After the accident, that projection has been cut in half, agency chief economist Fatih Birol said, citing the pressure to halt new nuclear plants and phase out older ones sooner than planned.
The gap is likely to be filled equally by renewable energy, coal and gas. The result will mean an additional 5 percent — or 500 million tons — of carbon dioxide emitted globally by 2035, Birol said in an interview.
"The doors are fast closing on the 2-degree target, and with a decrease in nuclear energy it makes it even more difficult," Birol said. "It's all bad news — cost of energy will increase, energy security and diversification decrease and carbon emission will go up."
Experts wonder whether countries really will slash nuclear power as much as their initial reactions to the Fukushima tragedy suggest, and if so, whether they will they speed toward renewables or simply burn more coal.
Ryding said she is concerned that several governments, already backtracking on earlier pledges to reduce emissions, may use Fukushima as an argument to do even less.
Birol of the IEA, which advises governments on energy policy, says some world leaders may have been "too abrupt" in moving away from nuclear energy in wake of the Japanese disaster.
"When we have all the input from Fukushima, I am sure that policy makers will take another look, especially given the big economic stakes," he says.
The scene is hardly uniform around the globe, where there are currently 507 nuclear power plants in operation or under construction and where oil, coal and gas still provide the bulk of energy in most countries.
In Japan, climate negotiators expect a greater, short-term reliance on fossil fuels to fill the nuclear power gap and are concerned the country could reduce its pledge to cut emissions by 2020 — from 25 percent down to 20 percent.