was estimated to be 27% of the total resource. "Wet natural gas" is methane plus natural gas liquids, and is more valuable than dry gas.What Makes Wet Gas Wet? For the rest of the world (excluding US), EIA estimated (2013) a total wet natural gas resource of . Shale gas was estimated to be 32% of the total resource. Europe has a shale gas resource estimate of compared with America's reserves , but its geology is more complicated and the oil and gas more expensive to extract, with a well likely to cost as much as three-and-a-half times more than one in the United States. Europe would be the fastest growing region, accounting for the highest CAGR of 59.5%, in terms of volume owing to availability of shale gas resource estimates in more than 14 European countries. Environment The extraction and use of shale gas can affect the environment through the leaking of extraction chemicals and waste into water supplies, the leaking of greenhouse gases during extraction, and the pollution caused by the improper processing of natural gas . A challenge to preventing pollution is that shale gas extractions varies widely in this regard, even between different wells in the same project; the processes that reduce pollution sufficiently in one extraction may not be enough in another. In 2013 the European Parliament agreed that environmental impact assessments will not be mandatory for shale gas exploration activities and shale gas extraction activities will be subject to the same terms as other gas extraction projects. Climate Barack Obama's administration had sometimes promoted shale gas, in part because of its belief that it releases fewer greenhouse gas (GHG) emissions than other fossil fuels. In a 2010 letter to President Obama, Martin Apple of the Council of Scientific Society Presidents cautioned against a national policy of developing shale gas without a more certain scientific basis for the policy. This umbrella organization that represents 1.4 million scientists noted that shale gas development "may have greater GHG emissions and environmental costs than previously appreciated." In late 2010, the U.S. Environmental Protection Agency issued a report which concluded that shale gas emits larger amounts of methane, a potent greenhouse gas, than does conventional gas, but still far less than coal. Methane is a powerful greenhouse gas, although it stays in the atmosphere for only one tenth as long a period as carbon dioxide. Recent evidence suggests that