Lecture 32: Climate Change Flashcards
-Proxy and Understanding Past Climate -Fast and Slow Feedbacks -Human Impact on the Atmosphere and Lead to Changes of the Other Earth Systems
What is a proxy?
A source of climate information that is from natural and human records that can be used to estimate past climate conditions
How is proxy data helpful?
It allows to infer information about past climate and environments in the absence of direct measurements
What are some human records that can be used for proxy data?
1) Agricultural or shipping records
2) Pictures, sketches, paintings
3) Writings
- Egyptians recording the Nile flood levels going back to 3000 BC
What was the climate like in the last millennium?
- Medieval Warm Period: around AD 900, lasting for a couple hundred years
- Little Ice Age: followed the Medieval Warm Period, marked by biggest advances in glaciers since the end of the last glaciation
What are some natural records that can be used for proxy data?
1) Pollen, plant macrofossils, shells, tree-rings
- Can be related to temperature, humidity, precipitation
- Indicator species
- Landscape reconstruction
2) Isotopes
- Total solar irradiation
- Temperature, elevation, CO2, Ice volume
What are some examples of organisms that have annual growth rings?
- Trees
- Corals
- Varves (lake sediment that has laminated beds)
- Ice cores
How is pollen used as a natural proxy?
Each plant has unique looking pollen, so pollen fossils from a sediment core can reveal a plant assemblage.
-This can be used to estimate climate conditions
What are indicator species?
Organism (often a microorganism or a plant) that serves as a measure of the environmental conditions that exist in a given locale.
-have very defined habitats, temperature and/or precipitation requirements
Why are ice cores so important?
Because the ice preserves gas bubbles from past atmospheric compositions (also dust and aerosols)
-Isotopes of O and H can reconstruct past temperature, humidity, and precipitation patterns
What natural proxy has the longest and detailed records?
Marine sediment cores
The ratio of 18^O and 16^O in sea water depend on what?
Water temperature and ice volume of land
What is the advantage of marine sediment cores?
Global coverage, very long records but also very high resolution shorter records
What are the complications with marine sediment cores?
- No direct measurements of atmosphere gas concentrations
- Complex proxies that only get more complex the further back you go
What are fast feedbacks?
Feedbacks that responds on shorter time-scales
What are slow feedbacks?
Feedbacks that take much longer to take full effect
-Can be considered forcings
What is climate sensitivity?
The sensitivity of the climate system to a change in radiative forcing.
-expressed in terms of the global mean temperature (GMT)
What is Equilibrium (Charney) climate sensitivity?
The amount of warming that will occur once all the processes have reached equilibrium
What is Transient (effective) climate sensitivity?
The amount of warming that might occur at the time when CO2 doubles, having increased gradually by 1% each year
What is Earth system sensitivity?
Similar to equilibrium climate sensitivity, but on longer time-scales
What are some main anthropogenic greenhouse gas sources?
- CO2: fossil fuel combustion
- CH4: natural gas leaks, landfills, livestock, coal (GWP=30)
- N2O: agriculture (GWP=270)
What is global warming potential (GWP)?
Warming potential of a greenhouse gas compared to CO2 over a defined time period.
What is polar amplification?
the northern latitudes experience much higher rates of warming due to feedbacks
What are the consequences of melting sea ice?
- Less ice to reflect solar radiation back to space
- Warmer sea
- Higher sea level
What is the current rate of sea level rise?
3.3 mm/yr
Why is there a ‘cold blob’ in the North Atlantic?
It is the result of slowing of thermohaline circulation in the region likely due to fresh water
What two things are causing global rise of sea level?
1) Thermal expansion
2) Melting glaciers and ice sheets
How much CO2 has been absorbed by the oceans?
26%
Why are oceans a major buffer?
Because they absorb ~93% of the excess heat caused by increasing greenhouse gases
What are some consequences of warmer ocean water?
- decreased capacity for CO2
- increased CO2 = increased acidification
- coral bleaching
- more violent storms
