It is only possible to grasp the true dimension of the Amazon forest from space, occupying as it does one-third of the South American continent, an area larger than the entire European Union. Not marked are the land borders of the nine countries that share this ecosystem, although by far the largest part of the territory—over 60 percent—lies inside Brazil. At the heart of this extravaganza of nature is the Amazon River which, fed by some 1,100 tributaries, including 17 over 1,500 kilometers (930 miles) long, disgorges 20 percent of the world's freshwater when it finally enters the Atlantic Ocean. The rainforest also plays a crucial role in slowing climate change, notably as what is known as a "carbon sink." Put simply, every year its trees absorb around two billion tons of carbon dioxide, equivalent to five percent of total emission of greenhouse gases driving global warming. At the same time, the forest not only produces an important portion of the oxygen we breathe, but it also determines how much rain is delivered to other regions of South America and beyond. Nonetheless, with at least 17.25% of the biomass already cut down, the fear is that deforestation may soon reach "a point of no return" where the biome cannot recover, turning large areas of forest into tropical savannas.