Impacts in the Next Few Decades and Coming Centuries - Climate Stabilization Targets - page 206

3,130 km 2 . Without aid from humans these species are probably not going
to be able to persist.
Extinction is irreversible. Choices among stabilization targets can be
expected to determine the scope of future extinction (e.g., types of spe-
cies, geographic regions, etc.) that could be caused by climate change, or
alternatively the scale of protective adaptation measures such as species
management that could be considered to avoid extinctions.
5.8 BIOLOGICAL OCEAN
Impacts of CO 2 , pH, and Climate Change in the Ocean's Biology
Marine ecosystems will be affected by climate change via physical
changes in ocean properties and circulation (Sections 4.1, 4.4, and 4.7),
ocean acidification via altered seawater chemistry from rising atmospheric
CO 2 (Section 4.9), and sea-level rise via coastal habitat loss. Some of the
key potential impacts will involve changes in the magnitude and geographi-
cal patterns of ecological and biogeochemical rates and shifts in the ranges
of biological species and community structure (Boyd and Doney, 2002).
Impacts are expected to include both direct physiological impacts on organ-
isms through, for example, altered temperature, CO 2 , and nutrient supply,
and indirect effects through altered food-web interactions such as chang-
ing seasonal timing (phenology) of phytoplankton blooms or disruptions in
predatory-prey interactions.
Primary production by upper-ocean phytoplankton forms the base of
the marine food-web and drives ocean biogeochemistry through the export
flux of organic matter and calcareous and siliceous biominerals from plank-
tonic shells. Plankton growth rates for individual species are temperature
dependent and tend to increase under warming up to some threshold. When
viewed in aggregate, plankton community production rates approximately
follow an exponential curve in nutrient replete conditions, which would sug-
gest increasing global primary productivity over this century as sea surface
temperatures increase (Sarmiento et al., 2004). In most regions of the ocean,
however, primary production rates are limited by nutrients such as nitrogen,
phosphorus, and iron. Diatoms, a key shell-forming group of phytoplankton,
are also limited by silicon. The rates of many other biological processes,
such as bacterial respiration and zooplankton growth and respiration, also
speed-up as temperature rises, the integrated effect at the ecosystem level is
difficult to predict from first principles. Warming also occurs in conjunction