Climate Change and Variability Questions and Answers

Q: The observed cooling of the stratosphere alongside surface warming is significant because it

Correct answer: is the fingerprint of a greenhouse forcingThe pattern distinguishes the cause. Increased solar output would warm the whole atmospheric column, including the stratosphere. Increased greenhouse gases trap outgoing infrared in the troposphere, warming the surface while leaving less radiation to reach the stratosphere - where the additional carbon dioxide also radiates more efficiently to space. Surface warming with stratospheric cooling is therefore the signature of the greenhouse mechanism and not of the sun.

Q: Three of the following are modes of internal climate variability. Which is the odd one out?

Correct answer: the long rise of carbon dioxideThe rise in carbon dioxide is an external forcing imposed on the system, not an internal mode. The other three are genuine internal modes: patterns of redistribution within the coupled ocean and atmosphere that move heat and rainfall about without changing the total energy of the system. That is the distinction between something that changes the climate and something that reshuffles it.

Q: If a threshold is exceeded in one summer in twenty and the distribution shifts warmer by one standard deviation, the frequency becomes roughly

Correct answer: one summer in threeOne summer in twenty is the upper 5 per cent, which lies about 1.64 standard deviations above the mean. Shifting the distribution warmer by one standard deviation puts the same threshold at 0.64 standard deviations, and the area beyond that is about 26 per cent - roughly one summer in four, so of the options offered one in three is much the closest. A one-sigma shift has multiplied the frequency by about five.

11.

Consider the following statements about the pattern of observed warming.
1. The Arctic has warmed considerably faster than the global mean.
2. Land has warmed faster than the ocean.
3. Warming has been uniform across the globe.

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

Answer: C

The first two are correct and both follow from well understood mechanisms. The third is wrong, and the spatial pattern is itself part of the attribution evidence. Uniform warming was never expected. Pattern is part of the attribution case.

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12.

Assertion (A): The Arctic has warmed faster than the global average.
Reason (R): Loss of sea ice exposes darker ocean and the ice albedo feedback amplifies the warming locally.

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 principal mechanism, though changes in atmospheric and oceanic heat transport contribute as well. The amplification is roughly a factor of two or three over the global mean, and it is reproduced by the models.

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13.

The observed cooling of the stratosphere alongside surface warming is significant because it

A.is the fingerprint of a greenhouse forcing
B.shows that the atmosphere is cooling overall
C.contradicts the greenhouse explanation
D.indicates a change in the solar output

Answer: A

Correct answer: is the fingerprint of a greenhouse forcing

The pattern distinguishes the cause. Increased solar output would warm the whole atmospheric column, including the stratosphere. Increased greenhouse gases trap outgoing infrared in the troposphere, warming the surface while leaving less radiation to reach the stratosphere - where the additional carbon dioxide also radiates more efficiently to space. Surface warming with stratospheric cooling is therefore the signature of the greenhouse mechanism and not of the sun.

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14.

Assertion (A): Stratospheric cooling with tropospheric warming points to a greenhouse cause rather than a solar one.
Reason (R): A brighter Sun would warm the whole atmosphere while more greenhouse gas warms below and cools above.

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 discriminating power of the observation, which is exactly what a fingerprint argument requires. A measurement that both explanations predict equally carries no weight in deciding between them.

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15.

Three of the following are modes of internal climate variability. Which is the odd one out?

A.the North Atlantic Oscillation
B.the Pacific Decadal Oscillation
C.the long rise of carbon dioxide
D.the El Nino Southern Oscillation

Answer: C

Correct answer: the long rise of carbon dioxide

The rise in carbon dioxide is an external forcing imposed on the system, not an internal mode. The other three are genuine internal modes: patterns of redistribution within the coupled ocean and atmosphere that move heat and rainfall about without changing the total energy of the system. That is the distinction between something that changes the climate and something that reshuffles it.

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16.

The North Atlantic Oscillation describes

A.a temperature oscillation in the tropical Atlantic
B.the overturning circulation of the Atlantic
C.a cycle in the Atlantic hurricane numbers
D.the Icelandic to Azores pressure difference

Answer: D

A positive phase brings stronger westerlies and mild wet winters to north-western Europe. It is the dominant mode of winter variability in the North Atlantic region. Both phases have their impacts. Winter westerlies respond to the index.

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17.

Consider the following statements about climate extremes.
1. Heat extremes have become more frequent as the mean has risen.
2. Heavy rainfall events have intensified in many regions.
3. A rise in the mean cannot change the frequency of extremes.

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

Answer: A

The first two are correct. The third is plainly wrong, since shifting a distribution moves far more of it past a fixed threshold than the shift in the mean itself suggests. Tails move more than means do. Thresholds sit far out in the distribution. Small shifts move a great deal of the tail. The mean shift understates the change in extremes.

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18.

Assertion (A): A modest rise in mean temperature can produce a large rise in the frequency of extreme heat.
Reason (R): The threshold defining an extreme lies in the tail of the distribution, where a small shift changes the area greatly.

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 is the statistical mechanism. Extremes are defined by a threshold far out in the tail of the distribution, where the density is low and falling steeply. Shifting the whole distribution slightly warmer therefore moves a disproportionate amount of probability past that threshold, so the frequency of exceedance rises far faster than the mean does - as the next item quantifies.

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19.

If a threshold is exceeded in one summer in twenty and the distribution shifts warmer by one standard deviation, the frequency becomes roughly

A.one summer in fifty
B.one summer in a hundred
C.one summer in three
D.one summer in twenty still

Answer: C

Correct answer: one summer in three

One summer in twenty is the upper 5 per cent, which lies about 1.64 standard deviations above the mean. Shifting the distribution warmer by one standard deviation puts the same threshold at 0.64 standard deviations, and the area beyond that is about 26 per cent - roughly one summer in four, so of the options offered one in three is much the closest. A one-sigma shift has multiplied the frequency by about five.

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20.

Mitigation of climate change refers to

A.adjusting to the effects as they come about
B.measuring the change more accurately
C.predicting the future change ahead
D.reducing emissions or removing the gases

Answer: D

Adaptation is the separate business of adjusting to changes that happen anyway. Both are needed, since some change is already committed by past emissions. The two are complementary. Committed change is already in the system.

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