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The impact humans are having on Earth’s resources depends essentially on three factors; population size, the affluence of this population and technological efficiency. This simple equation, laid out by the Stanford professor Paul Ehrlich nearly 40 years ago, makes for pretty scary math in 2010.
In a sobering, post-global financial crisis book, "Prosperity Without Growth; Economics for a Finite Planet," Tim Jackson uses Ehrlich’s equation to succinctly illustrate the challenges ahead if we are going to live sustainably and equitably on this planet. 

Carbon dioxide emissions make a good proxy for the rate at which we are using our planet’s resources. If, as the IPCC is calling for, we aim to stabilize atmospheric carbon dioxide at 450 parts per million by 2050, this means reducing our total carbon dioxide emissions by at least 4.9 percent per year between now and 2050. 

However, affluence and global population are both growing, and appear unlikely to do anything else between now and 2050. What government could deliberately limit the affluence of its citizens? This means that the burden of reducing carbon dioxide emissions must fall on the efficiency with which we use the planet’s resources. Jackson lets the numbers tell the story:

  • In 2006, our technological efficiency was such that globally, for every U.S. dollar spent, we emitted on average 770 grams of carbon dioxide.
  • According to the U.N.’s mid-range estimate, the world’s population is expected to increase to 9 billion people by 2050.
  • To achieve the necessary emissions reductions, this would mean that by 2050, the efficiency with which we use resources would need to drop from 770 grams to only 40 grams of carbon dioxide per U.S. dollar by 2050.
But this calculation assumes the world remains a very unequal place — developed countries getting steadily richer, China and India getting rapidly richer, and most of the rest of the world remaining crushingly poor. If we are serious about equality and wanted all of those 9 billion people to enjoy prosperity similar to U.S. citizens today, then our efficiency would need to improve to 14 grams of carbon dioxide per U.S. dollar — 55 times more efficient than today.

And this still assumes no income growth in developed nations. If we want an equal world where on average U.S. citizens still get a little richer by 2050, then we must improve efficiency to the point where only a measly 6 grams of carbon dioxide are needed for each U.S. dollar. This is 130 times more efficient than today.

If we dare contemplate population and affluence continuing to grow beyond 2050, every dollar of economic activity must actually take carbon out of the atmosphere!

These simple numbers — no more than primary school arithmetic — offer a stark reminder of how we must use our planet’s finite resources a great deal more carefully than we currently are. A sustainable and equitable world means a very different one from that in which we currently live.

— Text by Eddie GameCool Green Science Blog