Chapter 4 Flashcards
The two dominant climate states
Greenhouse Earth
Icehouse Earth
Greenhouse earth
no continental glaciers due to warming processes - e.g. high levels of greenhouse gasses
Icehouse earth
when large ice sheets are present on earth - global ice age
The climate fluctuates between cooler glacials (ice advancing) and warmer interglacials (ice retreating)
Quaternary Ice Age
the most recent of Earth’s 5 known ice ages
2.6 million years bp - present
Why has the earth been so cold for the past 2.6m years?
Continental drift: the Antarctic has moved to the South Pole - there is normally only ocean at the pole - land cools quickly so Antarctic has become permanent ice sheet
This cools the rest of the planet due to the Albedo Effect - ice and fresh snow have 90% albedo - 90% of sunlight is reflected which cools the planet
Why is the Arctic Ocean so cold?
Permanent sea ice
The North Pole is almost completely surrounded by land so warm water from the Pacific and Atlantic can’t mix with the cold water in the Arctic
Milankovitch cycles
Tiny changes in the Earth’s orbit around the sun that are responsible for glacial and interglacial periods as it changes the amount of sun radiation received
- Eccentricity cycle
The shape of the Earth’s orbit varies from circular to elliptical over 100,000 year cycles
Elliptical orbit: high seasonality and interglacial conditions (snow melts in warm summer)
Circular orbit: low seasonality and glacial conditions as Earth is always same distance from sun
- Obliquity cycle
The tilt of the Earth’s axis varies between 21.5° and 24.5° over 41,000 year cycles which changes the severity of the seasons
Min tilt: 21.5 = less sunlight in summer = ice cannot melt and expands = glacial conditions
Max tilt: 24.5 = ice melts bc of more sunlight in summer = interglacial conditions
Loch Lomond Stadial (Younger Dryas Event)
A sudden cold period that took place 12,500-11,500 years BP where temperatures dropped 6-7°c
What caused the younger dryas event?
- Disruption to the thermohaline circulation
(The circulation of water across the Atlantic Ocean that keeps the UK warm)
Drainage of fresh water from the the huge proglacial Lake Agassizq diluted and stopped the circulation because it is the salty water that sinks and continues the circulation
Cryosphere
The cold environments of our planet, where water is in its solid form of ice
Includes:
snow cover; lake, river, sea ice; glaciers; ice caps and sheets, frozen ground (permafrost)
Periglacial environments
Do not feature glaciers but usually found on the edge of glacial areas
- permanently frozen ground (permafrost)
- occurs in high-latitude or high-altitude areas - e.g. Siberia, Alaska, Northern Canada
Glaciers
Large, slow-moving body of ice that flows downhill due to gravity
Two types of glacial environments
- Polar glacial environments - found at high latitudes in the Antarctic and Arctic - low levels of precipitation and extremely cold temperatures (mean annual -30 to -40c)
- Alpine glacial environments - high altitudes in mountain ranges - e.g. Alps, Himalayas, Andes - high levels of precipitation and wide temperature range with frequent freeze-thaw cycles
