LONDON - A climate change deal to be agreed in Paris in December will not be able to come up with a global carbon price, the United Nations' climate chief, Christiana Figueres, said on Tuesday.

Big multinational companies and investors, and most recently oil majors, have called for a global carbon price to help spur investments in low-carbon energy.

A global carbon price would help to create an incentive for operators of power plants and factories to switch to cleaner fuels such as gas or to buy more energy-efficient equipment.

When the European Union launched a carbon trading scheme in 2005 there were expectations this would eventually lead to a global carbon scheme by 2020 worth around $2 trillion.

But the difficulties of bringing together different carbon schemes from countries around the world means the goal of a global carbon price remains elusive.

"(Many have said) we need a carbon price and (investment) would be so much easier with a carbon price, but life is much more complex than that," Figueres told a climate investor event in London.(Reuters)