week 10 lecture

Question 1

What are the drivers of climate change of the last
1000 years?

Answer 1

Orbital forcing
• Solar variability
• Volcanic eruptions
• Internal climate variability
• Land use / Land cover change
• Greenhouse gases
• Aerosols
• Feedbacks

Question 2

How would climate change over the last 1000years be characterised?

Answer 2

Changes are relatively small
• High regional variability
• Focussing in on centennial, decadal and annual
variability

Question 3

What archives are used for studying last 1000years?

Answer 3

• Tree rings
• Mountain glaciers
• Corals
• Speleothems

Question 4

What is the impact of volcanic eruptions?

Answer 4

• *Dust and Ash** can block sunlight causing temporary cooling effect
• *Sulphur dioxide (SO2)** reflect incoming solar radiation has significant cooling effect
• *Greenhouse gas**: warming effect

Question 5

What is solar varibility and what is its effect?^-2

Answer 5

11 year sunspot cycle

small total effect around 1Wm-2

Question 6

What is the Medival climate Anomaly?

Answer 6

Warm period in Europe and North Atlantic, temperatures 0.3-1.0 ℃ higher than 1960-1990

• Some areas were cooler than today - eastern tropical Pacific Ocean

Question 7

When did the medival warm period occur?

Answer 7

1000 to 1300 AD (European Middle Ages), possibly earlier

Question 8

When did the little ice age occur?

Answer 8

1450-1850

Question 9

What caused the little ice age?

Answer 9

multiple volcanic eruptions over a 50 year period

sea ice-albedo feedback.

Solar irradiance also lower during this period.

Question 10

What where the features of the little ice age?

Answer 10

Colder winters and shorter growing season in northern Europe led to failed crops and local famine

• Lakes, rivers and ports in Northern Europe froze
• Abandonment of settlements in Greenland

Question 11

What ended the little ice age?

Answer 11

Likely the industrial revolution as natural cylceles would indicate it ending 50 years latter than it did?

Question 12

What is the Holocene period

Answer 12

The current interglacial period

11,650 years BP to present

Question 13

What are the drivers of climate varibility in the holocene?

Answer 13

• Changes in insolation
• Volcanism
• Solar irradiance
• Atmosphere – ocean interactions
• Atmosphere – vegetation interactions

Question 14

What is the holocence Thermal Maximum?

Answer 14

The period of peak warmth during the Holocene

Question 15

When did the holocence thermal maximum occur?

Answer 15

~9-5 kyr BP

soon after the ice sheets melted enough to reduce their chilling effect on climate,

• but before renewed cooling due to falling insolation.

Question 16

Is the timing of the holocene thermal maximum constant?

Answer 16

No: timing of maximum warmth varies regionally, depending on when nearby ice melted

Question 17

What is the 8.2 ka Event?

Answer 17

A period of abrupt cooling of North Atlantic and northern hemisphere

is Largest climate excursion during Holocene

Question 18

How long did the 8.2Ka Event last for?

Answer 18

Occurred 8.2 ka BP, lasting for ~160 years

Question 19

What where the conditions of the 8.2 Ka event?

Answer 19

Cold, dry and dusty

Decrease in temperature (of 3.3± 1.1 °C) and snow accumulation in Greenland

Increase in dust and forest fire frequency

Decrease in methane

Question 20

What caused the 8.2Ka event?

Answer 20

• Outburst of final drainage proglacial lake Agassiz and Ojibway ~ 8.45 ka BP
• Lakes drained into Labrador sea in space of 0.5 – 5 years, having a cooling effect.
• Likely slowing of the Atlantic Meridional Overturning Circulation (AMOC)

Question 21

What event is the 8.2 ka simlur too and why?

Answer 21

Somewhat similar to the Younger Dryas due to Similar mechanism, but shorter lived and smaller in magnitude

Question 22

What has Northern hemishpere summer insolation been doing throughout the holocene?

Answer 22

Northern hemisphere summer insolation has been slowly decreasing throughout the Holocene, since a peak ~10 kyr BP

Question 23

How much higher was the summer insolation during the 10kyr peak?

Answer 23

10 kyr BP NH summer insolation was ~8% higher than today

Question 24

When does the Northern hemishpere experiance summer?

Answer 24

at the aphelion

Question 25

What where monssons like 9000 years ago relative to today?

Answer 25

Stronger across northern tropical

Green Sahara period

Question 26

How does the holocence compare to past interglacials?

Answer 26

Both MIS 5e and MIS 11c were globally warmer than the Holocene