The report, the first published by the UN Environment Programme’s (UNEP) International Panel for Sustainable Resource Management, acknowledges that in the future land-use restrictions will often pit solar-energy developers and biofuel producers against each another.

Open-field biomass can generally only store 1%-6% of the solar radiation that reaches the Earth’s surface. In contrast, PV and solar-thermal systems perform must better, with efficiencies averaging around 15% and stretching as high as 25%. Solar-energy systems have the added advantage that they can be installed on rooftops and facades, requiring no additional land use.

The report acknowledges that solar energy is currently far more expensive than energy from biomass, but points out that the cost is dropping rapidly, and may one day be competitive.

At the heart of the UNEP’s report is the conclusion that the debate over biofuels requires much more nuance and sophistication. In many instances, biofuels offer a significant reduction in greenhouse gas emissions compared with traditional fossil fuels.

For example, the use of ethanol from sugar cane as currently practiced in Brazil offers emissions reductions of between 70% and 100% compared with petrol.

But such hopeful statistics often cloud deeper – and growing – problems within the world of biofuels. Production and use of biodiesel from palm oil on deforested peatlands can lead to greenhouse gas emissions increases of up to 2,000% as a result of the carbon released from the soil and land.

“Biofuels are neither a panacea nor a pariah, but like all technologies they represent both opportunities and challenges,” says Achim Steiner, UN under-secretary general, and executive director of the UNEP.

Steiner emphasises that biofuels have a clear future role in humanity’s energy matrix, particularly second-generation biofuels. But he says that rather than blindly pursuing liquid biofuel production, there are often other options that do a better job at combating climate change and improving rural livelihoods, such as PV.

“It is a choice about how humanity best manages its finite land bank, and balances a range of competing interests in a world of six billion people, rising to more than nine billion in 2050,” he says.