Mining giant Rio Tinto said Tuesday clean coal was key to tackling climate change and that developing the technology was a challenge greater than the first moon landing.

The firm's energy chief Harry Kenyon-Slaney compared the twin challenges of meeting the world's energy needs, including growing demand from Asia, and combating climate change to the difficulties the US had to overcome for the 1969 lunar mission.

"The challenge now faced by the whole world is far more urgent and important," Kenyon-Slaney said.

"But it can be solved by the same methodical, determined process. The world has no choice."

Kenyon-Slaney's remarks came ahead of a World Meteorological Organization report released Tuesday that showed global concentrations of CO2, the main culprit in global warming, soaring to a new high in 2013.

The energy boss, who described emissions-driven climate change as "among the world's biggest and most pressing" problems, said he supported the development of all power-generating technologies including renewables.

But he said the abundance of coal meant it would remain the world's main source of "large-scale, reliable, affordable energy".

Advancing research and development in carbon capture storage, known as CCS, to make it commercially viable should therefore be a key goal for governments and businesses, Kenyon-Slaney said.

"(The technologies) can all help to combat climate change but breakthroughs in low-emissions coal generation will be fundamental. They could break the back of this problem," he said.

While CCS has been hailed as a solution to make fossil fuels cleaner, the technology has at this stage been too risky, costly and energy inefficient in its own right.

The technology involves trapping CO2 emissions from power plants and other large sources, liquefying them and storing them deep underground.

Kenyon-Slaney criticised "climate warriors" on both sides of the global warming debate, saying the world should be focusing on power-generating solutions instead.

Rio's energy section, composed mostly of coal, narrowed its losses to US$19 million in the six months to June 30, from US$52 million during the previous reporting period.