GPHY 314 Quiz: Week 3

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29 Dec 2020
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WEEK 3: Climate History of Earth
Introduction to Paleoclimatology
Paleoclimatology: study of past climates
o Focus on understanding magnitude and causes of past climate change
o Primary methods for studying the past:
Climate reconstruction using climate proxies
Climate reconstruction and sensitivity tests using climate models
Linkages with historical geography
Historical documentation compared to recent period
Geological time scale:
o Earth is 4.6 billion years old, moon ~30 million years younger
o Over earth’s history, six major extinctions occurred
o Relative time: older things at the base, young things at the top
Based on the principle of superposition, assumes no disturbances
o Absolute time: based on radiometric dating, provides accurate age
o Tectonic: billions to millions of years
o Orbital: hundreds of thousands to tens of thousands of years
o Millennial: tens of thousands to hundreds of years
o Historical/instrumental: period of widespread human observation of climate
Quality of our records decline…
o Time periods we can represent with climate proxies pretty small as you go back in time
Historical records -> Only understand short-term variations
Tectonic time scales show much larger changes
o Much higher resolution record but less noticeable changes as we get closer to present
Quality of climate proxies:
o Tree rings can go down to annual years but won’t give us information
deeper in time
o Continental coastal sediments could go thousands or millions of years back
o Need to find balance between them to get reliable estimate of change
Take series of sources to piece together climate record
Most Common Climate Proxies
Fossil records (tectonic to millennial)
o Help point us to what climate conditions were at time of organism death
o Fossilized plants really hand because size gives indication of temperature
Warmer temperatures tend to lead to rounder leaves
Sediment cores (tectonic to orbital)
o Sediment sources to continental margins and oceans are from physical, chemical and
biological processes, in order to be dated
Affected by sediment production and deposition
o Tend to take sediments from oceans, use deep ocean cores for deep time, use lake
sediments for more recent periods
Deep ocean only thousands of years of information since deposition so slow
o Lots of ocean coring sites, especially North Atlantic base
Ice cores (orbital to historical)
o Usually taken from ice sheets -> Annual layers accumulate through time which have
bubbles trapped in them
o Temporal resolution usually decreases with depth of ice core
Upper layers don’t have great record since shallow ice doesn’t lock in the air
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o Best place is continental ice sheets since tend to be thickest, especially those with fairly
regular precipitation records
o Lots of ice coring sits -> Longest records from East Antarctic ice sheet
o Oxygen isotopes
Ice cores -> Oxygen from frozen water analyzed with mass spectrometry
Ocean cores -> Oxygen included in foraminifera shells
Organism dies, shells fall to sea floor and are eventually covered
Use isotopic analysis when we have more of a certain type of isotope than
another, giving us information as to whether it was warmer or cooler
Dating of rocks and organics
o Radiometric dating (tectonic to orbital)
o Carbon-14 dating (orbital to historical)
Pollen records from lake cores (millennial to historical)
o Look at types of pollen in layers, see what kind of vegetation available in past
Tree rings (millennial to historical)
o Interpret growth sometimes to have association with temperature or precipitation
o Tree ring data collected in the southern Yukon can show strong correlation with summer
temperature
Climate Models and the Past (Ted Talk)
Scales that give us information about climate change have 14 orders of magnitude 10-6 to 108
Subscale processes tough to approximate, which lead to emergent processes of climate
Increasing by one order of magnitude about each decade
Each kick to the system provides us with information about whether we can make an estimate
about the system
Question to ask is whether model tells you more information than you would have otherwise had
o If it does, it’s skillful
Models are skillful in response to…
o Solar cycles
o Orbital changes over last 6,000 years
o Ice sheets 20,000 years ago
o 20th C multi-decadal trends
o Lake outburst into North Atlantic 8,000 years ago
^Each evaluation allows us to add more scope to these models
Choices for the future… some mitigation vs aggressive mitigation vs business-as-usual
o Differences between these choices can’t be answered by looking at models
Carbon Cycle
Bathtub drain plug = output flux, bathtub tap = input flux
o Based on their balance, results in reservoir size
o If have slightly greater input, over time see influx in reservoir
o If you get change in flux, large reservoir able to sustain itself with those changes for
longer than small reservoir
Most of our carbon stored in sediments and rocks, some in ocean, atmosphere, soils, vegetation
o If any out of balance, over time see gradual change in size of major carbon reservoirs
1990s complete picture of the carbon cycle
o Drawdown of carbon from the atmosphere, and fossil fuel burning which adds
to atmosphere
Primary absorption of carbon is in the summer (included in photosynthesis process)
Overarching increase in carbon dioxide in atmosphere
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