1. Glaciers
Jus’ chillin’

2. Formation Successive years of snowfall build up.
Under huge weight, air bubbles are squeezed out, leaving rock-hard glacial ice.
As it becomes denser and has fewer bubbles, the color changes from white to blue.

3. Bro, does this look ablated?
Zone of accumulation: High up a mountain, it’s colder, so more snow falls than melts and the glacier thickens.
Zone of ablation: Lower down the slope, there is more melting than deposition, so the glacier thins.

4. Ice sheets
Earth currently has two ice sheets – in Greenland and Antarctica.
During the last glaciation, Scandinavia and North America had ice sheets, too.
The Greenland ice sheet is 3x the size of Texas.
The Antarctic ice sheet is the size of the US and Mexico combined.

5. Last glacial maximum
Note lower sea level changed coastlines. Ice covered 32% of the land surface. Today it’s 10%. Temperature was 8C below 20th century average.

6. Ebb and flow
You have been born during an interglacial (a warm period in-between ice ages).
There have been 8 ice ages over the last 750,000 years, caused by small changes in Earth’s orbit. (Milankovitch cycles, if you’d like to learn more).

7. Good news/bad news
If civilization hadn’t developed, we would expect to slip into a new ice age sometime in the next 20,000 years.
Industry has put so much CO2 into the atmosphere that we don’t have to worry about that.
But we built our cities and farms in places that made sense for the climate of the last several centuries.

8. Ice sheets
The Greenland ice sheet contains enough water to raise global sea level by 6m.
The Antarctic ice sheet contains enough water to raise sea level by 60m.
So if the whole thing went, we’d have serious problems adapting.

9. Ice sheets
Satellite observations beginning in 1979 show that melting in Greenland is accelerating, and overall the ice sheet is losing mass.
The West Antarctic Ice Sheet (WAIS) is also thinning.
East Antarctica, being higher in elevation and much colder, appears stable for now.

10. Greenland melt zones
spark.ucar.edu

11. Greenland melt zones Ice sheet mass changes 2003-2009
Mass is being lost at lower elevations, while the higher ground is cooler, allowing it to stay in mass balance.

12. It’s…alive!
Well, not really. But ice sheets and glaciers do flow downhill under their own weight.
When they reach the sea, the ice sheet is called an ice shelf (no land under it) and huge chunks break off, or calve (like a cow).
These mountains of ice are called icebergs.

13. It’s…alive!
Flow rates change as climate changes. Melting ice flows into cracks in the ice sheet called moulins.
This meltwater lubricates the base of the glacier and causes flow to speed up.