Climate change impacts and vulnerability in Europe 2016

Climate change impacts on environmental systems
4.1.4 Sea surface temperature
Key messages
• All European seas have warmed considerably since 1870, and the warming has been particularly rapid since the late
1970s. The multi-decadal rate of sea surface temperature rise during the satellite era (since 1979) has been between
0.21 °C per decade in the North Atlantic and 0.40 °C per decade in the Baltic Sea.
• Globally averaged sea surface temperature is projected to continue to increase, although more slowly than atmospheric
temperature.
Relevance
Sea surface temperature (SST) is an important physical
characteristic of the oceans. SST varies naturally
with latitude, being warmer at the equator and
coldest in Arctic and Antarctic regions. As the oceans
absorb more heat, SST will increase (and heat will be
redistributed to deeper water layers). Information on
changes in regional SST complements the information
on changes in global OHC presented in Section 4.1.3.
Increases in SST can lead to an increase in
atmospheric water vapour over the oceans,
influencing entire weather systems. For Europe,
the North Atlantic Ocean plays a key role in the
regulation of climate over the European continent
by transporting heat northwards and by distributing
energy from the atmosphere into the deep parts of
the ocean. The Gulf Stream and its extensions, the
North Atlantic Current and Drift, partly determine
weather patterns over the European continent,
including precipitation and wind regimes. One of
the most visible physical ramifications of increased
temperature in the ocean is the reduced area of
sea ice coverage in the Arctic polar region (see
Section 3.3.2).
Temperature is a determining factor for the
metabolism of species, and thus for their distribution
and phenology, such as the timing of seasonal
migrations, spawning events or peak abundances
(e.g. plankton bloom events) (Box 4.3). There is an
accumulating body of evidence suggesting that many
marine species and habitats, such as cetaceans in the
North Atlantic Ocean, are highly sensitive to changes
in SST (Pinsky et al., 2013; Lambert et al., 2014).
Increased temperature may also increase stratification
of the water column. Such changes can have a
significant influence on vertical nutrient fluxes in the
water column, thereby influencing primary production
and phytoplankton community structure (Hordoir
and Meier, 2012). Further changes in SST could have
widespread effects on marine species and cause the
reconfiguration of marine ecosystems (Edwards and
Richardson, 2004; Poloczanska et al., 2013; Glibert
et al., 2014).
Past trends
The production of consistent, long time series of SST
faces challenges owing to different measurement
devices (in situ measurements from ships and buoys,
as well as remote measurements from satellites),
associated different definitions (e.g. water depth and
time of day of measurement), different bias correction
methods, and different interpolation methods to
account for incomplete spatial and temporal coverage.
As a result, substantially different values for absolute
SST and for SST trends may be reported for a
particular ocean basin, depending on the underlying
global or regional SST dataset. In fact, there is still
considerable uncertainty about the trend in global
SST for the recent period 1979–2012 (Hartmann et al.,
2013, Table 2.6). Furthermore, observed SST trends
for regional seas reflect the combined effects of
anthropogenic warming and natural climate variability
(e.g. Atlantic Multidecadal Oscillation) (Macias et al.,
2013). Despite those uncertainties, it is undisputed
that SST has been increasing globally and in Europe
during the last century.
The current indicator primarily uses information
from the Hadley Centre Sea Ice and Sea Surface
Temperature (HadISST1) dataset (Rayner et al., 2006).
Information on the Mediterranean for the satellite
era is complemented by data from the Copernicus
Marine Environmental Monitoring Service (CMEMS).
The trends, although not necessarily the absolute SST
levels, are consistent between HadISST1 and available
high-resolution SST datasets for the regional seas
(Mediterranean Sea, Baltic Sea and North Sea). The
trends reported here cannot be directly compared
with those in previous versions of this indicator, which
used different underlying datasets.
Climate change, impacts and vulnerability in Europe 2016 | An indicator-based report
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