A team led by one of the world’s leading climate scientists, Dr. Jim Hansen, have indicated that preserving a planet similar to that on which civilization developed and to which life on earth is adapted, requires reducing the level of carbon dioxide in the atmosphere to at most 350 parts per million (from today’s level of ~400ppm) by the end of the century. And the scientific prescription for achieving this level required at least a 6% annual reduction of carbon dioxide emissions globally (starting in 2014/15) in addition to a substantial increase in the amount of carbon stored in the biosphere (through, for example, reforestation and changes in soil management practices).
Reducing the concentration of carbon dioxide in the atmosphere will require human related carbon dioxide emissions to shrink to where it is less than the amount being absorbed by the earth (or go from net positive emissions to net zero emissions to net negative emissions).
By saying “net zero,” it leaves a bit of practical wiggle room for some continued but drastically reduced emissions (the Report Card assumes 10-15% of today’s levels), as long as they’re balanced out by natural factors that remove carbon pollution from the atmosphere, or possibly by purchasing a small amount of carbon offsets.
A Climate Action Plan that achieves net zero by 2040 is graded as an A and includes about a 9% per year reduction, while achieving net zero by 2050 is about a 6% per year reduction. As the 6% is the average of what is needed globally, it is assigned an average score of C.The reason iMatter is pushing for a 9% per year reduction is because the global effort will have a far better chance of success if the U.S., as the world’s largest economy, and the largest cumulative emitter of greenhouse gases by far, takes a real leadership role.