Climate Change and Variability Questions and Answers

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.