A fearsome collision between two giant ice masses drew attention to the world’s southernmost continent this week, just as an important United States scientific body warned about its melting. A tongue of ice about the size of Luxembourg broke off the Mertz Glacier in the Eastern Antarctic, after a similarly large iceberg slammed into it. The new 2,500 km2 iceberg will likely change the size of a lake that forms, giving algae a place to live, as the sea freezes each winter. Any decline in the amount of algae in turn will reduce populations of krill and fish. Fewer fish and krill would then mean less food for a nearby Emperor Penguin colony, the same one featured in the film “The March of the Penguins”.
The Mertz Glacier collision was spotted by satellite, the same tool that the US Geological Survey (USGS) has been using to study glaciers on the other side of the continent. The process of glaciers such as those in the Antarctic flowing towards the sea and breaking off to form icebergs – known as calving – is normal. Warmer temperatures, however, speed that process. “The Antarctic ice sheet contains 91 percent of Earth’s glacier ice,” explained USGS scientist Jane Ferrigno. “The loss of ice shelves is evidence of the effects of global warming. We need to be alert and continually understand and observe how our climate system is changing.”
Along with researchers from the UK and Germany, the US team studied Palmer Land, the southern part of a long projection known as the Antarctic Peninsula. From analysing satellite images back as far as the 1970s and maps before that, they found that every ice front in this area has retreated overall from 1947 to 2009. The most dramatic changes have happened since 1990. Palmer Land has the peninsula’s coolest temperatures, and the USGS says that the comprehensively retreating ice there shows that global warming is affecting its entire length.
Meanwhile, in hotter areas of the world, cyclones are likely to become fewer but stronger, says a review paper in Nature Geoscience this week. “Whether the characteristics of tropical cyclones have changed or will change in a warming climate — and if so, how — has been the subject of considerable investigation, often with conflicting results,” write Tom Knutson and colleagues. Part of the problem is that long-term climate models themselves do not simulate cyclones well. Instead their outcomes must be fed into separate models.
The World Meteorological Organization’s Expert Team on Tropical Cyclones and Climate Change looked at how researchers had interpreted existing data and used it to create such models. They concluded that past changes in cyclone activity are very like what you’d expect from natural variation – which can be large – but this may be partly because of uncertainty about some of the records. While there are also uncertainties in the modelling, Knutson and coworkers say that improved methods are pointing more strongly to an increase in the most severe tropical cyclones as the climate – and in particular the sea – warms further. “We project that a future increase in the globally averaged frequency of the strongest tropical cyclones is more likely than not — a higher confidence level than possible at our previous assessment,” they write.