I have rarely seen a more miserable sight. A tiny, shivering Gentoo penguin chick stood dripping in the rain on the guano-stained rocks of Peterman Island. This drenched native of the frozen continent was as unused to Antarctic rain as I was. I would survive the experience, but it was unlikely that this poor undersized individual would. There are winners and losers in the changing climate. Gentoos are believed to be one of the beneficiaries of the warming that has so affected the Antarctic Peninsula, and they are spreading south as the sea ice retreats, whereas their neighbors, the Adélies, withdraw to more icy conditions. Adélies are in decline in the South Atlantic, but they flourish further south, whereas Gentoo numbers are on the increase in the north. These population changes are undoubtedly climate related, though some have tried to link them to changes in the population of krill, or the influence of the krill fishery, or the increase in fur seal numbers. And therein lies the problem. There are multiple environmental changes occurring simultaneously so how can we disentangle cause and effect, and how do we dispassionately assess causation?