Global warming is causing glaciers and ice sheets to melt at increasing rates. The largest single retreat of ice shelves in Antarctica was observed over the last 30 years, attributed to regional climate warming. Glacial melting is expected to accelerate as temperatures continue rising, with consequences for sea level rise and reduced fresh water supplies. Observational evidence from 2004 found a 30% decline in the southward flow of cold deep water in the Atlantic, indicating a weakening of ocean currents that transport heat to Europe. Computer models have long predicted such effects from Arctic warming and increased fresh water inputs, with potential impacts of 4-6 degree Celsius cooling over Europe if currents shut down completely.