APES Unit 9.5 (Global Climate Change)
Historic Climate Change
Earth’s climate has varied over geologic time, largely due to variations in earth’s orbit around the sun
Varies in eccentricity (~100,000 years) bringing it closer to and further from the sun at different times
More eccentric = further from sun
Varies in Obliquity (~40000 years) exposing northern latitudes to higher insolation at different times
Leads to predictable variation in Earth’s climate called Milankovitch cycles
Earth’s Historical Climate
Scientists have measured and estimated earth’s historical temperature and CO2 levels using 3 main pieces of evidence
Foraminifera shells in ocean sediments - different species have different temperature tolerance
Air bubbles in ice cores that contain ancient atmospheric gas (CO2 levels)
16O vs. 18O isotope concentrations in ancient ice (higher 18O = higher temperature)
Global ice ages, folowed by warmer periods occur roughly every 100,000 years
CO2 levels are strongly correlated with temperature but casuality isn’t fully understood
Effects of Climate Change
Rising Temperature - habitat/sepcies loss, drought, soil dessiccation, heat waves, increasesd precipitation in some regions
Rising Sea level - due to glacial, polar ice melt + thermal expansion
Melting of Permafrost - permanetly frozen tundra soils that begin to thaw and release methane & CO2 from anaerobic decomposition
Impact on Coastal Communities
Property Loss, damage, potential relocation: Coastal communities, especially poorer ones that can’t build up may need to relocate inland
Seawalls or other barriers can be built higher, but this just delays eventual flooding
Loss of barrier islands: islands that buffer coastal communities/ecosystems from wind & waves may be lost as sea level rises
Impact on Atmospheric Currents
Widening & weakening of hadley cell: as temp. diff. between equator and poles decreases, air ascending and expanding form equator travels further before sinking
This shifts subtropical zones (dry, desert biomes) toward the poles and expands the tropics
Regions between 30o and 60o may experience drier climate as cool, dry, descending air from hadley cell shifts north & south
Weakened, destabilized Jet Stream: as arctic warms faster than other areas of earth, temperature difference between equator & poles weakens
Because temperature & pressure differs between polar & subtropical regions is what drives polar jet stream, less differerence between them means weaker, wobblier jet stream
Leads to extreme cold spells in eastern US & dry spells in western US
Impact on Marine Ecosystems
Altered range of marine ecosystems: some new marine habitats will be formed by rising sea level flooding coastline
Some areas of ocean will become too deep to receive sunlight & photic zone will shift up, further from ocean floor
Altered ranges for organisms: warm water holds less O2, so many fish populations have declined, or migrated to cooler waters
Impact on Ocean Circulation
Suppression of thermohaline circulation: global ocean current that redistributes heat from the equator, salt, and nutrients by mixing ocean waters could slow or stop altogether
Ice melt from Greenland → especially cold, fresh water buildup in north atlantic
Freshwater is less dense than salt, preventing it from sinking
The cold north atlantic slows warmer Gulf Stream waters, cooling Europe & slowing global thermohaline circulation
Unequal Global Warming
Polar regions of earth are warming faster than other regions (polar amplification)
Especially the arctic (N pole) becasue there is more land & less water to absorb heat
Melting sea ice = more exposed ocean water, which absorbs more sunlight than ice & snow, leading to more ice melting (positive feedback loop)
Distribution of tropical heat to poles by thermohaline circulation also warms poles
Melting of Permafrost - permanently frozen tundra soils that begin to thaw & release methane & CO2 from anaerobic decomposition
Air pollution adds soot & other PM to atmosphere, distributed to poles by atmospheric circulation
Darker, soot/PM covered ice absorbs even more heat due to lower albedo
Impact on Polar Ecosystems
Arctic sea ice loss = habitat
Seals use it for resting and find holes for breathing
Algae grow on ice, forming base of arctic food web
Polar bears use ice for hunting seals at breathing holes
Historic Climate Change
Earth’s climate has varied over geologic time, largely due to variations in earth’s orbit around the sun
Varies in eccentricity (~100,000 years) bringing it closer to and further from the sun at different times
More eccentric = further from sun
Varies in Obliquity (~40000 years) exposing northern latitudes to higher insolation at different times
Leads to predictable variation in Earth’s climate called Milankovitch cycles
Earth’s Historical Climate
Scientists have measured and estimated earth’s historical temperature and CO2 levels using 3 main pieces of evidence
Foraminifera shells in ocean sediments - different species have different temperature tolerance
Air bubbles in ice cores that contain ancient atmospheric gas (CO2 levels)
16O vs. 18O isotope concentrations in ancient ice (higher 18O = higher temperature)
Global ice ages, folowed by warmer periods occur roughly every 100,000 years
CO2 levels are strongly correlated with temperature but casuality isn’t fully understood
Effects of Climate Change
Rising Temperature - habitat/sepcies loss, drought, soil dessiccation, heat waves, increasesd precipitation in some regions
Rising Sea level - due to glacial, polar ice melt + thermal expansion
Melting of Permafrost - permanetly frozen tundra soils that begin to thaw and release methane & CO2 from anaerobic decomposition
Impact on Coastal Communities
Property Loss, damage, potential relocation: Coastal communities, especially poorer ones that can’t build up may need to relocate inland
Seawalls or other barriers can be built higher, but this just delays eventual flooding
Loss of barrier islands: islands that buffer coastal communities/ecosystems from wind & waves may be lost as sea level rises
Impact on Atmospheric Currents
Widening & weakening of hadley cell: as temp. diff. between equator and poles decreases, air ascending and expanding form equator travels further before sinking
This shifts subtropical zones (dry, desert biomes) toward the poles and expands the tropics
Regions between 30o and 60o may experience drier climate as cool, dry, descending air from hadley cell shifts north & south
Weakened, destabilized Jet Stream: as arctic warms faster than other areas of earth, temperature difference between equator & poles weakens
Because temperature & pressure differs between polar & subtropical regions is what drives polar jet stream, less differerence between them means weaker, wobblier jet stream
Leads to extreme cold spells in eastern US & dry spells in western US
Impact on Marine Ecosystems
Altered range of marine ecosystems: some new marine habitats will be formed by rising sea level flooding coastline
Some areas of ocean will become too deep to receive sunlight & photic zone will shift up, further from ocean floor
Altered ranges for organisms: warm water holds less O2, so many fish populations have declined, or migrated to cooler waters
Impact on Ocean Circulation
Suppression of thermohaline circulation: global ocean current that redistributes heat from the equator, salt, and nutrients by mixing ocean waters could slow or stop altogether
Ice melt from Greenland → especially cold, fresh water buildup in north atlantic
Freshwater is less dense than salt, preventing it from sinking
The cold north atlantic slows warmer Gulf Stream waters, cooling Europe & slowing global thermohaline circulation
Unequal Global Warming
Polar regions of earth are warming faster than other regions (polar amplification)
Especially the arctic (N pole) becasue there is more land & less water to absorb heat
Melting sea ice = more exposed ocean water, which absorbs more sunlight than ice & snow, leading to more ice melting (positive feedback loop)
Distribution of tropical heat to poles by thermohaline circulation also warms poles
Melting of Permafrost - permanently frozen tundra soils that begin to thaw & release methane & CO2 from anaerobic decomposition
Air pollution adds soot & other PM to atmosphere, distributed to poles by atmospheric circulation
Darker, soot/PM covered ice absorbs even more heat due to lower albedo
Impact on Polar Ecosystems
Arctic sea ice loss = habitat
Seals use it for resting and find holes for breathing
Algae grow on ice, forming base of arctic food web
Polar bears use ice for hunting seals at breathing holes
