Vice President Al Gore visited Glacier National Park and suggested that the major reduction in glaciers in the park reflects global warming. Is this a valid point or just a political point?

There is irrefutable evidence that the glaciers in Glacier National Park are decreasing in mass and have been doing so for many years, however the reasons for their reduction in size are less obvious. Before assigning all the blame to global warming, it is worth considering other factors that could contribute to negative glacial mass balance. In the same way that one’s weight is a function of the number of calories eaten and the number of calories expended, the mass balance of a glacier is a function of the accumulation of snow and the ablation of snow and ice. When ablation consistently (over a period of years) exceeds accumulation, then a glacier will retreat, and when accumulation consistently exceeds ablation, then a glacier will advance. The glacial retreat in Glacier National Park can be examined on two dimensions: its spatial source and the process of shrinkage, as shown in the diagram below. It is worth noting that in complex situations, local and global effects and changes in the rates of accumulation and ablation can occur simultaneously.

The diagram above shows that the glacial retreat in Glacier National Park is not necessarily an indication of global warming, and at the opposite extreme, could simply mark a local reduction in precipitation. However, Al Gore had other information when he drew his conclusion. Firstly, the glaciers in Glacier National Park are not alone in their retreat; glaciers in the Alps, Alaska and Siberia are also retreating. This suggests that the spatial source of the retreat is global rather than local. Secondly, scientists are in general agreement that global warming is real and that the average air temperature on Earth has increased by at least 1°F over the last century. It is a simple scientific principle that if the energy applied to the surface of a glacier, in the form of heat, is increased consistently over a long period of time, then the mass of the glacier will decrease, in the form of melting or calving. Because records have only recently been kept, and because response times to temperature changes are not entirely clear, care should be taken when drawing direct conclusions about global climate change from fluctuations in glacial mass balance. However, in this case, Al Gore was well informed and made a valid point.

If this true, why is Frans Joseph Glacier in New Zealand now advancing?

There is general agreement that global warming is real and yet glaciers in New Zealand, Scandinavia, Greenland, Iceland, and most probably Antarctica are advancing. This apparent paradox can be explained by the succession of processes involved in climate change. As the Earth warms up, so the atmosphere is able to hold more water vapor, so precipitation increases, and so more snow accumulates on glaciers. Even though ablation rates may increase as more ice melts in a warmer atmosphere, this is more than offset on some glaciers by the increase in accumulation. It is not by accident that the retreating glaciers are generally in low and mid-latitudes, while those that are growing tend to be in higher latitudes or, as is the case with the Frans Joseph Glacier, close to large bodies of water. Clearly, an increase in air temperature will only lead to an increase in melting if the O°C trigger point is approached, and this is more likely to happen on temperate glaciers than on those in high latitudes.

The specific case of the Frans Joseph glacier is more readily explained by its proximity to the ocean. Warmer air can hold more moisture that falls as snow as it is forced to rise over mountains. Interestingly, the long-term trend for the glacier is one of retreat with intermittent, fairly regular, advances on an approximately 20-year cycle. Such regularity might be explained by factors other than simply global warming, such as changes in oceanic currents, in the same way that El Niño occurs on a rough 7-year cycle in North America.

There are many apparent paradoxes within global climate change because the chain of events that is triggered by a change in one element of the climate system is so complex. The greatest irony is that global warming itself may induce the next ice age, should melting ice flood oceans with fresh water so depriving currents of their energy to transfer heat around the globe. It should come as no surprise then, that not all glaciers react identically to global warming.