Achieving carbon neutrality. The global population is expected to rise from the present 7.1 billion (mid 2011) to 8 billion by 2020. The global GDP, at present just under $1,000 per head of...

Achieving carbon neutrality. The global population is expected to rise from the present 7.1 billion (mid 2011) to 8 billion by 2020. The global GDP, at present just under $1,000 per head of population, is expected to increase by 40% over the same period. If, over that period, improved manufacturing technology reduces the energy intensity of GDP by 20% by what factor must the carbon intensity of energy production be reduced to keep carbon emissions at today’s level?