A UNITED States energy expert who has advised three White House administrations has warned that there is still much to be learned about fracking, the controversial technique used to extract gas from shale rock underground.

The widespread adoption of hydraulic fracturing by states across the US has significantly reduced the price of natural gas across the Atlantic since 2008, tapping into a resource feared to be close to running out in the early 1990s.

But Dan Reicher, executive director of Stanford University's Steyer-Taylor Center for Energy Policy and Finance, insists its impact on the environment and its future as a long-term energy source for the US is still unknown.

Speaking after delivering a low carbon masterclass, sponsored by The Herald and Scottish Enterprise, Reicher said: "Not too many years ago, we did not think this resource was there; we didn't think we were going to develop it. Now it is being developed in a fairly aggressive way.

"The environmental questions remain significant. Carbon emissions is one of them, also methane emission - a very potent greenhouse gas … whereas some carbon emissions questions are fairly well understood, the science of this one isn't.

"We do know there are some significant carbon emissions along the way, the question is, is this the right way to displace coal, and where is it taking us?

"What's the mix going to look like? Is this a 10-year cycle? Is this a 50-year cycle? It remains an open question."

Asked what the nascent fracking sector in the UK could learn from the US experience, Reicher said: "It is important to understand the challenges and the opportunities going in, strike the right balance in terms of understanding the technologies, understanding the regulatory structure, addressing public concerns."

Scottish Enterprise strategy manager John Crawford, who took questions with Reicher after the presentation last week, called for a "single voice" to communicate what was available to help Scottish ­businesses develop low-carbon technologies.

Crawford said: "If I was First Minister, I would declutter the landscape entirely to have a coherent message around behaviours and around cultures, with a simple follow-through about who can do what to support the business community."