SUMMARY:
None of the following
scientific determinations
support the popular belief
that coral reefs are in
grave danger due
to human activity
and global warming.
Modern corals have existed
for millions of years longer
than humans have existed.
They’ve survived
brief warm periods,
and long cold periods.
DETAILS:
In the Western Indian Ocean,
sea surface temperatures (SSTs)
have cooled by -0.8°C
since the 1980s
( Watanabe et al., 2019 ).
Exposure to extremely low
temperatures cause coral
bleaching and high mortality
rates, just as much as
warm SSTs do.
Colder periods have been
documented to coincide with
dramatic reef
“switch-off” phases
( Yan et al., 2019,
Humblet et al., 2019 ).
In many of the regions
where reef-building corals
are common, there has been
no significant increase
in sea surface temperatures
(SSTs) since the 1980s.
In fact, large sections
of the Indo-Pacific
have been cooling.
Watanabe et al. (2019)
have found corals
have been exposed
to a cooling trend
of -0.03°C per year
for the past 26 years
(-0.78°C) in the
Western Indian Ocean.
Great Barrier Reef corals
have also not experienced
any detectable SST warming
since 1990
(Brenner et al., 2017 ).
The Western Pacific Ocean
has been cooling
in recent decades
( Deng et al., 2013,
as shown in
Wei et al., 2015 ).
Coral bleaching occurs
during unusually cood
temperature conditions
It is commonly thought
coral bleaching events
are directly tied to
unusually warmig SSTs
during the warming phase
of El Niño events.
Recent research indicates
bleaching events were
more common during
the 1750s and 1890s
than in recent decades
( Kamenose and Hennige, 2018 ).
The cooler Little Ice Age SSTs
may have had decades
of mass coral bleaching
because bleaching can occur
in unusually cool water too.
( Saxby et al., 2003,
Hoegh-Guldberg et al., 2005 ).
Corals experience bleaching
and extremely high death rates
from exposure to SSTs
that dip below 14°C.
For example, a 2003 (August)
cold-water event
( 13.3°C, 9°C wet bulb )
wiped out all but 12% of corals
living near Heron Island
( Hoegh-Guldberg et al., 2005 ).
Corals are harmed
by falling sea levels,
by exposing
shallow-dwellers
to UV radiation
During El Niño events,
the slowing of tropical Pacific
trade winds enhance
the clarity of surface waters.
That allows more harmful
solar UV radiation to penetrate
into the ocean, bleaching corals
( Gleason and Wellington, 1993 ).
Shallow-dwelling corals
are also exposed to harmful
UV radiation when sea levels fall.
During the latest (2015-2016) El Niño,
corals in Indonesia were already
bleached due to a locally rapid
sea level fall before the higher
El Niño-induced SSTs could
have an impact
( Ampou et al., 2017 ).
Dechnik et al. (2017)
determined that neither
high sea surface temperatures,
cyclone activity, or El Niño
variability could be responsible
for centennial-scale coral
“turn-offs” (cessations
in growth) during
the Holocene.
Instead they attribute
Great Barrier Reef
growth hiatuses to
falling sea levels
and “relatively cold” SSTs.
Corals thrive and
expand their range
during warm periods.
During the last
glacial maximum
( 20,000 years ago ),
when sea levels were
120 meters lower
than they are now,
and ice sheets covered
much of the Northern
Hemisphere, corals
were very limited in their
ecosystem ranges.
As sea levels rose at rates
of up to six meters per century
( 60 mm/yr ), reef growth and
recolonization was “vigorous”
( Humblet et al., 2019 ).
The reef growth trends
continued through
the Early Holocene
as the Earth warmed
and sea levels rose.
Yan et al. (2019) determined
that reef “switch-on”
(growth) phases
occurred during
warm periods
such as the
Holocene Thermal
Maximum
( 2.0°C warmer than today ),
the Medieval Warm Period,
and even the current
Modern Warm Period.
Reef “switch-off” phases
( hiatuses and declines )
occurred during the Dark Age
Cold Period and the Little Ice Age,
and were associated with
falling sea levels.
