Lecture Thirty Three - Climate Change (natural processes) Flashcards
What controls the climate of the Earth (non-human)?
Atmospheric components. Natural greenhouse effects. Milankovich cycles. Tectonic driven climate change. Volcanic effects. Past climate extremes.
What is in our atmosphere?
N2 - 78.1%
O2 - 20.9%
Ar - 0.93%
CO2 - 0.04% - increased by 20% in the past 20 years.
What is the origin of the atmosphere (several theories, not all right)?
Left over from the original accretion 4,250 Ma ago:
- Earths surface originally too hot.
- Volatiles (gasses and water) from original formation atmosphere would have escaped.
- Wrong isotope ratios in modern atmosphere to be from original accretion.
Captured from space since formation:
- Cometary debris constantly hitting the Earth, but not very much of it.
- Less than 0.0001% of current atmosphere.
- Some water, organic molecules could originate like this, but not enough.
Generated by a major meteorite impact:
- Volatiles are given off from crushed and fused rocks.
But many major impacts would have heated earth surface causing original and impact volatiles to escape.
- Composition of atmosphere doesn’t contain right amounts of some elements to have originated entirely from meteorites.
Gases from earths interior freed during volcanic eruptions:
- Volcanism has occurred through geological time.
- Composition of volcanic gases mirrors composition of early atmosphere trapped in rocks and minerals.
What is the composition of volcanic gasses?
Volcanic gases: H2O - 77% (by volume). CO2 - 11.7% SO2 - 6.5% N2 - 3% H2 - 0.5% CO - 0.5% S2 - 0.3% Cl2 - 0.05% Ar - 0.05% O2 - NONE!
Atmospheric gases: H2O - variable. CO2 - 0.04% N2 - 78.1% Ar - 0.93% O2 - 20.9%
Significant differences in O2, CO2, N2 and SO2.
No O2 from volcanoes.
(Don’t need to know exact numbers, just general trends).
If no O2 is produced from volcanoes, and volcanic gases are responsible for the origin of the atmosphere on Earth, how can O2 exist on Earth?
Photosynthesis.
Plants take up the CO2 in the atmosphere and O2 is a byproduct of the photosynthetic reaction.
What is insolation and albedo?
Incident solar radiation (insolation = amount of sunshine) per unit surface area varies with latitude.
- Highest at the equator, and lowest at the poles.
Insolation varies with albedo:
Albedo = reflectivity of the earths surface to incident radiation.
Albedo is highest (most reflective) for - dense clouds, deserts, snow, ice, water at low angles of incidence (poles).
Albedo is lowest (least reflective) for - vegetation, soil, rocks, water at high angles of incidence.
Insolation low at poles and high at the equator.
Insolation varies with the distance of earth from the sun (seasons).
greatest insolation during southern hemisphere summer and less insolation drink norther hemisphere summer.
How can climate change be attributed to the earth orbital behaviour?
Shape of the orbit around the sun is an ellipse whose shape (eccentricity) can change regularly.
- Periodicity of 100,000 years = distance of earth from sun changes.
- This changes insolation.
The earths axial tilt varies (axial tilt obliquity):
- Angle of tilt of the earths axis of rotation relative to plant of orbit around the sun varies.
- Periodicity of 41,000 years.
- Changes in insolation levels at different latitudes.
The earths axis ‘wobble:’
- Conical path.
- Precession - the earths axis moves in a circular pattern.
- Periodicity of 23,000 years.
- Influences insolation relative to latitude and time of the year.
Milankovitch cycles:
- Eccentricity, obliquity, precession combine to give you regular cycles of climate change called Milankovitch cycles.
- Sequences of warm winters, cold summers around poles.
- Increased evaporation, precipitation.
- Periodicity and intensity not enough to trigger ice age, but may enhance smaller scale global and interglacial stages during and ice age.
What is the greenhouse effect?
Increase of temperature due to trapping of heat.
CO2, H2O and CH4 and other gases absorb radiant hear from earths surface and radiate it back - average T = 15 degrees C, without it average T = -18 degrees C.
CO2 levels have been naturally variable over time, therefore T has been variable.
The development of photosynthetic organisms have caused the CO2 levels to drop significantly.
What are indicators of temperatures in the past?
Ratio of isotopes:
Ratio of isotopes - O18:O16 - in ocean water is sensitive to global temperatures.
Warm water evaporates H2 O16 in preference to H2 O18, and therefore H2 O18 rains out earlier.
Measure the change in O18 in the CaCO3 shells of marine organisms/fossils, or in ice or sediment cores.
highly sensitive to ocean temperature changes, can measure past temperature to fractions of a degree.
Essentially, a higher temperature = more O18 in shells because O16 is being preferentially evaporated.
Therefore temp can be predicted by looking at these ratios.
Global sea level changes:
Sea level is proportional to the temperature.
Ice age = water trapped on land therefore lower sea levels.
Greenhouse periods = higher sea levels.
What are some non-gaseous causes of climate change?
Plate tectonics:
Changing positions of continents can:
- Alter ocean current paths = cooling or warming of polar regions - increase of decrease in albedo.
More chance of ice age when there re continents at the poles.
Increase or decrease in desertification:
- Deserts larges in pangaeal times, smallest in fragmented times.
Increasing desert areas = increasing albedo (more reflective) = drops in temperatures.
What have been the effects of major volcanic eruptions on climate change?
Release of CO2:
- Short term, ‘small’ addition relative to existing levels.
- Minor enhancement of green house effect.
Fine volcanic ash dispersed into troposphere and stratosphere:
- Increased atmospheric albedo.
- Rapid fallout of ash (weeks, months).
- Limited effect int he long term.
