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Science of Climate Change > Week 8 > Flashcards

Week 8 Flashcards

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1
Q

What two satelittes are used to look at clouds through a laser?

A

CALIPSo and LIDOR

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2
Q

What was the orbit train?

A

a series of satilettes orbiting in a train - originally they were 12 seconds apart

this enabled an in depth analysis of processes in the atmosphere which could be used to constrain or improve processes in climate models

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3
Q

What is the idea of equations and models?

A

Climate models solve sets of equations by stepping forward in time

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4
Q

Can you give some examples of natural processes that are difficult to include in climate models?

A

Roseby waves - information propogating around the atmosphere

El Nino - 100s and 1,000s of km and time scale of years

all of these get resolved by other processes that happen at smaller and faster time scales - but not explicitly due to the fact that they often happen at much smaller scales

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5
Q

What does uncoupling mean in models and can you give ma an example?

A

individual components of a climate model can be run separately

the other components become the boundary conditions

eg. running the atmospheric model only, with the prescribed SST as a lower boundary condition

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6
Q

Why would you uncouple the climate model?

A

it can be expensive to run the full model

eg. running an ocean model is expensive if you are just looking at the atmosphere, you can just fix the ocean at a certain ermpature

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7
Q

what are some of the advatnages of running a single component?

A
  • increased resolution
  • easier to control resemblance to reality
  • useful for physical understanding of the processes
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8
Q

What is required for a regional climate model?

A

boudary conditions on the side walls

  • grid boxes don’t have to be the same size globally

this requires a high resolution model over the bit you care about - can run at a v low resolution everywhere else

typically use a global climate model run

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9
Q

what is the advantage of regional climate models?

A

increased resolution and ability to control forcing

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10
Q

how are small scale processes delt with in models?

A

not all process key to the cliamte can be captured using climate models
- cloud processes occur on v small spatial and temporal scales that cant be resolved
eg. surface drag, radiative fluxes and convection

in these cases climate models are limited by resolution and subgrid-scale processes need to be parameterised

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11
Q

what is a physical parameter

A

simplifications of unresolved physics

eg. % of the grid box covered by cloud - high relative humidity - high cloud cover but what is the relationships?

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12
Q

Why are parameters important?

A

parameterised processes can have a large effect on global climate - feedbacks etc.

important to develop parameters that are useful and good in terms of global climate - but a major problem is trying to determine what a good equation or parameter is

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13
Q

Why might climate models have errors?

A
  • parameterisation is not perfect- there is uncertainty in how to represent certain aspect of the climate
  • not high enough resolution

numerical errors - drift in temperatures when there shouldn’t be

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14
Q

What are some of the key things to look at when evaluating climate models?

A

Mean climate - should be the right climatology

trends - models should correctly reproduce climate trends of the 20th cent

Natural variability - models should be able to simulate natural modes of variability

spatial patterns - models should get not only the global quantities right, but also their geographical patterns

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15
Q

what is the multi-model mean

A

the mean results from all the models

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16
Q

what was the global warming hiatus?

A

In the early 2000s the observations seem to indicate a slowdown of warming

the hiatus has since ended - rapid increase in global temperature since 2010 in observations

most likely it was caused by natural variability

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17
Q

what are some of the boundary conditions that a model requires

A

SST

sea ice location

Co2 emissions

need an initial state to start from - need to be a valid state of the atmosphere

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18
Q

What is a model bias?

A

model errors relative to observations

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19
Q

Why is the mean bias of all models small?

A

idea of averaging - compensating errors among models

the average surface temperature of models vary significantly - however the MMM is quite a good estimate

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20
Q

Is it important that most models cannot get the right temperature?

A

not really as it is more important that they get the same trend

as long as the change is correct it doesn’t really matter what the temrpature it is - being at a particular temperature wont significantly impact the response to this change.

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21
Q

Why are tempeature anomonlies better to look at ?

A

temp anomollies are better observations corelated over long distances when average temperature is harder to estimate

difficult to get a good value for average temperature of earth - how it varies from average is easier to estimate

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22
Q

In surface temperature what does the pattern for MM bias look like? Why?

A

Too hot on the western cost of south America and south Africa and eastern coast of America

due to clouds - regions of low lying couds are coarse in models - they are low and thin thus difficult to model and simulate
- causes the ocean to absorb more sunlight causing errors in ocean circulation - upwelling and cooling currents

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23
Q

What are the MMM biases for precipitation? what is the consequence of this?

A

model have too much rainfall south of the equator

there are two inter-tropical convergence zone (ITCZ) double rainy band that doesn’t exist in observations giving you two peaks in precipitation that don’t exist

24
Q

What drives the bias in MMM precipitation patterns?

A
  • changes in temperature in the southern ocean
  • how the winds move around and within the equator
  • parameterization issues

key - there is no one cause for it

also more generally there is model uncertainty - feedback loops are not well understood and depend on parameterization of processes - different mean temperatures can have huge impacts on feedback loops

25
Q

When is the min of sea ice?

A

September

26
Q

What are two other natural pheomena which the MMM gets pretty well?

A
  • arctic sea ice depsire large biases in models with some far too much or too little sea ice
  • ocean heat transport
27
Q

Why can enso be used to test models?

A

models can be evaluated based on natural variability

a good model should have realistic variability

  • climate models are generally able to simulate enso however there are some biases in SST - leads biases in ENSo impacts like rainfall and temperature
28
Q

Why does the IPCC publish simple, unweighted MMM?

A

the underlying rationale for validating modles against observations is ….the smaller the model bias, the better the model

but it is unclear whether smaller bias translates to a more accurate climate projects

this is why the IPCC publishes simple, unweighted MMMs

29
Q

Why might a model that accurate simulates today not be good for future predictions?

A

might have tweaked values for certain aspects like solar radiation to get temp correct

might distort future predictions

30
Q

Why are we not that bothered about bias for future model projections?

A

there is no obvious relationship between historical temperatures and climate sensitivity in models

it is unlikely that reducing biases in global temperature would reduce the range of climate sensitivity in models

31
Q

How do we objectively evaluate model climate performance?

A

objective, quantitive evaluation is useful as it allows a comparison with each model and can be used to assess how changes in the model code affect the model performance

  • pattern correlation
  • root mean-square error (RMSE)
32
Q

What is pattern correlation?

A

the correlation between two patterns

typically you would compare models with some reference observation dataset

high correlation means that the model can reproduce the observed pattern well

33
Q

What does TAS stand for?

A

surface temperature

observed pretty well - models get it pretty accurate

34
Q

What is RLUT?

A

outgoing longwave radiation

upwelling at the TOA - how much and where is it escaping from - can be observed from satellites - models get it pretty accurate

35
Q

What is PR?

A

precipitation

harder to predict - temp is well correlated over reasonable difference but there is a high uncertainty

36
Q

What is SW CRE?

A

shortwave cloud-radiative effect

how much clouds reflect sunlight back into space - observations are reasonable and models are not doing a great job

somewhat correct but could be doing a lot better

37
Q

What is the comparison between CMIP3 and CMIP 5?

A

CMIP 5 models tend to perform better than CMIP3

models are getting better but there are still issues

large spread between models

38
Q

What is RMSE?

A

root mean-square error

a measure of the size of the verticle bars

large bars = large error = higher RSME

if the models were perfect the dots would lie on the line of model and observations

normally on a scatter plot - look how they deviate vertically

39
Q

How does the MMM perform in terms of RSME in CMPI5 models?

A

it is better than any single model

40
Q

What is model tuning?

A

climate model parameterisation use many parameters whose values are uncertain

cloud parameters

surface roughness parameters

ocean mixing parameters

–> because these values are uncertain, model developers optimise these parameters to reduce model biases in historical climate

41
Q

how can you improve model parameters?

A

using observations - use an observational parameter and determine the plausible range of values for the observational range

42
Q

In models what is typically tunned?

A

climatologies of temperautre, radiative flux, clouds

spatial patters of some variables

most models are not tuned for a given climate sensitivity or historical trend but they can be

43
Q

What are examples of good constraints to tell if a model behaviour is working?

A

use constraints like sea ice extent

44
Q

What is an example of an emergent constraint?

A

eg. snow-albedo feedback - the percent albedo change per degree of warming

when temperature increases, snow cover decreases and albedo goes down

positive radiative feedback therefore negative numbers

seasonal variation is critical for this - idea that it can be measured and we can correlate this value to changes in climate - we can use this rule to evaluate model projections

45
Q

Why is seasonal variation importat?

A

seasonal variation is a very good predictor of cliamte change feedback

models with large seasonal feedback have a large climate feedback etc.

the seasonal feedback can be estimated with good confidence

this allows us to rule out many of the model projections and to provide a most likely value for a true feedback like albedo in the future

46
Q

What is detection and attribution?

A

detection = demonstrating that cliamte has changed in some defined statistical sense, without providing a reason for that change

attribution = establishing that the likely cause for the detected change with some defined level of confidence

important for both weather and climate - extreme events linked to climate change and the attribution of this to anthropogenic forces

47
Q

What do you mean when you talk about the fingerprint of human activities?

A

human-induced ghg leave specific fingerprints on climate, distinguishable from the effects of natural variability, volcanoes and the sun or other forcing

48
Q

why are human fingerprints useful to look at?

A

they are patterns in space and time

important for attributing cc to human activities

can help us determine what these fingerprints should look like

the pattern is the fingerprint is much more important than the mag of the signal - we know that climate models may get the mag wrong but they should get the pattern in space and time correct

49
Q

What are the three key forcings that demonstrate the change of global temperature

A

the fingerprints of volcanoes, solar activity and human activity (CO2)

cannot explain current temperatures without solar forcing

they all have very different fingerprints

50
Q

Can you describe the GHG fingerprint?

A

warming in the lower atmosphere but cooling in the stratosphere/upper atmosphere

observations show this fingerprint

51
Q

How does anthropogenic fingerprints differ from natural and volcanic fingerprints?

A

NV= gives you a warmish enviroment more high altutde than in the poles

VF= depends on whether there has been an eruption - in 1979-2012 it gives you a warming pattern as there were more volcanoes earl on and then cooler because of volcanoes as they disappear it warms

52
Q

Are there any other places other than the atmosphere where the human fingerprint is visible?

A

the oceans - ocean salinity

increase in atlantic and reduction in the pacific, has to do with evaporation and transpiration

53
Q

How do you include small scale processes in a climate model?

A

these processes are simiplified - parameterised.
this is a significant source of uncertainty - what is the equation for a cloud

54
Q

what constraints can we place on climate model behaviour?

A

we can match models to observations -eg. energy fluxes. emergent constraints also allow us to understand behaviour under climate change

55
Q

how do we attribute climate change to different causes?

A

models can uncover the fingerprints or warming from different sources

running models with only natural forcings can provide a control earth for comparison

Science of Climate Change (10 decks)

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