NCAR: We can't measure natural variability; also, we conclude that half of a recent ice fluctuation was natural variability

Arctic summer ice could increase before it disappears | TG Daily

They concluded that around half the observed decline was due to human emissions of greenhouse gases, and the other half to climate variability.

"The changing Arctic climate is complicating matters," says Kay. "We can’t measure natural variability now because, when temperatures warm and the ice thins, the ice variability changes and is not entirely natural."