Lecture 3
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CO2 levels have not been this high in? Why?
80,000 years, possibly due to human interaction and Earth’s natural changes and fluctuations
Why do we know that climate change was caused by human activity?
Because the changes are only changing a little because of the seasons, the sharp increase was caused by humans using fossil fuels
What is the Milocanovic cycle?
The Earth’s changes in climate caused by earth’s long term rotation and orbit
The temperature from 1860-1920 was?
0.4 degrees below the average
The temperature from 1990 to the present is?
0.4 degrees above the average
Why was there a period of global warming dropping?
Aerosols which reflected solar radiation, but they were banned for being harmful.
Proxy data
preserved physical characteristics of the environment that can stand in for measurements
What proxy data is used as natural recorders of climate variability?
tree rings, ice cores, fossil pollen, ocean sediments, and corals
How do we reconstruct temperatures in the geological past?
Use natural processes that are temperature-dependent, like isotopic fractionation (seperation of isotopes)
What are isotopes?
Atoms that have the same number of protons but different numbers of neutrons
What is the difference between isotopes?
They have a different number of neutrons, resulting in different atomic masses
In the isotopes O-16 and O-18 which is heavier?
O-18 because it has more neutrons meaning it takes more energy to move than O-16 and will seperate due to weight
H2O has O16 and O18, which will evaporate more easily?
O16
How will O16 and O18 move in colder climates if they are in H2O?
O18 will be preferentially removed by precipitation, but will drop out early. O16 will evaporate easily, and is lighter, allowing it to travel further before getting locked in glaciers and snow and won’t move back to the ocean.
What does the O18/O16 ratio mean in colder climates?
When it is cold, there is relatively more O18 in the seawater, causing the ratio to increase as the numerator grows
How will O16 and O18 move in warmer climates if they are in H2O?
O16 will still move more easily than O18 which is preferentially removed and will drop out first. The O16 rich cloud will still drop off in the mountains, but with no glaciers and snow it can flow right back into the ocean.
What does the O18/O16 ratio mean in warmer climates?
There is more O16 in the seawater causing the ratio to decrease as the denominator is getting bigger
How do we reconstruct temperatures in the geological past?
Forams (foraminifera) and ice cores
What are forams?
Microscopic marine plankton that are shell builders. They make shells of calcium, carbon, and oxygen that are durable and accumulate at the bottom of the ocean, forming layers that can be broken apart and looked at.
What do ice cores do?
The preserve bubbles of ancient air, including H2O, as a natural material that traps oxygen isotopes going back about a million years. The oxygen can be tested to determine when that bubble was formed and what the temperature was like then
What is thermohaline circulation?
Called the Great Ocean Conveyor, it channels oxygen, carbon, heat & nutrients around the world’s oceans, driven by density differences.
How long does it take for the conveyor to be completed?
1000 years
How do you change the density of water?
You have to change the temperature (thermo) and the salinity (haline). The saltier the water the more dense it will be, the fresher the water the less dense
Why is the water less dense around the equator and more dense in North America.
By the equator there is more precipitation and it is warmer, but in North America there is more ice formation and it is cold which is taking all of the freshwater and leaving salty seawater