Quaternary Lecture 1- The Cold Planet- Are We Still In the Grip of an Ice Age? Flashcards
When has a rapid increase in climate change been observed?
1970s
Are we consistently over 400ppm carbon dioxide? Is there seasonal variation?
Yes and Yes
What does the quaternary period include?
The last 2.6 million years
What has the quaternary period been dominated by?
Long, cold glacial cycles separated by shoer, warm interglacials.
What are the dominant climate mode in the Quaternary?
Ice ages
Is the beginning of the next glaciation highly unlikely in the next 120 kyr?
Yes
How has high cumulative anthropogenic CO2 influenced glaciation? (Talento and Ganopolski, 2021)
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.
What is the cenozoic?
Current geological era
Discuss climate change in the Cenozoic.
‘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
When did the Holocene start?
11.5 Ka ago
Westerhold et al., 2020
In terms of temperatures we may be heading back to ones similar to Paleocene and Eocene.
Has there been times when Co2 has been over 500ppm?
Yes
What boundary did the Quaternary start?
Pliocene/Pleistocene boundary.
Quaternary (separated into warm and cold periods) within the Pleistocene
How many stages are there roughly in the Quaternary?
104
Are we technically still in the grip of an ice age?
yes but anthropogenic influences may decouple this
What can proxy data show?
Regular and frequent climate fluctuations
What is the EPICA core in Antarctica?
CO2, CH4 and temperature record.
Glacial and interglacial cycles from last 800 ka.
What is a ‘forcing function’?
A mechanism that causes a system to change from its equilibrium state.
Driven by perturbations in the earth-atmosphere system
What is external forcing?
Extra-terrestrial/non-earth processes
What is internal forcing?
Driven by earth processes
What is positive feedback?
Amplifies changes in the climate system
What is negative feedback?
Counter changes within a system
Name two external forcing mechanisms
Solar output and orbital patterns
Name internal forcing mechanisms
Feedback by earth processes such as GHG, ocean currents and albedo.
Do external and internal forcing mechanisms have specific spatial and temporal impacts?
Yes
How may a glacial climate started in terms of tectonic uplift?
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)
Discuss post Cretaceous inception of ice cover due to tectonic uplift.
- 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
Discuss Wegener and the disposition of land masses and ocean gateways in terms of glaciation.
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)
Discuss tectonic changes at the Pliocene-Pleistocene transition (5.3-2.6 million yrs ago) which may have influenced glaciation.
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
Discuss increased volcanism and how this may have caused a glaciated climate.
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?)
What is the climate cycle periodicity?
41,000 years prior to 800ka BP
100,000 years after 800ka BP
What happened at the Mid-Pleistocene Transition?
Intensification of glaciation since 800ka BP
Why was the change in rhythm of glaciation at 800ka BP noticed?
The cycles are driven by orbital forcing (external forcing) which is controlled by our relationship to the sun
Discuss Milankovitch astronomical theory.
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
What is eccentricity?
(100ka & 400ka) Change in shape of Earth’s orbit from circular to elliptical
= 0.03% max change in annual insolation receipt. Dominant post 800ka.
What is obliquity?
(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
What is precession?
(23ka & 19ka) - Wobble of Earth on its axis due to gravitational attraction of sun & moon. Alters timing & variability of seasons.
Where can the effects of orbital forcing be found?
Palaeo-environmental records such as
- River terraces
- Loess (soil sequences)
- Ice cores
- Lake/ocean cores
What amplified orbital forcing?
Internal forcing and feedbacks
What is an example of positive feedback?
- 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
Willeit et al. (2019)
: 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??
How long has the last glacial cycle lasted?
100 ka
How much will the onset of the next glaciation be delayed by?
100,000 to 600,000 years
