Climate change impacts and vulnerability in Europe 2016

Climate change impacts on society
5.4.2 Heating and cooling degree days
Key messages
• The number of population-weighted heating degree days (HDD) decreased by 8.2 % between the periods 1951–1980 and
1981–2014; the decrease during the period 1981–2014 was on average 9.9 HDDs per year (0.45 % per year). The largest
absolute decrease occurred in northern and north-western Europe.
• The number of population-weighted cooling degree days (CDD) increased by 49.1 % between the periods 1951–1980 and
1981–2014; the increase during the period 1981–2014 was on average 1.2 HDDs per year (1.9 % per year). The largest
absolute increase occurred in southern Europe.
• The projected decrease in HDDs as a result of future climate change during the 21st century is somewhat larger than the
projected increase in CDDs in absolute terms. However, in economic terms, these two effects are almost equal in Europe,
because cooling is generally more expensive than heating.
• The projected increases in the cooling demand in southern and central Europe may further exacerbate peaks in electricity
demand in the summer unless appropriate adaptation measures are taken.
Relevance
Space heating and cooling is responsible for a large
fraction of European energy use. HDDs and CDDs
are proxies for the energy demand needed to heat
or cool, respectively, a home or a business. Both
variables are derived from measurements of outside air
temperature. The heating and cooling requirements for
a given structure at a specific location are considered,
to some degree, proportional to the number of HDDs
and CDDs at that location. However, they also depend
on a large number of other factors, in particular
building design, energy prices, income levels and
behavioural aspects.
HDDs and CDDs are defined relative to a base
temperature — the outside temperature — below
which a building is assumed to need heating or cooling.
They can be computed in different ways, depending,
among other things, on the specific target application
and the availability of sub-daily temperature data.
The previous version of this EEA report (EEA, 2012)
applied the methodology of Eurostat, which uses daily
mean temperature only and has a jump discontinuity
when daily mean temperature falls below the base
temperature (Eurostat, 2014). This report uses an
approach developed by the UK Met Office, which uses
daily mean, minimum and maximum temperatures
and does not exhibit a discontinuity. Note that this
approach, being based on both minimum (T n ) and
maximum (T x ) temperatures and not solely on the
mean temperature (T m ), increases the accuracy of HDDs
and CDDs for the purpose of gauging the impacts of
climate change on energy demand, because the cooling
of the environment depends more on T x than on T m ,
while T n is more relevant for heating. The baseline
temperatures for HDDs and CDDs are 15.5 °C and
22 °C, respectively (Spinoni et al., 2015). As a result of
the methodological changes, the magnitudes of the
trends between the previous report and this report
cannot be directly compared.
The aggregation of regional changes in HDDs and
CDDs to larger areas can be done using area weighting
or population weighting (with a fixed population).
Population weighting is preferable for estimating
trends in energy demand over large regions with an
uneven population distribution (e.g. Scandinavia or
Europe) (EPA, 2014).
Past trends
The number of population-weighted HDDs decreased
by 8.2 % between the periods 1951–1980 and
1981–2014. The decrease during the period
1981–2014 was on average 9.9 HDDs per year,
although with substantial interannual variation
(Figure 5.8, left); this linear trend corresponds to an
annual decrease of 0.45% (relative to the 1951–1980
average). The largest absolute decrease occurred
in northern and north-western Europe, where the
heating demand is highest (Map 5.17, left panel).
The number of population-weighted CDDs increased by
49.1 % between the periods 1951–1980 and 1981–2014.
The increase during the period 1981–2014 was on
average 1.2 CDDs per year, although with substantial
interannual variation (Figure 5.8, right); this linear trend
corresponds to an annual increase of 1.9 % (relative to
the 1951–1980 average). The largest absolute increase
246 Climate change, impacts and vulnerability in Europe 2016 | An indicator-based report