Shale gas is a fossil fuel which releases the greenhouse gas CO2 when burnt. Humanity needs to significantly reduce fossil fuel consumption (unless combined with very efficient carbon capture and storage (CCS) which is not yet widely available and, if implemented, would only capture 1% of today’s global power sector emissions) to avoid dangerous climate change.
Shale gas is not a clean fuel - it is basically methane, a greenhouse gas 84 times worse than CO2 over 20 years. Studies suggest that it has a higher carbon footprint than conventional gas due to the extra energy used in its extraction (pumping water, chemicals used, transport of water and chemicals on/off site). Emissions associated with transporting the gas from a well to its end-user are also relevant. These are thought to be lower for shale gas extracted and used in the UK, if compared to conventional gas imported by pipeline from outside the EU or as liquefied natural gas (LNG). One life cycle assessment has even suggested that shale gas has a carbon footprint which is greater than that of coal although this is a minority view.
There is contention over the amount of gas that is leaked to the atmosphere: two studies suggested as much as 8% or 12% is lost. This leakage has to be accurately accounted for in determining the life cycle emissions of shale gas.
A 2013 report by DECC stated that expert views differ on the overall effect that shale gas production would have on global emission rates. At one end of the spectrum it is argued that shale gas will displace coal, which has a higher carbon intensity, and thus reduce emissions. At the other end of the spectrum it is argued that, in an energy-hungry world it is difficult to imagine that shale gas would not largely be used in addition to other fossil fuels thereby adding to emissions. The real world, determined partly by price differentials, will lie between these extremes.
In the UK, according to a 2013 report from Bloomberg New Energy Finance, shale gas production is unlikely to significantly reduce our CO2 emissions. The report also points out that UK production of shale gas will, at best, have only a limited impact on gas prices, and household energy bills in particular, because of the dominance in the marketplace of supplies from continental Europe. Neither conclusion provides support for shale gas exploitation in UK.
Without an effective global cap on total greenhouse gas emissions, shale gas exploitation is likely to increase the overall amount of fossil fuels burnt, even if there is some displacement of coal. It makes more sense to invest in cutting energy consumption, in energy efficiency and in sources of renewable energy. Exploiting shale gas is likely to divert investments from these critical areas.
Hydraulic fracturing (fracking) is required to release gas from the shale rocks in which it is trapped. This process, which takes up to 10 days, requires a lot of water (on average about 15 million litres per fracking operation). However, up to 40-50% of this water flows back to the surface after fracking and may be re-used several times (see Water consumption and treatment). The withdrawal of large quantities of water from local surface water (reservoirs or rivers) or ground water (aquifers) sources may have a significant impact on water availability depending on the location and the time of year. Lowering the water table of an aquifer can also lead to problems of water quality. Clearly, water abstraction is a concern which has to be carefully evaluated for each situation. South-east England in particular has been classed by the Environment Agency as an area of ‘severe water stress’ (defined according to the availability of water, current and forecasted demand, and population growth). Therefore it is arguable whether SE England can spare the water required for fracking.