Climates of the past; lecture 4+5

Question 1

Name the main features of the Holocene epoch

Answer 1

• covers a period of about 11,700 years
• it began as the last glacial period ended
• involves the melting of ice sheets, a sea level rise of about 140m
• spread of human civilization throughout the globe

Question 2

What life dominates the Holocene?

Answer 2

• human life

Question 3

What were the impacts of humans in the Holocene?

Answer 3

• habitat destruction
• anthropogenic pollution
• mass extinction of plants+ animals species

Question 4

How has the Holocene been accurately dated?

Answer 4

• dendrochronology (tree rings)

- valves (glacial lake sediments)

Question 5

What is dendrochronology?

Answer 5

• the reconstruction of a timescale from tree rings, each ring represents a year of growth for the tree

Question 6

What is dendroclimatology?

Answer 6

• the interpretation of climates from tree rings

Question 7

what is the thermohaline circulation driven by?

Answer 7

• density differences controlled by heat and salinity, creates a gradient between north and south which drives the system

Question 8

Describe the transport of heat in the Atlantic circulation in the summer?

Answer 8

• warm waters from south travel to the north in summer
• cooling occurs where it becomes dense and sinks
• transporting heat from the tropics to the north

Question 9

Describe the winter Atlantic circulation?

Answer 9

in the winter, warm water currents is pushed south due to build up of ice in the north

Question 10

What are the Dansgaard - Oeschger cycles?

Answer 10

Dansgaard–Oeschger events are rapid climate fluctuations that occurred 25 times during the last glacial period

Question 11

How were the dansgaard - oeschger events caused?

Answer 11

Quasi-stationary modes of the atmosphere-ocean system as instability in the ice build up would’ve caused this

Question 12

What was the main cause of the Heinrich events?

Answer 12

• large ice sheets in the North Atlantic released large amounts of freshwater
• this reduced ocean salinity enough to slow deep water formation and the thermohaline circulation
• a slowdown would cause the NA to cool.
• Later, the addition of freshwater decreased, ocean salinity and deep water formation increased and climate conditions recovered.

Question 13

What is the younger dyras?

Answer 13

a return to glacial conditions which temporarily reversed the glacial climate warming after the last glacial maximum 12.9 to 16.6 ka before present

Question 14

What caused the younger dyras?

Answer 14

a massive flow of glacial meltwater into the north atlantic which restricted the overturning circulation

Question 15

Define a monsoon

Answer 15

-A seasonal wind reversal which brings lots of precipitation to the tropics

Question 16

How are monsoons formed in the tropics?

Answer 16

• heating of earth creates a pressure difference between earth and ocean
• warm air moving from the ocean to land which causes a lot of precipitation

Question 17

What is the Anthropocene?

Answer 17

• the time interval in which humans now rival global geophysical processes e.e. that the earth system is now modified

Question 18

Name the 3 views on when the anthropocene should start

Answer 18

1. earlt mega faunal extinction by early human hunters
2. land clearance and flooding for rice farming (ruddiman 2007)
3. the great acceleration, increase in population since 1750, industrial revolution

Question 19

How do we study climate change?

Answer 19

• direct measurements
• climate models
• study of the past, look in ocean for sediments and date them, previous temperature changes and predict how it will change in the future

Question 20

How is the earth’s climate system governed?

Answer 20

• by heat energy arriving from the sun in the form of waves of electromagnetic radiation, heat is radiated back to space as longer wave infra-red radiation

Question 21

What controls the earth’s energy balance?

Answer 21

• albedo reflects light back to atmosphere as well as co2 trapping most of this heat and warming the earth

Question 22

What is the strongest greenhouse gas?

Answer 22

• water vapour as it contributes 36-66% of overall vapour alone

Question 23

Why is co2 more dangerous than water vapour even there is a higher concentration of vapour in the atmosphere?

Answer 23

because co2 stays in the atmosphere for centuries which a lot of time to have substantial and long-lasting effects on the climate system

Question 24

What is the keeling curve and what does it show?

Answer 24

• a graph to show the accumulation of co2 in the atmosphere
• it fluctuates yearly due to plant growth cycles
• overall increase due to human activities.

Question 25

what is the el nino?

Answer 25

the warming of sea surface temperature that occurs every few years, typically concentrated in the central-east equatorial Pacific.

Question 26

What is la nina?

Answer 26

episodes of cooler than average sea surface temperature in the equatorial Pacific. T

Question 27

How does el nino affect south east asia?

Answer 27

it brings a lot of drought, decrease in plants lead to a decrease in photosynthesis and as a result, an increase in the accumulation of co2 in the atmosphere

Question 28

How does la nina affect south east asia?

Answer 28

It brings a lot of rainfall in south east asia