Climate change in the UKOTs an overview of the ... - JNCC - Defra

The carbon dioxide imbalance
It is true that natural sources of carbon
dioxide - plant respiration and decomposition
of organic matter - generate more than
10 times the amount of carbon dioxide produced
by human activities such as driving
motor vehicles, heating homes and powering
factories. However, in the past, natural
processes that remove or sequester
carbon dioxide from the atmosphere,
namely photosynthesis and the carbon
reservoir function of the oceans, balanced
out these releases.
We now have a situation where not only
are additional sources producing and
emitting carbon dioxide in significant
quantities, but the natural sinks that
remove carbon dioxide are also being
compromised. Trees and forests are being
cut down for a variety of reasons, including
agriculture and human settlements. At the
same time, oceans, including the North
and South Atlantic oceans, are reaching
their carbon dioxide saturation point
because their absorptive capacity is failing
to keep pace with the increase in carbon
dioxide emissions. A 10-year study by the
University of East Anglia found that the
North Atlantic halved its absorption of
carbon dioxide between the mid-90s and
2005 (Schuster and Watson, 2007). Scientists
previously thought the carbon sink
function of the oceans would help offset
the increase in anthropogenic carbon
dioxide emissions. However, this appears
not to be the case. Even though a
decrease in the ability of the oceans to
absorb carbon dioxide was anticipated by
scientists and even factored into some climate
models, it seems to be happening 40
years earlier than expected.
Ocean acidification
Scientists are now observing trends
of ocean acidification, a decrease in
the pH due to increased absorption of
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atmospheric carbon dioxide. Surface
ocean pH is already 0.1 units lower than
pre-industrial values and, in one emissions
scenario, by the end of the century
it could be lowered by an additional
0.14–0.35 units. Research is suggesting
that if the acidification trend continues,
marine organisms such as coral, plankton
and shellfish, might not be able to make
their skeletons and this could have ramifications
for coastal and marine environments.
Under normal conditions, carbonate ion
levels are high in the ocean, but when the
water becomes more acidic, they
decrease. When this happens, structures
that are made of calcium carbonate are at
risk of dissolution. In the case of corals,
this could cause slower or more fragile
growth and lead to a decrease in coral
cover and a smaller reef framework
(Kleypas et al., 2006; Orr et al., 2005; The
Royal Society, 2005). The Caribbean is one
of the regions where reefs are expected to
suffer the effects of ocean acidification
(Hoegh-Guldberg, et al., 2007).
Coral reefs play an important role in protecting
the shoreline from wave erosion.
They generate coral sand, provide nurseries
and habitats for fish and other marine
species and provide opportunities for
recreation activities, particularly diving and
snorkelling. Compromised coral reefs
weaken coastal defences and can have a
negative effect on fisheries, beach quality
and tourism.
2.4 How do we know that
climate change is
occurring?
The mass media have made much of the
fate of polar bears in the Arctic due to
losses of summer sea ice. Although
melting sea ice and glaciers and drowning
bears are some of the widely known early
warning signs of change, they are not the