Climate change in the UKOTs an overview of the ... - JNCC - Defra

Number of reef provinces with
moderate to severe bleaching
the trade winds that blow from east to west
along the equator in the Pacific decrease in
intensity (this is the Southern Oscillation)
and bring about an increase in the ocean
temperature. This in turn affects where
storms occur along the equator and triggers
ripple effects worldwide.
Under normal conditions, the westward
blowing winds push the ocean’s water
towards western Pacific. In the deeper
eastern Pacific, cold water is pulled from the
ocean’s depths to replace the water that is
blown west. The normal ocean temperature
balance is therefore warm water (30°C) in
the west and cold water (22°C) in the east.
El Niño events occur about every two to
eight years and are considered a normal
phenomenon. In an El Niño event, the
trade winds weaken and less water is
pushed westwards. Cold water in the
eastern Pacific is not pulled up, making
the water in that part of the ocean warmer
than usual. The warmer water contributes
to the weakening of the winds in a self-perpetuating
or positive feedback cycle.
El Niño events generally cause droughts in
several regions, including the Caribbean,
32
12
10
8
6
4
2
0
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
Year
Figure 3. Number of reef provinces bleaching since 1978.
Arrows indicate strong El Nino years. While some of the
trend can be explained by observer bias, this factor does
not completely explain the increasing trend with time.
Source: Hoegh-Guldberg 1999
the western Pacific, Southeast
Asia and Southern Africa. They
are also associated with coral
bleaching, a phenomenon
brought about by high water
temperatures that cause corals
to lose the symbiotic algae that
boost their metabolism, respiration,
waste excretion and growth
rate. Very severe coral
bleaching occurred in the tropical
Indian Ocean in 1998, the
hottest year on record to date
and the year of the strongest El
Niño recorded. That year, ocean
temperatures were between 3°C
and 5°C above normal (World
Wildlife Fund and McGinley,
2007).
El Niño events are generally followed by a
period of opposite conditions called La
Niña. In La Niña conditions, the water in the
eastern Pacific is cooler and the winds that
blow from east to west are stronger than
normal. In most locations, the phenomenon
is associated with increased rainfall. Preliminary
findings suggest that climate change
will cause El Niño events to increase in frequency.
When the El Niño events are superimposed
on the upward climate
change-induced temperature trends, phenomena
such as coral bleaching will
become more frequent There appears to
be a correlation between strong El Nino
events and severe coral bleaching. (Figure
3). It has been suggested that bleaching
may become an annual event by 2020
(Hoegh-Guldberg, 1999).
2.3 The science behind
global climate change
What is climate change?
Climate change is any significant modification
in the climate of a zone or region
over time. There are natural processes of
climate change that have been taking