DAVOS - Energy transition would not complete in an easy way, and the public should be ready for higher energy price, said Total CEO Christophe de Margerie on Wednesday.

"This transition will be long and slow," said de Margerie in a written address posted on the website of the ongoing World Economic Forum 2014 Annual Meeting, adding that fossil energies accounted for 80 percent of the world's current energy mix.

"Even if we decided to do it, it would be physically impossible to 'decarbonize' our societies overnight," he said.

The CEO of the French company said global energy demand was expected to increase 30 percent between 2010 and 2035, a more diversified energy mix, which combined carbon energy and an increasing share of renewable ones, would be needed in order to meet the demand.

Total forecasted that oil and gas would still account for half of global energy mix in 2035. Carbon energy would then be replaced by gas and sustainable energies. Gas would be the second most consumed energy due to its abundance, low carbon emission and high flexibility, and would be used to fill in gaps in supply from the renewables during the transition period.

According to him, massive investment would be required in conventional energy production as more innovation are needed to overcome technological and environmental constraints.

Transition to the renewables, however, would also be costly due to current subsidization policies, which would taper when the renewables arrive at technical and economic maturity.

In its energy roadmap 2050, the European Commission estimated that the price of electricity would increase in Europe until 2030 and decrease from there on, said de Margerie.

"It appears important to us to awaken public opinion to the fact that this transition will necessarily come at a cost and will, at least in the short term, involve a price increase," he said.