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Lecture 26

EPS 7 Lecture Notes - Lecture 26: Sea Level Rise, Tacticity, Thermal Expansion

1 Page
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Fall 2017

Department
Earth And Planetary Science
Course Code
EPS 7
Professor
David Romps
Lecture
26

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Lecture 25 10/25/17
Ice and sea level: Where to invest in property
Paleo sea level data exhibit no discernable change in sea level over the past 3000
years
- Salt marshes and tide gauges
- Tide gauges
- Satellite altimetry
- Everything together
Observations show a sea level rise of 0.3 m (a foot) so far
With sudden warming, sea level rises at an initial rate of roughly 3mm/year/K
- T = +1K, 3mm/ year
- T = +2K, 6mm/year
- T = +3K, 9mm/year
Climate has warmed (on average) +1K = 0.3m
In the U.S. and most of Europe, sea level rise is around the global average of
3mm/year
In parts of Canada and northern Europe, sea level is falling due to isotactic rebound
During a glacial vs. during an interglacial
Isotactic rebound in mm/year (blue is positive)
For a sustained amount of global warming, the committed sea-level rise is the
eventual amount of rise you will get once the ocean and ice sheets have equilibrated
to the new global temperature
To understand sea-level rise, you must understand history
Forecast year 2100, cant tell
With warming, the committed sea-level rise is about 6m/K (what is coming to you)
- T = +1K, 6m
- T = +2K, 12m
- T = +3K, 18m
- If the mean global warming hangs out at +3K for thousands of years, roughly what
is the final sea-level rise?
20m (very uncertain)
- What is the timescale for adjustment to the new sea level?
We have two numbers
3mm/year/K and 6m/K
3mm/year/K = 3mm/K/year
6m/K = (6 m/K) X (1000 mm/m) = 6000 mm/K
(6000 mm/K) / (3mm/K/year) = 2000 years
Timescale for ice sheets to respond to warming is about 2000 years
PCP 8.5, sea level will have risen about 1m in 2100
-What contributes to sea level rise?
- Thermal expansion is currently contributing about half of the sea-level rise
- How much will melting Arctic sea ice contribute to sea-level rise?
Practically zero
- Why?
Archimedes principle says that a floating objects displaces its weight in water
When floating ice melts, it simply fills out the space it takes
Only the ice out of the water contributes to sea level rise
When an ice sheet melts, it pours into the ocean and raises the sea level
GRACE observations and Antarctic Ice Mass Change

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Description
Lecture 25 102517 Ice and sea level: Where to invest in property Paleo sea level data exhibit no discernable change in sea level over the past 3000 years Salt marshes and tide gauges Tide gauges Satellite altimetry Everything together Observations show a sea level rise of 0.3 m (a foot) so far With sudden warming, sea level rises at an initial rate of roughly 3mmyearK T = +1K, 3mm year T = +2K, 6mmyear T = +3K, 9mmyear Climate has warmed (on average) +1K = 0.3m In the U.S. and most of Europe, sea level rise is around the global average of 3mmyear In parts of Canada and northern Europe, sea level is falling due to isotactic rebound During a glacial vs. during an interglacial Isotactic rebound in mmyear (blue is positive) For a sustained amount of global warming, the committed sealevel rise is the eventual amount of rise you will get once the ocean and ice sheets have equilibrated to the new global temperature To understand sealevel rise, you must understand history Forecast year 2100, cant tell With warming, the committed sealevel rise is about 6mK (what is coming to you) T = +1K, 6m T = +2K, 12m T = +3K, 18m If the mean global warming hangs out at +3K for thousands of years, roughly what is the final sealevel rise? 20m (very uncertain) What is the timescale for adjustment to the new sea level? We have two numbers 3mmyearK and 6mK 3mmyearK = 3mmKyear 6mK = (6 mK) X (1000 mmm) = 6000 mmK (6000 mmK) (3mmKyear) = 2000 years Timescale for ice sheets to respond to warming is about 2000 years PCP 8.5, sea level will have risen about 1m in 2100 What contributes to sea level rise? Thermal expansion is currently contributing about half of the sealevel rise How much will melting Arctic sea ice contribute to sealevel rise? Practically zero Why? Archimedes principle says that a floating objects displaces its weight in water When floating ice melts, it simply fills out the space it takes Only the ice out of the water contributes to sea level rise When an ice sheet melts, it pours into the ocean and raises the sea level GRACE observations and Antarctic Ice Mass Change
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