Average sea ice extent for September 2010 was 1.89 million square miles, about 830,000 square miles less than the average September extent between 1979 and 2000. The minimum this year, however, was still 230,000 square miles more than in 2007, which had the lowest Arctic sea ice coverage ever measured. For only the second time since satellite records began, the U.S. National Ice Center declared both the Northwest Passage above Canada and the Northern Sea Routes above Scandinavia and Russia in the late summer.
Thanks to , we know Arctic sea ice has declined dramatically over at least the past thirty years, and scientists have attributed this in large part to increasing concentrations of greenhouse gases in the atmosphere from burning fossil fuels such as coal and oil.
8. Lake Mead Record Low
The Hoover Dam (originally known as the Boulder Dam) was erected in the 1930s, and by 1943 Lake Mead had risen out of the Colorado River to a height of 1,220 feet above sea level. But this year, on October 18, Lake Mead reached a , dropping down to just 1083.9 feet, having lost about 12 stories of height. Though still about eight feet above the designated point of a critical water shortage, the low water levels are a warning signal to the millions of people in Southwest states who rely on this resource for drinking water and irrigation.
The level of Lake Mead has been steadily falling since 2000, with the exception of a slight rise in 2005, reflecting the drought that has afflicted the American Southwest over the same period. In the past ten years, a particularly dry and warm climate has lingered in Utah, Nevada, Arizona and Southern California, leading to reduced flow along the Colorado River. In fact, scientists have already that the stress on the water resources in the Southwest region is consistent with the effects of a warmer climate, and that increased emissions of heat-trapping gases are linked to recent changes in river flows and winter snow pack. In addition to this ongoing drought, cities that draw water from Lake Mead, like Las Vegas, have grown in recent years and are further taxing the water supply.
The through the winter does not look encouraging, as a strong La Niña event has taken hold in the tropical Pacific Ocean. La Niña conditions, which are characterized by colder than average waters off the coast of South America and along the equator, tend to be associated with drier than average winters in the American Southwest.
9. Amazon Drought
For the second time in five years, the Amazon River basin in northwestern Brazil is in . Brought on by a particularly arid dry season through April and May, the drought has extended through to November. One of the primary Amazon tributaries, the Rio Negro, dropped to its since records began in 1902, according to the Brazilian Geological Service. As water levels along the Rio Negro , water temperatures in the river also began to climb, killing millions of fish and contaminating the water supplies for thousands that live in the region.