinavia with the
exception of Denmark, alpine Balkan and Carpathian Europe, nearly all the Russian
nations and north-eastern China, much of Chile and south-western Argentina and the
south of New Zealand's South Island. In these regions ecosystems downstream rely
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