It's Only 45 Trillion Dollars

According to an International Energy Agency report, the world needs to invest $45 trillion in renewable energy projects to reduce carbon emissions 50% by 2050 and still maintain economic growth. Bringing emissions back to 2005 levels by 2050 would require $17 trillion. Under both scenarios, the most inexpensive gains will come from reducing end-user waste, from energy efficient buildings to solar heating. The most expensive gains will come from transition from coal for carbon friendly sources like nuclear, clean coal, and natural gas.