Shale gas could turn out to be "a liability" to global efforts limit climate change, the United Nations' top environmental official has warned.
Supporters of the shale gas boom, which has spread across America and more recently to Europe, claim the fuel could help wean economies off the more carbon-intensive coal,.
But Achim Steiner, who heads the United Nations Environmental Programme (UNEP), said there was a far greater risk that the switch from coal to natural gas would only delay the much more critical energy transition from fossil to renewable fuels.
"If it is used as a means of not investing in the transition to a renewable energy economy then I think it will become a liability in our struggle to meet climate change targets over this century," Steiner said in an interview.
"If it turns into a 20 to 30-year delay to making the transition towards real low-carbon and zero-emission energy matrixes then I think it could actually become a distraction and in that sense slow down our efforts," he went on.
Natural gas burns more cleanly than coal, and is lower in carbon dioxide emissions. The fuel produces methane emissions along its production line, and methane is a far more powerful greenhouse gas over the short-term.
But for Steiner, the greater risk was time. He argued the rapid spread of natural gas through fracking was putting off the transition to low-carbon or zero-carbon fuels that would help limit temperature rise, and avoid a climate catastrophe.
"We sometimes have to take a step back and ask ourselves: for the sake of having another 20 years of dirt cheap energy are we really going to put millions of years of evolution, of ecosystems, of ecosystem services at risk?" he said.
The UNEP chief was speaking on the sidelines of a high-level ocean summit hosted by the Economist and Natural Geographic.
The oceans are under threat from overfishing, pollution, and climate change and Steiner said there was growing recognition of the risks to the economy and global food supply.
About 1 billion people – mainly in the developing world – rely on fish for survival.
However, the conference was repeatedly told the international community has failed to come up with ways to manage and protect the ocean.
Fish stocks have fallen drastically over the last 50 years. Ocean dead zones, caused by run-off from agricultural and industrial pollution, are multiplying. The changing chemistry of the oceans, due to carbon dioxide emissions, is eating up coral reefs.
The Global Ocean Commission, which is co-chaired by the former UK foreign secretary David Miliband and the former Costa Rican president José María Figueres, has called for the UN to adopt ocean protection as a separate sustainable development goal.
Other UN officials were cool to the idea, however, arguing that adopting such a goal would not – on its own – lead to any measurable improvement in ocean health.
Steiner acknowledged there was rising frustration at global failure to protect oceans.
"If you were a company and you had these kinds of numbers, you would have people on the stock market basically fleeing from your company because it is essentially pointing towards bankruptcy," he said.