With the UK government expected to give the go-ahead for shale gas exploitation "soon", it's a good time to re-enter the smoke and mirrors world of fracking.

There are plenty of people bubbling with excitement at the prospect of the drilling beginning. They argue that shale gas has been the biggest cause of carbon dioxide emission cuts in the US recently, thanks to the replacement of coal. It's cheap too, they say, again pointing again to the US, and there's a vast amount under our feet here in the UK, just waiting to be freed. Lastly, shale gas is popular with the free market enthusiasts who lambast the subsidies given to renewable energy. Yet not one of these arguments stand up.

Let's take the emissions cuts first. In May, the International Energy Agency claimed that annual US emissions fell by 1.7% in 2011 "primarily due to on-going switching from coal to natural gas in power generation and an exceptionally mild winter." The coal-to-gas switch has been driven by gas prices that are falling due to large volumes of shale gas. But a new analysis of US government energy data by Greenpeaces's upcoming energy news site, Energydesk shows renewable energy in fact played a bigger role than gas in cutting climate-warming gases.

The analysis shows that electricity generation from coal did indeed fall significantly from 2010-2011, by 113TWh. But gas generation rose only by 29TWh. Generation from wind, hydro-electricity and other renewables rose by three times that amount: 92TWh. Looking at a longer period, 2008-11, coal's share of the US power mix fell by over 6%, while gas rose by 3.3%, Greenpeace found. But renewable generation rose by 3.6% and, given that renewable energy emits far less carbon than gas, again we see that renewable energy is contributing the lion's share of the emissions cuts. (It's worth noting at this point that the UK's renewable energy generation grew by 6.5% in the last year.)

Cheap trick

Fracking's boosters might well say, forget carbon, shale gas is going to be cheap. Not so, again. "Shale will not be a 'cheap' source of gas and there is unlikely to be a repeat of the US experience," says a new report from the Energy Contract Company (ECC), reported in the FT. In fact, they reach the same conclusion as Deutsche bank had already, and for very similar reasons: tougher regulation, different mineral rights.

The CBI, which represents over 250,000 UK businesses, is also deeply unconvinced about the prospect of cheap shale gas. Its director general, John Cridland, said this week: "Look at European gas price projections. They all disagree on the number, but they all agree on the direction – up. European shale will help, but not on a US scale."

These arguments appear immaterial to ex-BP boss Lord John Browne, who again used the US example to argue in the FT that "the prize is substantial" if "good practice and the UK's tough safety regulations mean [fracking] can be performed safely and without endangering water supplies." What the FT failed to tell its readers in Browne's article was that he is a director of Cuadrilla Resources Holdings Ltd, the main fracking company drilling in the UK. Perhaps he meant the prize for his company would be substantial?

Ed Davey, secretary of state for energy and climate change, derided Browne's "regrettably partial" analysis and addressed the myth that shale gas is all set to flow and transform the UK's energy future: "Until we have more certainty about the potential scale and costs of shale gas production in the UK it is unwise to assume it will be some kind of silver bullet."

New energy minister John Hayes, who is no green having (wrongly) labelled wind power as a "failure" on both environmental and economic grounds, recently said the same in parliament: "Shale gas in the UK is still in its earliest days; just one well in the UK has been drilled and fracked, and the production prospects are unknown at this stage." Several geologists have told me that you need hundreds, or even a thousand wells, before you really know how much gas you're going to get out.

The ECC report projected that shale gas production might hit about a quarter of UK demand by 2030 - the same year by which the UK has to decarbonise its electricity supply, according to the Libdems, Labour and the government's official advisors, the Committee on climate change.

Hostage to fortune

That, as the Institution of Mechanical Engineers point out in their recent report, means "the development of shale gas must be coupled with the development of carbon capture and storage technology for use with gas-fired power plants." CCS isn't going to be cheap and the IME's Tim Fox added: "UK shale gas could make a helpful contribution to the UK's energy security, but it is not the silver bullet many claim it is. It is unlikely to have a major impact on energy prices. A general over-reliance on gas will render the UK a hostage to volatile global energy markets, with or without UK shale gas."

Lastly, let's tackle the idea that shale gas conquered the US without the huge subsidies critics say are need to prop up renewable energy. "The free market has worked its magic," the Barnett Shale Energy Education Council, an industry group, claimed in July, reported AP. But again, this isn't true, as AP's article goes on to reveal: "Over three decades, from the shale fields of Texas and Wyoming to the Marcellus in the Northeast, the federal government contributed more than $100 million in research to develop fracking, and billions more in tax breaks."

So there we have it. Shale gas from UK fracking might, with state help and many years from now, produce a relatively small amount of gas, which won't reduce gas prices and would bust our carbon budgets unless emissions are expensively buried. I am not opposed to shale gas in principle, if all the environmental concerns are addressed, especially methane leakage. But as I think the analysis above shows clearly it's not so much a silver bullet as a lead balloon.