Climate Modelling Basics Questions and Answers

Q: All of the following are sources of uncertainty in a climate projection EXCEPT

Correct answer: the value of the gravitational constantThe gravitational constant is known to many significant figures and is not a source of projection uncertainty at all. The three genuine sources are the ones listed, and they are of quite different kinds: how the model represents feedbacks, the unforced internal variability of the system itself, and the future path of emissions - which is a matter of human choice rather than of physics.

Q: Match each source of projection uncertainty with the timescale on which it dominates.List IA. Internal variabilityB. Model response uncertaintyC. Emission scenario uncertaintyD. Observational uncertaintyList II1. the second half of the century2. the first decade or two3. the interpretation of the recent past4. the middle of the century

Correct answer: A-2, B-4, C-1, D-3Each source dominates over a different horizon. Internal variability dominates the first decade or two, since a forced trend is small over that period against natural fluctuation. Model response uncertainty dominates the middle of the century, when the forcing is appreciable but the scenarios have not yet diverged. Emission scenario uncertainty dominates the second half, when what humanity does swamps everything else. And observational uncertainty bears on interpreting the recent past rather than on the projection.

11.

All of the following are sources of uncertainty in a climate projection EXCEPT

A.the model's representation of feedbacks
B.internal variability of the climate system
C.the value of the gravitational constant
D.the future path of emissions

Answer: C

Correct answer: the value of the gravitational constant

The gravitational constant is known to many significant figures and is not a source of projection uncertainty at all. The three genuine sources are the ones listed, and they are of quite different kinds: how the model represents feedbacks, the unforced internal variability of the system itself, and the future path of emissions - which is a matter of human choice rather than of physics.

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12.

Match each source of projection uncertainty with the timescale on which it dominates.
List I
A. Internal variability
B. Model response uncertainty
C. Emission scenario uncertainty
D. Observational uncertainty
List II
1. the second half of the century
2. the first decade or two
3. the interpretation of the recent past
4. the middle of the century

A.A-4, B-2, C-1, D-3
B.A-2, B-4, C-3, D-1
C.A-3, B-1, C-4, D-2
D.A-2, B-4, C-1, D-3

Answer: D

Correct answer: A-2, B-4, C-1, D-3

Each source dominates over a different horizon. Internal variability dominates the first decade or two, since a forced trend is small over that period against natural fluctuation. Model response uncertainty dominates the middle of the century, when the forcing is appreciable but the scenarios have not yet diverged. Emission scenario uncertainty dominates the second half, when what humanity does swamps everything else. And observational uncertainty bears on interpreting the recent past rather than on the projection.

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13.

Assertion (A): Near term climate projections are dominated by internal variability rather than by scenario choice.
Reason (R): Emissions under different scenarios have not yet diverged much in the first decade or two.

A.Both A and R are true, and R is the correct explanation of A
B.Both A and R are true, but R is not the correct explanation of A
C.A is true but R is false
D.A is false but R is true

Answer: A

Both are true and the reason gives the cause, and it means the near term is genuinely uncertain in a way that better models cannot remedy. Effort spent refining the models buys most where the scenario and the response dominate instead.

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14.

An ensemble of model runs is used to

A.eliminate all of the uncertainty entirely
B.sample the range of possible outcomes
C.make the model run rather faster
D.reduce the grid spacing used

Answer: B

Perturbing the initial conditions, the parameters or using several models each samples a different kind of uncertainty. The spread of the ensemble is as informative as its mean. Different ensembles sample different things.

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15.

Consider the following statements about model ensembles.
1. An initial condition ensemble samples internal variability.
2. A multi-model ensemble samples structural uncertainty.
3. The ensemble mean is always the most likely outcome.

A.1 only
B.All of them
C.1 and 2 only
D.3 only

Answer: C

The first two are correct and describe two distinct kinds of ensemble. The third overstates it, since the models are not independent and the mean may fall in a region no individual model supports. The models are not independent of one another.

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16.

State whether the following is true or false.
Climate models are evaluated by testing whether they reproduce the observed climate and its variability.

A.False
B.True only at large scales
C.False only at small scales
D.True

Answer: D

Simulating the mean state, the seasonal cycle and known past changes are all standard tests. No model passes every test, and the choice is between models with different strengths. No model passes every test that is set.

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17.

Three of the following are ways of evaluating a climate model. Which is the odd one out?

A.confirming that it agrees with other models
B.comparing its mean climate with observations
C.testing its simulation of the seasonal cycle
D.checking whether it reproduces past climate changes

Answer: A

Agreement between models says nothing about whether either is right, since they share assumptions and sometimes code. The other three all test the model against something independent. Shared assumptions produce shared errors.

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18.

Assertion (A): Agreement between climate models is not by itself evidence that they are correct.
Reason (R): The models share assumptions, parametrisation approaches and sometimes code.

A.A is false but R is true
B.Both A and R are true, and R is the correct explanation of A
C.Both A and R are true, but R is not the correct explanation of A
D.A is true but R is false

Answer: B

Both are true and the reason gives the limitation, and it is why evaluation against observations rather than against other models is what carries weight. A shared error would appear as agreement rather than as a warning.

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19.

An emission scenario used in a climate projection is

A.an observation of the past emissions
B.a fixed physical constant of nature
C.a plausible future path of emissions
D.the model's best forecast of future emissions

Answer: C

Scenarios are inputs chosen to span a range of possible futures, and which one occurs depends on decisions not on physics. Reporting a projection without its scenario is meaningless. Which path occurs is a matter of decisions.

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20.

Assertion (A): A climate projection is always reported together with its emission scenario.
Reason (R): The projection is conditional on the scenario, which is an assumption rather than a prediction.

A.Both A and R are true, but R is not the correct explanation of A
B.A is true but R is false
C.A is false but R is true
D.Both A and R are true, and R is the correct explanation of A

Answer: D

Both are true and the reason gives the conditionality, and a figure quoted without its scenario cannot be interpreted at all. A high projection under a high emission path says nothing about what will happen under a low one.

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