External causes of climate change

Question 1

How does Interstellar dust affects radiative transmissivity of interplanetary space?

Answer 1

Influences cloud formation on entry to atmosphere which leads to greater reflection.

Question 2

What has the Solar System having crossed Galaxy arms four times in last 520 Million years caused?

Answer 2

Alternating warm and cold periods.

Question 3

What do molecular dust clouds called?

Answer 3

Decreased solar radiation which leads to a decreased temperature of 5-7 degrees.

Question 4

What do stellar models predict?

Answer 4

a star’s luminosity is proportional to the nth power of its mean molecular weight, where n = 6 or 7.

Question 5

How do stars produce energy?

Answer 5

Nuclear fusion - conversion of hydrogen to helium which leads to an increase in mean molecular weight.

Question 6

Faint young sun paradox?

Answer 6

-Ice age conditions today.
-Oldest known rocks >3.7 Gy old, in Greenland show sedimentary features, demonstrating oceans not frozen.
-Evolution of life during first billion years suggests Earth surface was quite warm.
- Could have been warm due to intense greenhouse effect.

Question 7

What are the three variations in earths orbital geometry?

Answer 7

-Obliquity
-Precession of the equinoxes
-Eccentricity

Question 8

What caused Pleistocene ice age?

Answer 8

-caused mainly by periodic changes in distribution of solar radiation at Earth’s surface from variations in Earth’s orbital geometry.
-Milutin Milankovitch (1941)

Question 9

What’s obliquity and what does it determine?

Answer 9

-Angle of tilt of earth from plane perpendicular to orbital plane.
-Varies from 22.1 degrees to 24.5 degrees - currently 23.5 degrees.
-Determines latitudes of polar circles and tropics

Question 10

What happens when angle of obliquity increases? And what does it cause?

Answer 10

-Summer radiation receipts at poles increase
-Winter radiation receipts at poles decrease
-Little effect at low latitudes
-Affects equator to pole temperature gradient as it controls strength of atmospheric circulation which has seasonal contrast.

Question 11

What are the two components of the precession of the equinoxes?

Answer 11

-‘Wobble’ in axis of rotation
-Orbit ‘swings around’ in space

Question 12

Features of the precession of the equinoxes?

Answer 12

-Affects timing of the extreme earth sun distances.
-Today - Perihelion (Earth closest to the sun) during Northern Hemisphere winter.
-11,000 years ago - perihelion (Earth closest to the sun) during Northern Hemisphere hotter summers colder winters
-Greatest effect in low latitudes

Question 13

What is eccentricity? Features?

Answer 13

-Degree of egg shapedness of earth’s orbit.
-Varies from near circular to markedly elliptical.
-Influences the effect of the precession of the equinoxes.
-Maximum difference in receipt of solar radiation (perihelion and aphelion (earth furthest away from sun)) is 30 %.

Question 14

What are the conditions of orbital configurations (position of earth to sun) that favours ice sheet growth?

Answer 14

-Minimum obliquity
-High eccentricity
-Aphelion during NH summer
(These conditions induce northern hemisphere glaciation)

Question 15

Consequences of orbital configurations (position of earth to sun) that favours ice sheet growth?

Answer 15

-low levels of summer radiation especially at poles.
Low ice melt
increased equator to pole temperature gradient
Which leads to increased poleward transport of moisture which feeds snowfall
-Warm NH winters leads to evaporation from oceans.
Causes expansion of NH ice cap

Question 16

What is the evidence of an Orbital Signature in the Palaeoclimatic Record?

Answer 16

-O18O of calcareous marine fauna incorporated in sediments show dominant 100,000 y cycle.

Question 17

What supports the evidence of an Orbital Signature in the Palaeoclimatic Record?

Answer 17

-Other proxy climate records that show spectral peaks consistent with effects of orbital forcing:
-Land-based sediments
-Pollen records
-Ice cores
-Coral reef sea level records

Question 18

Problems with Orbital Signature being in plaeoclimatic record?

Answer 18

-Dominance of 100,000 y cycle
-Eccentricity important only in emphasising precession effects
-Simultaneous termination of last glaciation in NH and SH

Question 19

Why is internal amplification of orbital forcing important in terms of CO2?

Answer 19

-CO2 trends closely follow deuterium isotope temperature record in Antarctic ice core.
-This leads to positive feedback as CO2 changes reinforce and amplify temperature change.

Question 20

Why is internal amplification of orbital forcing important in terms of sea level changes?

Answer 20

-Sea level changes explain synchronicity of NH and SH deglaciation.
-Increased summer insolation and temperature at N Pole leads to substantial ice melt.
-Increased atmospheric CO2.
-Sea-level rise and greenhouse warming lead to melting and break-up of Antarctic marine ice shelf.

Question 21

Co2 changes involve changes in marine primary production?

Answer 21

Increased production leads to utilisation of dissolved CO2 leads to atmospheric CO2 (‘draw-down’).

Question 22

How could changes in marine primary production be driven by nutrient availability?

Answer 22

-Stronger atmospheric circulation (enhanced equator to pole temperature gradient).
-Enhanced upwelling.
-Enhanced atmospheric transport of minor nutrient elements (e.g., Fe).
-Fall in sea level during glacial periods leads to exposure of nutrient-rich continental shelf sediments leads to erosion.

Question 23

What do sunspot numbers directly correlate with?

Answer 23

Solar magnetic activity.

Question 24

How have we recorded solar activity?

Answer 24

-Observing sunspots
-Measuring variable amplitude
-Cosmogenic nucleotide data

Question 25

How do cosmogenetic nuclides show solar variability?

Answer 25

-Cosmic radiation leads to neutron bombardment of atmospheric N atoms in upper atmosphere which creates 14C.
-14C is oxidised rapidly to 14CO2 which diffuses and mixes in atmosphere.
-Cosmic radiation penetration modulated by solar magnetic activity.
- Overall, low sunspot number leads to low solar magnetic activity leads to increased cosmic radiation penetration leads tp increased 14C.

Question 26

True or false? There is correlation between cold and warm periods and low and high solar activity?

Answer 26

True.

Question 27

Indirect effects of cosmic radiation intensity?

Answer 27

-Ionisation.
-Formation of radiacals.
-More intense=more low level cloud coverage.
-Less intense=less low level cloud coverage.

Question 28

How does increased cosmic radiation lead to a lower surface temperature?

Answer 28

Increased cosmic radiation means low solar activity which leads to increased low level cloud coverage which leads to decreased surface temperature.

Question 29

How could cosmic radiation intensity potentially explain the increase in solar activity over the last 100 years?

Answer 29

in last 100 years there has been a 8% decrease in cosmic radiation intensity which has caused a 2% decrease in cloud cover which has caused a 0.5% increase in solar radiation receipts?

Question 30

What does a long residence time of materiel in stratosphere mean?

Answer 30

-Eruptions must be strong enough to get material into stratosphere
-A long residence of material in stratosphere means a great hemispheric or global influence.

Question 31

How does materiel in stratosphere affect radiation balance? And what does this lead to?

Answer 31

-Sulfur dioxide absorbs UV radiation which produced heat.
-Sulfur dioxide also quickly gets converted to the aerosol sulfate which reflects and scatters solar short wave radiation.
-Dust also absorbs terrestrial long wave radiation.
-Leads to warming of stratosphere and cooling of troposphere

Question 32

What are the emperical studies?

Answer 32

-Hubert Lamb’s ‘Dust Veil Index’ of Volcanic Activity
Based on eye-witness accounts (volcanic blasts, colourful sunsets, hazy skies)
-Tree Growth-Ring Chronologies
Narrow growth rings associated with colder conditions following volcanic eruptions
Discrepancies, so not particularly reliable
-Ice Core Data
High acidity levels shows well known and unidentified eruptions
Compared with ice core temperature record
Dating imprecision limits observance of clear cause and effect

Question 33

What is the superposed epoch analysis? And what is it restricted to?

Answer 33

-Surface temperature trends around time of volcanic events composited to maximise signal to noise ratio.
-Period for which surface temperature trends are available

Question 34

How are record of eruption scales and dates compiled for superposed epoch analysis?

Answer 34

-Observational chronologies (historical records)
-Geological evidence (volcanic deposits)
-Ice core dust/acidity levels
-Pollen records (dust layers)

Question 35

What’s the eruption selection criteria for superposed epoch analysis?

Answer 35

-Evidence consistent
-Well-dated events
-VEI greater or equal to 5 and/or DVI greater or equal to 300
-Small number of events selected (NH = 5; SH = 4)

Question 36

Features of Standardisation of Temperature Data to Remove Seasonal Bias for superposed epoch analysis?

Answer 36

-Data for each eruption selected for months -60 to +48 around eruption dates.
-Each monthly temperature subtracted from long-term mean for month.
-Each monthly value divided by long-term standard deviation for month.

Question 37

Process of compositing data for superposed epoch analysis?

Answer 37

-Standardised temperature data expressed for each month as a departure from the monthly mean for the 5 years preceding eruption date.
-Data for each eruption composited for months -24 to +48 around eruption dates.

Question 38

Results of superposed epoch analysis?

Answer 38

-Rapid response in NH with little lag (0.3 degrees in summer, 0.6 degrees in winter).
-Differences in hemispheric response reflect differences in land/sea distribution.
-Individual eruptions can cause significant cooling up to 2-3 years after event.

Question 39

Details of study of Mt Pinatubo?

Answer 39

-Globally averaged radiation balance at top of atmosphere was –3 W per square metre.
-Average reduction in surface temperature of 0.5 degrees.
-Reduced global precipitation (reduced radiation receipts lowered SST and affected evaporation).
-Long term effects
Temperature and precipitation anomalies vanish in 7 y.
Sea ice extent and volume anomalies vanish in 10 y.
Changes in interior ocean temperature, sea level and strength of overturning circulation persist for decades to a century.

Question 40

The Impact of Volcanic Activity on Expected Anthropogenic Warming?

Answer 40

(Satellite and other ground-based observations)
-Aerosol distributions and optical properties
-Estimates of radiative forcing and temperature changes
-Cumulative volcanic forcing effect currently offsets one third of anthropogenic warming