Transcript Document

Equivocal evidence for a thermostat and unusually
low levels of coral
bleaching in the Western Pacific Warm Pool
and
Snakes tell a torrid tale
Ruben van Hooidonk and Mathew Huber
Nathaniel Shutt
Atmospheric Science Major
Coral Bleaching
-Caused by an abnormal increase in Sea Surface
Temperatures(SST)
-Corals release symbiotic algae that results in a white or
“bleached” appearance
Thermostat-bleaching hypothesis
-A naturally occurring thermostat over the western pacific
warm pool is limiting the sea surface temperature between 2931 degrees Celsius that is in turn reducing coral bleaching
Importance of Research
-Global warming could have a detrimental impact on corals in
the next 50 years due to coral bleaching
-A significant loss of coral could result in a crippling of small
fish who rely on corals to survive
The Data
-Hadley Centre Sea Ice and Sea Surface Temperature
data set (HadISST)
- Extended Reconstructed Sea Surface Temperatures,
version 3 (ERSST.v3)
Conditions
1. In regions where the SST is 29°C or warmer the
trend in max SST should be zero or negative
2. Negative feedback on SST should be unique to
warmest areas of the ocean
3. Anomalously low bleaching must be observed in the
regions of the WPWP where the average max SST I
greater than 30°C
4. A physical basis for the thermostat has to be
identified
5. Evidence of the thermostat should be in geological
archive
The Results
Condition 1(SST trend should be zero or negative)
- satisfied over the small eastern region of the WPWP
where the trend in max SST is close to zero or
negative
The Results
Condition 2 (Negative feedback unique
to warmest areas of the ocean)
- negative feedback is not unique to
the warmest regions of the ocean
- Implies another mechanism other
than a “thermostat” may be at
work
Condition 3(Anomalously low bleaching)
-Hooidonk and Huber discovered an alarming amount of
unobserved coral reefs in the WPWP that
could result in a bias for low bleaching
-Had to estimate the amount of bleaching that
occurs in the WPWP
-Estimations based on observed
monthly thermal thresholds for reefs
nearby with observations of bleaching
-Estimations on coral bleaching are not
anomalously low
Condition 4(A physical basis for the thermostat)
- A physical basis for a true hard limit or thermostat has
yet to be proven valid
- Recent work using a coupled atmosphere-ocean model
indicates that the observed limit of tropical SST will rise
in a warming world
- While a mechanism is definitely slowing the warming of
the tropics there is little evidence for a mechanism that
sets a hard limit on SSTs
Condition 5(Evidence of the thermostat in geological archives)
- Analysis of unaltered planktonic foraminifer shells
showed that tropical SST did increase to 30 –35°C between
33 and 56 million years ago
-Geological archives do not support evidence of a thermostat
Conclusion
-Not enough conditions are meet to suggest a natural
thermostat over the WPWP is the cause of a lower rate of
coral bleaching in the WPWP
- Likely cause for the low number of reports of coral
bleaching in the WPWP is due to its remoteness
-Coral bleaching will continue to occur with a possibility of
a record setting event in the next 30 to 50 years
- Other evidence for a potential “thermostat’?
SNAKES!
Snake palaeothermometry
-Scientists relate size to minimum annual
temperature
-Use empirical relationship between temperature
and size derived from modern organisms
-Scientists used the fossil vertebrae of a giant snake discovered in
Columbia aged between 58 million and 60 million years old
-It was estimated that the giant snake required
minimum temperatures of 32–33 °C, much warmer than values today
-The snake observed was an
estimated 13 meters(~43ft) long
and weighed more than
one tonne(2,204.6 pounds)
-Scientists compared values derived
from fossil vertebrae and climate
models from 58 million years ago and
found several similar results for the
average surface temperature
-Snake palaeothermometry provides evidence against a
thermostat with much of the estimated values well above current
mean surface temperatures
-Snake palaeothermometry must be proven to be a valid way of
estimating the surface temperatures before any results are taken
as hard evidence against a potential thermostat
Summary
-Very little evidence today for a “thermostat” limiting the sea surface
temperatures over the tropics
-Without a thermostat to protect coral reefs from bleaching we must
turn to ourselves to help lessen the magnitude of the global warming
trend
-While snake palaeothermometry is good in theory more research is
needed to prove the validity of the process
-More observations are needed to conclude that there is not a
abnormal low rate of bleaching in the WPWP. Is so what
mechanism is responsible?
-Continue to improve snake palaeothermometry through
research in hopes of better understanding if a true
“thermostat” exists