week 10 lecture Flashcards
What are the drivers of climate change of the last
1000 years?
Orbital forcing
• Solar variability
• Volcanic eruptions
• Internal climate variability
• Land use / Land cover change
• Greenhouse gases
• Aerosols
• Feedbacks
How would climate change over the last 1000years be characterised?
Changes are relatively small
• High regional variability
• Focussing in on centennial, decadal and annual
variability
What archives are used for studying last 1000years?
- Tree rings
- Mountain glaciers
- Corals
- Speleothems
What is the impact of volcanic eruptions?
- *Dust and Ash** can block sunlight causing temporary cooling effect
- *Sulphur dioxide (SO2)** reflect incoming solar radiation has significant cooling effect
- *Greenhouse gas**: warming effect
What is solar varibility and what is its effect?-2
11 year sunspot cycle
small total effect around 1Wm-2
What is the Medival climate Anomaly?
Warm period in Europe and North Atlantic, temperatures 0.3-1.0 ℃ higher than 1960-1990
• Some areas were cooler than today - eastern tropical Pacific Ocean
When did the medival warm period occur?
1000 to 1300 AD (European Middle Ages), possibly earlier
When did the little ice age occur?
1450-1850
What caused the little ice age?
multiple volcanic eruptions over a 50 year period
sea ice-albedo feedback.
Solar irradiance also lower during this period.
What where the features of the little ice age?
Colder winters and shorter growing season in northern Europe led to failed crops and local famine
- Lakes, rivers and ports in Northern Europe froze
- Abandonment of settlements in Greenland
What ended the little ice age?
Likely the industrial revolution as natural cylceles would indicate it ending 50 years latter than it did?
What is the Holocene period
The current interglacial period
11,650 years BP to present
What are the drivers of climate varibility in the holocene?
- Changes in insolation
- Volcanism
- Solar irradiance
- Atmosphere – ocean interactions
- Atmosphere – vegetation interactions
What is the holocence Thermal Maximum?
The period of peak warmth during the Holocene
When did the holocence thermal maximum occur?
~9-5 kyr BP
soon after the ice sheets melted enough to reduce their chilling effect on climate,
• but before renewed cooling due to falling insolation.
Is the timing of the holocene thermal maximum constant?
No: timing of maximum warmth varies regionally, depending on when nearby ice melted
What is the 8.2 ka Event?
A period of abrupt cooling of North Atlantic and northern hemisphere
is Largest climate excursion during Holocene
How long did the 8.2Ka Event last for?
Occurred 8.2 ka BP, lasting for ~160 years
What where the conditions of the 8.2 Ka event?
Cold, dry and dusty
Decrease in temperature (of 3.3± 1.1 °C) and snow accumulation in Greenland
Increase in dust and forest fire frequency
Decrease in methane
What caused the 8.2Ka event?
- Outburst of final drainage proglacial lake Agassiz and Ojibway ~ 8.45 ka BP
- Lakes drained into Labrador sea in space of 0.5 – 5 years, having a cooling effect.
- Likely slowing of the Atlantic Meridional Overturning Circulation (AMOC)
What event is the 8.2 ka simlur too and why?
Somewhat similar to the Younger Dryas due to Similar mechanism, but shorter lived and smaller in magnitude
What has Northern hemishpere summer insolation been doing throughout the holocene?
Northern hemisphere summer insolation has been slowly decreasing throughout the Holocene, since a peak ~10 kyr BP
How much higher was the summer insolation during the 10kyr peak?
10 kyr BP NH summer insolation was ~8% higher than today
When does the Northern hemishpere experiance summer?
at the aphelion
