(Repeating Sept. 20 column with not changes to text. The opinions expressed here are those of the author, a columnist for Reuters.)

By Clyde Russell

BARCELONA, Sept 20 (Reuters) - Natural gas is no longer merely a transition fuel between the past of dirty coal and crude oil and the future of renewables, according to an increasingly confident cross-section of the industry.

A procession of senior executives of major companies, including Royal Dutch Shell and Exxon Mobil Corp , espoused this view while speaking at this week's GasTech event, the industry's biggest annual gathering.

While the industry has plenty to be buoyant about, including rapid and sustained Chinese demand for liquefied natural gas (LNG) and the shale gas revolution in the United States, it is running the risk of getting ahead of itself, while ignoring the threats it faces.

The idea of natural gas as a transition fuel was largely cemented by the International Energy Agency in 2011, when it published a report on what it termed the "golden age of gas," which would see demand for the fuel jump by 50 percent to become 25 percent of global energy consumption by 2035.

Natural gas was seen as a cleaner alternative to coal, a factor the industry was happy to seize upon as it allowed them to boost output while being seen as part of the solution to climate change, rather than part of the problem.

The rapid expansion of shale gas production in the United States was largely behind the demise of many coal-fired power stations, while in China coal used in industries and for residential heating is being replaced by natural gas as part of the government's efforts to reduce air pollution.

These dynamics are part of the reason why many players in the natural gas industry expect the market for LNG to rise from around 300 million tonnes a year currently to at least 450 million by 2025, and possibly even higher.

But for this to happen, almost everything has to work in LNG's favour, and the risks must remain only possibilities.

LNG faces several challenges in Asia, the market expected to take the bulk of planned new output.

LNG IN THE MIDDLE

For countries that aren't concerned with limiting carbon emissions, LNG is still more expensive than coal, especially if you plan to use low-grade Indonesian thermal coal.

For countries that do care about emissions, LNG will struggle to remain competitive with renewables backed up by battery storage.

For any would-be developer of a multi-billion dollar LNG project, the question has to be whether they can deliver the fuel at a price that can compete with what renewables plus storage are likely to cost in the future, not what they cost now.