The correct answer is - there is no evidence that the changes of O'Higgins are being affected by global warming. It has retreated 9 miles in the past 100 years because of melting.
O'Higgins, as well as the other glaciers in Patagonia and Tierra del Fuego, are still a mystery to scientists as to why are they retreating. They suspect that maybe the global warming is the main cause, but there is no enough data available because of the remoteness and harshness of the region, so for now, it's all just speculation until there's enough data available to make a scientifically proven statement.