As contributors to the United Nations Environment Programme report criticized by Peter Victor and Tim Jackson (Nature 472, 295; 2011), we stand by its claim that a green economy can grow faster than a brown economy.

Victor and Jackson argue that the report's G2 green investment scenario sets out inadequate target reductions for carbon dioxide emissions by 2050. But G2 is only one path projected for the next 40 years. The assumed technologies and costs derive mainly from International Energy Agency reports. Modelling a faster transition would require stronger assumptions about future technologies.

Contrary to the authors' implication, the analysis does not assume that the funds needed to achieve this target under a green-investment scenario would exceed those under a business-as-usual (BAU) scenario. The report explains that G2 was compared against a BAU2 scenario in which the same amount of investment (2% of global gross domestic product; GDP) is allocated to existing patterns of gross capital formation (see http://go.nature.com/wdmgbb).

Neither does the analysis overlook different living standards between countries. The T21 global model presents global totals, and it is calibrated to reflect the past 40 years, during which the ratio of the GDP per capita in high-income countries to that in low- and medium-income countries has declined from about 22:1 in 1990 (according to the World Bank) to 15:1 in 2007. Even though convergence of living standards was not set as a target, the modelled scenarios do probably represent further convergence.

We cannot claim that a green economy will always grow faster than a brown economy. But the report does provide evidence to counter the long-standing view that such an outcome is unlikely, even when limited to conventional GDP as a measure.