Norway has received negative press because its GHG emissions increased by 15% from when it implemented a carbon tax in 1991 to 2008. Others justify the increase in GHG emissions by noting that Norway also experienced an increase in gross domestic product of 70% since 1990. (Abboud 2008) Industrial efficiency gains in Norway may have been achieved because of the carbon tax. Emissions per unit of production were 22% lower in 2003 than they were in 1991, but since 1996, emissions per unit of production have been steady or even rising slightly. Norwegian officials recognize that the carbon tax is not the only factor contributing to changes in industrial