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Module We are already committed to changes based on past emissions of GHGs into the atmosphere, and it is
the future that is being decided. Some of the observed changes include (UNEP, 2009):
? Of the last 12 years (1995-2006), 11 are among the 12 warmest since records began in 1850. The
temperature increase is widespread across the world but is most marked in the northern polar
regions.
? Sea levels across the globe have risen in a way consistent with the warming. The total global rise in
9-12 December, 2013 ? Satellite data recorded since 1978 show the annual average Arctic sea ice extent has shrunk by 2.7
the twentieth century amounted to 17 centimetres.
per cent each decade, with larger decreases in summer. Mountain glaciers and average snow cover
have declined in both hemispheres.
From 1900 to 2005, precipitation (rain, sleet and snow) increased significantly in parts of the
?
Americas, northern Europe and northern and central Asia resulting in floods, but declined in the
Sahel, the Mediterranean, southern Africa and parts of southern Asia, causing serious droughts.
Furthermore, floods and cyclones have occurred more frequently in the last 30 years, while other
disasters not influenced by climate (such as earthquakes) are constant over decades. However, a
lack of systematic high quality observation before satellite observations makes it difficult to detect
a long-term trend (Figure 2).
When identifying impacts of global changes, including climate change, we are concerned about changes
happening at a fast pace that would make it impossible for humans and ecosystems to adapt. Although
Earth’s complex systems sometimes respond smoothly to changing pressures, it seems that this will
prove to be the exception rather than the rule. Many subsystems of Earth react in a nonlinear, often
abrupt, way, and are particularly sensitive around threshold levels of certain key variables. If these
thresholds are crossed, then important subsystems, such as a monsoon system, could shift into a new
state, often with deleterious or potentially even disastrous consequences for humans (Rockstr?m, et
al., 2009).
Critical elements of climate change impacts include the possibility of sudden changes linked to
thresholds or tipping points, especially for vulnerable complex systems; a tiny perturbation can
qualitatively alter the state or development of a system, leading to large and widespread consequences.
Examples of such changes include climate impacts, such as those arising from ice sheet disintegration
and leading to large sea-level rises or changes to the carbon cycle, or those affecting natural and
managed ecosystems, infrastructure and tourism in the Arctic (Schneider, et al., 2007).
When we are looking into the future, a wide range of impacts attributed to climate change are projected.
Even if GHG and aerosol concentrations were kept constant at 2000’s levels, some anthropogenic
14 Volume Two - Themes
Vulnerability and Impact assessments for Adaption to Climate Change (VIA Module)