Thinking Skills: Critical Thinking and Problem Solving

4.1 Inference 127

Commentary

We’ll consider the inferences in turn. The first

one, A, as well as being a bit vague, has little

support from the text. If we take ‘any

millennium now’ to mean in the next one or

two – which is its natural meaning – then A

would mean sticking with the standard view,

despite the most recent findings casting doubt

upon it. The standard view is that the present

warm phase should be reaching its time limit;

but according to the last three warm phases the

limit has already been passed. The latest ice core

also suggests that some interglacials could last

as long as 30,000 years. Evidence that the

Earth’s present alignment with the Sun’s rays

resembles that of the last long interglacial,

pours even more cold water on A. (Interestingly,

even without the most recent evidence, the

grounds for A would still be weak: half-a-

million years is a blink of an eye in geological

terms, and the sample of just three warm

phases is too small to call a reliable trend.)

B might seem consistent with what has just

been said about A. If we are not near the start of

a new ice age, the standard view must be

wrong. But there is a lot of difference between

saying that an inference is unsafe, and

declaring it false. B is a much stronger claim

than can be supported by the data in Doc 1. We

might be near the end of a warm phase: one

that is longer than the last three and shorter

than the one before that. There is little or no

positive evidence for such a claim; but nor is

there proof that it is false. Remember the

significance of strong and weak claims (see

Chapter 2.2). A strong claim requires much

more to justify it than a more moderate claim.

Had B asserted that the standard view is now

less plausible than it was, instead of plainly

false, that would have been defensible.

C suffers from the same fault as B: it, also, is

too strong. A single example of a 30,000-year

coming to the end of the present warm

phase, which has already lasted just over

10,000 years. Indeed, data from Antarctic

ice cores* indicated that the previous

three interglacials have lasted between

6000 and 9000 years which, if repeated,

would have seen parts of Europe, Asia and

North America covered in ice since before

the rise of the Roman Empire. The most

recent Antarctic ice cores have revealed

that the warm phase before that lasted for

30,000 years. It is known, too, that the

Earth’s alignment relative to the Sun during

that long interglacial was similar to its

alignment at the present time.

* An ice core is a sample obtained by drilling

down into the ice cap. The state of the ice at

different levels provides a climatic record that

can extend over hundreds of thousands of

years.

From the information in Doc 1, which of the

following can reliably be concluded?

A Another ice age is due any millennium

now.

B The standard view is wrong.

C The present warm phase is set to last

another 20,000 years.

D According to the recent geological

record, ice-age conditions are the norm,

and it is Earth’s present climate which

is unusual.

E Global warming is delaying the start of

the next ice age.

Give a brief reason for each response.

Activity