In their 21 February report Towards a Green Economy, the United Nations Environment Programme (UNEP) claims that “a green economy grows faster than a [conventional] brown economy, while maintaining and restoring natural capital”. We contend that this claim is founded on flawed assumptions.

First, it is based on an inadequate target for reducing energy-related carbon dioxide emissions. The reduction by 2050 under UNEP's G2 green-economy scenario is only 35% relative to 2011 emissions. This cannot achieve the 450 parts per million (p.p.m.) target arising from IPCC's Fourth Assessment, let alone more recent calls for 350 p.p.m. Also, UNEP is assuming that the investment needed to achieve this target is additional to (rather than just a reallocation of) business-as-usual investment funds, ignoring crucial questions about financing. This additional 'green' investment is 10% higher than that applied to the 'brown' scenario, causing partiality in the analysis.

In addition, the claim hinges on the modelling of the world as a single economy, which overlooks substantial regional inequities and obscures the interplay between economic growth, social justice and climate-change mitigation. Assuming no change in the 2007 15:1 ratio in GDP per capita between high- and low/medium-income countries, for example, UNEP's G2 scenario requires a rate of decline in average CO2 intensities in both country income groups of 3.9% per year. By 2050, this would lead to an increase in absolute per capita income differences of US$104,000 from $42,000 per capita in 2011, and would reduce emissions by only a third.

For full convergence of living standards by 2050, coupled with the 80% reduction in global CO2 emissions required to meet a 450 p.p.m. target, we would need a decline in average CO2 intensities in both regions of 8.2% per year.

Taking these factors into account, we cannot presume that a green economy would grow faster than a brown one.