Sea level rise These ecosystem changes will be accompanied by
Because our understanding of some important caus- shifts in the geographical ranges of both animal and
es of sea level rise is too limited, the IPCC is careful plant species, with mainly harmful consequences
in making predictions: it does not provide a best esti- for the natural world and for the goods and servic-
mate or an upper limit of the rise to be expected. The es which ecosystems provide – like water and food.
range of rise projected for 2090–2099 is from 18 to 59 Many ecosystems are “likely” to exhaust their capaci-
cm relative to 1980–1999, but this does not include ties to cope with changes inflicted on them by climate
the possible acceleration of ice flow from the polar ice change and the upheavals associated with it.
sheets and is therefore not an upper boundary. Other
factors contributing to uncertainty in this area include Ecosystems will probably find their net carbon up-
feedbacks between the climate and the carbon cycle take peak before the middle of the century and then
and the expansion of ocean water due to warming weaken or even reverse, which would amplify climate
(“thermal expansion”). change (a positive feedback).
The shrinking of the Greenland ice sheet is project- Approximately 20–30 per cent of species are at in-
ed to contribute to rising sea levels until after 2100. creased risk of extinction if global average warming
Models suggest a nearly complete melting of the exceeds 1.5–2.5°C. As global average temperature
ice sheet. increase exceeds about 3.5°C, model projections
suggest significant extinctions of 40–70 per cent of
The Antarctic ice sheet is projected to remain too cold known species around the globe. This is one of the
for widespread surface melting: instead, it is expected irreversible impacts of climate change.
3
to grow because of increased snowfall. But a net loss
of ice from Antarctica could still be possible, depend- Food security and human health
ing on the extent and pace at which ice moves from The effects of more frequent and intense extreme
the land into the sea. weather events will cause emergencies and reverse
progress towards development. Extreme events cou-
Ecosystems
2
pled with sea level rise, are expected to be mainly
Since the IPCC’s Third Assessment Report, confi- adverse for humans. Food is an obvious worry. In
dence has increased that a 1–2°C increase in global higher latitudes there may be an initial slight increase
mean temperature above 1990 levels (about 1.5–2.5°C in crop productivity for temperature rises below 3ºC,
above pre-industrial levels) poses significant risks to to be followed by a decrease in some areas. For
many unique and threatened systems, including many lower latitudes, productivity may decrease for even
biodiversity hotspots. small temperature rises.
2. An ecosystem is a natural unit consisting of all the plants, ani- 3. Many species have evolved to live in a particular and often
mals and micro-organisms in a defined area functioning together narrowly-defined environment. As temperatures rise and other
with all the non-living physical factors of the environment. effects of a changing climate intensify, their environments are
likely to change too quickly for them to either adapt to or to
migrate to somewhere more suitable.
Projected climate change and its impacts 27
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