The Climate System and Climate Variation

Question 1

What is a climate?

Answer 1

Product of interactions between different sub-systems

Question 2

What defines a global and regional climate?

Answer 2

Nature of interactions defines global and regional climate.

Question 3

Features of the atmosphere?

Answer 3

-Coupled to other components through energy exchanges and chemical interactions at surface (sensible and latent heat fluxes, CO2, WV).
-Low mass and turbulent mixing leads to rapid response to external influences.
-Changes in atmospheric composition thought to have had profound influence on past climates, and are responsible for expected climate change.
-Clouds dominate planetary albedo in low latitudes.
-Atmospheric circulation dominates poleward transport of heat.

Question 4

Features of the Oceans?

Answer 4

-High heat capacity leads to slow response to external influences leads to buffer against large seasonal temperature contrast:
Hemispheric scale: hemispheric differences in seasonal temperature contrast due to differences in landsea distribution.
Regional scale: climate strongly influenced by proximity to ocean.
-Ocean currents important in poleward transfer of heat.
-Changes in ocean circulation brought about by:
Plate tectonics (affecting landsea distribution and sea level).
Growth/decay of ice sheets (affecting sea level).
Changes in distribution and/or volume of freshwater discharges.
Changes in atmospheric circulation.
-Critical role in chemical balance of atmosphere.
Source/sink for CO2 (dependent on ocean surface temperature and rates of primary production).

Question 5

High land mass low land mass rule?

Answer 5

Higher percentage of land mass = higher seasonal temperature contrast.
Lower percentage of land mass = higher seasonal temperature contrast.

Question 6

Features of Land surface?

Answer 6

-Distribution of land affects distribution of albedo.
Oceans: 2 - 10 %; land surface: 6 - 45 %.
High latitude land masses promote accumulation of snow and ice (albedo 80 %)
Enhanced equatorpole temperature gradient
Stronger SH circulation due to high elevation Antarctic plateau south of 75 degrees.
Asymmetry between hemispheres in position of climatic zones (on average, ITCZ north of equator).
Frequency of continental glaciations increased as plates moved to more polar positions (plate tectonics).
-Mountain building
Dynamic effects on circulation
High elevation persistence of snow increases albedo
Collision of India with Asia (to Himalayas) to long-term cooling trend since 65 My BP.

Question 7

Features of Cryosphere?

Answer 7

-Climatic importance due to high albedo
8% of surface permanently covered
-Seasonal expansion to 16 % from Aug to Dec
-Hemispheric differences (NH: 4  24 %; -SH: 7  13 %) reflect landsea distributions:
NH expansion due to continental snow & ice
SH expansion due to sea ice

Question 8

Features of Biosphere?

Answer 8

-Albedo
Tropical forest: 13 %
Farmland/natural grassland: 20 %
Desert: 37 %
-Atmospheric composition
Forests and woodlands (34 % of continental area) important in removal of atmospheric CO2
Deserts and desert scrublands (13 %) important sources of wind-blown dust
-Evapotranspiration

Question 9

Features of feedback systems?

Answer 9

-Components in climate system are intimately linked.
-Disturbance in one component  changes throughout.

Question 10

What is an amplifying or dampening effect from an initial disturbance in a climate system?

Answer 10

Amplifying effect = positive feedback that leads to destabilisation.
Dampening effect = negative feedback that leads to stabilisation.

Question 11

What is the ‘snowball earth’ initial disturbance?

Answer 11

Lower temperatures leads to
Continental ice sheet growth leads to
Higher albedo leads to
Lower radiation receipts leads to
Repeat

Question 12

What is the ‘Runaway Greenhouse Effect ‘ initial disturbance?

Answer 12

Higher atmospheric Co2 leads to
Increased absorption of terrestrial radiation leads to
Higher tropospheric temperatures leads to
Higher temperature of ocean surface layer leads to
repeat

Question 13

Why is ‘snowball earth’ initial disturbance unlikely?

Answer 13

Lower temp. leads to lower evaporation leads to less snow.

Question 14

Why is ‘Runaway Greenhouse Effect’ initial disturbance less likely?

Answer 14

-Increased temperatures leads to increased evaporation leads to increased cloudiness.
-Increased temperatures at high latitudes leads to increased poleward advection of moisture leads to increased snowfall.

Question 15

Process of the changes in the North Atlantic Ocean Circulation and Climate over the Last Glacial-Interglacial Cycle?

Answer 15

-Sensible and latent heat losses in surface waters of Norwegian and Greenland Seas leads to
cooling and increases in salinity leads to
sinking and southward flow leads to
North Atlantic Deep Water (NADW)
AND
-Compensating poleward movement of warm saline surface waters (Gulf Stream and North Atlantic Drift leads to mild W European climate)
-Called Atlantic Meridional Overturning Circulation (AMOC) = heat ‘conveyor belt’

Question 16

Disturbances that slow or stop Atlantic Meridional Overturning Circulation?

Answer 16

-Increased freshwater in N Atlantic (from increased run-off from ice sheet melting) leads to cold low-salinity surface layer.
-Reduction /cessation of sinking (NADW formation slows/stops; bottom waters dominated by Antarctic Bottom Water (AABW).
-Poleward flow of warm saline water slows/stops.
-Colder W European climate.

Question 17

Evidence for Changes in the North Atlantic Circulation?

Answer 17

-Isotopic signature (o13C) of benthic foraminifera used as a tracer of deep water masses.
o13C of seawater at equilibrium with atmosphere = +3.5 ‰.
o13C of organic matter = –20 to –25 ‰.
Oxidation of organic matter falling through water column leads to a decrease in o13C in bottom waters.
o13C in bottom waters strongly reflects productivity in surface waters.
o13C in carbonate tests of benthic foraminifera derived from dissolved CO2 in bottom waters leads to record of bottom water o13C
Nutrient-rich, productive Antarctic surface waters leads to low o13C AABW
Lower nutrient, moderately productive N Atlantic surface waters leads to higher o13C NADW
This is index of strength of AMOC

Question 18

What does the evidence for changes in North Atlantic Circulation show?

Answer 18

-Significant changes in N Atlantic circulation have occurred over last glacial-interglacial cycle.
-Glacial periods characterised by reduction/cessation of NADW production.
-Large temperature fluctuations associated with last glacial period (Heinrich Events).

Question 19

Process of glacial periods?

Answer 19

-Orbital trigger leads to warm SSTs & warm winters
-Increased evaporation & precipitation at high latitudes
-Increased Freshwater in N Atlantic
-Decreased NADW formation
-Decreased poleward transport of warm saline water
-Decreased SST
-Decreased evaporation
-Maintenance of low salinity surface water

Question 20

What are Heinrich events?

Answer 20

-Episodes of rapidly accumulating ice-rafted debris characterize N Atlantic sediment cores.

Question 21

Features of Heinrich events?

Answer 21

-Appear to be correlated with temperature fluctuations in Greenland ice cores.
-Possibly caused by growth of ice shelves to the point where they developed instabilities leads to iceberg calving and ice stream surges.
-Subsequent regrowth of ice shelf reduced ice flow to ocean leads to increase in NADW formation leads to warming.

Question 22

What were the changes at the end of the last glaciation?

Answer 22

-Period of climate deterioration during last glacial-interglacial transition (11,000 y ago) lasted several hundred years = ‘Younger Dryas’.
-Re-advance of glacial ice in Scotland, and more severe climatic conditions over UK.

Question 23

Recent theory for cause of changes at the end of the last glaciation?

Answer 23

-Temporary major diversion of glacial meltwater from retreating Laurentide ice sheet from Mississippi (Gulf of Mexico) to Mackenzie (Arctic) and St Lawrence (North Atlantic).
- This has caused an influx of cold, low salinity meltwater to N Atlantic.

Question 24

What causes warm and cold fronts?

Answer 24

Rossby waves

Question 25

What is sensible and latent heat?

Answer 25

Sensible heat - heating of atm. by conduction and convection
Latent heat - heating of atm. by evaporation and condensation