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availability and the potential for hydropower (often Ocean acidification
a feasible alternative to fossil fuel-based electricity The increased amount of carbon dioxide from human
generation which reduces CO
2
emissions). Climate activities that has entered the oceans via the atmos-
change is also expected to change the seasonal flows phere since about 1750 has made them more acidic,
in regions fed by melt water from mountain ranges, with an average decrease in pH (the measure of the
like the Hindu Kush, the Himalayas and the inter-tropi- acidity or alkalinity of a solution) of 0.1 units. Increasing
cal Andes. More than a sixth of the world’s population atmospheric CO
2
concentrations are causing further
lives in these regions. Two thousand million people acidification. Today the average ocean surface pH is
depend on the water provided by seven of the major about 8.1. Projections suggest a further acidification
rivers in Asia, all of them originating in the Himalayas. over this century, leading to a reduction in average glo-
bal surface ocean pH of between 0.14 and 0.35 units.
Changes in precipitation and temperature also affect This progressive acidification is expected to harm ma-
run-off and water availability. Run-off
5
will increase by rine creatures which form shells, for instance corals,
10–40 per cent by mid-century at higher latitudes and and the species which depend upon them.
in some wet tropical areas, and decrease by 10–30
per cent over some dry mid-latitude and tropical re- Studies published since the 2001 IPCC assessment
gions. Some semi-arid areas, for example around the report allow a more systematic understanding of the
Mediterranean, in the western USA, southern Africa timing and extent of impacts linked to different rates
and north-eastern Brazil, will have less water. Areas of climate change.
affected by drought are projected to increase, threat-
ening food, water, energy production and health by
increasing malnutrition and infectious and respiratory
Global ocean acidification
diseases. Large regional increases in demand for ir-
Oceanic CO
rigation water are projected.
2 Ocean water
concentration
acidity
The negative impacts on freshwater systems will
atm pH
outweigh the benefits of climate change. Available 380 8.14
research suggests a future increase in heavy rain-
fall events in many regions and some regions where
average rainfall is projected to decrease. This will
360 8.12
mean an increased flood risk. It is likely that up to
20 per cent of the world’s people will be living in ar-
eas where the river flood potential could increase
340 8.10
by the 2080s. More frequent and severe floods and
droughts will harm sustainable development, rising
temperatures will affect fresh water quality, and in
320 8.08
coastal areas rising sea levels will mean more saline
contamination of groundwater.
300 8.06
5. The water that falls to Earth and does not infiltrate the ground 1985 1990 1995 2000 2005 1985 1990 1995 2000 2005
or evaporate but flows over or through the ground to swell sur-
Source: IPCC, 2007.
face or ground water sources.
30 Planet in Peril
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