Weigh chance's share of the climate

1 · Question the Pacific

Beginner

Since 1980 the eastern equatorial Pacific has warmed less than the west. According to the network, what would forcing alone have produced?

The same east-west contrast, a little less marked The opposite contrast, weak, the east warming more No contrast at all, east and west at the same pace

2 · Size up the Arctic boost

Arctic amplification: the ratio of Arctic warming to global warming. Forced part, nearly constant: about 3. Recent observed value: about 4.

Intermediate

Relative to its forced value, by how much did natural swings inflate the amplification?

By roughly one third By roughly one quarter By roughly three quarters

3 · Catch a hasty calculation

A reader argues: the Arctic warmed 4 times faster than the globe, forcing explains 3 times; so three quarters of the observed Arctic warming is forced and the remaining quarter is natural.

Expert

How does this reasoning stand, given the study's figures?

Fine: three quarters forced, the remaining quarter natural Too high: the forced share falls short of three quarters Too low: the forced share exceeds three quarters

4 · Judge the models

Model simulations rarely reproduce the La Niña-like pattern observed since 1980.

Expert

For the authors, does this rarity prove that the models' forced response is biased?

Yes: a pattern the models miss betrays their forced response No: a genuinely rare draw can escape models that are right Yes, as long as their natural variability is simulated well

Chance's share weighed

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