Climate Change and Variability Questions and Answers

Q: Which among the following gases has the highest global warming potential?

The gas with the highest global warming potential is N2O.Global warming potential (GWP) compares the warming caused by a mass of gas over a time horizon, usually 100 years, with the same mass of CO2, which is defined as 1. Over 100 years, nitrous oxide has a GWP of roughly 270 to 300 because it absorbs strongly and lasts more than a century in the atmosphere. Methane's GWP is about 28 to 30: it absorbs strongly but survives only around a decade.CO2 is the reference, GWP 1. Water vapour is not usually assigned a GWP, because its concentration is set by temperature and it stays in the air only days; it acts as a feedback rather than a forcing.

Q: Climate variability differs from climate change in that variability

Correct answer: refers to fluctuations about a fixed meanVariability is the natural swing of the system around its mean state - a warm year, a cold decade, an El Nino - and it occurs whether or not anything is forcing the climate. Change is a shift in the mean itself. Both are present in any real record, which is why separating them is the whole business of detection.

Q: All of the following contribute to global sea level rise EXCEPT

Correct answer: melting of Arctic sea iceSea ice already floats, so it displaces its own weight of water and its melting leaves the level essentially unchanged - Archimedes’ principle. The other three all add: thermal expansion of the warming ocean, and mass transferred from land to sea by the Greenland ice sheet and by mountain glaciers. Expansion and land ice each account for a large share of the observed rise.

Which among the following gases has the highest global warming potential?

A.\(CO_{2}\)
B.Water vapor
C.Methane
D.\(N_{2}O\)

Exam Year(s)

GATE XE - 2023,

Answer: D

The gas with the highest global warming potential is N₂O.

Global warming potential (GWP) compares the warming caused by a mass of gas over a time horizon, usually 100 years, with the same mass of CO₂, which is defined as 1. Over 100 years, nitrous oxide has a GWP of roughly 270 to 300 because it absorbs strongly and lasts more than a century in the atmosphere. Methane's GWP is about 28 to 30: it absorbs strongly but survives only around a decade.

CO₂ is the reference, GWP 1. Water vapour is not usually assigned a GWP, because its concentration is set by temperature and it stays in the air only days; it acts as a feedback rather than a forcing.

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Climate variability differs from climate change in that variability

A.refers to fluctuations about a fixed mean
B.refers to a long term shift in the mean value
C.is always caused by some human activity
D.occurs only in the tropics and nowhere else

Answer: A

Correct answer: refers to fluctuations about a fixed mean

Variability is the natural swing of the system around its mean state - a warm year, a cold decade, an El Nino - and it occurs whether or not anything is forcing the climate. Change is a shift in the mean itself. Both are present in any real record, which is why separating them is the whole business of detection.

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Assertion (A): Detecting a climate trend requires an estimate of the natural variability first.
Reason (R): A trend can only be judged significant against the background of fluctuations that occur anyway.

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

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the logic. A record contains fluctuations that would occur anyway, so a trend is meaningful only when it is large relative to them. Estimating that natural variability - from long observational records, from proxies, or from model runs with no forcing - is therefore the first step, and it is why short records support no conclusions.

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Attribution of an observed change to a cause is normally done by

A.extending the record backwards in time
B.waiting for the change to become larger still
C.matching the observed pattern to modelled ones
D.measuring the change a good deal more precisely

Answer: C

Each forcing produces a characteristic spatial and vertical fingerprint, and the observations are matched against them. This is why attribution rests on models as well as observations. Each forcing has its own fingerprint. Models supply the expected patterns.

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Consider the following statements about detection and attribution.
1. Detection establishes that a change has occurred beyond natural variability.
2. Attribution assigns the change to particular causes.
3. The two are the same exercise under different names.

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

Answer: D

The first two are correct and the order matters, since attribution presupposes detection. The third conflates two distinct steps in the argument. Detection must come first of the two. Attribution presupposes a detected change.

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Match each observed change with its measured direction.
List I
A. Global mean surface temperature
B. Arctic sea ice extent in September
C. Global mean sea level
D. Ocean heat content
List II
1. risen by around twenty centimetres over the last century
2. risen by about one degree since pre-industrial times
3. increased steadily through the recent decades
4. declined markedly over the satellite era

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

Answer: A

Each is an independent line of evidence and they are mutually consistent, which is what makes the overall picture robust. Ocean heat content is the least noisy of the four. The four lines agree with one another. Consistency is what makes the picture robust.

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Assertion (A): Ocean heat content is a better indicator of the planetary energy imbalance than surface temperature.
Reason (R): Most of the excess energy goes into the ocean, and its heat content is far less noisy than the surface record.

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

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives both halves. Over ninety per cent of the excess energy accumulating in the system goes into the ocean, so ocean heat content measures the imbalance directly rather than one of its consequences. And because water has an enormous heat capacity and the ocean is not stirred by weather in the way the surface air is, the record is far smoother - it shows no hiatus where the surface record does.

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Sea level rise arises principally from

A.increased rainfall over the open ocean
B.changes in the ocean tides
C.thermal expansion and melting land ice
D.the melting of the floating sea ice

Answer: C

Sea ice is already floating and its melting does not raise the level appreciably. Thermal expansion dominated in the twentieth century and land ice loss has grown in importance since. Floating ice contributes almost nothing.

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State whether the following is true or false.
Melting of floating sea ice raises global sea level substantially.

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

Answer: D

Floating ice already displaces its own weight of water, so its melting changes the level hardly at all. Land based ice is the component that matters for sea level. Archimedes settles the question. Expansion dominated the twentieth century rise.

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10.

All of the following contribute to global sea level rise EXCEPT

A.melting of Arctic sea ice
B.thermal expansion of ocean water
C.loss of mass from the Greenland ice sheet
D.melting of mountain glaciers

Answer: A

Correct answer: melting of Arctic sea ice

Sea ice already floats, so it displaces its own weight of water and its melting leaves the level essentially unchanged - Archimedes’ principle. The other three all add: thermal expansion of the warming ocean, and mass transferred from land to sea by the Greenland ice sheet and by mountain glaciers. Expansion and land ice each account for a large share of the observed rise.

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