Lecture 16: Recent Climates

Question 1

How is historic climate data determined?

Answer 1

Proxy data & direct measurements

Question 2

What are the types of proxy data used to measure climates?

Answer 2

-Ice cores
- Pollen data
- Tree rings
- Coral and bivalve rings
- Genetics

Question 3

How are glaciers formed?

Answer 3

Seasonal snowfall gets compressed over time as more and more falls

Question 4

What are ice cores?

Answer 4

vertical chunks of glaciers removed

Question 5

How do ice cores show climate changes?

Answer 5

Ratio of oxygen-16 vs oxygen-18 trapped in ice cores shows temperatures:

cold climate means less O-18 evaporates and more O-18 precipitates. Therefore increase O-18 in glaciers means era of cold climate

Question 6

How does pollen data show past climates?

Answer 6

Plants produce pollen which is super decomposition resistant and builds up in soils (soil cores)

Plant migration can be tracked –> specific plants grow in specific climates –> therefore by knowing which plants grew where and when, we know what the climate was like at that time.

Question 7

How do tree rings show past climates?

Answer 7

Each ring is a new growth season: larger rings = more growth at that time = optimal climate conditions for that tree = now we know what the climate was like

Question 8

How do coral rings/bivalves show changing climates?

Answer 8

corals have growth seasons/cycles and mineral deposits within the rings indicate the climate of the time

Question 9

How do genetics show changing climates?

Answer 9

Ex: if two marine populations share genetics but are separated by ice sheets, then at one point, we know the ice sheets must have been melted to allow them to interbreed.

Question 10

How do direct measurements show changing climates?

Answer 10

Only in recent years we can directly measure changing climates:
- thermometers for temperature changes
- barometers for pressure changes
- ships logging ocean climatic conditions

Question 11

What has the recent climate been like (past 20,000 years)

Answer 11

unusually stable but not entering a period of intense climate change

Question 12

What is the pleistocene era?

Answer 12

• Successive waves of glacial and interglacial periods (~5˚ colder than today)
• Last glacial maximum occurred then (peak of glacier extent)

Question 13

What happened to humans during the pleistocene era?

Answer 13

Africa: homo sapiens evolved and then migrated out of Africa

Europe: glaciers forced humans to the south which caused genetic bottlenecking

Question 14

What helped migrations during the Pleistocene?

Answer 14

Cold weather formed land bridges between asia and north africa which increased migration

Question 15

How did the pleistocene begin/end?

Answer 15

Isthmus of panama forced warm ocean currents further north, which increased precipitation (more snow in norther parts = increased albedo = becomes even colder)
* Positive feedback loop

Ended due to release of CO2 from southern oceans (GHG increase temp) & Milankovic cycles increase strength of the sun

Question 16

What is the younger Dryas?

Answer 16

Period of extreme cooling at the end of the pleistocene era caused by release of fresh water to the ocean by melting glaciers, shutting down certain ocean currents

Question 17

What is the holocene era?

Answer 17

Began ~11,650 years ago –> remarkable climate stability with huge changes in environmental pattersn (precipitations, vegetation, sea levels, coastlines…)

Question 18

How did humans evolve during the holocene?

Answer 18

agricultural revolution began (plants became domesticated)

Question 19

What was the little ice age?

Answer 19

Colder temps between 1300-1850 causing starvation and famine, and dramatic landscape changes in europe –> rivers and lakes froze over, glaciers grew

Question 20

How did the little ice age end?

Answer 20

Indistrialization caused more GHGs ending the little ice age