GPHY 314 Quiz: Week 7

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29 Dec 2020
Department
Course
Professor
WEEK 7: Contemporary Impacts of Climate Change
Global Sea Level Rise
Impact that has the most truly global effect Canada has large disparity between spaces
vulnerable to this change
Miami has a lot of areas close to sea level, where they’re seeing widespread flooding due
to tidal fluctuations
o Reflection of long-term increase at these sites in terms of water levels, and tidal
influence superimposed onto it
Important chart organizing hazards and
impacts we could expect to see
o Local mean sea level rise
Expect average position to
increase over time
o Local extreme sea level rise
Also expect more potential
for extreme events, and
regional dynamics that lead to
greater than global average
rise across certain areas
o Submergence of land a big hazard we face, also have to add that we get variations
in local sea level and variations with erosion of coastline, add in effect of
potential wave action
Take components together (northwestern Canadian Arctic and
northeastern Alaska) where these impacts of sea level rise and wave action
cause massive erosion to coastline, since majority of coastline permafrost
o If working in wage economy reliant on fisheries, changes to sea level impacts
where you can do those activities
Best estimates of amount of sea level rise (according to tidal records) about 25cm
o Satellite data shows broadly quite a fair bit of agreement there
Different data sources for satellite records since 1992 all come out to rate of change about
3.3 to 3.4mm/year
Pattern of global sea level rise since satellite-era (1993) focused on higher rates of sea
level rise at lower latitudes, and lower rates at higher latitude areas
o Slightly below 3.3mm/year moving down to areas around Antarctica and north-
Atlantic Basic vs southeast Asia where they’ve experienced faster sea level rise
Two main mechanisms
o Thermal expansion of oceans
Warmer fluids have more volume (steric changes)
o Mass changes to the oceans
Glaciers and ice sheet melt/discharge (mass changes)
Remember: sea ice changes do not really impact global sea level rise
o Expect thermal expansion to be occurring at relatively continuous rate
o Fairly large acceleration of mass changes in polar regions last couple of decades
Greenland, west/east Antarctica become accustomed to larger amount of
melt and discharge -> Expect alteration in sea level change in result of that
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Factors only occurring as dominant process for past decade, but see some
evidence sea level rise is accelerating
Trend line on satellite records -> See last few years have more and
more time above that trend line, could be indicative of acceleration
Can also use statistical methods to generate representation from curves
Estimate instantaneous rate of change long-term trend since
1990s, rate over last 5 years has increased to 4 or 5mm/year
Past period (2005-2015) -> Greenland ice sheet, Antarctic ice sheets, glaciers (outside
of ice sheets) have been contributing more to rise than thermal expansion on its own
o Areas there’s bound to be an uncertainty about, for how much impact they will
have in future
Why future sea level risk is complicated
o Integrated system and we have
contributions from glaciers, currents
and surface winds that make sea
level rise not as uniform as you’d
expect, certain areas warming faster
than others, gravitational pull
o On local scale, factors like how high
the waves are can make a difference
i.e. whether you have storm surges
o One of very challenging aspects is outside of these factors on local scale, there’s
even a lot of uncertainty on global scale how much temperatures will rise, and
amount of sea level rise that will result from that
Projection of changes in global mean temperature and seal level under RCP
emissions and Special Report on Emissions Scenarios, up to 2100
o Pretty big differences between RCP 8.5 and RCP
2.6/4.5 in terms of sea level rise
o Already seen 25cm increase since beginning of
our modern instruments measuring changes in
tidal environments
Tells us the scenario ranges from being x2
to x4 that amount over next 80 years
Implies fast rate of sea level rise
o For global mean sea level, RCP 2.6/4.5 see pretty
consistent agreement/overlap between AR5 and
SROCC but as you get to RCP 8.5, start to disagree more
Reflects new understanding of factors that may impact rise in future
Climate models show large difference from 2081-2100 compared to 2046-2065
o A lot of sea level rise expected to occur near the end of the century, especially on
the more extreme values
o Portions of Canada, parts of southeastern US, Southern Africa and Australia near
areas where rate expected to be particularly high (exceeding 1.2m in some
localized areas)
o Over Hudson’s Bay, sea levels still expected to be falling
o When there’s temperature change, takes a long time for sea levels to equilibrate
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o Even as far out as 2300, still seeing sea level rise under both
RCP 2.6 and RCP 8.5
Under RCP 8.5, expected 2-5m of sea level rise
Majority from land ice and melt from ice sheets
Under RCP 2.6, expected 50cm of sea level rise
o Extend into 2500, range expands up to potentially 7m of sea level rise
Long-term sea level change
o Pretty substantial rise last 20,000 years,
especially associated with
shrinkage/disappearance of Laurentide ice sheet
o Under current scenarios, expecting pretty
dramatic rise if we go on extreme end of things
o Sea level change rate (m/100 years) at bottom
depending on scenario we take, could be going
back to rate of change similar to when we had
melting of Laurentide ice sheet in response to insulation changes
Graphic depicting enhanced scenario
o Sea level rise projections into future are not necessarily reflecting
all the ice loss that could occur in Antarctica
o Assumption that it will not lose much ice over next century, but
we do see some evidence that this could be a possibility
o This graphic includes larger amount of ice discharge from
Antarctica -> Suddenly massively bump up amount of rise
Using enhanced scenario for calculations of projected rise by 2100
o Low (RCP 2.6) likely rise 44mm
o Medium (RCP 4.5) likely rise 53mm
o High (RCP 8.5) likely rise 74mm
o Enhanced (RCP 8.5 + Antarctic ice sheet reduction) likely rise shoots to 139mm
IPCC reports have largely been within grey ranges on graphic
o But lots of recent studies from independent researchers point to a
rise that is a lot larger than the IPCC range
o Even those within the range are on the higher end of it
o Show how much uncertainty there is with this
From Global to Regional Sea Level Rise
Key challenges assessing local SLR potential
o Future global sea level rise is highly uncertain
Highly scenario dependent (i.e. RCP 2.6 to RCP 8.5)
Hard to predict future sheet losses (is west Antarctica a large contributor?)
o Sea level rise is not uniform through time and space
Different rates of warming across the oceans (thermal expansion)
Regional impacts of gravitational pull of ice sheets
If west Antarctica loses a lot of ice, it’s exerting a lot less
gravitational pull on northern hemisphere and low latitudes
If Greenland loses a lot, it pulls less on oceans at southern
hemisphere
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