Quaternary Lecture 1- The Cold Planet- Are We Still In the Grip of an Ice Age?

Question 1

When has a rapid increase in climate change been observed?

Answer 1

1970s

Question 2

Are we consistently over 400ppm carbon dioxide? Is there seasonal variation?

Answer 2

Yes and Yes

Question 3

What does the quaternary period include?

Answer 3

The last 2.6 million years

Question 4

What has the quaternary period been dominated by?

Answer 4

Long, cold glacial cycles separated by shoer, warm interglacials.

Question 5

What are the dominant climate mode in the Quaternary?

Answer 5

Ice ages

Question 6

Is the beginning of the next glaciation highly unlikely in the next 120 kyr?

Answer 6

Yes

Question 7

How has high cumulative anthropogenic CO2 influenced glaciation? (Talento and Ganopolski, 2021)

Answer 7

May cause ice-free conditions in the N Hemisphere throughout the next half a million years, postponing glacial inception up to 600 kyr after present or later.

Question 8

What is the cenozoic?

Answer 8

Current geological era

Question 9

Discuss climate change in the Cenozoic.

Answer 9

‘Warmhouse’ in Palaeocene, Eocene
‘Coolhouse’ in Oligocene and half of Miocene
‘Icehouse’ in Miocene, Pliocene and Pleistocene.
Warming starting towards end of Pleistocene and into the Holocene

Question 10

When did the Holocene start?

Answer 10

11.5 Ka ago

Question 11

Westerhold et al., 2020

Answer 11

In terms of temperatures we may be heading back to ones similar to Paleocene and Eocene.

Question 12

Has there been times when Co2 has been over 500ppm?

Answer 12

Yes

Question 13

What boundary did the Quaternary start?

Answer 13

Pliocene/Pleistocene boundary.

Quaternary (separated into warm and cold periods) within the Pleistocene

Question 14

How many stages are there roughly in the Quaternary?

Answer 14

104

Question 15

Are we technically still in the grip of an ice age?

Answer 15

yes but anthropogenic influences may decouple this

Question 16

What can proxy data show?

Answer 16

Regular and frequent climate fluctuations

Question 17

What is the EPICA core in Antarctica?

Answer 17

CO2, CH4 and temperature record.
Glacial and interglacial cycles from last 800 ka.

Question 18

What is a ‘forcing function’?

Answer 18

A mechanism that causes a system to change from its equilibrium state.
Driven by perturbations in the earth-atmosphere system

Question 19

What is external forcing?

Answer 19

Extra-terrestrial/non-earth processes

Question 20

What is internal forcing?

Answer 20

Driven by earth processes

Question 21

What is positive feedback?

Answer 21

Amplifies changes in the climate system

Question 22

What is negative feedback?

Answer 22

Counter changes within a system

Question 23

Name two external forcing mechanisms

Answer 23

Solar output and orbital patterns

Question 24

Name internal forcing mechanisms

Answer 24

Feedback by earth processes such as GHG, ocean currents and albedo.

Question 25

Do external and internal forcing mechanisms have specific spatial and temporal impacts?

Answer 25

Yes

Question 26

How may a glacial climate started in terms of tectonic uplift?

Answer 26

Post Cretaceous inception of ice cover due to tectonic uplift of mid-latitude regions (post 66 million yrs ago)? (e.g. Tibetan Plateau/ Himalaya & American Cordillera)

Question 27

Discuss post Cretaceous inception of ice cover due to tectonic uplift.

Answer 27

- Raised areas above the regional glaciation limit - Modified atmospheric circulation patterns Increased weathering rates resulting in removal of CO2 from atmosphere - Increased dustiness of atmosphere due to uplift of Tibetan Plateau suggesting increased aridity between 3.6-2.6 Ma

Question 28

Discuss Wegener and the disposition of land masses and ocean gateways in terms of glaciation.

Answer 28

Disposition of land masses and ocean gateways - Poleward migration of major land masses - Separation of Antarctica & Australia - Isolation of Antarctica by 40Ma (Antarctic Ice Sheet stable ever since)

Question 29

Discuss tectonic changes at the Pliocene-Pleistocene transition (5.3-2.6 million yrs ago) which may have influenced glaciation.

Answer 29

Increased tectonic activity – mountain building - (Himalaya/Tibetan plateau = 3,000m in 2Ma) - changed the wave structure of airstreams in upper atmosphere & cooled the N. hemisphere - isthmus of Panama closing (3-3.5Ma) Feedback mechanisms - ocean/atmosphere circulation

Question 30

Discuss increased volcanism and how this may have caused a glaciated climate.

Answer 30

First evidence of widespread glaciation (esp. in N. Hemisphere) = deep ocean cores reveal larger & more persistent volumes of ice-rafted debris at c.2.6Ma BP Cores also show increase in volcanic ash from 2.6Ma = increased global volcanism - SO2 aerosols (increase in earth’s albedo?)

Question 31

What is the climate cycle periodicity?

Answer 31

41,000 years prior to 800ka BP 100,000 years after 800ka BP

Question 32

What happened at the Mid-Pleistocene Transition?

Answer 32

Intensification of glaciation since 800ka BP

Question 33

Why was the change in rhythm of glaciation at 800ka BP noticed?

Answer 33

The cycles are driven by orbital forcing (external forcing) which is controlled by our relationship to the sun

Question 34

Discuss Milankovitch astronomical theory.

Answer 34

Main premise = changes in intensity of seasons in Northern Hemisphere (NH) control ice sheet inception & decay NH high latitude summer temps key to the onset of glaciation. If cold enough winter snows would not completely melt & would grow into glaciers. Earth’s distance from the sun varies seasonally - perihelion (nearest in NH winter) - aphelion (furthest away in NH summer) This uneven receipt of insolation is further accentuated by orbital parameters of: Eccentricity Obliquity Precession

Question 35

What is eccentricity?

Answer 35

(100ka & 400ka) Change in shape of Earth’s orbit from circular to elliptical = 0.03% max change in annual insolation receipt. Dominant post 800ka.

Question 36

What is obliquity?

Answer 36

(41ka) - Change in tilt of Earth’s axis of rotation from 21.8o-24.4o Larger differences between seasons as tilt increases. Dominant pre 800ka

Question 37

What is precession?

Answer 37

(23ka & 19ka) - Wobble of Earth on its axis due to gravitational attraction of sun & moon. Alters timing & variability of seasons.

Question 38

Where can the effects of orbital forcing be found?

Answer 38

Palaeo-environmental records such as - River terraces - Loess (soil sequences) - Ice cores - Lake/ocean cores

Question 39

What amplified orbital forcing?

Answer 39

Internal forcing and feedbacks

Question 40

What is an example of positive feedback?

Answer 40

- Increased albedo = more incoming solar reflected back to space - Reduced incoming solar rad = cooler air and ocean temps - Cooler oceans = more CO2 locked in the oceans - Less CO2 = reduced GHG in the atmosphere = atmosphere cooling - More cooling = more snow and ice - Ice sheets get bigger

Question 41

Willeit et al. (2019)

Answer 41

: Gradual lowering of atmospheric CO2 and regolith removal essential to reproduce the evolution of climate variability through the Quaternary period. The long-term CO2 decrease leads to the initiation of Northern Hemisphere glaciation and an increase in the amplitude of glacial-interglacial variations CO2 lowering past a critical threshold leads large ice sheets to develop in NH (cold enough for long enough). Does removal of subglacial regolith mean stickier beds and so a change in thickness??

Question 42

How long has the last glacial cycle lasted?

Answer 42

100 ka

Question 43

How much will the onset of the next glaciation be delayed by?

Answer 43

100,000 to 600,000 years