// lecture 28

Question 1

there are two ice sheets in the world:

Answer 1

• Greenland: 7 m sea level equivalent

- Antarctica: 61 m sea level equivalent

Question 2

ice sheets gains

Answer 2

mass from snow on top and loses mass from melting and calving of icebergs.

• both loss and gain are increasing (increased precipitation at high latitudes).
• Greenland is losing mass though.

Question 3

overall, ice sheet losses

Answer 3

are exceeding gains in Greenland. Also losses from calving have accelerated in the last 10 years.

Question 4

Greenland is very big though -

Answer 4

it took tens of thousands of years to grow and at the current rates it would take many thousands of years to melt.
- now it’s contributing less than 10% of the sea level rise.

Question 5

Could Greenland ice loss accelerate?

Answer 5

maybe because more melting causes larger melt ponds meltwater can fall through the cracks and make it to the bedrock below.

• water dripping through could cause it to stick to the bottom less and flow faster (moulin - hole in ice).
• still unclear how relevant this is in causing recent accelerations of calving.

Question 6

A 2 C temp. rise would almost certainly

Answer 6

melt Greenland (eventually). this would likely take centuries though.

Question 7

Currently, Greenland melting is a

Answer 7

small contribution to sea level rise. this is likely to become a larger percentage in the future though.

Question 8

Antarctica has two giant

Answer 8

and many smaller, ice shelves.

Question 9

ice shelves

Answer 9

float, but are connected to the sheet.

Question 10

acceleration of melt has occurred in

Answer 10

w. antarctica recently. even more acceleration than in greenland.

Question 11

glaciers along W. Antarctica’s Amundsen Sea would

Answer 11

raise sea levels by 1.2 m if they melted.

Question 12

Antarctica has experienced relatively

Answer 12

small warming to this point, except the bits near South America.

• this was long ago forecast by climate models.
• strong jet stream keeps warmer air out of high latitudes.
• also ocean nearby takes up a lot of heat.
• no sea ice decrease has happened in Antarctica either. although, nearly all Antarctic sea ice melts each summer anyways.

Question 13

East Antarctic is not

Answer 13

warming, but West Antarctic is warming.

Question 14

Ice shelves reduce

Answer 14

calving by buttressing the ice.

Question 15

Antarctica’s icy surfaces are

Answer 15

very cold, but warming in the surrounding ocean is a problem for the shelf base.

Question 16

Ice shelf collapse can

Answer 16

then lead to acceleration of calving.

Question 17

Antarctica has the most

Answer 17

land ice (61 m of potential sea level rise), but East. Antarctica (the big part) is thought to be safe.

Question 18

West Antarctica is potentially dangerous:

Answer 18

5 m sea level rise.

• much of the w. antarctic ice sheet is under sea level so warmer ocean water could get in and melt much more after melting starts.
• recent studies (modeling) suggest that the melting of several large ice shelves is underway and unstoppable. Twaites would account for 3-4 m of the sea level rise.
• would take hundreds up to a thousand years to complete the process.

Question 19

UW and NASA work indicate that the Twaites ice shelf is already

Answer 19

unstable and will slide into the sea and melt, but it might take 500 years. 1-2 m of sea level.

Question 20

Twaites ice stream and Pine Island Glacier

Answer 20

are being undermined by ocean water.

Question 21

undermining process

Answer 21

each day 8 cubic miles of warm ocean water circulate under the Pine Island ice shelf. that water melts and thins the ice from beneath, causing the glacier to slide more quickly into the ocean.

Question 22

Presently melting mountain glaciers are contributing

Answer 22

more to sea level rise than Greenland and Antarctica combined. probably won’t be the case in 50 years (ice sheets are much bigger).

Question 23

mass balance of a mountain glacier:

Answer 23

gain due to snowfall, loss due to melting, sublimination.

Question 24

mountain glaciers don’t lose mass due to

Answer 24

breaking off chunks into the sea.

Question 25

mountain glaciers are rapidly

Answer 25

losing mass in most places. increased melt is outpacing snowfall in all but a few places.

Question 26

Himalayan glaciers may be melting from

Answer 26

black carbon deposition too.

Question 27

much of the snow on glaciers fell

Answer 27

a long time ago.

Question 28

melting of glaciers has revealed:

Answer 28

inca mummies, 550 year old ice man, planes from WWI and WWII, and a british plane from the 1940s that was rumored to have gold in its cargo.

Question 29

Kilimanjaro snow is

Answer 29

disappearing from sublimination because the atmosphere there is drier now. may still be caused by humans, but not directly by warming.

Question 30

permafrost

Answer 30

ground that’s frozen year-round. typically has a thin layer on top that melts in the summer: “the active layer.”

Question 31

ice is usually

Answer 31

underground. can be visible at river channel.

Question 32

drunken forest

Answer 32

ice expands upon freezing so this causes potholes in roads in winter, etc. Frozen ground causes weird formations. when permafrost thaws, trees point in all directions.

Question 33

widespread evidence of permafrost thaw causing:

Answer 33

damage to roads and buildings, methane to be liberated, vegetation to increase.

Question 34

to melt all the permafrost will take

Answer 34

centuries.

Question 35

permafrost thawing will be accelerated if

Answer 35

summer sea ice continues to retreat.

Question 36

will thawing permafrost release or take up greenhouse gases?

Answer 36

• snow-free season is short so plant growth rates are low. plants are cold adapted, which is their strategy for survival. not adapted for much competition. likely more vegetation will come in after thaw.
• soils are very carbon rich (decaying plants and animals). some fear methane release from thaw. others say greater vegetation will draw down CO2.

Question 37

methane hydrates (calthrates)

Answer 37

water ice cages enclosing methane. methane caged in a matrix oc ice at high pressure or low temp.
- carbon stored is 500-10,000 Gtons C (coal is 3,200 Gtons C). need high pressure - under ice massive in permafrost or ocean sediments.

Question 38

risk from methane hydrates

Answer 38

the risk form them this century is speculative. however, their release would possibly cause a positive feedback.

Question 39

55 million years ago methane hydrates appear to have been

Answer 39

released to the atmosphere at a time when the earth also warmed 2-3 C. there are pockmarks in ocean sediments as indication of past catastrophic release.

Question 40

snow covered land is by far the largest area component of the

Answer 40

cryosphere. snow is part of the ice albedo feedback cycle, such that if snow melts earlier in spring, it causes spring warming and soil drying. snow is an important reservoir for water in some communities.

Question 41

precipitation is increasing in

Answer 41

high latitudes with global warming. snow covered season is shorter but depth may be greater.