They're probably both right.

By mid-century, the world may have an extra 3 billion people and four times the wealth but somehow it must also at least halve carbon emissions from its main energy source -- fossil fuels -- to rein in dangerous global warming, scientists say.

Power generation accounts for about two-fifths of global emissions, from burning fossil fuels, of the main man-made greenhouse gas, carbon dioxide, and coal for most of that.

"You've got to say -- 'Right, here's the line in the sand, we're going to stop it here because it's madness to continue'," said Connor O'Brien, spokesman for protesters against a proposed new coal-fired power station in southern England, which would be Britain's first for nearly 30 years.

The Camp for Climate Action in Kingsnorth, Kent, has so far recruited about 600 people, organisers say, and joins four similar protests worldwide this year, targeting the coal industry in Australia, Germany and North America.

The Kent camp protesters aim to try and shut on Saturday the existing coal-fired power station which is slated for replacement, owned by the UK arm of German utility E.ON.

Despite environmentalists' concerns, energy companies say they are racing to meet demand for coal, especially in developing countries where the fuel is cheap and plentiful even in a year where coal price rises have outstripped those of oil.

"It doesn't paint a very good picture of the future for carbon emissions but there is no other real choice -- coal is one of the few fuel sources which has a real capacity to expand," said Francisco Blanch, head of global commodities research at Merrill Lynch.

Meanwhile, industrialised nations want to avoid over-dependence on imported, cleaner gas, given security of supply concerns. Ukraine is a case in point, now switching to domestic coal after neighbouring Russia halted gas supplies in a price dispute two years ago.

FUTURE

Dilemmas of choice, to balance competing benefits and tradeoffs, have left the world's energy future wide open.

Nuclear, for example, is hemmed in by public opposition in much of the developed world, while developing countries may be geologically unstable, or else, like India, face a political leap to sign a non-proliferation treaty which grants access to imported uranium.

Wind farms are growing rapidly but grid connection poses an extra expense, while in poorer nations antiquated networks struggle to handle the volatile power source. Solar power is booming, but only provides a tiny fraction of all power.

Environmentalists stress the benefits of renewable energy, which is often more expensive than oil and coal, in saved fuel and avoided climate change, and have won some battles.

In June, a state court in Georgia overturned an air permit for a new coal plant, saying the plant needed to limit emissions of carbon dioxide. On Monday, green groups dropped opposition to a Texas coal plant after the utility agreed to pay for emissions cuts elsewhere.

Former US vice president and Nobel prize-winning climate crusader Al Gore called last month for a complete US conversion to renewable electricity sources within 10 years -- a proposal that won support from both presidential candidates.

Despite such apparent setbacks, coal's future looks safe.

In the United States utilities are building 28 coal-fired plants and another 66 are in early planning, as gas price hikes motivate new interest.