Sully, S., Burkepile, D.E., Donovan,
M.K., Hodgson, G. and van Woesik, R.
2019
"A global analysis
of coral bleaching
over the
past two decades."
Nature Communications 10:
1264, doi: 10.1038/s41467-019-09238-2.
NOTE:
It's rare for scientists to admit
a global warming-related model
has been invalidated
by actual observations,
but that's what Sully et al.
have done.
The team of five researchers
set out to "synthesize field
observations of coral bleaching
at 3,351 sites in 81 countries
from 1998 to 2017, and use
a suite of environmental
covariates and temperature
metrics to analyze bleaching
patterns," hoping their findings
would be used to improve
the next generation of models
predicting coral bleaching.
SUMMARY:
Model projections of future
coral reef demise have been
invalidated by observationals
showing that present coral
populations have a
higher thermal threshold
for bleaching, giving them
an increased likelihood
of persisting
well into the future.
Sully et al. (2019) write:
"compared with
coarse-grained
global models
that predict
minimal coral survival
in the tropical oceans
within the next 100 years,
recent field work shows
considerable geographic
variability in both
temperature stress
and coral survival."
And they add that:
" ... this mismatch
between global models
and field results
underscores the
urgent need to develop
better models that
accurately predict
the geographical
heterogeneity
of coral bleaching
as corals respond
to ocean warming."
DETAILS:
Sully et al. report that:
"significantly more
coral bleaching
occurred at
mid-tropical
latitude sites,
between 15 and 20°
north and south
of the Equator
than in the
equatorial regions,
where coral diversity
is highest."
Another interesting finding
is the observation that
in the past decade,
"the onset
of coral bleaching
has occurred
at significantly
higher sea surface
temperatures
( ~0.5 °C )
than in the
previous decade."
Sully et al. write that
"at the thousands
of sites surveyed,
the mean sea
surface temperature
recorded during
coral bleaching
in the first decade
of the dataset,
from 1998 to 2006,
was 28.1 °C,
whereas the
mean sea surface
temperature recorded
during coral bleaching
in the second decade,
from 2007 to 2017,
was 28.7 °C."
The researchers say it
" ... suggests that
past bleaching events
may have culled
the thermally susceptible
individuals, resulting in a
recent adjustment
of the remaining
coral populations
to higher thresholds
of bleaching temperatures,"
or that
"coral communities
also may have
acclimatized to
increasing sea surface
temperatures."