Sub-Milankovitch climate change Flashcards
What drives sub-Milankovitch climate change?
- Volcanism
- Solar irradiance
- Ice sheet dynamics
- Changes to Ocean circulation
- Human impacts
Volcanism and climate change
• Volcanic aerosols cause relatively short-term
climatic cooling
• Increased activity in last 600 years->
correlates with proxy climate data showing N. hemisphere cooling
• Abrupt rise in N. hemisphere temperatures between 1920-50 coincides with phase of reduced volcanic activity
• Modelling suggests that volcanism accounts for
22% of temp variability over the last 1000 years
Volcanic activity alone cannot account for all short-term climate forcing
Episodes of explosive volcanic forcing tend to amplify changes that are already occurring through positive and negative feedbacks
Solar irradiance changes
- Radiation output of the sun changes cyclically e.g. 11, 200, 1500 yrs
- Reduced sunspot activity = less solar output + weaker solar wind
Ice sheets, oceans and climate
- Some changes in great ice sheets are independent of Milankovitch cycles
- These changes may have global consequences
Ice sheet instability in Antarctica
• Surging west Antarctic ice at the end of an interglacial
could release up to 10 million km3 of ice
• Resulting in global sea-level rise of 20 m
• ..and massive global cooling
Causes of ice sheet surging?
- Irregular surging of ice sheets may be unrelated to long-term climate forcing
- It may have more to do with the distribution of basal till which lubricated the flow of the ice sheet
Evidence for rapid sub-Milankovitch climate change
Examples of sub-Milankovitch climate change over the
last 100,000 years:
(1) Devensian glaciation (20+ ‘short-lived’
interstadials)
(2) Lateglacial (false-start to the Holocene interglacial)
(3) Holocene (8200 cal. BP widespread ‘cooling’
event)
Discharges of meltwater and icebergs can
– (a) raise sea levels
– (b) disrupt thermohaline circulation (THC) by reducing
deep water formation
