The human ecology of climate change - Climate Change: Biological and Human Aspects - page 435

means and rainfall showed deficits of up to 30 cm year − 1 . This extreme weather event
impeded primary productivity and reversed these ecosystems' former net carbon
sequestration.
The work (Ciais et al., 2005) was conducted as part of the EU CarboEurope
research programme and, although not as detailed an assessment as many ecologists
would like, as a partial snapshot it gives cause for thought. The researchers looked at
the programme's monitoring of carbon dioxide, water and energy from one grassland
and 14 forest sites for 2003 (the heatwave year) and 2002 (the control year). They
also analysed crop-harvest data at country level and compared 2003's figures with the
1998-2002 annual averages. Finally, they linked these field data to a sophisticated
ecosystem computer model that necessitated supercomputing facilities (which were
provided by the French Commissariat a l'Energie Atomique). The results sugges-
ted that the 2003 heatwave months resulted in a 30% reduction in gross primary
productivity for the year and that carbon release across Western Europe was about
500 GtC. Up to then it had (tentatively) been thought that Europe's soils had slowly
been accumulating carbon. This carbon loss roughly equalled some 4 years of such
accumulation. What was not known is the effect of this on the following year's carbon
balance. However, what is known is that the 2003 European heatwave temperatures,
while those of an extreme event early in the 21st century, are destined to be average
summer temperatures later in the century (and that heatwave summers then will be
correspondingly warmer; see Chapter 6). In short, Western Europe's 2003 carbon loss
was not a one-off event.
All of this does not bode well for a system of trading of greenhouse permits that
uses carbon sequestration in natural systems, because it assumes that these systems
are known and can be taken for granted given a certain management regime in the
future. As a way of mitigating fossil emissions, it can at the very best only be as good
as however long is the commitment to ecosystem management. ('At the very best'
because, as noted, a warmer world facilitates ecosystem carbon release regardless of
commitment and present carbon savings could easily turn into future carbon losses).
The success of such trading schemes also depends on our knowledge (currently not
sufficiently complete) as to agricultural sinks and especially soils, and our ability to
monitor them, as well as the schemes' robustness lest they be open to gamesmanship
by fossil-energy producers and consumers. Nonetheless, in the 1990s and early 2000s
many policy-makers welcomed such permit-trading schemes.
However, whereas permit-trading schemes that rely on soils as carbon sinks may
not function properly, carbon sequestration can still play a role in helping (albeit
temporarily) reduce the rate at which atmospheric carbon dioxide builds up. This last
could help slow the rate of climate change and may (marginally) help both ecosystems
and human systems adapt even if a hectare of ecosystem cannot be equated with the
consumption of a specific amount of fossil fuel.
7.5.2 Manipulatingmarinephotosynthesis
Compared to a very broad figure of around 50 GtC for annual net terrestrial biological
productivity for a biotic carbon stock of 550 GtC, the oceans have a small biotic
carbon stock of only around 3 GtC. Much of the 1 Tt of carbon in the oceans that