Lec 10 - Recent Climate Changes

Question 1

Why might sea level appear to change differently depending on where you are?

Answer 1

ice sheet rebound
- northern areas are rising, areas just south of ice sheets are sinking
- ocean basins are sinking from the weight of extra water, locally counteracting SOME sea level rise

Question 2

Why are our records of the past 200yrs of CC so accurate?

Answer 2

• thermometers
• regular monitoring and record keeping
• remote sensing (recent)

Question 3

Aside from added water, what might affect sea level rise?

Answer 3

water expanding with temperature!

Question 4

What recent climate changes do we have records of?

Answer 4

• sea level
• mountain glaciers
• subsurface ground temperatures
• sea ice

Question 5

How are subsurface ground temperatures changing?

Answer 5

getting warmer
- warming is getting deeper into the earth

Question 6

What does the positive phase of the Pacific Decadal Oscillation look like?

Answer 6

• warmer waters in the tropics and NA, cooler in North Pacific

Question 7

What does the negative phase of the Pacific Decadal Oscillation look like?

Answer 7

• cooler waters in the tropics and NA, warmer in the North Pacific

Question 8

Why don’t most natural factors explain recent climate changes?

Answer 8

• tectonics happen over too short a time scale
• orbital changes also too slow
• sun spots are too subtle to be responsible
• El Nino effects are too temporary
• volcanism - most large eruptions cause short temporary cooling (not what we are seeing)

Question 9

What 2 phases of anthropogenic C additions are there?

Answer 9

1. late 1700s - land clearing, burning (farmland expansion and Industrial Revolution)
2. Post-1900 - fossil fuel reservoirs (coal -> oil and natural gas)

Question 10

How do we know that the recent CO2 emissions come from fossil fuels?

Answer 10

chemical signaturea!

• ratio of 13C:12C has fallen, showing that there is more plant matter (uses more 12C)
• less 14C (radioactive) shows that the added C is ancient

Question 11

Where does methane come from?

Answer 11

sources with lots of organic C but little oxygen

Question 12

Where have recent additions of methane come from?

Answer 12

• more human and livestock populations

Question 13

What atmospheric additions have slowed global warming?

Answer 13

CFCs - stratospheric ozone holes cool planet slightly
Sulfate Aerosols - dispersed farther in atmosphere due to smokestacks, reflect sunlight and act as nuclei for cloud formation

Question 14

What human activities/atmospheric additions have reduced global warming?

Answer 14

• CFCs
• sulfate aerosols
• brown clouds (cool surface around megacities)
• land clearance (higher albedo)