In the next two decades, the world would exceed the Intergovernmental Panel on Climate Change- (IPCC-) established carbon budget, limiting global warming to 2 °C by 2100, the latest PwC Low Carbon Economy Index revealed on Monday.

Despite a rapid move to adopt renewable energy worldwide, efforts to ease the use of fossil fuels and initiatives to limit the amount of energy-related carbon emitted per unit of gross domestic product (GDP) needed to contain global warming to 2 °C over the next 89 years, the surface temperature would most likely rise by 4 °C on average by 2100.

The world’s energy mix remained dominated by fossil fuels, with reductions in carbon intensity globally averaging 0.7% a year over the last five years. This was well below the 2008 calculations of 3.5% a year – required to maintain growth without warming the planet more than 2°C – and a fraction of the recalculated reductions of 6% a year now required to 2100.

This is a decarbonisation target never achieved in a single year and would not be sustained for the rest of the century, said the report.

By 2100, the global energy system would need to be virtually zero-carbon.

“If the world continues at current rates of decarbonisation, the carbon budget outlined by the IPCC for the period 2012 to 2100 would be spent in less than one-quarter of that time and be used up by 2034,” the report said.

This puts the world’s climate path on the most extreme scenario illustrated in the IPCC’s fifth assessment report on climate science, eliciting warnings of “serious and far reaching implications” of levels this high.

“We've gone over the carbon cliff. It's time to figure out the steps that are going to get us back,” said PwC sustainability and climate change partner Leo Johnson.

“To achieve what the IPCC deems the ‘safe’ amount of carbon in the atmosphere [thereby limiting] the extreme impacts of climate change, carbon intensity [would have to be halved] in the next ten years and reduced to one-tenth of today’s levels by 2050,” added PwC sustainability and climate change director Jonathan Grant.

The report warned that the sustainable cuts in energy use per unit of GDP were limited.

The US, Australia and Indonesia achieved significant reductions in carbon intensity in 2012, but no country had sustained major reductions over several years.

The G7 group, comprising the US, UK, France, Germany, Italy, Canada and Japan, averaged a 2.3% reduction, while E7, which included seven major emerging economies, namely China, Russia, India, Brazil, Mexico, Indonesia and Turkey, only managed a 0.4% reduction.

“The G20 countries are still consuming fossil fuels like there’s no tomorrow. Despite rapid growth in renewables, they still remain a small part of the energy mix and are overwhelmed by the increase in the use of coal,” said Grant.

“While the fracking revolution has helped lower emissions in the US, cheaper coal contributed to higher coal use elsewhere, for example, in the EU, raising concerns that decarbonisation in one country can just shift emissions elsewhere,” PwC noted.

Grant commented that this raised “real questions” about the viability of the globe’s vast fossil fuel reserves and the way economies were powered.

“The 2 °C carbon budget is simply not big enough to cope with the unmitigated exploitation of these reserves,” he noted.