Present climate and biological change - Climate Change: Biological and Human Aspects - page 249

atmospheric concentration of carbon dioxide been a constant average) we have far less
time before saturation is reached. Emissions for the last 50 years of the 20th century
were very roughly equal to total emissions for the 200 years up to 1950. Furthermore,
as we continue to approach saturation so the oceans become ever more acidic: the
reduction in pH of a more acidic ocean has a greater biological impact than the same
lowering of pH in a less acidic ocean. Alongside the paper by Chris Sabine et al. was
another from a team led by Sabine's co-worker, Richard Feely (2004). They concluded
that, under the IPCC's 2001 forecasts for the end of the 21st century, atmospheric
carbon dioxide levels could be around 800 ppm. At that level ocean pH would further
decline, by about 0.4, to a level not seen for more than 20 million years. At lower pH
values calcium carbonate shells of forams will begin to dissolve faster and growth will
be compromised. Calcification rates can drop by as much as 25-45% at carbon dioxide
levels equivalent to atmospheric concentrations of 700-800 ppm. These levels will
be reached by the end of this century if fossil fuel consumption continues at projected
levels.
Effects will be worse in those parts of the ocean where carbonic acid concen-
trations are highest. They would have a profound effect on ocean acidity and the
oceans' biological community that relies structurally on carbonate. Already one of
the researchers on the team (Victoria Fabry) has observed partial shell dissolution
in one of the pteropods (a group of marine gastropod molluscs), a live pyramid clio
( Clio pyramidata ) in the sub-Arctic North Pacific. Groups and phyla at possible risk
include calcareous green algae, echinoderms (the phylum of starfish and sea urchins),
bryozoans (those of a phylum of colonial animals also known as the ectoproctans)
and the deep-sea benthic forams.
About half of the anthropogenic carbon dioxide taken up over the last 200 years -
the 118 19 Pg of carbon - can be found in the upper 10% of the ocean. In turn,

this 118 Pg very approximately represents less than 40% of the carbon released as
carbon dioxide by human action (both fossil fuel burning and land-use change). If
this carbon had not been absorbed by the oceans, atmospheric concentrations would
be higher. Recalling that pre-industrial atmospheric carbon dioxide was 280 ppm
(Table 1.1), with the 2003 concentration being 376 ppm, this last would be some
55 ppm higher still were it not for oceanic uptake. So, in one sense what is bad for
the ocean is good for the atmosphere (although do note that this use of 'good' and
'bad' is unscientific).
Of the ocean DIC from anthropogenic carbon dioxide, more than 23% is found in
the North Atlantic, which might be surprising considering its small size (15% of the
global ocean surface) compared to other oceans such as the Indian Ocean and North
and South Pacific. However, the North Atlantic is bounded by the north-western
European and the North American countries, which together have historically (up
to 2000) been responsible for very roughly half the planet's anthropogenic carbon
dioxide emissions. This in turn suggests that a good proportion of carbon dioxide
enters the ocean by being washed out by rain, as opposed to ocean-surface diffusion
and wave mixing. However, because so much of the southern hemisphere is ocean,
some 60% of ocean DIC from anthropogenic carbon dioxide is stored in that hemi-
sphere's seas. Taking all this together we might expect signs of a major impact on
carbonate species to first begin to manifest themselves in the cool North Atlantic

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