BSEP116B Biodiversity in the Baltic Sea - Helcom

the Baltic biota (see, e.g., Chapter 3, Fish communities
and Zooplankton communities). However, it
has not been possible to establish a distinct causal
link between these changes and anthropogenically
induced climate changes, partly because of the large
natural climate variability, but also owing to possible
impacts from other human pressures (Dippner et al.
2008). The observed changes, however, point to
the considerable impacts that climate-related factors
have on the Baltic Sea biodiversity.
Regional climate models for the Baltic Sea area
project increased precipitation during the 21st
century which may cause a decrease in salinity.
Hydrographic models also project a higher seawater
temperature in the Baltic Sea. This section
addresses impacts of these possible future climate
changes on the Baltic Sea biodiversity.
6.10.1 Projected changes in climate in
the Baltic Sea region
Most recent regional climate projections indicate
that near-surface air temperatures will further
increase by 3–5°C during this century in the Baltic
Sea area (Graham et al. 2008). Depending on the
future climate scenario, this would translate into
a two- to six-week longer growing season in the
region. Conversely, this means shorter and warmer
winter seasons, and the length of the ice season
would decrease by 1 to 2 months in the northern
Baltic Sea and 2 to 3 months in the central parts.
During the 21st century, anthropogenic climate
change is expected to increase precipitation, particularly
in the north, while summers are expected
to become drier in the south (Graham et al. 2008).
This is projected to cause 15% higher riverine
runoff during winters (averaged for the whole
area), possibly causing decreased salinity in the
Baltic Sea and higher nutrient loads from the surrounding
catchment area. Average annual sea
surface temperatures could increase by approximately
2–4°C by the end of the 21st century
(Döscher & Meier 2004, Räisänen et al. 2004).
increase of CO 2
concentration to 650 ppm (Caldeira
& Wickett 2005). In the Baltic Sea, acidification
by 0.15 pH units has already been observed
during the past 20–30 years (Perttilä 2008). Acidification
of seawater leads first to a decrease of calcification
and, in the lower pH regime, to dissolution
of calcified structures of, for example, certain
plankton groups, bivalves and snails. In the Baltic
Sea, where calcification is already lower owing to
low salinity, this effect may be more pronounced
than in the oceans.
Ecosystem effects of increased seawater temperature
and changes in sea ice regime
Globally, rising water temperatures have already
caused range shifts and changes in abundance
of algae, plankton and fish in some freshwater
and marine systems (IPCC 2007). An increase in
water temperature may also increase bacterial
activity, which can affect the recycling and biological
uptake of nutrients (HELCOM 2007d). Higher
summer temperatures and milder winters will likely
bring new species, alter migration patterns of
birds, and result in exclusion of some native species
or ecosystem functions of the Baltic Sea. Warming
may, for example, stimulate typical warm-water
species such as cyanobacteria, whereas cold-water
species, such as diatoms, may decrease in the
system (Dippner et al. 2008). Because ringed seals
and grey seals give birth to pups on ice, a reduc-
Ringed seal (Phoca hispida) pup
Because the oceans are a major sink for CO 2
,
storing about 30% of the anthropogenic CO 2
emissions, a long-term increase in CO 2
results
in acidification of the ocean water (Sabine et al.
2004). According to the IPCC, the pH in the world
oceans would drop by 0.30 by 2100 assuming an
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