Any boost to renewable energy sparked by countries abandoning nuclear power in the wake of the Fukushima disaster is likely to be overshadowed by a massive increase in coal use that could have devastating consequences for the fight against climate change.

That was the stark message delivered today at the World Future Energy Summit in Abu Dhabi by Fatih Birol, chief economist at the International Energy Agency (IEA), who warned that those countries now committed to phasing out nuclear power are likely to see greenhouse gas emissions rise in the short to medium term.

Germany has already put plans in place to phase out nuclear power by 2022, with Switzerland following suit. Meanwhile, countries such as Japan, France and China have scaled back programmes for new reactors since the disaster.

Birol said that the intention to replace nuclear with renewables was bold, but warned that in reality countries were likely to increase production of coal-derived electricity to pick up the slack.

"We will see higher CO2 levels if we take out one of the major technologies that will help us deal with climate change," he said, adding that the IEA forecast emissions would be 6.2 per cent higher by 2035 as a result of the policy changes.

He said that the world was on track to see an increase in coal demand twice the size of Australia's current steam coal exports and a rise in natural gas requirements equivalent to two-thirds of Russia's current net gas exports.

Speaking just a day after warning that the growth of the renewable energy sector could slow over the next few years as a result of austerity measures around the globe, Birol said that half the growth in global energy use over the last decade came from coal.

He also reissued the long-standing IEA call for the phasing out of the $409bn subsidies given to fossil fuel industries each year.

"To say we want renewables, but then on the other hand give fossil fuels subsidies doesn't work," Birol told delegates. "It's like you go for a run and then have a big lunch of junk food."

Birol also took issue with the argument that fossil fuel subsidies ensure poorer people have access to energy.

"This is wrong – only eight per cent of subsidies go to the 20 per cent [of people] on the lowest incomes," he said. "A well designed subsidy reform with direct assistance for the poor may be a very well thought out energy policy."

He added that without a move to phase out fossil fuel subsidies, the world could find itself "locked in" to a path that would leave it unable to limit global temperature rises to two degrees, paving the way for temperature rises of up to six degrees this century.

Even if the world built no more power stations or factories and used the same number of cars, the world would have already used up 80 per cent of the emissions allotted for a two degree rise, he explained.

"Even schoolchildren know a six degree rise will have grave consequences for our planet – if we don't have a major change in terms of moving to a sustainable energy system ... by 2017 we will be locked in [to a six degree pathway]," Birol cautioned. "The door to a two degrees trajectory may be closing and closing very soon."