The head of one of the world's biggest oil giants has said unless carbon dioxide emissions are dealt with he sees "very little hope for the world".
Environmentalists blame oil firms for producing greenhouse gasses
In a frank interview, Ron Oxburgh told the Guardian newspaper that climate change made him "very worried for the planet".
He said a technology to trap harmful emissions, blamed by many scientists for climate change, must be developed.
But he said he feared "the timescale might be impossible".
"No one can be comfortable at the prospect of continuing to pump out the amounts of carbon dioxide that we are at present," said the Shell boss.
"People are going to go on allowing this atmospheric carbon dioxide to build up, with consequences that we really can't predict, but are probably not good."
He said a technique called carbon sequestration urgently needs to be developed to capture greenhouse gas emissions like carbon dioxide, so they can be stored underground, rather than be allowed to enter the atmosphere.
"You may be able to trap it in solids... and probably have to put it under the sea, but there are other possibilities.
"Sequestration is difficult, but if we don't have sequestration then I see very little hope for the world. I don't see any other approach."
His comments echo those of the UK government's chief science adviser Sir David King, who declared in January that climate change was a far greater threat to the world than international terrorism, and challenged the US to do more to tackle greenhouse gas emissions.
Lord Oxburgh continued: "You can't slip a piece of paper between David King and me on this position."
The remarks are likely to anger other bosses within the oil industry who argue a link between the use of fossil fuels and global warming still has many uncertainties.
UK Friends of the Earth's director Tony Juniper said: "We are pleased that Shell appears to realise the serious threat posed by global climate change.
"But until it gets out of fossil fuels, Shell will continue to be a major part of the problem."
THREE WAYS TO CAPTURE CO2
Carbon is chemically removed before hydrocarbons are burnt, leaving a hydrogen-based fuel
Carbon dioxide is removed from waste gases after combustion
Oxygen is fed into a fossil-fuel burning power plant instead of air, resulting in pure carbon dioxide which does not need separation
He added: "Technical fixes such as sequestration may have a role to play, but are likely to prove more expensive and less effective than simple measures to reduce emissions such as more fuel efficient vehicles and renewable sources of energy."
Lord Oxburgh took the top slot at Shell in March and was charged with restoring its battered image.
The company had been rocked after it was found to have overstated its oil and gas reserves, which led to the departure of former boss Philip Watts and several top executives.
THREE WAYS TO STORE CO2
Carbon dioxide is pumped into fossil fuel reservoirs like oilfields or coal beds
The captured material is stored in deep saline aquifers
Carbon dioxide is used for a commercial purpose like enhancing plant growth in greenhouses
Two months ago Prime Minister Tony Blair spoke at the launch of an international campaign aimed at speeding up greenhouse gas emission reductions.
He said there was "no bigger long-term question facing the global community" than the threat of climate change.