Climate change in the Holocene

Question 1

What was the 8.2Ka event?

Answer 1

A period of cooling around the north Atlantic region in the Holocene which caused droughts in the Middle East.

Question 2

What caused the 8.2ka event?

Answer 2

A big input of freshwater into the Atlantic which decreased the transfer of energy/heat from the equator to the Poles.

Question 3

What is believed to have caused the large input of freshwater which triggered the 8.2ka event?

Answer 3

The burst of Lake Agassiz, which was a lake in Canada.

Question 4

Why did cooling of the Atlantic (8.2Ka event) cause drought in the Middle East?

Answer 4

Middle East gets precipitation from the Atlantic. If the Atlantic gets cooler, there is less energy for evaporation, which weakens the storm tracks to the Middle East.

Question 5

What is expected to happen if parts of Greenland keep melting?

Answer 5

North Atlantic Circulation (NAC) has already been weakened due to ice melting. If melting continues, NAC could get shut down causing cooling in the UK and other nearby areas and drought in the Middle East (which we know from the 8.2Ka event).

Question 6

What does the African Humid Period refer to?

Answer 6

The period where the continent had more humid climate and the Sahara was a grassland.

Question 7

How long has the Sahara been a desert?

Answer 7

The Sahara has been a desert for the past 5-6 thousand years.

Question 8

What caused the African Humid Period to end?

Answer 8

The amount of sun in the northern hemisphere declined which reduced energy for evaporation and monsoons causing rains to stop reaching the Sahara.

Question 9

What is some of the proof we have that the Sahara was once a grassland?

Answer 9

Historic drawings from the Sahara show species that could not survive there now in the current climate.

Question 10

Why do many academics argue positive feedbacks greatly helped cause the African Humid Period to end?

Answer 10

Because the change was very rapid; some argue it only took a few centuries.

Question 11

What kind of positive feedback helped turn the Sahara into a desert?

Answer 11

Less rainfall killed many plants, which reduces water storage, which enhances drying trend.

Question 12

What happened during the Mid Holocene Transition in the Middle East?

Answer 12

Declining solar energy in the northern hemisphere reduced westerly storm tracks.

Question 13

Was climate overall wet or dry at the start of the Holocene?

Answer 13

Wet.

Question 14

What influences how much energy the sun emits?

Answer 14

Sunspots.

Question 15

How can ocean sediments provide records of past climates on land?

Answer 15

Glaciers pick up sediments as they travel towards oceans. Upon entering oceans they become ice burgs, melt, and deposit sediments in the sea.

Question 16

How long have humans been contributing to CO emissions? How have they contributed to this?

Answer 16

For thousands of years via agriculture (cows, rice etc) and deforestation.

Question 17

How long has the Holocene lasted so far?

Answer 17

11,700 years.

Question 18

What climatic trend is human activity expected to end?

Answer 18

The warming-cooling trend due to increasing greenhouse gas emissions and global warming.

Question 19

What does bond events refer to?

Answer 19

A 1,500 year cycle of climate variability (the interglacial equivariant of D-O events) proposed by Bond, however many academics question this cycle.

Question 20

Name some significant climatic changes that occurred during the Holocene:

Answer 20

8.2Ka event (cooling of North Atlantic, drought in Middle East), African Humid period - desert, the Medieval warm period (MWP), Little Ice Age (LIA), shift of the Northern Hemisphere (NH) summer position of the Intertropical Convergence Zone (ICZ), increasing amplitude of ELSO, weakening monsoon seasons across Africa and Asia.

Question 21

What did orbital forcing during the Holocene result in?

Answer 21

The Northern Hemisphere (NH) summer position of the Intertropical Convergence Zone (ITCZ) moving gradually southward due to redistribution of solar energy via orbital forcing (Wanner et al., 2008)

Question 22

What caused the amplitude of El Nino Southern Oscillation to increase during the Holocene?

Answer 22

Summertime cooling of the Northern Hemisphere and changing temperature gradients in the worlds oceans (Wanner et al., 2008).

Question 23

What theories are there as to why the Medieval Warm Period (MWP) occurred in the Holocene?

Answer 23

Increases in solar radiation / no volcanic activity so limited aerosols / changes in ocean circulation patterns (Rafferty, 2014).

Question 24

What theories are there as to why the Little Ice Age (LIA) occurred during the Holocene?

Answer 24

Decreased solar radiation / strong volcanic eruptions (aerosols) increasing cloud cover & reflection as evidenced by radiocarbon dated vegetation remains / low summer insolation in Northern Hemisphere (Matthews & Briffa, 2005).

Question 25

What helped maintain the Little Ice Age (LIA)?

Answer 25

Positive feedbacks from sea ice. This caused the albedo effect to reflect much of the sun’s energy back into space.

Question 26

What was climate like at the start of the Holocene and how did vegetation in Turkey respond to this?

Answer 26

Climate became wetter and warmer. This made it possible for trees to grow in central Turkey.

The response was slow; could be due to the time needed for trees to spread from refugia back to central Turkey & the seasonality of the climate (might have had wetter climate overall, but records suggests most rainfall occurred in winter, so still had dry springs and summers).