text: This natural-color satellite image shows small blue and green lakes in northern Siberia, near the Gulf of Ob. 
   
   Until now, no one knew for sure how many lakes exist on Earth. 
   
   Blame geography — most of the world's lakes are in places where humans don't live, said David Seekell, an environmental scientist at Umea University in Sweden. "This is something one would have assumed had been done long ago, and was in a textbook somewhere," Seekell said. 
   
   Lake size was a liability, too. Millions of lakes are too small for mapmakers to bother charting. 
   
   Instead of counting lake by lake, earlier estimates were statistical guesses, based on the number of lakes in a parcel of land or on average lake size. One widely cited study from 2006 estimated the lake total at 304 million. [5 Surprising Facts About Lakes ] 
   
   A new study published Sept. 16 in the journal Geophysical Research Letters sidesteps these problems. With high-resolution satellite data and supercomputers to check every cloudless pixel, researchers now have the best count yet of lakes on Earth. The result? There are 117 million lakes in the world. 
   
   Yet the bodies of water cover more land (3.7 percent of Earth's surface) than previous studies had predicted. This is because quite a few medium- to large-size lakes were missing from older databases, said Cory McDonald, a research scientist with the Wisconsin Department of Natural Resources, who was not involved in the study. 
   
   "I was surprised that the total surface area they measured was much greater than previous estimates," said Cory McDonald, a research scientist with the Wisconsin Department of Natural Resources, who was not involved in the study. "We knew there problems with the extrapolation methods used to fill the data gap for the small lakes, but previous estimates assumed we had a pretty good handle on the medium- to larged-sized ones," he told Live Science in an email interview. "This study largely puts to rest the long-debated questions of 'How many lakes there are in the world and how much surface area do they cover?'" 
   
   About 90 million of the lakes fall in the smallest size category, measuring 0.5 to 2.5 acres (0.2 to 1 hectare), the study reports. That's equal to a country house lot, a large farm pond or 1.9 American football fields. 
   
   "Most lakes are in the far North, and there's actually quite a few of them," said Seekell, a co-author of the new study. "Even if they're small and no one sees them, they are potentially important for global-scale environmental issues like the carbon budget," he told Live Science. 
   
   Climate scientists believe lakes influence greenhouse gas levels in the atmosphere. Lakes pump out carbon dioxide and methane — both greenhouse gases — but they can also lock away carbon for centuries by trapping it in their cool bottom muds. Without an accurate count, the role of lakes is difficult to assess, Seekell said. 
   
   According to the new results, the world's lakes cover about 2 million square miles (5 million square kilometers), which is 3.7 percent of the land uncapped by glaciers. 
   
   Most lakes are in the Northern Hemisphere between 45 degrees north latitude and 75 degrees north latitude. (Think about Canada, Russia, Alaska, Northern Europe and the Great Lakes.) This results from the tectonic scattering of continental landmasses and the past positions of glaciers, the researchers said. There is less land in the southern high latitudes, and the North's sizable plains were scraped by ice age glaciers, leaving behind millions of pothole lakes. 
   
   The majority (85 percent) of Earth's millions of lakes are at low altitudes, found at elevations less than 1,600 feet (500 meters) above sea level. 
   
   The study excluded the Caspian Sea, the world's largest lake, which covers an area of about 143,000 square miles (371,000 square km). Antarctica and Greenland were also left out of the study. (Antarctica has about 400 lakes buried by ice.) 
   
   The researchers plan to freely release the lake database, Seekell said. They also intend to update the count with higher-resolution data from the Landsat 8 satellite. 
   
   "Lakes are not static on the landscape, and in some parts of the world, they are disappearing quite quickly," Seekell said. 
   
   In certain regions of Russia and Alaska, higher temperatures are causing what was once permanently"frozen ground, called permafrost, to thaw, causing small lakes to dry up. Melting permafrost under a lake is like a cracked tub liner — the lakes drain out from their bottoms. Drought and overuse are also shrinking lakes. In northern China, for instance, more than 100 lakes disappeared during the 2000s from these causes. 
   
   Email Becky Oskin or follow her @beckyoskin. Follow us @livescience, Facebook & Google+. Original article on Live Science. ||||| The Aral Sea has been retreating over the last half-century since a massive Soviet irrigation project diverted water from the rivers that fed it into farmland. 
   
   Images taken from the Moderate Resolution Imaging Spectroradiometer on Nasa's Terra satellite have now depicted how since the turn of the century the lake has increasingly shrunk until this year saw its eastern lobe dry up completely. 
   
   The lake was at one time fed by the Syr Darya and Amu Darya rivers which flow down from the mountains before making their way through the Kyzylkum Desert where they pooled together at the lowest part of the basin. 
   
   An irrigation project by the Soviet Union in the 1960s however took water from the rivers to transform the desert into cotton farms. 
   
   While the massive diversion of water allowed the desert to thrive, it had a devastating effect on the Aral Sea. 
   
   This series of images starts in the year 2000, by which time the lake was already a fraction of what it was before the irrigation project started in the 1960s. 
   
   The Nasa images show how by 2000 the lake was already a fraction of what it had been before the irrigation project started in the 1960s 
   
   The images show how the smaller Northern Aral Sea had separated from the Southern Aral Sea, which itself had broken up into an eastern and a western lobe, the two sides still barely connected at both ends. 
   
   The following year however this connection had been broken and the eastern part, although larger in surface area, rapidly disappeared in the subsequent years. 
   
   While there appears to have been some fluctuation between 2009 and 2014, as a result of alternately dry and wet years, the overall pattern sees the eastern lobe consistently shrink until dry conditions this year caused it to completely disappear. 
   
   In 2005, Kazakhstan built a dam between the Northern Aral Sea and the Southern Aral Sea in a bid to save part of the lake, according to the Nasa Earth Observatory. 
   
   Kazakhstan built a dam in 2005 between the Northern Aral Sea and the Southern Aral sea in a bid to save part of the lake 
   
   The changes have also brought dire consequences to the people surrounding the lake, with the communities that depended on them collapsing as the water dried up. 
   
   Meanwhile, the water left in the lake became polluted with fertilizer and pesticides, which has caused a public health hazard now contaminated dust is blown up from the exposed lakebed, the Nasa Earth Observatory reports. 
   
   To compound matters, more water has been taken from the rivers to flush out the cropland affected by the blowing contaminated dust. 
   
   By 2014, the eastern lobe of the lake had completely dried up 
   
   The loss of the water has also made the winters colder while the summers have become hotter and drier. 
   
   In 2010, a documentary depicted the dramatic desiccation of the Aral Sea, which has now become a byword for ecological calamity. 
   
   Video: Emma Thompson at a climate change rally last week 
   
   At that time the lake still covered half of its original area of 25,500 square miles, while the volume of water had been reducted to a quarter, according to the We Are Water Foundation. 
   
   Spanish director Isabel Coixet made the film for the foundation, which seeks "to enable the equitable development and sustainable management of the world's water resources." 
   
   People walkg on a desert that was once a boat harbor on the Aral Sea 
   
   At the time the foundation said: "The region has the highest infant mortality rate in all of the former USSR" and "chronic bronchitis has increased by 3,000 per cent and arthritis 6,000 per cent, and in part of Uzbekistan" liver cancer has increased 200 per cent.
target: – Eight years ago, a much-discussed study estimated that there were 304 million lakes on Earth—but a careful count reveals that the number is closer to a third of that. The planet holds 117 million lakes, researchers find in what LiveScience calls the "best count yet." And while they may be fewer in number, they take up more of the Earth's surface than scientists had thought: some 3.7% of it, it turns out. Experts used computers to count the bodies of water using high-resolution satellite images. "This is something one would have assumed had been done long ago, and was in a textbook somewhere," says a researcher. One reason it wasn't: Most lakes are far from human residences, and millions are so small they haven't appeared on maps, LiveScience reports. Indeed, 90 million of the lakes counted were between 0.5 to 2.5 acres, or less than two football fields. The new figure measures the lakes around today, a number that can easily change; indeed, the Aral Sea, once the fourth-biggest lake on Earth, is now almost dry, the Independent reports. So what's the point of all this counting? "If we are to be able to make realistic estimates of the collected effects of the different processes in lakes, for example their contribution to global warming, we first need a good map," a researcher says in a press release. (Of course, we're not the only planet with lakes.)