The GWPF seems to saving that shale gas offers a cheaper alternative too oil, nuclear and renewable's. I doubt that when you consider the environmental and human cost of extraction and the GHG emissions caused by burning shale gas into the future... They also criticise environmental groups and other fossil fuel energy producers. I'd like to know who funded their study?
I would recommend this documentary out http://topdocumentaryfilms.com/gasland/
, there may be some fibs but the pictures speak for themselves
Some commentators are saving there may be as much as 250 years worth of this shale gas, and I can see why its considered a great solution, anythings better than Gasprom having a monopoly..
this gives some background to normal natural gas http://www.theoildrum.com/node/3673
while this http://peakoil.com/production/shale-...em-with-eroei/
gives you an idea of the hidden issues
To address the OPs question, there is no fossil fuel 'relatively clean' energy source, IMHO or best options are to start producing massive amounts of wind, solar and wave systems and solve the storage problem, probably easiest with the proposed inter-connectors and some pumped storage reservoirs. Even then Nuclear seems like it will be in the mix, probably bought from the UK as is the case at the moment.
"a modest IEA scenario, by 2035, three-quarters of the world’s oil production from existing fields will need to be replaced" Mr Tanaka (IEA)
May I also recommend these two books, in lieu of Ireland having any decent literature on the subject