Meanwhile, the share of energy supply investment in fossil fuels rose for the first time since 2014. To meet climate targets, fossil fuel investment needs to drop to 40 percent by 2030 -- instead it rose to 59 percent in 2017.

The drop in renewables investment has largely been attributed to declining interest in wind and hydropower. Solar power hit record levels last year, but it's not been enough to offset spending on oil, gas and electricity. Similarly, $43bn was spent on electric cars and hybrid vehicles last year, accounting for half of global growth in car sales, but this hasn't put any significant dent in oil demand.

Dr Faith Birol, executive director of the IEA, said the figures pointed towards a "worrying trend," and urged governments to create less investment uncertainty for green energy. "I was myself worried to see there is a contradiction between a) the statements the governments make and b) what the world needs today vis-a-vis the investment numbers, where we see a decline."