Paleoclimate change Flashcards
What can we learn from past climates?
- context for current observations
- natural variability
- ‘baseline’ reference for man-made climate change
- test predictive models
Which past epoch is the best analogue for our current situation?
Pliocene
What were CO2 concentrations during the Mid-Pliocene?
Estimated between 360-400ppm
When was the Mid-Pliocene?
3.3 to 3 Ma years ago
What were sea levels like during the Mid-Pliocene?
25-30m higher
What were higher latitude air temperature likes during the Mid-Pliocene?
10-20ºC higher
What is the speed like when transitioning into a glacial period? and interglacial period?
Slow descent into glacial periods but rapid descent into interglacials (shown in the Vostok ice core)
How does sea level change at glacial maximums?
130m below current levels
What are general conditions like in glacial periods?
Colder, dustier and generally drier than interglacial periods
What is Milanković theory?
Theory that orbital changes cause interglacial and glacial periods
When was Milanković theory first proposed?
1920
What is eccentricity?
Changes in the earths orbit around the sun from circular to elliptical
How often does eccentricity vary?
Varies on a time scale of 96k years
How much does eccentricity vary by?
0-0.07 (i.e. the orbit is can be stretched 7% away from a circle)
How does eccentricity vary radiation?
Same incoming solar radiation is the same but can alter intensity between the two hemispheres
What impact does an eccentricity have on radiation intensity over the globe?
28% difference between the hemispheres
What is our current eccentricity?
0.0174 … the southern hemisphere receives 6.7% more radiation a year
What is obliquity?
Tilt .. variations in this can occur
What is current obliquity?
23.5º
How does obliquity vary?
Varies between 21.5º and 24.5º with a period of 41k years
What happens during large obliquity?
Seasons become more exaggerated
What is precession?
The wobble of the axis that can change the difference between seasons
What is the earths period of precession?
19-21 k years
What was deglaciation triggered by in the last glacial period?
Rise in insulation in the northern hemisphere causing a change in radiative budget
What is the Bølling-Warming event?
An abrupt warm and moist interstadial period that occurred at the end of the last glacial period. We don’t know what caused this.
What was the temperature rise during the Bølling-Warming event?
4-5ºC in a few decades
What was the Younger Dryas event?
A cooling period for around 1ka due to a change in meltwater route which created a fresh water input, affecting density structures and ocean circulation, weakening a warm current that brought warm water from the tropics to the mid latitudes
How did temperatures in the late and early Holocene compare?
Early Holocene was warmer than the late Holocene (not what we would expect from model predictions)
What is the Holocene?
Time of earth history (epoch) since the last glacial. The last 12,000 years and the current interglacial period.
What factor had a major effect on climate over the last 500 Ma that isn’t relevant to present day climate change?
Continental drift
Since the end of the Cretaceous, what was the maximum CO2 concentration experienced?
2000-2500ppm (over five times higher than current conditions)
On what time scaled does obliquity change?
41k years
