Climate change impacts and vulnerability in Europe 2016

Changes in the climate system
3 Changes in the climate system
This chapter describes observed and projected changes
in key components of the climate system. Section 3.1
gives an overview of the human influence on the
Earth's climate, primarily as a result of the emission
of greenhouse gases. Section 3.2 presents several
indicators of changes in the atmosphere, such as
temperature and precipitation. Section 3.3 presents
several indicators of changes in the cryosphere, such
as ice and snow cover. The hydrosphere is another
key component of the climate system. Changes in the
ocean and its impacts on the marine environment are
presented jointly in the following chapter in Section 4.1.
Changes in freshwater systems are described in
Section 4.3.
3.1 Human influence on the climate
system
3.1.1 The climate system
Climate is the statistical description (averages, trends,
magnitude and variability) of the climate system
over a long time period (usually at least 30 years).
The climate system is a highly complex system that
includes five major components: the atmosphere
(see Section 3.2), the cryosphere (see Section 3.3), the
hydrosphere, the upper lithosphere and the biosphere
(see Chapter 4).
The Earth's climate system is powered by the incoming
solar shortwave radiation (SWR), which is nearly in
balance with the outgoing longwave radiation (LWR).
Of the incoming solar SWR, about half is absorbed
by the Earth's surface; the rest is reflected back to
space or absorbed in the atmosphere (Figure 3.1).
The energy absorbed by the Earth's surface warms
it and is then emitted as LWR (terrestrial radiation)
back to the atmosphere, where it is partly absorbed
by certain radiatively active atmospheric constituents:
water vapour, carbon dioxide (CO 2 ), methane (CH 4 ),
nitrous oxide (N 2 O), other greenhouse gases, clouds
and (to a small extent) aerosols. These constituents
also emit LWR in all directions and the component
emitted downwards adds heat to the lower layers of
the atmosphere and to the Earth's surface, further
warming it. This is called the greenhouse effect (for
details, see Cubasch et al., 2013).
Key messages
• The current average annual concentration of CO 2 in the atmosphere is close to 400 parts per million (ppm), which is the
highest level for at least the last 800 000 years and about 40 % higher than the pre-industrial levels.
• Even if anthropogenic emissions of CO 2 and other greenhouse gases were to fall to zero in the very near future, the
atmospheric residence time of greenhouse gases and the dynamics of the climate system would lead to further
anthropogenic climate change for many decades, with rising temperatures, changing precipitation and drought patterns,
more frequent and longer heat waves, and changes in other extreme climate events; sea levels would continue to
increase for several centuries.
• The length and quality of meteorological records differs substantially across Europe and globally. Short records limit the
detection of any long-term trends in extreme climate events. However, recent progress in extreme event attribution has
provided increasing evidence that anthropogenic climate change has substantially increased the probability of various
extreme weather events.
• The length, frequency and intensity of record-breaking temperature events is projected to increase on a global scale and
within Europe. Furthermore, available climate projections agree that the frequency of heavy precipitation and droughts
will increase in many areas in the 21st century.
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