State whether the following is true or false.
Melting of floating sea ice raises global sea level substantially.
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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All of the following contribute to global sea level rise EXCEPT
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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Global mean surface temperature has risen by roughly how much since pre-industrial times?
Answer: B
Correct answer: about 1.1 degrees
Global mean surface temperature is roughly 1.1 to 1.2 degrees above the 1850–1900 baseline. The figure sounds small beside the day-to-day range at any one place, but it is a global annual mean - and the last glacial maximum, with ice sheets over northern Europe and North America, was only about 5 degrees colder than the pre-industrial state.
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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.
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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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.
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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The observed cooling of the stratosphere alongside surface warming is significant because it
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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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.
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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Three of the following are modes of internal climate variability. Which is the odd one out?
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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The North Atlantic Oscillation describes
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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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.
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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