Protection Agency lowered its estimate of how much methane leaks from wells, pipelines and other facilities during production and delivery of natural gas by 20 percent. The EPA report on greenhouse emissions credited tighter pollution controls instituted by the industry for cutting an average of 41.6 million metric tons of methane emissions annually from 1990 through 2010, a reduction of more than 850 million metric tons overall. The Associated Press noted that "The EPA revisions came even though natural gas production has grown by nearly 40 percent since 1990." Using data from the Environmental Protection Agency's 2013 Greenhouse Gas Inventory yields a methane leakage rate of about 1.4%, down from 2.3% from the EPA's previous Inventory. A five-year set of studies coordinated by the Environmental Defense Fund (EDF) and released 2018, found that methane leaks in the U.S. are 60% higher than estimates by the EPA. The study, which was conducted by researchers from 40 institutions, estimated a 2.3% methane leak rate, "enough to erode much of the climate advantage gas has over coal". Life cycle comparison for more than global warming potential A 2014 study from Manchester University presented the "First full life cycle assessment of shale gas used for electricity generation." By full life cycle assessment, the authors explained that they mean the evaluation of nine environmental factors beyond the commonly performed evaluation of global warming potential. The authors concluded that, in line with most of the published studies for other regions, that shale gas in the United Kingdom would have a global warming potential "broadly similar" to that of conventional North Sea gas, although shale gas has the potential to be higher if fugitive methane emissions are not controlled, or if per-well ultimate recoveries in the UK are small. For the other parameters, the highlighted conclusions were that, for shale gas in the United Kingdom in comparison with coal, conventional and liquefied gas, nuclear, wind and solar (PV). Shale gas worse than coal for three impacts and better than renewables for four. It has higher photochemical smog and terrestrial toxicity than the other options. Shale gas a sound environmental option only if accompanied by stringent regulation. Dr James Verdon has published a critique of the data produced, and the variables that may affect the results. Water and air quality Chemicals are added to the water to facilitate the underground fracturing process that releases natural gas. Fracturing fluid