HAVANA, (Reuters) – Former Cuban leader Fidel Castro  said on Thursday the world was on an “inexorable march toward  the abyss,” which he blamed in part on the discovery and  exploitation of vast reserves of so-called “shale gas” around     the world.

Shale gas is natural gas locked in rock formations that in    the past decade has been found in great abundance around the    world and is now considered a top source of future energy.

Castro, 85, wrote in one of his occasional columns published  in Cuban state media that “numerous dangers threaten us, but two  of them – nuclear war and climate change – are decisive and both  are ever further from approaching a solution.”

He said he had only recently heard about the shale gas    phenomenon, which has created a drilling boom in some parts of  the United States, and when he asked several acquaintances both  inside and outside of Cuba about the topic, “none of them had  heard a word about it.”

Shale gas production is criticized in some quarters because  it requires extensive “fracking,” which uses water, sand and  chemicals to fracture the rock where the gas is trapped to allow  it to flow out of the well. Fracking, opponents say,  contaminates groundwater sources and can cause other problems.

Castro sided with the critics, quoting reports on the  negative effects of fracking and research that said shale gas  emits more greenhouse gases than gas produced from conventional  wells.

“It is sufficient to point out that among the numerous  chemical substances injected with the water to extract this gas  is found benzene and toluene, which are substances terribly  carcinogenic,” he wrote.

The information on shale gas was something “no political  cadre or sensible person could ignore,” he said.

Castro said he was so intent on getting the word out, he had  “let the festive days of the old and new year pass by” working  on his column.
The column was the first he had written since Nov. 13 and  followed an outburst of rumours on Twitter on Monday that Castro  had died.