Week 7 Flashcards
Name some old volcanic eruptions that caused disturbances to the atmosphere?
Pinatubo
Krakatoa
Tambora
Why do volcanic eruptions not cause lasting perturbations to the climate?
the material released from volcanoes eneters high in the atmosphere (strateosphere) eg. 15kms - everything at this level is very well mixed by convection
the only way out of the stratosphere is through dispersal downward - pollution in the lower part of the atmosphere gets dissolved into water and then rained out
however, sulphate particles in the stratosphere take a long time to fall ot therefore doo cool the earth for a while, mixed around the earth gives you a layer that can reflect more sunlight than usual
What is hysteresis?
the multiple equilibrium climates for a given set of boundary conditions
- strong self-sustainabing feedbacks in some component of the climate system eg. ice sheets, ocean circulation or clouds
- multiple ice sheet equilibria likely to be important for inter/glacail cycles
What is a tipping point?
beyond a certain Co2 temperature threshold, some components of the climate system may change abruptly
these can associated with stronger positive feedbacks eg. ice sheets and albedo - which can lead to accelerated warming
as you reduce temperature again you don’t move back along the same path - to get the same amount of sea ice back after the tipping point has been reached would need to get to a much lower temperature than how you started.
Use subtropical clouds to explain tipping points and hysteresis
- subtropical clouds display both hysteresis and tipping points
- low cloud amount can modify the underlying ocean surface temperature - via radiation which feeds back on the cloud properties
- clouds depend on being able to cool to space, infrared energy emitting at the top of the cloud has to be cool
- as you increase Co2 concentrations the cloud fraction tay at about 100% but at a certain point the cloud cannot cool enough - not sufficient temp difference to form a cloud - cloud collapse therefore reduce to about 25% cloud cover
- if there is enough co2 in the atmosphere not possible to maintain the cloud
= cloud tipping point
even if you start taking Co2 out the atmosphere - you come back along a different pathway - sunlight can now warm the earths surface and the modified temperature still clouds cannot form
How is the Sahara an example of a tipping point?
until about 6,000 years ago, the sahara was much less arid than today
- used to be similar to south Africa but climate change rapidly - 1-2 centuries
not entirely clear what the cause was but could be due to the Atlantic ocean circulation
What is the big fear about tipping point?
there are many proposed tipping points some are more likely than others
many of the tipping points are highly uncertain and difficult to model - the processes are poorly represented in climate models
they are difficult to model as they can be dependent on small scale properties and processes such as clouds - cannot accurately model for each potentially important particle in a cloud
difficult to model how certain elements of the earth will respond to tipping points - individual trees, small scale processes are not represented well in climate models
What was one of the motiviations for the pairs agreements limiting of temperature increases?
to avoid possible tipping points, we should limit global warming and co2 emissions as much as possible
this is one of the motivators for the 2oc global warming target for the pairs agreement
the higher the temperature the more likely it is that we will break the tipping points - and it is difficult to get back once these have been passed
Can you give me some examples of possible tipping points?
Pine island and thwaites glacier - sea water underneath melting the glacier - big glacial retreat no longer holding the glacier effectively, uncertain if the tipping point has already been reached
species such as plankton are important feedback int he climate system - getting them back once they are all killed would require much lower temperature than we are - very difficult to represent in a climate model
what are models?
they are a way of making sense of observations and allowing us to make predictions about new situations
scientific representations of reality - enables you to calculate something useful
they are not necessarily on a computer
What is a climate model?
a climate model is a representation of reality
used for
- testing hypothesis - what happens if I increase Co2?
- improving understanding of the current system - how does ENSo work?
- simulating past and future cliamtes - what will climate look like in 1,000 yrs
they are representations of the real world, physical descriptions using mathematical equations and assumptions or simplifications
How does a weather model differ from a climate model?
they are versions of the same thing
but weather forecast models tend to assimilate observation to initial forecasts
- run at higher resolution - more grid boxes
- have simplified representations of slow processes eg. oceans and veg.
climate models don’t really care what the weather is like to predict the future weather
Why is the statement wrong: scientists can’t even predict the weather in 10 days, so how would they be able to predict cc?
- weather modeling is an initial value problem, climate modeling is a boundary value problem
- if you want to know the weather next week, need to know what the weather is like now - initial conditions
- if you want to know the climate in 2050, need to know what CO2 emissions are going to be - boundary conditions
we can predict future average climate but cannot predict the exact weather decades from now
idea that external forcing drives climate therefore need to view it as a different problem
In a simple cliamte model what are some of the essential components?
an atmosphere is required to get a sensible temperature estimate
- a greenhouse gas effect is required
- a more complex simulation is needed to represent the other elements of the earths atmosphere
Why did we only use one and not 2 temps for the atmosphere?
this would lead to many different layers of the atmosphere
the earths surface, the lower atmosphere and the upper atmosphere
equations get longer but they are solvable
