Climate
Change and
its Effects on
the Global
Ocean
Nicole Del Monaco
Physical Processes and Feedback: Overview
•
The key issue with climate change to be addressed is the
response to the changes in forcing i.e. concern on large-scale
global circulation in the atmosphere and ocean. This forcing
determines overall climate sensitivity
•
Within atmospheric and oceanic circulation, there are many
coupled, comprehensive, large-scale dynamical feedbacks
•
These large-scale dynamical feedbacks are coupled with small
scale processes within the climate system
•
The various feedbacks in the climate system may amplify
(positive feedbacks) or diminish (negative feedbacks) the
original response
•
Take home point: Forcings, feedbacks and the dynamics of the
climate system determine how much and how fast the climate
changes.
Atmospheric Processes and Feedbacks:
Water Vapor Feedback
•
Generally, Earth’s radiation balance is closely achieved since the
Outgoing Longwave Radiation (OLR) equals the Shortwave
Absorbed Radiation (SAR) received at high energy from the sun
•
An increase in the amount of greenhouse gases contained in
Earth’s atmosphere would reduce the emission of OLR. To
compensate, the climate achieves a new equilibrium by warming
until the OLR increases enough to balance the SAR
•
Enhanced warming of the atmosphere
enhanced
evaporation
more water vapor
further warming
further evaporation
ever more water vapor
•
Water vapor is a very powerful greenhouse gas. As water vapor
increases as the climate warms, the additional reduction of OLR
requires a new equilibrium to be met. Referred to as a positive
feedback loop
Figure 1
https://www.eeducation.psu.edu/drupal6/files/meteo469/lesson01/p_feedback.gif
Atmospheric Processes and Feedbacks:
Ice-Albedo Feedback
• Ice has a high albedo. As ice expands, more solar radiation is
reflected to space, less is absorbed by the surface, and
temperatures decrease.
• Cooler temperatures
more ice growth
more reflection
of solar radiation back to space
even cooler temperatures
• Positive feedback loop
• However, can also have opposite effect (similar to cloud
feedback) – damped feedback
• Ice melts
solar radiation will be absorbed by surface
raises temperature
more ice melts
• This feedback may act more quickly over oceans then land
because sea ice melts faster than large continental sheets
Figure 2
http://www.grida.no/climate/ipcc_tar/wg1/pdf/tar-07.pdf
Atmospheric Processes and Feedbacks:
Cloud Feedback
•
Clouds are formed by condensed water vapor. They therefore
become a problem because they effect OLR in the same way
that water vapor does, increasing the temperature of the
atmosphere. However, clouds also reflect incoming solar radiation
because of its high albedo.
•
•
However, recent research suggests that cloud feedback is
generally warming
•
•
•
Clouds have a warming and cooling effect
There was hesitance because of cloud changes near the equator, tropics,
and subtropics.
Data and research conducted suggested that warming is occurring in all of
these regions
To further prove that clouds have a generally positive feedback:
Cloud Feedback
Figure 5
Figure 3
Figure 4
http://www.sciencemag.org/content/325/5939/460.full#F2
http://www.sciencemag.org/content/325/5939/460.full#F2
Figure 4A and 4B represent climate shifts
.
between
the years
1976-1978,over
while
figures
Figure 3 represents
data
for a
typical
El Nino with the
Enhanced
upper-level
cloud
cover
is consistent
weakening
of subsidence
the
NE 2C
and 2D represent climate shifts of 1997-1998
event
Pacific.
http://www.skepticalscience.com/graphics/Cloud_Feedback_500.jpg
Figure 6
http://journals.ametsoc.org/doi/pdf/10.1175/JCLI-3243.1
Feedback Loops
•
Only a fairly small fraction (40 W/m2 or
10.3%) of the 390 W/m2 of infrared
radiation emitted from Earth's surface
makes it directly into space without first
being trapped by various greenhouse
gases in the atmosphere. In other words,
about 89.7% of the outgoing infrared
radiation is affected by the greenhouse
effect. Water vapor "intercepts" about 32%
to 59% (36% to 66% times 89.7%) of the
outgoing infrared. Clouds "intercept"
about 17% to 27% (19% to 30% times
89.7%) of the outgoing infrared. Water
vapor plus cloud droplets combine to
"intercept" about 59% to 76% (66% to 85%
times 89.7%) of the outgoing longwave
radiation.
•
The bottom line? Water vapor and clouds
already play a huge role in producing the
greenhouse effect, and thereby
Figure 7
http://www.windows2universe.org/earth/climate/warming_clouds_albedo_feedback.html
Oceanic Processes and Feedbacks:
Thermohaline Circulation
Figure 8
http://www.windows2universe.org/earth/Water/images/thermohaline_circulation_conveyor_belt_big.gif
Oceanic Processes and Feedbacks:
Thermohaline Circulation
• A special concern are possible reductions of the Atlantic THC caused by warming
and freshening of high latitude surface water associated with global warming
• Increased air moisture, heat, and precipitation in pole regions and the resulting
increase in river discharge into the Arctic Ocean can lower salinity and cause
warmer surface temperatures, as well as create weaker water circulation in the
Atlantic Ocean. This overall contributes to the reduction of water density in the
formation regions of NADW
Figure 9
http://www.grida.no/climate/ipcc_tar/wg1/pdf/tar-07.pdf
• Damped feedback: low latitude
advection
increased sea
surface temperature
reduction
in the Atlantic THC
• Self-reinforced feedback: low
latitude advection
increased
evaporation
increased sea
surface salinity
normal Atlantic
THC (sinking at poles)
Oceanic Processes and Feedbacks:
Thermohaline Circulation
•
No such deep overturning occurs in the North Pacific,
where surface waters are too fresh to sink.
•
Strong cooling also occurs in the Bering Sea in the North
Pacific, but the lack of a meridional land barrier (i.e.
MidAtlantic Ridge) in the Southern Ocean prevents the
existence of strong east–west pressure gradients needed
to balance a southward geostrophic surface flow
Works Cited
•
Clark, Peter U., Nicklas G. Pisias, Thomas F. Stocker, and Andrew J.
Weaver. Science 415 (2002): n. pag. Nature. Web.
•
Clement, Amy C., Robert Burgman, and Joel R. Norris. "Observational
and Model Evidence for Positive Low-Level Cloud FeedbackScience."
Science 325.5939 (2009): 460-64. Print.
•
"Global Warming, Clouds, and Albedo: Feedback Loops." Global
Warming, Clouds, and Albedo: Feedback Loops. N.p., n.d. Web. 06
Dec. 2012.
•
Stephens, Graeme L. "Cloud Feedbacks in the Climate System: A Critical
Review." Journal of Climate 18 (2005): n. pag. Web.
•
Stocker, T. F. Physical Climate Processes and Feedbacks. Rep. no. 7.
IPCC, n.d. Web.
•
"Wetter Arctic Could Influence Climate Change, Study Finds."
ScienceDaily. ScienceDaily, 05 Sept. 2012. Web. 06 Dec. 2012.
•
"What Are Positive Feedbacks?" NOAA Paleoclimatology Program. N.p.,
20 Aug. 2008. Web. 06 Dec. 2012.