Environmental Engineering Reference
In-Depth Information
see (rather exceptionally, as most of these studies tend to have indefensibly alarming
conclusions) the authors of a recent multidisciplinary appraisal of the impacts of
climate change on China's water resources and agriculture admitting that “current
understanding does not allow a clear assessment of the impact of anthropogenic
climate change” (Piao et al. 2010a, 43).
The ocean's primary productivity will be affected by both the warming and the
acidii cation. Bathythermograph measurements show a robust warming of the global
upper ocean, a trend amounting to 0.64 W/m
2
between 1993 and 2008 (Lyman
et al. 2010). In 2006, Behrenfeld et al. (2006) analyzed satellite data from an ocean
color sensor and found an initial brief increase in NPP (1.93 Gt C/year), followed
by a prolonged decrease at an annual rate of 190 Mt C. Subsequently, Boyce, Lewis,
and Worm (2010) combined ocean transparency measurements and in situ chloro-
phyll observations to estimate long-term trends of the global phytoplankton biomass
since 1899.
In addition to the expected interannual and decadal l uctuations (observable
thanks to the post-1978 satellite monitoring of phytoplankton), they concluded that
phytoplankton mass has declined in eight out of ten ocean regions, and put the rate
of decrease at about 1%/year. These temperature-driven declines in marine NPP
should have already affected the productivity of marine zoomass, and if the trend
were to continue it would amount to a fundamental shift in the biosphere produc-
tivity. Even if this trend were to slow down or reverse, other concerns would remain.
Many i sheries have shown large-scale decadal and annual stock l uctuations (Lae-
vastu 1993), and their future amplitudes may increase.
Marine i shes could be affected by a growing disparity between their demand for
oxygen and the capacity of warmer waters to meet it, as well as by the freshening
of Arctic waters, the changes in nutrient supply brought by upwelling, more persis-
tent pathogens, and the loss of coral habitats as a result of the progressive acidi-
i cation of the ocean (Parry et al. 2007; Pörtner and Knust 2007). Another concern
has been the increase in the number of reported oxygen minimum zones whose
existence, and persistence, limit the vertical habitat available for pelagic organisms
(Bertrand, Ballo, and Chaigneau 2010). On the other hand, recent reports of chang-
ing NPP have included a positive effect of stronger monsoon winds blowing over
the western Arabian Sea: because of the increased nutrient upwelling, the average
summertime phytoplankton mass was boosted by more than 350% (Goes et al.
2005).
The future extent and pace of natural responses and feedbacks will be strongly
inl uenced by human actions, and the future rate of population growth, pace of
