West Antarctica and the Antarctic Peninsula have recently undergone dramatic climate change, but not all of the changes are outside the range of natural variability seen in the past two millennia, report two papers published online this week in Nature Geoscience.

Nerilie Abram, Robert Mulvaney and colleagues assessed the historical context for the increase in summer ice melt in the Antarctic Peninsula over the past 50 years, using an ice core that spanned the last 1,000 years. By looking for layers that show signs of melting and refreezing, they find that the amount of ice melt in recent decades has been unprecedented over the past 1,000 years.

In contrast, Eric Steig and colleagues looked at the isotopic signature of the ice itself, using an array of ice cores from West Antarctica. Using model simulations, they show that the isotopic composition of ice in recent decades is related to variability in climate in the tropical Pacific Ocean. They find that the isotopic composition of the ice over the past 50 years is unusual when compared with the past 2,000 years. They note, however, that the Pacific variability that drove these isotopic changes was not outside the range of natural variability.